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      1天前 北大袁萌最新正确认识国际华人数学家大会的历史使命

正确认识国际华人数学家大会的历史使命

2019614日,在清华大学举行为期6天的第八届国际华人数学家大会(ICCM)胜利闭幕。

第八届ICCM大会传达了什么信息?一言以蔽之,建设强大国家必须拥有世界一流数学家队伍。

世界一流数学家,从何而来?除了自己动手培养人才,别无他法。

六年前,我们主张国内高高等学校微积分课程需要彻底改革,大力倡导公理化无穷小微积分就是为了实现这个目的。

   请见本文附件。

袁萌  陈启清  616

附件:International Congress of Chinese Mathematicians

The International Congress of Chinese Mathematicians (ICCM) (Chinese: 国际华人数学家大会) is an international non-governmental organization dedicated to bringing together Chinese mathematicians to discuss current research in mathematics as well as recognizing the achievements of Chinese mathematicians and mathematicians of Chinese descent around the world.      

The Congress was founded in 1998 and has been held every three years since.[1]

The first Congress was convened in Beijing at the Great Hall of the People in December 1998. Since then, there have been six Congresses, held in Hong Kong, Hangzhou, Taipei in addition to Beijing. Universities and institutions in Mainland China, Hong Kong, and Taiwan host the Congress on a rotating basis.[1][2]

 

Contents

1 Leadership

2 Prizes

3 List of Congresses

4 References

Leadership

Past Congresses have been led by prominent mathematicians such as Fields Medalist Shing-Tung Yau, Kai Lai Chung, Alice Chang, among others.[2] The Congress is sponsored by Shing-Tung Yau and Hong Kong entrepreneur Ronnie Chan.[3] ICCM is run in collaboration with institutions such as the Chinese Academy of Sciences and the Academia Sinica of China Taiwan.[2]

Prizes

The ICCM awards the Chern Prize and the Morningside Medal, among other prizes, to Chinese mathematicians who have made significant contributions to pure or applied mathematics. The Morningside Medal was established with the First Congress in 1998 and is awarded to mathematicians younger than 45; winners are traditionally announced on the first day of the ICCM.[1] The Chern Prize was first awarded at the Second Congress in 2001 in honor of differential geometer Shiing-Shen Chern; thus it predates the Chern Prize awarded by the International Mathematical Union by nine years.[2] Winners of both prizes are selected by a committee of prominent Chinese mathematicians.[3]

The ICCM also presents the International Cooperation Award to individuals who promote mathematics through collaboration, teaching, and other forms of support.[2]

List of Congresses

Year

City

Country

2016

Beijing

 China

2013

Taipei

 China Taiwan

2010

Beijing

 China

2007

Hangzhou

 China

2004

Hong Kong

 Hong Kong

2001

Taipei

 China Taiwan

1998

Beijing

 China

 

References

^

Jump up to:

a b c "International Congress of Chinese Mathematicians". Tsinghua University. Retrieved 1 February 2015.

^

Jump up to:

a b c d e Lizhen Ji; Yat Sun Poon; Lo Yang; Shing-Tung Yau, eds. (2010). Fifth International Congress of Chinese Mathematicians. American Mathematical Society and International Press. p. xiii-xiix. ISBN 9780821875551.

^

Jump up to:

a b "ICCM 2007". Fourth International Congress of Chinese Mathematicians. Archived from the original on 10 March 2015. Retrieved 31 January 2015.

Categories: Mathematical societiesOrganizations established in 19981998 establishments in ChinaOrganizations based in Beijing

 



 

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16天前 北大袁萌华为5G产品大配套,火星人光电互联大科普

华为5G产品大配套,火星人光电互联大科普

    光电开放系统互联通信的发明荣获诺贝尔物理物理奖。这是5G技术实现的基础。

  光纤(Fiber)是什么?有何特性?请读者仔细阅阅读本文附件 必有收获。

袁萌  陈启清 62

附件:

光纤是光导纤维的简写,是一种由玻璃或塑料制成的纤维,可作为光传导工具。

传输原理是光的全反射”。

前香港中文大学校长高锟和George A. Hockham首先提出光纤可以用于通讯传输的设想,高锟因此获得2009年诺贝尔物理学奖。

 

中文名

光纤

外文名

Fiber

中文读音

gung xin

应用学科

电力;输电线路

英文简称

FDDI

目录

1 定义

2 发展历史

发明

大事记

3 原理种类

石英光纤

掺氟光纤

红外光纤

复合光纤

氟氯化物光纤

塑包光纤

塑料光纤

单模光纤

多模光纤

色散位移光纤

色散平坦光纤

色散补偿光纤

偏振保持光纤

双折射光纤

抗恶环境光纤

密封涂层光纤

碳涂层光纤

金属涂层光纤

掺稀土光纤

喇曼光纤

偏心光纤

发光光纤

多芯光纤

空心光纤

高分子光导

保偏光纤

4 传输优点

频带宽

损耗低

重量轻

抗干扰能力强

保真度高

工作性能可靠

成本不断下降

5 结构原理

6 光纤衰减

本征

弯曲

挤压

杂质

不均匀

对接

人为衰减

7 生产方法

管棒法

双坩埚法

分子填充法

太空融拉法

8 施工方法

热熔接法

冷接法

9 光纤分类

10 系统运用

通信应用

医学应用

传感器应用

艺术应用

井下探测技术

光纤收发器

11 辨别方法

12 国内发展

13 光纤之父

 

 

 

定义

编辑

 

光纤

微细的光纤封装在塑料护套中,使得它能够弯曲而不至于断裂。通常,光纤的一端的发射装置使用发光二极管(light emitting diode,LED)或一束激光将光脉冲传送至光纤,光纤的另一端的接收装置使用光敏元件检测脉冲。

在日常生活中,由于光在光导纤维的传导损耗比电在电线传导的损耗低得多,光纤被用作长距离的信息传递。

通常光纤与光缆两个名词会被混淆。多数光纤在使用前必须由几层保护结构包覆,包覆后的缆线即被称为光缆。光纤外层的保护层和绝缘层可防止周围环境对光纤的伤害,如水、火、电击等。

光缆分为:缆皮、芳纶丝、缓冲层和光纤。光纤和同轴电缆相似,只是没有网状屏蔽层。中心是光传播的玻璃芯。 [1] 

在多模光纤中,芯的直径是50μm62.5μm两种, 大致与人的头发的粗细相当。而单模光纤芯的直径为8μm~10μm,常用的是9/125μm。芯外面包围着一层折射率比芯低的玻璃封套, 俗称包层,包层使得光线保持在芯内。再外面的是一层薄的塑料外套,即涂覆层,用来保护包层。光纤通常被扎成束,外面有外壳保护。 纤芯通常是由石英玻璃制成的横截面积很小的双层同心圆柱体,它质地脆,易断裂,因此需要外加一保护层。

说明:9/125μm指光纤的纤核为9μm,包层为125μm9/125μm是单模光纤的一个重要的特征,50/125μm指光纤的纤核为50μm,包层为125μm50/125μm是多模光纤的一个重要的特征。

其中金砖国家光缆计划是直接连通5个金砖国家的海底光缆项目,将于2014年初开工,2015年中启用。该项目总长3.4万千米,其中直接连通5个金砖国家的海底光缆长约2.4万千米。

2013年,全球100G光纤的收入预计将首次超过10亿美元。该公司分析了2013年一季度全球光网络市场的财务结果,发现了一些趋势,包括一个令人失望的趋势,即市场的总体增长仍然是困难的,只有日本的富士公司利润逐年增长。

虽然光纤市场在第一季度出现衰退的情况并不少见,但这次下降令人担忧是因为这已经是连续第五个季度市场有所下降,并且季度收入达到六年来的最低值。

100G光纤的情况较为乐观,不管环比、同比都表现出强劲增长。2013年一季度,100G光纤的出货量较2012年四季度增长了41%,收入较2012年四季度增长了24%。以此计算,年收入有望首次超过10亿美元。2013年一季度,有20家供应商出售100G光纤,将有更多的厂商加入市场竞争。供应商持谨慎乐观的态度,短期订单量看涨,长期订单量并不乐观。

 

 

 

发展历史

编辑

 

 

 

 

发明

1870年的一天,英国物理学家丁达尔到皇家学会的演讲厅讲光的全反射原理,他做了一个简单的实验:在装满水的木桶上钻个孔,然后用灯从桶上边把水照亮。结果使观众们大吃一惊。人们看到,放光的水从水桶的小孔里流了出来,水流弯曲,光线也跟着弯曲,光居然被弯弯曲曲的水俘获了。

人们曾经发现,光能沿着从酒桶中喷出的细酒流传输;人们还发现,光能顺着弯曲的玻璃棒前进。这是为什么呢?难道光线不再直进了吗?这些现象引起了丁达尔的注意,经过他的研究,发现这是光的全反射 [2]  的作用,由于水等介质密度比周围的物质(如空气)大,即光从水中射向空气,当入射角大于某一角度时,折射光线消失,全部光线都反射回水中。表面上看,光好像在水流中弯曲前进。

后来人们造出一种透明度很高、粗细像蜘蛛丝一样的玻璃丝──玻璃纤维,当光线以合适的角度射入玻璃纤维时,光就沿着弯弯曲曲的玻璃纤维前进。由于这种纤维能够用来传输光线,所以称它为光导纤维。

 

 

 

 

大事记

1880 AlexandraGrahamBell发明光束通话传输

 

光纤

1960 电射及光纤之发明

1960 玻璃纤维的传输损耗大于1000dB/km,其他材料包括光圈波导、气体透镜波导、空心金属波导管等

1966 七月,英籍、华裔学者高锟博士(K.C.Kao)在PIEE 杂志上发表论文《光频率的介质纤维表面波导》,从理论上分析证明了用光纤作为传输媒体以实现光通信的可能性,并预言了制造通信用的超低耗光纤的可能性

1970美国康宁公司三名科研人员马瑞尔、卡普隆、凯克用改进型化学相沉积法(MCVD 法)成功研制成传输损耗只有20dB/km的低损耗石英光纤。

1970 美国贝尔实验室研制出世界上第一只在室温下连续波工作的砷化镓铝半导体激光器

1972 传输损耗降低至4dB/km

1974 美国贝尔研究所发明了低损耗光纤制作法CVD法(汽相沉积法),使光纤传输损耗降低到1.1dB/km

1976 美国在亚特兰大的贝尔实验室地下管道开通了世界上第一条光纤通信系统的试验线路。采用一条拥有144个光纤的光缆以44.736Mbps的速率传输信号,中继距离为10 km。采用的是多模光纤,光源用的是发光管LED,波长是0.85微米的红外光。

1976 传输损耗降低至0.5dB/km

1977 贝尔研究所和日本电报电话公司几乎同时研制成功寿命达100万小时(实用中10年左右)的半导体激光器

1977 世界上第一条光纤通信系统在美国芝加哥市投入商用,速率为45Mb/s

1977 首次实际安装电话光纤网路

1978 FORT在法国首次安装其生产之光纤电

1979赵梓森拉制出我国自主研发的第一根实用光纤,被誉为“中国光纤之父”

1979 传输损耗降低至0.2dB/km

1980 多模光纤通信系统商用化(140Mb/s),并着手单模光纤通信系统的现场试验工作

1990 单模光纤通信系统进入商用化阶段(565Mb/s),并着手进行零色散移位光纤和波分复用及相干通信的现场试验,而且陆续制定数字同步体系(SDH)的技术标准

1990 传输损耗降低至0.14dB/km,已经接近石英光纤的理论衰耗极限值0.1dB/km

1990 区域网络及其他短距离传输应用之光纤

1992贝尔实验室与日本合作伙伴成功地试验了可以无错误传输9000公里的光放大器,其最初速率为5Gbps,随后增加到10Gbps

1993 SDH产品开始商用化(622Mb/s 以下)

1995 2.5Gb/s SDH产品进入商用化阶段

1996 10Gb/s SDH产品进入商用化阶段

1997 采用波分复用技术(WDM)的20Gb/s 40Gb/s SDH产品试验取得重大突破

2000 到屋边光纤=>到桌边光纤

2005 3.2Tbps超大容量的光纤通信系统在上海至杭州开通

2005 FTTHFiber To The Home)光纤直接到家庭

 

 

 

原理种类

编辑

光及其特性:

1.光是一种电磁波

可见光部分波长范围是:390~760nm(纳米)。大于760nm部分是红外光,小于390nm部分是紫外光。光纤中应用的是:850nm1310nm1550nm三种。

2.光的折射,反射和全反射。

因光在不同物质中的传播速度是不同的,所以光从一种物质射向另一种物质时,在两种物质的交界面处会产生折射和反射。而且,折射光的角度会随入射光的角度变化而变化。当入射光的角度达到或超过某一角度时,折射光会消失,入射光全部被反射回来,这就是光的全反射。不同的物质对相同波长光的折射角度是不同的(即不同的物质有不同的光折射率),相同的物质对不同波长光的折射角度也是不同。光纤通讯就是基于以上原理而形成的。

1.光纤裸纤一般分为三层:中心高折射率玻璃芯(芯径一般为5062.5μm),中间为低折射率硅玻璃包层(直径一般为125μm),最外是加强用的树脂涂层。光线在纤芯传送,当光纤射到纤芯和外层界面的角度大于产生全反射的临界角时,光线透不过界面,会全部反射回来,继续在纤芯内向前传送,而包层主要起到保护的作用。

 

光纤

2.数值孔径:

入射到光纤端面的光并不能全部被光纤所传输,只是在某个角度范围内的入射光才可以。这个角度就称为光纤的数值孔径。光纤的数值孔径大些对于光纤的对接是有利的。不同厂家生产的光纤的数值孔径不同(AT&T CORNING)。

3.光纤的种类:

光纤的种类很多,根据用途不同,所需要的功能和性能也有所差异。但对于有线电视和通信用的光纤,其设计和制造的原则基本相同,诸如:

损耗小;

有一定带宽且色散小;

接线容易;

易于成统;

可靠性高;

制造比较简单;

价廉等。光纤的分类主要是从工作波长、折射率分布、传输模式、原材料和制造方法上作一归纳的,兹将各种分类举例如下。

1)工作波长:紫外光纤、可观光纤、近红外光纤、红外光纤(0.85μm1.3μm1.55μm)。

2)折射率分布:阶跃(SI)型光纤、近阶跃型光纤、渐变(GI)型光纤、其它(如三角型、W型、凹陷型等)。

3)传输模式:单模光纤(含偏振保持光纤、非偏振保持光纤)、多模光纤。

4)原材料:石英光纤、多成分玻璃光纤、塑料光纤、复合材料光纤(如塑料包层、液体纤芯等)、红外材料等。按被覆材料还可分为无机材料(碳等)、金属材料(铜、镍等)和塑料等。

5)制造方法:预塑有汽相轴向沉积(VAD)、化学汽相沉积(CVD)等,拉丝法有管律法(Rod intube)和双坩锅法等。

 

 

 

 

石英光纤

石英光纤(Silica Fiber)是以二氧化硅(SiO2)为主要原料,并按不同的掺杂量,来控制纤芯和包层的折射率分布的光纤。石英(玻璃)系列光纤,具有低耗、宽带的特点,已广泛应用于有线电视和通信系统。

石英玻璃光导纤维的优点是损耗低,当光波长为1.01.7μm(约1.4μm附近),损耗只有1dB/km,在1.55μm处最低,只有0.2dB/km

 

 

 

 

掺氟光纤

掺氟光纤(Fluorine Doped Fiber)为石英光纤的典型产品之一。通常,作为1.3μm波域的通信用光纤中,控制纤芯的掺杂物为二氧化锗(GeO2),包层是用SiO2作成的。但接氟光纤的纤芯,大多使用SiO2,而在包层中却是掺入氟素的。由于,瑞利散射损耗是因折射率的变动而引起的光散射现象。所以,希望形成折射率变动因素的掺杂物,以少为佳。氟素的作用主要是可以降低SIO2的折射率。因而,常用于包层的掺杂。

石英光纤与其它原料的光纤相比,还具有从紫外线光到近红外线光的透光广谱,除通信用途之外,还可用于导光和图像传导等领域。

 

 

 

 

红外光纤

作为光通信领域所开发的石英系列光纤的工作波长,尽管用在较短的传输距离,也只能用于2μm。为此,能在更长的红外波长领域工作,所开发的光纤称为红外光纤。红外光纤(Infrared Optical Fiber)主要用于光能传送。例如有:温度计量、热图像传输、激光手术刀医疗、热能加工等等,普及率尚低。

 

 

 

 

复合光纤

复合光纤(Compound Fiber)是在SiO2原料中,再适当混合诸如氧化钠(Na2O)、氧化硼(B2O3)、氧化钾(K2O)等氧化物制作成多组分玻璃光纤,特点是多组分玻璃比石英玻璃的软化点低且纤芯与包层的折射率差很大。主要用在医疗业务的光纤内窥镜。

 

 

 

 

氟氯化物光纤

氟化物光纤氯化物光纤(Fluoride Fiber)是由氟化物玻璃作成的光纤。这种光纤原料又简称 ZBLAN(即将氟化锆(ZrF2)、氟化钡(BaF2)、氟化镧(LaF3)、氟化铝(AlF3)、氟化钠(NaF)等氯化物玻璃原料简化成的缩语。主要工作在210μm波长的光传输业务。由于ZBLAN具有超低损耗光纤的可能性,正在进行着用于长距离通信光纤的可行性开发,例如:其理论上的最低损耗,在3μm波长时可达10.210.3dB/km,而石英光纤在1.55μm时却在0.15~0.16dB/Km之间。ZBLAN光纤由于难于降低散射损耗,只能用在2.42.7μm的温敏器和热图像传输,尚未广泛实用。最近,为了利用ZBLAN进行长距离传输,正在研制1.3μm的掺镨光纤放大器(PDFA)。

 

 

 

 

塑包光纤

塑包光纤(Plastic Clad Fiber)是将高纯度的石英玻璃作成纤芯,而将折射率比石英稍低的如硅胶等塑料作为包层的阶跃型光纤。它与石英光纤相比较,具有纤芯粗、数值孔径(NA)高的特点。因此,易与发光二极管LED光源结合,损耗也较小。所以,非常适用于局域网(LAN)和近距离通信。

 

 

 

 

塑料光纤

这是将纤芯和包层都用塑料(聚合物)作成的光纤。早期产品主要用于装饰和导光照明及近距离光键路的光通信中。原料主要是有机玻璃(PMMA)、聚苯乙稀(PS)和聚碳酸酯(PC)。损耗受到塑料固有的CH结合结构制约,一般每km可达几十dB。为了降低损耗正在开发应用氟索系列塑料。由于塑料光纤(Plastic Optical fiber)的纤芯直径为1000μm,比单模石英光纤大100倍,接续简单,而且易于弯曲施工容易。近年来,加上宽带化的进度,作为渐变型(GI)折射率的多模塑料光纤的发展受到了社会的重视。最近,在汽车内部LAN中应用较快,未来在家庭LAN中也可能得到应用。

 

 

 

 

 

单模光纤

单模光纤这是指在工作波长中,只能传输一个传播模式的光纤,通常简称为单模光纤(SMFSingle ModeFiber)。目前,在有线电视和光通信中,是应用最广泛的光纤。由于,光纤的纤芯很细(约10μm)而且折射率呈阶跃状分布,当归一化频率V参数<2.4时,理论上,只能形成单模传输。另外,SMF没有多模色散,不仅传输频带较多模光纤更宽,再加上SMF的材料色散和结构色散的相加抵消,其合成特性恰好形成零色散的特性,使传输频带更加拓宽。SMF中,因掺杂物不同与制造方式的差别有许多类型。凹陷型包层光纤(DePr-essed Clad Fiber),其包层形成两重结构,邻近纤芯的包层,较外倒包层的折射率还低。

 

 

 

 

多模光纤

多模光纤将光纤按工作波长以其传播可能的模式为多个模式的光纤称作多模光纤(MMFMUlti ModeFiber)。纤芯直径为50μm,由于传输模式可达几百个,与SMF相比传输带宽主要受模式色散支配。在历史上曾用于有线电视和通信系统的短距离传输。自从出现SMF光纤后,似乎形成历史产品。但实际上,由于MMFSMF的芯径大且与LED等光源结合容易,在众多LAN中更有优势。所以,在短距离通信领域中MMF仍在重新受到重视。MMF按折射率分布进行分类时,有:渐变(GI)型和阶跃(SI)型两种。GI型的折射率以纤芯中心为最高,沿向包层徐徐降低。由于SI型光波在光纤中的反射前进过程中,产生各个光路径的时差,致使射出光波失真,色激较大。其结果是传输带宽变窄,目前SIMMF应用较少。

 

 

 

 

色散位移光纤

单模光纤的工作波长在1.3Pm时,模场直径约9Pm,其传输损耗约0.3dB/km。此时,零色散波长恰好在1.3pm处。石英光纤中,从原材料上看1.55pm段的传输损耗最小(约0.2dB/km)。由于现在已经实用的掺铒光纤放大器(EDFA)是工作在1.55pm波段的,如果在此波段也能实现零色散,就更有利于应用1.55Pm波段的长距离传输。于是,巧妙地利用光纤材料中的石英材料色散与纤芯结构色散的合成抵消特性,就可使原在1.3Pm段的零色散,移位到1.55pm段也构成零色散。因此,被命名为色散位移光纤(DSFDispersionShifted Fiber)。加大结构色散的方法,主要是在纤芯的折射率分布性能进行改善。在光通信的长距离传输中,光纤色散为零是重要的,但不是唯一的。其它性能还有损耗小、接续容易、成缆化或工作中的特性变化小(包括弯曲、拉伸和环境变化影响)。DSF就是在设计中,综合考虑这些因素。

 

 

 

 

色散平坦光纤

色散移位光纤(DSF)是将单模光纤设计零色散位于1.55pm波段的光纤。而色散平坦光纤(DFFDispersion Flattened Fiber)却是将从1.3Pm1.55pm的较宽波段的色散,都能作到很低,几乎达到零色散的光纤称作DFF。由于DFF要作到1.3pm1.55pm范围的色散都减少。就需要对光纤的折射率分布进行复杂的设计。不过这种光纤对于波分复用(WDM)的线路却是很适宜的。由于DFF光纤的工艺比较复杂,费用较贵。今后随着产量的增加,价格也会降低。

 

 

 

 

色散补偿光纤

对于采用单模光纤的干线系统,由于多数是利用1.3pm波段色散为零的光纤构成的。可是,现在损耗最小的1.55pm,由于EDFA的实用化,如果能在1.3pm零色散的光纤上也能令1.55pm波长工作,将是非常有益的。因为,在1.3Pm零色散的光纤中,1.55Pm波段的色散约有16ps/km/nm之多。如果在此光纤线路中,插入一段与此色散符号相反的光纤,就可使整个光线路的色散为零。为此目的所用的是光纤则称作色散补偿光纤(DCFDisPersion Compe-nsation Fiber)。DCF与标准的1.3pm零色散光纤相比,纤芯直径更细,而且折射率差也较大。DCF也是WDM光线路的重要组成部分。

 

 

 

 

偏振保持光纤

在光纤中传播的光波,因为具有电磁波的性质,所以,除了基本的光波单一模式之外,实质上还存在着电磁场(TETM)分布的两个正交模式。通常,由于光纤截面的结构是圆对称的,这两个偏振模式的传播常数相等,两束偏振光互不干涉,但实际上,光纤不是完全地圆对称,例如有着弯曲部分,就会出现两个偏振模式之间的结合因素,在光轴上呈不规则分布。偏振光的这种变化造成的色散,称之偏振模式色散(PMD)。对于现在以分配图像为主的有线电视,影响尚不太大,但对于一些未来超宽带有特殊要求的业务,如:

相干通信中采用外差检波,要求光波偏振更稳定时;

光机器等对输入输出特性要求与偏振相关时;

在制作偏振保持光耦合器和偏振器或去偏振器等时;

制作利用光干涉的光纤敏感器等,

凡要求偏振波保持恒定的情况下,对光纤经过改进使偏振状态不变的光纤称作偏振保持光纤(PMFPolarization Maintaining fiber),或称其为固定偏振光纤。

 

 

 

 

双折射光纤

双折射光纤是指在单模光纤中,可以传输相互正交的两个固有偏振模式的光纤。折射率随偏振方向变异的现象称为双折射。它又称作PANDA光纤,即偏振保持与吸收减少光纤(Polarizationmaintai-ning AND Absorption reducing fiber)。它是在纤芯的横向两则,设置热膨胀系数大、截面是圆形的玻璃部分。在高温的光纤拉丝过程中,这些部分收缩,其结果在纤芯y方向产生拉伸,同时又在x方向呈现压缩应力。致使纤材出现光弹性效应,使折射率在X方向和y方向出现差异。依此原理达到偏振保持恒定的效果。 [3] 

 

 

 

 

抗恶环境光纤

通信用光纤通常的工作环境温度可在-40+60之间,设计时也是以不受大量辐射线照射为前提的。相比之下,对于更低温或更高温以及能在遭受高压或外力影响、曝晒辐射线的恶劣环境下,也能工作的光纤则称作抗恶环境光纤(Hard Condition Resistant Fiber)。一般为了对光纤表面进行机械保护,多涂覆一层塑料。可是随着温度升高,塑料保护功能有所下降,致使使用温度也有所限制。如果改用抗热性塑料,如聚四氟乙稀(Teflon)等树脂,即可工作在300环境。也有在石英玻璃表面涂覆镍(Ni)和铝(Al)等金属的。这种光纤则称为耐热光纤(Heat Resistant Fiber)。另外,当光纤受到辐射线的照射时,光损耗会增加。这是因为石英玻璃遇到辐射线照射时,玻璃中会出现结构缺陷(也称作色心:Colour Center),尤在0.40.7pm波长时损耗增大。防止办法是改用掺杂OHF素的石英玻璃,就能抑制因辐射线造成的损耗缺陷。这种光纤则称作抗辐射光纤(Radiation Resistant Fiber),多用于核发电站的监测用光纤维镜等。

 

 

 

 

密封涂层光纤

为了保持光纤的机械强度和损耗的长时间稳定,而在玻璃表面涂装碳化硅(SiC)、碳化钛(TiC)、碳(C)等无机材料,用来防止从外部来的水和氢的扩散所制造的光纤(HCFHermeticallyCoated Fiber)。目前,通用的是在化学气相沉积(CVD)法生产过程中,用碳层高速堆积来实现充分密封效应。这种 碳涂覆光纤(CCF)能有效地截断光纤与外界氢分子的侵入。据报道它在室温的氢气环境中可维持20年不增加损耗。当然,它在防止水分侵入,延缓机械强度的疲劳进程中,其疲劳系数(Fatigue Parameter)可达200以上。所以,HCF被应用于严酷环境中要求可靠性高的系统,例如海底光缆就是一例。

 

 

 

 

碳涂层光纤

在石英光纤的表面涂敷碳膜的光纤,称之碳涂层光纤(CCFCarbon CoatedFiber)。其机理是利用碳素的致密膜层,使光纤表面与外界隔离,以改善光纤的机械疲劳损耗和氢分子的损耗增加。CCF是密封涂层光纤(HCF)的一种。

 

 

 

 

金属涂层光纤

金属涂层光纤(Metal Coated Fiber)是在光纤的表面涂布NiCuAl等金属层的光纤。也有再在金属层外被覆塑料的,目的在于提高抗热性和可供通电及焊接。它是抗恶环境性光纤之一,也可作为电子电路的部件用。 早期产品是在拉丝过程中,涂布熔解的金属作成的。由于此法因被玻璃与金属的膨胀系数差异太大,会增微小弯曲损耗,实用化率不高。近期,由于在玻璃光纤的表面采用低损耗的非电解镀膜法的成功,使性能大有改善。

 

 

 

 

掺稀土光纤

在光纤的纤芯中,掺杂如铒(Er)、钦(Nd)、镨(Pr)等稀土族元素的光纤。1985年英国的索斯安普顿(Sourthampton)大学的佩思(Payne)等首先发现掺杂稀土元素的光纤(Rare Earth DoPed Fiber)有激光振荡和光放大的现象。于是,从此揭开了惨饵等光放大的面纱,现在已经实用的1.55pmEDFA就是利用掺饵的单模光纤,利用1.47pm的激光进行激励,得到1.55pm光信号放大的。另外,掺镨的氟化物光纤放大器(PDFA)正在开发中。

 

 

 

 

喇曼光纤

喇曼效应是指往某物质中射人频率f的单色光时,在散射光中会出现频率f之外的f±fR f±2fR等频率的散射光,对此现象称喇曼效应。由于它是物质的分子运动与格子运动之间的能量交换所产生的。当物质吸收能量时,光的振动数变小,对此散射光称斯托克斯(stokes)线。反之,从物质得到能量,而振动数变大的散射光,则称反斯托克斯线。于是振动数的偏差FR,反映了能级,可显示物质中固有的数值。 利用这种非线性媒体做成的光纤,称作喇曼光纤(RFRaman Fiber)。为了将光封闭在细小的纤芯中,进行长距离传播,就会出现光与物质的相互作用效应,能使信号波形不畸变,实现长距离传输。 当输入光增强时,就会获得相干的感应散射光。应用感应喇曼散射光的设备有喇曼光纤激光器,可供作分光测量电源和光纤色散测试用电源。另外,感应喇曼散射,在光纤的长距离通信中,正在研讨作为光放大器的应用。

 

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17天前 北大袁萌华为大搞5G光通信,火星人快步紧跟在两地之间,如何快速、有效地传输大批数据包


华为大搞5G光通信,火星人快步紧跟               


    在两地之间,如何快速、有效地传输大批数据包?除了借助光纤通信,别无他法。


  当今,华为大搞5G光通信,火星人快步紧跟               


   注:本文附件是光纤通信“迷”必读


袁萌  陈启清  61


附件:光纤通信必读


光纤通信


光纤通信Fiber-optic communication


是指一种利用光与光纤(Optical Fiber)传递信息的一种方式,属于有线通信的一种。光经过调制(Modulation)后便能携带信息。自1980年代起,光纤通信系统对于电信工业产生了革命性的作用,同时也在数字时代里扮演非常重要的角色。光纤通信具有传输容量大、保密性好等许多优点。光纤通信线在已经成为当今最主要的有线通信方式。将需发送的信息在发送端输入到发送机中,将信息叠加或调制到作为信息信号载体的载波上,然后将已调制的载波通过传输媒质发送到远处的接收端,由接收机解调出原来的信息。


根据信号调制方式的不同,光纤通信可以分为数字光纤通信、模拟光纤通信。纤通信的产业包括了光纤电缆、光器件、光设备、光通信仪表、光通信集成电路等多个领域。


利用光纤做为通信之用通常需经过下列几个步骤:


以发射机(Transmitter)产生光信号。


以光纤传递信号,同时必须确保光信号在光纤中不会衰减或严重变形。


以接收机(Receiver)接收光信号,并且转换成电信号。


 


目录


1 应用历史


3 核心技术


3.1


发射机


3.2


光纤


3.3


光放大器


3.4


接收机


3.5


波分复用


4


系统参数


4.1


带宽距离乘积(BL积)


4.2


传输速率


4.2.1


标准光纤


4.3


信号色散


4.4


信号衰减


4.5


信号再生


4.6


最后一公里光纤网络


5


与传统通信系统的比较


6


现行技术标准


7


参见


8


参考资料


9


外部链接


  应用


光纤常被电话公司用于传递电话、互联网,或是有线电视的信号,有时候利用一条光纤就可以同时传递上述的所有信号。与传统的铜线相比,光纤的信号衰减(attenuation)与遭受干扰[来源请求]interference)的情形都改善很多,特别是长距离以及大量传输的使用场合中,光纤的优势更为明显。然而,在城市之间利用光纤的通信基础建设(infrastructure)通常施工难度以及材料成本难以控制,完工后的系统维运复杂度与成本也居高不下。因此,早期光纤通信系统多半应用在长途的通信需求中,这样才能让光纤的优势彻底发挥,并且抑制住不断增加的成本。


2000年光通信(optical communication)市场崩溃后,光纤通信的成本也不断下探,当前已经和铜缆为骨干的通信系统不相上下[1]


对于光纤通信产业而言,1990年光放大器(optical amplifier)正式进入商业市场的应用后,很多超长距离的光纤通信才得以真正实现,例如越洋的海底电缆。到了2002年时,越洋海底电缆的总长已经超过25万千米,每秒能携带的数据量超过2.56Tb,而且根据电信运营商的统计,这些数据从2002年后仍然不断的大幅成长中。


历史[编辑]


自古以来,人类对于长距离通信的需求就不曾稍减。随着时间的前进,从烽火到电报,再到1940年第一条同轴电缆(coaxial cable)正式服役,这些通信系统的复杂度与精细度也不断的进步。但是这些通信方式各有其极限,使用电气信号传递信息虽然快速,但是传输距离会因为电气信号容易衰减而需要大量的中继器(repeater);微波(microwave)通信虽然可以使用空气做介质,可是也会受到载波频率(carrier frequency)的限制。到了二十世纪中叶,人们才了解使用光来传递信息,能带来很多过去所没有的显著好处。


然而,当时并没有相干性高的发光源(coherent light source),也没有适合作为传递光信号的介质,也所以光通信一直只是概念。直到1960年代,激光(laser)的发明才解决第一项难题。1970年代康宁公司(Corning Glass Works)发展出高质量低衰减的光纤则是解决了第二项问题,此时信号在光纤中传递的衰减量第一次低于光纤通信之父高锟所提出的每千米衰减20分贝(20dB/km)关卡,证明光纤作为通信介质的可能性。与此同时使用砷化镓(GaAs)作为材料的半导体激光(semiconductor laser)也被发明出来,并且凭借着体积小的优势而大量运用于光纤通信系统中。1976年,第一条速率为44.7Mbit/s的光纤通信系统在美国亚特兰大的地下管道中诞生。


经过五年的研发期,第一个商用的光纤通信系统在1980年问市。这个人类史上第一个光纤通信系统使用波长800纳米(nanometer)的砷化镓激光作为光源,传输的速率(data rate)达到45Mb/sbits per second),每10千米需要一个中继器增强信号。


第二代的商用光纤通信系统也在1980年代初期就发展出来,使用波长1300纳米的磷砷化镓铟(InGaAsP)激光。早期的光纤通信系统虽然受到色散(dispersion)的问题而影响了信号质量,但是1981年单模光纤(single-mode fiber)的发明克服了这个问题。到了1987年时,一个商用光纤通信系统的传输速率已经高达1.7Gb/s,比第一个光纤通信系统的速率快将近四十倍之多。同时传输的功率与信号衰减的问题也有显著改善,间隔50千米才需要一个中继器增强信号。1980年代末,EDFA的诞生,堪称光通信历史上的一个里程碑似的事件,它使光纤通信可直接进行光中继,使长距离高速传输成为可能,并促使DWDM的诞生。


第三代的光纤通信系统改用波长1550纳米的激光做光源,而且信号的衰减已经低至每千米0.2分贝(0.2dB/km)。之前使用磷砷化镓铟激光的光纤通信系统常常遭遇到脉冲延散(pulse spreading)问题,而科学家则设计出色散位移光纤(dispersion-shifted fiber)来解决这些问题,这种光纤在传递1550纳米的光波时,色散几乎为零,因其可将激光光的光谱限制在单一纵模(longitudinal mode)。这些技术上的突破使得第三代光纤通信系统的传输速率达到2.5Gb/s,而且中继器的间隔可达到100千米远。


第四代光纤通信系统引进光放大器(optical amplifier),进一步减少中继器的需求。另外,波分复用(wavelength-division multiplexing, WDM)技术则大幅增加传输速率。这两项技术的发展让光纤通信系统的容量以每六个月增加一倍的方式大幅跃进,到了2001年时已经到达10Tb/s的惊人速率,足足是80年代光纤通信系统的200倍之多。近年来,传输速率已经进一步增加到14Tb/s,每隔160千米才需要一个中继器。


第五代光纤通信系统发展的重心在于扩展波分复用器的波长操作范围。传统的波长范围,也就是一般俗称的“C band”约是1530纳米至1570纳米之间,新一带的无水光纤(dry fiber)低损耗的波段则延伸到1300纳米至1650纳米间。另外一个发展中的技术是引进光孤子(optical soliton)的概念,利用光纤的非线性效应,让脉冲能够抵抗色散而维持原本的波形。


1990年至2000年间,光纤通信产业受到互联网泡沫的影响而大幅成长。此外一些新兴的网络应用,如视频点播(video on demand)使得互联网带宽的成长甚至超过摩尔定律(Moore's Law)所预期集成电路芯片中晶体管增加的速率。而自互联网泡沫破灭至2006年为止,光纤通信产业透过企业整并壮大规模,以及委外生产的方式降低成本来延续生命。


核心技术[编辑]


现代的光纤通信系统多半包括一个发射机,将电信号转换成光信号,再透过光纤将光信号传递。光纤多半埋在地下,连接不同的建筑物。系统中还包括数种光放大器,以及一个光接收机将光信号转换回电信号。在光纤通信系统中传递的多半是数字信号,来源包括计算机、电话系统,或是有线电视系统。


发射机[编辑]


在光纤通信系统中通常作为光源的半导体组件是发光二极管(light-emitting diode, LED)或是激光二极管(laser diode)。LED与激光二极管的主要差异在于前者所发出的光为非相干性(noncoherent),而后者则为相干性(coherent)的光。使用半导体作为光源的好处是体积小、发光效率高、可靠度佳,以及可以将波长最优化,更重要的是半导体光源可以在高频操作下直接调制,非常适合光纤通信系统的需求。


LED借着电激发光(electroluminescence)的原理发出非相干性的光,频谱通常分散在30纳米至60纳米间。LED另外一项缺点是发光效率差,通常只有输入功率的1%可以转换成光功率,约是100微瓦特(micro-watt)左右。但是由于LED的成本较低廉,因此常用于低价的应用中。常用于光通信的LED主要材料是砷化镓或是砷化镓磷(GaAsP),后者的发光波长为1300纳米左右,比砷化镓的810纳米至870纳米更适合用在光纤通信。由于LED的频谱范围较广,导致色散较为严重,也限制了其传输速率与传输距离的乘积。LED通常用在传输速率10Mb/s100Mb/s的局域网(local area network, LAN),传输距离也在数千米之内。当前也有LED内包含了数个量子井(quantum well)的结构,使得LED可以发出不同波长的光,涵盖较宽的频谱,这种LED被广泛应用在区域性的波分复用网络中。


半导体激光的输出功率通常在100毫瓦特(mW)左右,而且为相干性质的光源,方向性相对而言较强,通常和单模光纤的耦合效率可达50%。激光的输出频谱较窄,也有助于增加传输速率以及降低模态色散(modal dispersion)。半导体激光亦可在相当高的操作频率下进行调制,原因是其复合时间(recombination time)非常短。


半导体激光通常可由输入的电流有无直接调制其开关状态与输出信号,不过对于某些传输速率非常高或是传输距离很长的应用,激光光源可能会以连续波(continuous wave)的形式控制,例如使用外置的电吸收光调制器(electroabsorption modulator)或是马赫·任德干涉仪(Mach-Zehnder interferometer)对光信号加以调制。外置的调制组件可以大幅减少激光的“啁啾脉冲”(chirp pulse)。啁啾脉冲会使得激光的谱线宽度变宽,使得光纤内的色散变得严重。


光纤[编辑]


主条目:光导纤维


光纤缆线包含一个纤芯(core),纤壳(cladding)以及外层的保护被覆(protective coating)。核心与折射率(refractive index)较高的纤壳通常用高质量的硅石玻璃(silica glass)制成,但是现在也有使用塑胶作为材质的光纤。又因为光纤的外层有经过紫外线固化后的压克力(acrylate)被覆,可以如铜缆一样埋藏于地下,不需要太多维护费用。然而,如果光纤被弯折的太过剧烈,仍然有折断的危险。而且因为光纤两端连接需要十分精密的校准,所以折断的光纤也难以重新接合。


光通信中主要使用多模、单模两种光纤。多模光纤纤芯直径更大(≥50微米),对发射机、连接器的要求更低。然而,多模光纤引入了多模色散,这会限制系统的带宽和长度。此外,由于有更高的杂质含量,多模光纤通常会有更高的衰减。单模光纤的纤芯直径较小(<10微米),对发射机、连接器的要求更高,但能够搭建传输距离更长、性能更好的系统。单模和多模光纤都有不同的等级。


光纤类型比较[1]


多模光纤 FDDI 62,5/125 µm(1987)


多模光纤 OM1 62,5/125 µm(1989)


多模光纤 OM2 50/125 µm(1998)


多模光纤 OM3 50/125 µm(2003)


多模光纤 OM4 50/125 µm(2008)


多模光纤 OM550/125 µm(2016)


单模光纤 OS19/125 µm(1998)


单模光纤OS29/125 µm(2000)


160 MHz·km@850 nm


200 MHz·km@850 nm


500 MHz·km@850 nm


1500 MHz·km@850 nm


3500 MHz·km@850 nm


3500 MHz·km@850 nm &1850 MHz·km@950 nm


1 dB/km@1300/1550 nm


0.4 dB/km@1300/1550 nm


光放大器[编辑]


主条目:光放大器


过去光纤通信的距离限制主要根源于信号在光纤内的衰减以及信号变形,而解决的方式是利用光电转换的中继器。这种中继器先将光信号转回电信号放大后再转换成较强的光信号传往下一个中继器,然而这样的系统架构无疑较为复杂,不适用于新一代的。


接收机[编辑]


构成光接收机的主要组件是光侦测器(photodetector),利用光电效应将入射的光信号转为电信号。光侦测器通常是半导体为基础的光二极管(photo diode),例如p-n结二极管、p-i-n二极管,或是雪崩型二极管(avalanche diode)。另外“金属-半导体-金属”(Metal-Semiconductor-Metal, MSM)光侦测器也因为与电路集成性佳,而被应用在光再生器(regenerator)或是波分复用器中。


光接收机电路通常使用转阻放大器(transimpedence amplifier, TIA)以及限幅放大器(limiting amplifier)处理由光侦测器转换出的光电流,转阻放大器和限幅放大器可以将光电流转换成幅度较小的电压信号,再透过后端的比较器(comparator)电路转换成数字信号。对于高速光纤通信系统而言,信号常常相对地衰减较为严重,为了避免接收机电路输出的数字信号变形超出规格,通常在接收机电路的后级也会加上时脉及数据恢复电路(clock and data recovery, CDR)以及锁相回路(phase-locked loop, PLL)将信号做适度处理再输出。


波分复用[编辑]


主条目:波分复用


波分复用的实际做法就是将光纤的工作波长分割成多个信道(channel),俾使能在同一条光纤内传输更大量的数据。一个完整的波分复用系统分为发射端的波分复用器(wavelength division multiplexer)以及在接收端的波长分波解多任务器(wavelength division demultiplexer),最常用于波分复用系统的组件是数组波导光栅(Arrayed Waveguide Gratings, AWG)。而当前市面上已经有商用的波分复用器/解多任务器,最多可将光纤通信系统划分成80个信道,也使得数据传输的速率一下子就突破Tb/s的等级。


系统参数[编辑]


带宽距离乘积(BL积)[编辑]


由于传输距离越远,光纤内的色散现象就越严重,影响信号质量。因此常用于评估光纤通信系统的一项指针就是带宽-距离乘积(BL积),单位是百万赫兹×千米(MHz×km)。使用这两个值的乘积做为指针的原因是通常这两个值不会同时变好,而必须有所取舍(trade off)。举例而言,一个常见的多模光纤系统的带宽-距离乘积约是500MHz×km,代表这个系统在一千米内的信号带宽可以到500MHz,而如果距离缩短至0.5千米时,带宽则可以倍增到1000MHz


传输速率[编辑]


每根光纤可以承载许多独立的信道,每个信道使用不同波长的光(波分复用)。每条光纤的净数据速率(没有开销字节的数据速率)是每信道数据速率减少了FEC开销,乘以信道数量(截至2008年,商用密集WDM系统通常高达80个)。


标准光纤[编辑]


以下总结了当前使用标准电信级单模单芯光纤电缆的最新研究成果。



机构


系统传输速率


WDM信道数


单信道传输速率


传输距离


2009


阿尔卡特朗讯[2]


15.5 Tbit/s


155


100 Gbit/s


7000 km


2010


NTT[3]


69.1 Tbit/s


432


171 Gbit/s


240 km


2011


NEC[4]


101.7 Tbit/s


370


273 Gbit/s


165 km


2011


卡尔斯鲁厄理工学院[5]


26 Tbit/s


>300


 


50 km


2016


英国电信和华为[6]


5.6 Tbit/s


28


200Gb/s


circa 140 km ?


2016


贝尔实验室、德国电信T-Labs和慕尼黑工业大学[7](第一个接近香农理论极限的成果)


1 Tbit/s


1


1Tb/s


 


2016


诺基亚网络[8]


65 Tbit/s


 


 


6600 Km


2017


英国电信和[./https://en.wikipedia.org/wiki/Huawei 华为][9]


11.2 Tbit/s


28


400 Gb/s


250 Km


特种光纤


以下总结了当前使用少模光纤等特种光纤进行空分复用完成的研究成果。



机构


系统传输速率


模式数量


纤芯数量


单芯WDM信道数


单信道传输速率


传输距离


2011


NICT[10]


109.2 Tbit/s


 


7


 


 


 


2012


NEC, 康宁公司[11]


1.05 Pbit/s


 


12


 


 


52.4 km


2013


南安普顿大学[12]


73.7 Tbit/s


 


1 (空芯光纤)


3x96(模式DM)[13]


256 Gb/s


310 m


2014


丹麦技术大学[14]


43 Tbit/s


 


7


 


 


1045 km


2014


艾恩德霍芬理工大学和中佛罗里达大学[15]


255 Tbit/s


 


7


50


~728 Gb/s


1 km


2015


NICT、住友电气和RAM光子[16]


2.15 Pbit/s


 


22


402 (C+L波段)


243 Gb/s


31 km


2017


NTT[17]


1 Pbit/s


单模


32


46


680 Gb/s


205.6 Km


2017


KDDI住友电气[18]


10.16 Pbit/s


6


19


739 (C+L波段)


120 Gb/s


11.3 Km


2018


NICT[19]


159 Tbit/s


3


1


348


414 Gb/s


1045 km


信号色散[编辑]


对于现代的玻璃光纤而言,最严重的问题并非信号的衰减,而是色散问题,也就是信号在光纤内传输一段距离后逐渐扩散重叠,使得接收端难以判别信号的高或低。造成光纤内色散的成因很多。以模态色散为例,信号的横模(transverse mode)轴速度(axial speed)不一致导致色散,这也限制了多模光纤的应用。在单模光纤中,模态间的色散可以被压抑得很低。


但是在单模光纤中一样有色散问题,通常称为群速色散(group-velocity dispersion),起因是对不同波长的入射光波而言,玻璃的折射率略有不同,而光源所发射的光波不可能没有频谱的分布,这也造成了光波在光纤内部会因为波长的些微差异而有不同的折射行为。另外一种在单模光纤中常见的色散称为偏振态色散(polarization mode dispersion),起因是单模光纤内虽然一次只能容纳一个横模的光波,但是这个横模的光波却可以有两个方向的偏振(polarization),而光纤内的任何结构缺陷与变形都可能让这两个偏振方向的光波产生不一样的传递速度,这又称为光纤的双折射现象(fiber birefringence)。这个现象可以透过偏振保持光纤(polarization-maintaining optical fiber)加以抑制。


信号衰减[编辑]


信号在光纤内衰减也造成光放大器成为光纤通信系统所必需的组件。光波在光纤内衰减的主因有物质吸收、瑞利散射(Rayleigh scattering)、米氏散射(Mie scattering)以及连接器造成的损失。虽然石英的吸收系数只有0.03dB/km,但是光纤内的杂质仍然会让吸收系数变大。其他造成信号衰减的原因还包括应力对光纤造成的变形、光纤密度的微小扰动,或是接合的技术仍有待加强。


信号再生[编辑]


现代的光纤通信系统因为引进了很多新技术降低信号衰减的程度,因此信号再生只需要用于距离数百千米远的通信系统中。这使得光纤通信系统的建置费用与维运成本大幅降低,特别对于越洋的海底光纤而言,中继器的稳定度往往是维护成本居高不下的主因。这些突破对于控制系统的色散也有很大的助益,足以降低色散造成的非线性现象。此外,光孤子也是另外一项可以大幅降低长距离通信系统中色散的关键技术。


最后一公里光纤网络[编辑]


虽然光纤网络享有高容量的优势,但是在达成普及化的目标,也就是“光纤到户”(Fiber To The Home, FTTH)以及“最后一公里”(last mile)的网络布建上仍然有很多困难待克服。然而,随着网络带宽的需求日增,已经有越来越多国家逐渐达成这个目的。以韩国为例,光纤网络系统已经开始取代使用铜线的数字用户回路系统。


与传统通信系统的比较[编辑]


对于某个通信系统而言,使用传统的铜缆作为传输介质较好,或是使用光纤较佳,有几项考量的重点。光纤通常用于高带宽以及长距离的应用,因为其具有低损耗、高容量,以及不需要太多中继器等优点。光纤另外一项重要的优点是即使跨越长距离的数条光纤并行,光纤与光纤之间也不会产生串扰(cross-talk)的干扰,这和传输电信号的传输线(transmission line)正好相反。


不过对于短距离与低带宽的通信应用而言,使用电信号的传输有下列好处:


较低的建置费用


组装容易


可以利用电力系统传递信息


因为这些好处,所以在很短的距离传输信息,例如主机之间、电路板之间,甚至是集成电路芯片之间,通常还是使用电信号传输。然而当前也有些还在实验阶段的系统已经改采光来传递信息。


在某些低带宽的场合,光纤通信仍然有其独特的优势:


能抵抗电磁干扰(EMI),包括核子造成的电磁脉冲。(不过光纤可能会毁于α或β射线)


对电信号的阻抗极高,所以能在高电压或是地面电势不同的状况下安全工作。


重量较轻,这在飞机中特别重要。


不会产生火花,在某些易燃的环境中显得重要。


没有电磁辐射、不易被窃听,对于需要高度安全的系统而言十分重要。


线径小,当绕线的路径被限制时,变得重要。


现行技术标准[编辑]


为了能让不同的光纤通信设备制造商之间有共通的标准,国际电信联盟(International Telecommunications Union, ITU)制定了数个与光纤通信相关的标准,包括:


ITU-T G.651, 多模光纤, "Characteristics of a 50/125 µm multimode graded index optical fibre cable"


ITU-T G.652, 标准单模光纤, "Characteristics of a single-mode optical fibre cable"


ITU-T 6.653, 色散位移单模光纤, "Characteristics of a dispersion-shifted single-mode optical fibre cable Superseded"


ITU-T 6.654, 截止波长位移单模光纤, "Characteristics of a cut-off shifted single-mode optical fibre and cable Superseded"


ITU-T 6.655, 非零色散位移单模光纤, "Characteristics of a non-zero dispersion-shifted single-mode optical fibre cable Superseded "


ITU-T 6.656, 宽传输带宽非零色散位移单模光纤,"Characteristics of a fibre and cable with non-zero dispersion for wideband optical transport"


ITU-T 6.657, 弯曲不敏感单模光纤, "Characteristics of a bending-loss insensitive single-mode optical fibre and cable"


其他关于光纤通信的标判据规定了发射与接收端,或是传输介质的规格,包括了:


10G以太网(10 Gigabit Ethernet


光纤分布式数据接口(FDDI


光纤信道(Fibre channel


HIPPI


同步数字层次结构(Synchronous Digital Hierarchy


同步光纤网络(Synchronous Optical Networking


此外,在数字音效的领域中,也有利用光纤传递信息的规格,那就是由日本东芝(Toshiba)所制定的TOSLINK规格。采用塑胶光纤(plastic optical fiber, POF)作为介质,系统中包含一个采用红光LED的发射机以及集成了光侦测器与放大器电路的接收机。


参见[编辑]


光导纤维


光通信


信息论


参考资料[编辑]


Encyclopedia of Laser Physics and Technology


Fiber-Optic Technologies by Vivek Alwayn


Agrawal, Govind P. Fiber-optic communication systems. New York: John Wiley & Sons. 2002. ISBN 978-0-471-21571-4.


外部链接[编辑]


How Fiber-optics work (Howstuffworks.com)


The Laser and Fiber-optic Revolution


Fiber Optics, from Hyperphysics at Georgia State University


"Understanding Optical Communications" - An IBM redbook


"光纤在线


[显示]


查论编


电话


[显示]


查论编


光通信


^ Charles E. Spurgeon. Ethernet: The Definitive Guide 2nd. O'Reilly Media. 2014. ISBN 978-1-4493-6184-6.


^ Alcatel-Lucent Bell Labs announces new optical transmission record and breaks 100 Petabit per second kilometer barrier (新闻稿). Alcatel-Lucent. 2009-10-28. (原始内容存档于2013-07-18.


^ World Record 69-Terabit Capacity for Optical Transmission over a Single Optical Fiber (新闻稿). NTT. 2010-03-25 [2010-04-03].


^ Ultrafast fibre optics set new speed record. New Scientist. 2011-04-29 [2012-02-26].


^ Laser puts record data rate through fibre. BBC. 2011-05-22.


^ BT Trial 5.6Tbps on a Single Optical Fibre and 2Tbps on a Live Core Link. ISPreview. 2016-05-25 [2018-06-30].


^ Scientists Successfully Push Fibre Optic Transmissions Close to the Shannon Limit. ISPreview. 2016-09-19 [2018-06-30].


^ 65Tbps over a single fibre: Nokia sets new submarine cable speed record. ARS Technica. 2016-12-10 [2018-06-30].


^ BT Labs delivers ultra-efficient terabit 'superchannel'. BT. 2017-06-19 [2018-08-03].


^ Ultrafast fibre optics set new speed record. New Scientist. 2011-04-29 [2012-02-26].


^ NEC and Corning achieve petabit optical transmission. Optics.org. 2013-01-22 [2013-01-23].


^ Big data, now at the speed of light. New Scientist. 2013-03-30 [2018-08-03].


^ https://www.extremetech.com/computing/151498-researchers-create-fiber-network-that-operates-at-99-7-speed-of-light-smashes-speed-and-latency-records


^ A Single Laser and Cable Delivers Fibre Optic Speeds of 43Tbps. ISPreview. 2014-07-03 [2018-06-30].


^ 255Tbps: World's fastest network could carry all of the internet's traffic on a single fiber. ExtremeTech. 2014-10-27 [2018-06-30].


^ Realization of World Record Fiber-Capacity of 2.15Pb/s Transmission. NICT. 2015-10-13 [2018-08-25].


^ One Petabit per Second Fiber Transmission over a Record Distance of 200 km (PDF). NTT. 2017-03-23 [2018-06-30].


^ Success of ultra-high capacity optical fibre transmission breaking the world record by a factor of five and reaching 10 Petabits per second (PDF). Global Sei. 2017-10-13 [2018-08-25].


^ Researchers in Japan 'break transmission record' over 1,045km with three-mode optical fibre. fibre-systems.com. 2018-04-16 [2018-06-30].


分类:光纤通信光电子学


 


 


 


 


    在两地之间,如何快速、有效地传输大批数据包?除了借助光纤通信,别无他法。

  当今,华为大搞5G光通信,火星人快步紧跟               

   注:本文附件是光纤通信“迷”必读

袁萌  陈启清  61

附件:光纤通信必读

光纤通信

光纤通信Fiber-optic communication

是指一种利用光与光纤(Optical Fiber)传递信息的一种方式,属于有线通信的一种。光经过调制(Modulation)后便能携带信息。自1980年代起,光纤通信系统对于电信工业产生了革命性的作用,同时也在数字时代里扮演非常重要的角色。光纤通信具有传输容量大、保密性好等许多优点。光纤通信线在已经成为当今最主要的有线通信方式。将需发送的信息在发送端输入到发送机中,将信息叠加或调制到作为信息信号载体的载波上,然后将已调制的载波通过传输媒质发送到远处的接收端,由接收机解调出原来的信息。

根据信号调制方式的不同,光纤通信可以分为数字光纤通信、模拟光纤通信。纤通信的产业包括了光纤电缆、光器件、光设备、光通信仪表、光通信集成电路等多个领域。

利用光纤做为通信之用通常需经过下列几个步骤:

以发射机(Transmitter)产生光信号。

以光纤传递信号,同时必须确保光信号在光纤中不会衰减或严重变形。

以接收机(Receiver)接收光信号,并且转换成电信号。

 

目录

1 应用历史

3 核心技术

3.1

发射机

3.2

光纤

3.3

光放大器

3.4

接收机

3.5

波分复用

4

系统参数

4.1

带宽距离乘积(BL积)

4.2

传输速率

4.2.1

标准光纤

4.3

信号色散

4.4

信号衰减

4.5

信号再生

4.6

最后一公里光纤网络

5

与传统通信系统的比较

6

现行技术标准

7

参见

8

参考资料

9

外部链接

  应用

光纤常被电话公司用于传递电话、互联网,或是有线电视的信号,有时候利用一条光纤就可以同时传递上述的所有信号。与传统的铜线相比,光纤的信号衰减(attenuation)与遭受干扰[来源请求]interference)的情形都改善很多,特别是长距离以及大量传输的使用场合中,光纤的优势更为明显。然而,在城市之间利用光纤的通信基础建设(infrastructure)通常施工难度以及材料成本难以控制,完工后的系统维运复杂度与成本也居高不下。因此,早期光纤通信系统多半应用在长途的通信需求中,这样才能让光纤的优势彻底发挥,并且抑制住不断增加的成本。

2000年光通信(optical communication)市场崩溃后,光纤通信的成本也不断下探,当前已经和铜缆为骨干的通信系统不相上下[1]

对于光纤通信产业而言,1990年光放大器(optical amplifier)正式进入商业市场的应用后,很多超长距离的光纤通信才得以真正实现,例如越洋的海底电缆。到了2002年时,越洋海底电缆的总长已经超过25万千米,每秒能携带的数据量超过2.56Tb,而且根据电信运营商的统计,这些数据从2002年后仍然不断的大幅成长中。

历史[编辑]

自古以来,人类对于长距离通信的需求就不曾稍减。随着时间的前进,从烽火到电报,再到1940年第一条同轴电缆(coaxial cable)正式服役,这些通信系统的复杂度与精细度也不断的进步。但是这些通信方式各有其极限,使用电气信号传递信息虽然快速,但是传输距离会因为电气信号容易衰减而需要大量的中继器(repeater);微波(microwave)通信虽然可以使用空气做介质,可是也会受到载波频率(carrier frequency)的限制。到了二十世纪中叶,人们才了解使用光来传递信息,能带来很多过去所没有的显著好处。

然而,当时并没有相干性高的发光源(coherent light source),也没有适合作为传递光信号的介质,也所以光通信一直只是概念。直到1960年代,激光(laser)的发明才解决第一项难题。1970年代康宁公司(Corning Glass Works)发展出高质量低衰减的光纤则是解决了第二项问题,此时信号在光纤中传递的衰减量第一次低于光纤通信之父高锟所提出的每千米衰减20分贝(20dB/km)关卡,证明光纤作为通信介质的可能性。与此同时使用砷化镓(GaAs)作为材料的半导体激光(semiconductor laser)也被发明出来,并且凭借着体积小的优势而大量运用于光纤通信系统中。1976年,第一条速率为44.7Mbit/s的光纤通信系统在美国亚特兰大的地下管道中诞生。

经过五年的研发期,第一个商用的光纤通信系统在1980年问市。这个人类史上第一个光纤通信系统使用波长800纳米(nanometer)的砷化镓激光作为光源,传输的速率(data rate)达到45Mb/sbits per second),每10千米需要一个中继器增强信号。

第二代的商用光纤通信系统也在1980年代初期就发展出来,使用波长1300纳米的磷砷化镓铟(InGaAsP)激光。早期的光纤通信系统虽然受到色散(dispersion)的问题而影响了信号质量,但是1981年单模光纤(single-mode fiber)的发明克服了这个问题。到了1987年时,一个商用光纤通信系统的传输速率已经高达1.7Gb/s,比第一个光纤通信系统的速率快将近四十倍之多。同时传输的功率与信号衰减的问题也有显著改善,间隔50千米才需要一个中继器增强信号。1980年代末,EDFA的诞生,堪称光通信历史上的一个里程碑似的事件,它使光纤通信可直接进行光中继,使长距离高速传输成为可能,并促使DWDM的诞生。

第三代的光纤通信系统改用波长1550纳米的激光做光源,而且信号的衰减已经低至每千米0.2分贝(0.2dB/km)。之前使用磷砷化镓铟激光的光纤通信系统常常遭遇到脉冲延散(pulse spreading)问题,而科学家则设计出色散位移光纤(dispersion-shifted fiber)来解决这些问题,这种光纤在传递1550纳米的光波时,色散几乎为零,因其可将激光光的光谱限制在单一纵模(longitudinal mode)。这些技术上的突破使得第三代光纤通信系统的传输速率达到2.5Gb/s,而且中继器的间隔可达到100千米远。

第四代光纤通信系统引进光放大器(optical amplifier),进一步减少中继器的需求。另外,波分复用(wavelength-division multiplexing, WDM)技术则大幅增加传输速率。这两项技术的发展让光纤通信系统的容量以每六个月增加一倍的方式大幅跃进,到了2001年时已经到达10Tb/s的惊人速率,足足是80年代光纤通信系统的200倍之多。近年来,传输速率已经进一步增加到14Tb/s,每隔160千米才需要一个中继器。

第五代光纤通信系统发展的重心在于扩展波分复用器的波长操作范围。传统的波长范围,也就是一般俗称的“C band”约是1530纳米至1570纳米之间,新一带的无水光纤(dry fiber)低损耗的波段则延伸到1300纳米至1650纳米间。另外一个发展中的技术是引进光孤子(optical soliton)的概念,利用光纤的非线性效应,让脉冲能够抵抗色散而维持原本的波形。

1990年至2000年间,光纤通信产业受到互联网泡沫的影响而大幅成长。此外一些新兴的网络应用,如视频点播(video on demand)使得互联网带宽的成长甚至超过摩尔定律(Moore's Law)所预期集成电路芯片中晶体管增加的速率。而自互联网泡沫破灭至2006年为止,光纤通信产业透过企业整并壮大规模,以及委外生产的方式降低成本来延续生命。

核心技术[编辑]

现代的光纤通信系统多半包括一个发射机,将电信号转换成光信号,再透过光纤将光信号传递。光纤多半埋在地下,连接不同的建筑物。系统中还包括数种光放大器,以及一个光接收机将光信号转换回电信号。在光纤通信系统中传递的多半是数字信号,来源包括计算机、电话系统,或是有线电视系统。

发射机[编辑]

在光纤通信系统中通常作为光源的半导体组件是发光二极管(light-emitting diode, LED)或是激光二极管(laser diode)。LED与激光二极管的主要差异在于前者所发出的光为非相干性(noncoherent),而后者则为相干性(coherent)的光。使用半导体作为光源的好处是体积小、发光效率高、可靠度佳,以及可以将波长最优化,更重要的是半导体光源可以在高频操作下直接调制,非常适合光纤通信系统的需求。

LED借着电激发光(electroluminescence)的原理发出非相干性的光,频谱通常分散在30纳米至60纳米间。LED另外一项缺点是发光效率差,通常只有输入功率的1%可以转换成光功率,约是100微瓦特(micro-watt)左右。但是由于LED的成本较低廉,因此常用于低价的应用中。常用于光通信的LED主要材料是砷化镓或是砷化镓磷(GaAsP),后者的发光波长为1300纳米左右,比砷化镓的810纳米至870纳米更适合用在光纤通信。由于LED的频谱范围较广,导致色散较为严重,也限制了其传输速率与传输距离的乘积。LED通常用在传输速率10Mb/s100Mb/s的局域网(local area network, LAN),传输距离也在数千米之内。当前也有LED内包含了数个量子井(quantum well)的结构,使得LED可以发出不同波长的光,涵盖较宽的频谱,这种LED被广泛应用在区域性的波分复用网络中。

半导体激光的输出功率通常在100毫瓦特(mW)左右,而且为相干性质的光源,方向性相对而言较强,通常和单模光纤的耦合效率可达50%。激光的输出频谱较窄,也有助于增加传输速率以及降低模态色散(modal dispersion)。半导体激光亦可在相当高的操作频率下进行调制,原因是其复合时间(recombination time)非常短。

半导体激光通常可由输入的电流有无直接调制其开关状态与输出信号,不过对于某些传输速率非常高或是传输距离很长的应用,激光光源可能会以连续波(continuous wave)的形式控制,例如使用外置的电吸收光调制器(electroabsorption modulator)或是马赫·任德干涉仪(Mach-Zehnder interferometer)对光信号加以调制。外置的调制组件可以大幅减少激光的“啁啾脉冲”(chirp pulse)。啁啾脉冲会使得激光的谱线宽度变宽,使得光纤内的色散变得严重。

光纤[编辑]

主条目:光导纤维

光纤缆线包含一个纤芯(core),纤壳(cladding)以及外层的保护被覆(protective coating)。核心与折射率(refractive index)较高的纤壳通常用高质量的硅石玻璃(silica glass)制成,但是现在也有使用塑胶作为材质的光纤。又因为光纤的外层有经过紫外线固化后的压克力(acrylate)被覆,可以如铜缆一样埋藏于地下,不需要太多维护费用。然而,如果光纤被弯折的太过剧烈,仍然有折断的危险。而且因为光纤两端连接需要十分精密的校准,所以折断的光纤也难以重新接合。

光通信中主要使用多模、单模两种光纤。多模光纤纤芯直径更大(≥50微米),对发射机、连接器的要求更低。然而,多模光纤引入了多模色散,这会限制系统的带宽和长度。此外,由于有更高的杂质含量,多模光纤通常会有更高的衰减。单模光纤的纤芯直径较小(<10微米),对发射机、连接器的要求更高,但能够搭建传输距离更长、性能更好的系统。单模和多模光纤都有不同的等级。

光纤类型比较[1]

多模光纤 FDDI 62,5/125 µm(1987)

多模光纤 OM1 62,5/125 µm(1989)

多模光纤 OM2 50/125 µm(1998)

多模光纤 OM3 50/125 µm(2003)

多模光纤 OM4 50/125 µm(2008)

多模光纤 OM550/125 µm(2016)

单模光纤 OS19/125 µm(1998)

单模光纤OS29/125 µm(2000)

160 MHz·km@850 nm

200 MHz·km@850 nm

500 MHz·km@850 nm

1500 MHz·km@850 nm

3500 MHz·km@850 nm

3500 MHz·km@850 nm &1850 MHz·km@950 nm

1 dB/km@1300/1550 nm

0.4 dB/km@1300/1550 nm

光放大器[编辑]

主条目:光放大器

过去光纤通信的距离限制主要根源于信号在光纤内的衰减以及信号变形,而解决的方式是利用光电转换的中继器。这种中继器先将光信号转回电信号放大后再转换成较强的光信号传往下一个中继器,然而这样的系统架构无疑较为复杂,不适用于新一代的。

接收机[编辑]

构成光接收机的主要组件是光侦测器(photodetector),利用光电效应将入射的光信号转为电信号。光侦测器通常是半导体为基础的光二极管(photo diode),例如p-n结二极管、p-i-n二极管,或是雪崩型二极管(avalanche diode)。另外“金属-半导体-金属”(Metal-Semiconductor-Metal, MSM)光侦测器也因为与电路集成性佳,而被应用在光再生器(regenerator)或是波分复用器中。

光接收机电路通常使用转阻放大器(transimpedence amplifier, TIA)以及限幅放大器(limiting amplifier)处理由光侦测器转换出的光电流,转阻放大器和限幅放大器可以将光电流转换成幅度较小的电压信号,再透过后端的比较器(comparator)电路转换成数字信号。对于高速光纤通信系统而言,信号常常相对地衰减较为严重,为了避免接收机电路输出的数字信号变形超出规格,通常在接收机电路的后级也会加上时脉及数据恢复电路(clock and data recovery, CDR)以及锁相回路(phase-locked loop, PLL)将信号做适度处理再输出。

波分复用[编辑]

主条目:波分复用

波分复用的实际做法就是将光纤的工作波长分割成多个信道(channel),俾使能在同一条光纤内传输更大量的数据。一个完整的波分复用系统分为发射端的波分复用器(wavelength division multiplexer)以及在接收端的波长分波解多任务器(wavelength division demultiplexer),最常用于波分复用系统的组件是数组波导光栅(Arrayed Waveguide Gratings, AWG)。而当前市面上已经有商用的波分复用器/解多任务器,最多可将光纤通信系统划分成80个信道,也使得数据传输的速率一下子就突破Tb/s的等级。

系统参数[编辑]

带宽距离乘积(BL积)[编辑]

由于传输距离越远,光纤内的色散现象就越严重,影响信号质量。因此常用于评估光纤通信系统的一项指针就是带宽-距离乘积(BL积),单位是百万赫兹×千米(MHz×km)。使用这两个值的乘积做为指针的原因是通常这两个值不会同时变好,而必须有所取舍(trade off)。举例而言,一个常见的多模光纤系统的带宽-距离乘积约是500MHz×km,代表这个系统在一千米内的信号带宽可以到500MHz,而如果距离缩短至0.5千米时,带宽则可以倍增到1000MHz

传输速率[编辑]

每根光纤可以承载许多独立的信道,每个信道使用不同波长的光(波分复用)。每条光纤的净数据速率(没有开销字节的数据速率)是每信道数据速率减少了FEC开销,乘以信道数量(截至2008年,商用密集WDM系统通常高达80个)。

标准光纤[编辑]

以下总结了当前使用标准电信级单模单芯光纤电缆的最新研究成果。

机构

系统传输速率

WDM信道数

单信道传输速率

传输距离

2009

阿尔卡特朗讯[2]

15.5 Tbit/s

155

100 Gbit/s

7000 km

2010

NTT[3]

69.1 Tbit/s

432

171 Gbit/s

240 km

2011

NEC[4]

101.7 Tbit/s

370

273 Gbit/s

165 km

2011

卡尔斯鲁厄理工学院[5]

26 Tbit/s

>300

 

50 km

2016

英国电信和华为[6]

5.6 Tbit/s

28

200Gb/s

circa 140 km ?

2016

贝尔实验室、德国电信T-Labs和慕尼黑工业大学[7](第一个接近香农理论极限的成果)

1 Tbit/s

1

1Tb/s

 

2016

诺基亚网络[8]

65 Tbit/s

 

 

6600 Km

2017

英国电信和[./https://en.wikipedia.org/wiki/Huawei 华为][9]

11.2 Tbit/s

28

400 Gb/s

250 Km

特种光纤

以下总结了当前使用少模光纤等特种光纤进行空分复用完成的研究成果。

机构

系统传输速率

模式数量

纤芯数量

单芯WDM信道数

单信道传输速率

传输距离

2011

NICT[10]

109.2 Tbit/s

 

7

 

 

 

2012

NEC, 康宁公司[11]

1.05 Pbit/s

 

12

 

 

52.4 km

2013

南安普顿大学[12]

73.7 Tbit/s

 

1 (空芯光纤)

3x96(模式DM)[13]

256 Gb/s

310 m

2014

丹麦技术大学[14]

43 Tbit/s

 

7

 

 

1045 km

2014

艾恩德霍芬理工大学和中佛罗里达大学[15]

255 Tbit/s

 

7

50

~728 Gb/s

1 km

2015

NICT、住友电气和RAM光子[16]

2.15 Pbit/s

 

22

402 (C+L波段)

243 Gb/s

31 km

2017

NTT[17]

1 Pbit/s

单模

32

46

680 Gb/s

205.6 Km

2017

KDDI住友电气[18]

10.16 Pbit/s

6

19

739 (C+L波段)

120 Gb/s

11.3 Km

2018

NICT[19]

159 Tbit/s

3

1

348

414 Gb/s

1045 km

信号色散[编辑]

对于现代的玻璃光纤而言,最严重的问题并非信号的衰减,而是色散问题,也就是信号在光纤内传输一段距离后逐渐扩散重叠,使得接收端难以判别信号的高或低。造成光纤内色散的成因很多。以模态色散为例,信号的横模(transverse mode)轴速度(axial speed)不一致导致色散,这也限制了多模光纤的应用。在单模光纤中,模态间的色散可以被压抑得很低。

但是在单模光纤中一样有色散问题,通常称为群速色散(group-velocity dispersion),起因是对不同波长的入射光波而言,玻璃的折射率略有不同,而光源所发射的光波不可能没有频谱的分布,这也造成了光波在光纤内部会因为波长的些微差异而有不同的折射行为。另外一种在单模光纤中常见的色散称为偏振态色散(polarization mode dispersion),起因是单模光纤内虽然一次只能容纳一个横模的光波,但是这个横模的光波却可以有两个方向的偏振(polarization),而光纤内的任何结构缺陷与变形都可能让这两个偏振方向的光波产生不一样的传递速度,这又称为光纤的双折射现象(fiber birefringence)。这个现象可以透过偏振保持光纤(polarization-maintaining optical fiber)加以抑制。

信号衰减[编辑]

信号在光纤内衰减也造成光放大器成为光纤通信系统所必需的组件。光波在光纤内衰减的主因有物质吸收、瑞利散射(Rayleigh scattering)、米氏散射(Mie scattering)以及连接器造成的损失。虽然石英的吸收系数只有0.03dB/km,但是光纤内的杂质仍然会让吸收系数变大。其他造成信号衰减的原因还包括应力对光纤造成的变形、光纤密度的微小扰动,或是接合的技术仍有待加强。

信号再生[编辑]

现代的光纤通信系统因为引进了很多新技术降低信号衰减的程度,因此信号再生只需要用于距离数百千米远的通信系统中。这使得光纤通信系统的建置费用与维运成本大幅降低,特别对于越洋的海底光纤而言,中继器的稳定度往往是维护成本居高不下的主因。这些突破对于控制系统的色散也有很大的助益,足以降低色散造成的非线性现象。此外,光孤子也是另外一项可以大幅降低长距离通信系统中色散的关键技术。

最后一公里光纤网络[编辑]

虽然光纤网络享有高容量的优势,但是在达成普及化的目标,也就是“光纤到户”(Fiber To The Home, FTTH)以及“最后一公里”(last mile)的网络布建上仍然有很多困难待克服。然而,随着网络带宽的需求日增,已经有越来越多国家逐渐达成这个目的。以韩国为例,光纤网络系统已经开始取代使用铜线的数字用户回路系统。

与传统通信系统的比较[编辑]

对于某个通信系统而言,使用传统的铜缆作为传输介质较好,或是使用光纤较佳,有几项考量的重点。光纤通常用于高带宽以及长距离的应用,因为其具有低损耗、高容量,以及不需要太多中继器等优点。光纤另外一项重要的优点是即使跨越长距离的数条光纤并行,光纤与光纤之间也不会产生串扰(cross-talk)的干扰,这和传输电信号的传输线(transmission line)正好相反。

不过对于短距离与低带宽的通信应用而言,使用电信号的传输有下列好处:

较低的建置费用

组装容易

可以利用电力系统传递信息

因为这些好处,所以在很短的距离传输信息,例如主机之间、电路板之间,甚至是集成电路芯片之间,通常还是使用电信号传输。然而当前也有些还在实验阶段的系统已经改采光来传递信息。

在某些低带宽的场合,光纤通信仍然有其独特的优势:

能抵抗电磁干扰(EMI),包括核子造成的电磁脉冲。(不过光纤可能会毁于α或β射线)

对电信号的阻抗极高,所以能在高电压或是地面电势不同的状况下安全工作。

重量较轻,这在飞机中特别重要。

不会产生火花,在某些易燃的环境中显得重要。

没有电磁辐射、不易被窃听,对于需要高度安全的系统而言十分重要。

线径小,当绕线的路径被限制时,变得重要。

现行技术标准[编辑]

为了能让不同的光纤通信设备制造商之间有共通的标准,国际电信联盟(International Telecommunications Union, ITU)制定了数个与光纤通信相关的标准,包括:

ITU-T G.651, 多模光纤, "Characteristics of a 50/125 µm multimode graded index optical fibre cable"

ITU-T G.652, 标准单模光纤, "Characteristics of a single-mode optical fibre cable"

ITU-T 6.653, 色散位移单模光纤, "Characteristics of a dispersion-shifted single-mode optical fibre cable Superseded"

ITU-T 6.654, 截止波长位移单模光纤, "Characteristics of a cut-off shifted single-mode optical fibre and cable Superseded"

ITU-T 6.655, 非零色散位移单模光纤, "Characteristics of a non-zero dispersion-shifted single-mode optical fibre cable Superseded "

ITU-T 6.656, 宽传输带宽非零色散位移单模光纤,"Characteristics of a fibre and cable with non-zero dispersion for wideband optical transport"

ITU-T 6.657, 弯曲不敏感单模光纤, "Characteristics of a bending-loss insensitive single-mode optical fibre and cable"

其他关于光纤通信的标判据规定了发射与接收端,或是传输介质的规格,包括了:

10G以太网(10 Gigabit Ethernet

光纤分布式数据接口(FDDI

光纤信道(Fibre channel

HIPPI

同步数字层次结构(Synchronous Digital Hierarchy

同步光纤网络(Synchronous Optical Networking

此外,在数字音效的领域中,也有利用光纤传递信息的规格,那就是由日本东芝(Toshiba)所制定的TOSLINK规格。采用塑胶光纤(plastic optical fiber, POF)作为介质,系统中包含一个采用红光LED的发射机以及集成了光侦测器与放大器电路的接收机。

参见[编辑]

光导纤维

光通信

信息论

参考资料[编辑]

Encyclopedia of Laser Physics and Technology

Fiber-Optic Technologies by Vivek Alwayn

Agrawal, Govind P. Fiber-optic communication systems. New York: John Wiley & Sons. 2002. ISBN 978-0-471-21571-4.

外部链接[编辑]

How Fiber-optics work (Howstuffworks.com)

The Laser and Fiber-optic Revolution

Fiber Optics, from Hyperphysics at Georgia State University

"Understanding Optical Communications" - An IBM redbook

"光纤在线

[显示]

查论编

电话

[显示]

查论编

光通信

^ Charles E. Spurgeon. Ethernet: The Definitive Guide 2nd. O'Reilly Media. 2014. ISBN 978-1-4493-6184-6.

^ Alcatel-Lucent Bell Labs announces new optical transmission record and breaks 100 Petabit per second kilometer barrier (新闻稿). Alcatel-Lucent. 2009-10-28. (原始内容存档于2013-07-18.

^ World Record 69-Terabit Capacity for Optical Transmission over a Single Optical Fiber (新闻稿). NTT. 2010-03-25 [2010-04-03].

^ Ultrafast fibre optics set new speed record. New Scientist. 2011-04-29 [2012-02-26].

^ Laser puts record data rate through fibre. BBC. 2011-05-22.

^ BT Trial 5.6Tbps on a Single Optical Fibre and 2Tbps on a Live Core Link. ISPreview. 2016-05-25 [2018-06-30].

^ Scientists Successfully Push Fibre Optic Transmissions Close to the Shannon Limit. ISPreview. 2016-09-19 [2018-06-30].

^ 65Tbps over a single fibre: Nokia sets new submarine cable speed record. ARS Technica. 2016-12-10 [2018-06-30].

^ BT Labs delivers ultra-efficient terabit 'superchannel'. BT. 2017-06-19 [2018-08-03].

^ Ultrafast fibre optics set new speed record. New Scientist. 2011-04-29 [2012-02-26].

^ NEC and Corning achieve petabit optical transmission. Optics.org. 2013-01-22 [2013-01-23].

^ Big data, now at the speed of light. New Scientist. 2013-03-30 [2018-08-03].

^ https://www.extremetech.com/computing/151498-researchers-create-fiber-network-that-operates-at-99-7-speed-of-light-smashes-speed-and-latency-records

^ A Single Laser and Cable Delivers Fibre Optic Speeds of 43Tbps. ISPreview. 2014-07-03 [2018-06-30].

^ 255Tbps: World's fastest network could carry all of the internet's traffic on a single fiber. ExtremeTech. 2014-10-27 [2018-06-30].

^ Realization of World Record Fiber-Capacity of 2.15Pb/s Transmission. NICT. 2015-10-13 [2018-08-25].

^ One Petabit per Second Fiber Transmission over a Record Distance of 200 km (PDF). NTT. 2017-03-23 [2018-06-30].

^ Success of ultra-high capacity optical fibre transmission breaking the world record by a factor of five and reaching 10 Petabits per second (PDF). Global Sei. 2017-10-13 [2018-08-25].

^ Researchers in Japan 'break transmission record' over 1,045km with three-mode optical fibre. fibre-systems.com. 2018-04-16 [2018-06-30].

分类:光纤通信光电子学

 

 

 

 



 

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17天前 北大袁萌“6.1国际儿童节”与开放系统互联7层框架模型

6.1国际儿童节”与开放系统互联7层框架模型

儿童是我们的未来,他们生活在开放系统互联7层框架模型(手机环境)之中。

数据包是一个最基本的概念。但是,数据包在什么环境中传输?答案是:智能5G环境。

华为与火星人在开放系统互联7层框架模型环境中阔步前进。

袁萌  陈启清   61

附件:OSI“迷”必读

开放系统互连参考模型

同义词 OSI七层模型一般指开放系统互连参考模型

开放系统互连参考模型 (Open System Interconnect 简称OSI)是国际标准化组织(ISO)和国际电报电话咨询委员会(CCITT)联合制定的开放系统互连参考模型,为开放式互连信息系统提供了一种功能结构的框架。它从低到高分别是:物理层、数据链路层、网络层、传输层、会话层、表示层和应用层。

 

中文名

开放系统互连参考模型

外文名

Open System Interconnect 

   

OSI

制定组织

ISOCCITT

   

开放系统互连参考模型

   

提供了一种功能结构的框架

应用学科

计算机、通信

目录

1 概述

2 物理层

3 数据链路层

4 网络层

5 传输层

6 会话层

7 表示层

8 应用层

 

 

 

概述

开放系统互连参考模型为实现开放系统互连所建立的通信功能分层模型,简称OSI参考模型。其目的是为异种计算机互连提供一个共同的基础和标准框架,并为保持相关标准的一致性和兼容性提供共同的参考。这里所说的开放系统,实质上指的是遵循OSI参考模型和相关协议能够实现互连的具有各种应用目的的计算机系统。OSI参考模型如图1所示。

 

1 OSI参考模型

OSI参考模型是计算机网络体系结构发展的产物。它的基本内容是开放系统通信功能的分层结构。这个模型把开放系统的通信功能划分为七个层次,从邻接物理媒体的层次开始,分别赋于12,……7层的顺序编号,相应地称之为物理层、数据链路层、网络层、传输层、会话层、表示层和应用层。每一层的功能是独立的。它利用其下一层提供的服务并为其上一层提供服务,而与其他层的具体实现无关。这里所谓的“服务”就是下一层向上一层提供的通信功能和层之间的会话规定,一般用通信原语实现。两个开放系统中的同等层之间的通信规则和约定称之为协议。通常把14层协议称为下层协议,57层协议称为上层协议。

1、国际标准化组织ISO1979年建立了一个分委员会来专门研究一种用于开放系统的体系结构,提出了开放系统互连OSI模型,这是一个定义连接异种计算机的标准主体结构。

  2OSI简介:OSI采用了分层的结构化技术,共分七层,物理层、数据链路层、网络层、传输层、会话层、表示层、应用层。

  3OSI参考模型的特性:是一种异构系统互连的分层结构;提供了控制互连系统交互规则的标准骨架;定义一种抽象结构,而并非具体实现的描述;不同系统中相同层的实体为同等层实体;同等层实体之间通信由该层的协议管理;相信层间的接口定义了原语操作和低层向上层提供的服务;所提供的公共服务是面向连接的或无连接的数据服务;直接的数据传送仅在最低层实现;每层完成所定义的功能,修改本层的功能并不影响其他层。

  4、物理层:提供为建立、维护和拆除物理链路所需要的机械的、电气的、功能的和规程的特性;有关的物理链路上传输非结构的位流以及故障检测指示。

  5、数据链路层:在网络层实体间提供数据发送和接收的功能和过程;提供数据链路的流控。

  6、网络层:控制分组传送系统的操作、路由选择、用户控制、网络互连等功能,它的作用是将具体的物理传送对高层透明。

  7、传输层:提供建立、维护和拆除传送连接的功能;选择网络层提供最合适的服务;在系统之间提供可靠的透明的数据传送,提供端到端的错误恢复和流量控制。

  8、会话层:提供两进程之间建立、维护和结束会话连接的功能;提供交互会话的管理功能,如三种数据流方向的控制,即一路交互、两路交替和两路同时会话模式

  9、表示层:代表应用进程协商数据表示;完成数据转换、格式化和文本压缩。

  10、应用层:提供OSI用户服务,例如事务处理程序、文件传送协议和网络管理等。

 

 

 

物理层

编辑

物理层并不是物理媒体本身,它只是开放系统中利用物理媒体实现物理连接的功能描述和执行连接的规程。物理层提供用于建立、保持和断开物理连接的机械的、电气的、功能的和过程的条件。简而言之,物理层提供有关同步和全双工比特流在物理媒体上的传输手段,其典型的协议有RS 232CRS 449/422/423V.24X.21X.21bis等。

物理层是OSI的第一层,它虽然处于最底层,却是整个开放系统的基础。物理层为设备之间的数据通信提供传输媒体及互连设备,为数据传输提供可靠的环境。

 

开放系统互连参考模型

物理层的媒体包括架空明线、平衡电缆、光纤、无线信道等。通信用的互连设备指DTEData Terminal Equipment)和DCEData Communications Equipment)间的互连设备。DTE即数据终端设备,又称物理设备,如计算机、终端等都包括在内。而DCE则是数据通信设备或电路连接设备,如调制解调器等。数据传输通常是经过DTE-DCE,再经过DCE-DTE的路径。互连设备指将DTEDCE连接起来的装置,如各种插头、插座。LAN中的各种粗、细同轴电缆、T型接头、插头、接收器、发送器、中继器等都属物理层的媒体和连接器。

物理层的主要功能是:为数据端设备提供传送数据的通路,数据通路可以是一个物理媒体,也可以是多个物理媒体连接而成。一次完整的数据传输,包括激活物理连接、传送数据和终止物理连接。所谓激活,就是不管有多少物理媒体参与,都要在通信的两个数据终端设备间连接起来,形成一条通路。传输数据。物理层要形成适合数据传输需要的实体,为数据传送服务。一是要保证数据能在其上正确通过,二是要提供足够的带宽(带宽是指每秒钟内能通过的比特(Bit)),以减少信道上的拥塞。传输数据的方式能满足点到点,一点到多点,串行或并行,半双工或全双工,同步或异步传输的需要。完成物理层的一些管理工作。

 

 

 

数据链路层

编辑

数据链路可以粗略地理解为数据通道。物理层要为终端设备间的数据通信提供传输介质及其连接。介质是长期的,连接是有生存期的。在连接生存期内,收发两端可以进行不等的一次或多次数据通信。每次通信都要经过建立通信联络和拆除通信联络两个过程。这种建立起来的数据收发关系就叫做数据链路。而在物理媒体上传输的数据难免受到各种不可靠因素的影响而产生差错,为了弥补物理层上的不足,为上层提供无差错的数据传输,就要能对数据进行检错和纠错。数据链路的建立,拆除,对数据的检错,纠错是数据链路层的基本任务。

链路层是为网络层提供数据传送服务的,这种服务要依靠本层具备的功能来实现。链路层应具备如下功能:

链路连接的建立、拆除和分离;

帧定界和帧同步。链路层的数据传输单元是帧,协议不同,帧的长短和界面也有差别,但无论如何必须对帧进行定界;

顺序控制,指对帧的收发顺序的控制;

差错检测和恢复。还有链路标识,流量控制等等。差错检测多用方阵码校验和循环码校验来检测信道上数据的误码,而帧丢失等用序号检测。各种错误的恢复则常靠反馈重发技术来完成。

独立的链路产品中最常见的当属网卡,网桥也是链路产品。数据链路层将本质上不可靠的传输媒体变成可靠的传输通路提供给网络层。在IEEE802.3情况下,数据链路层分成了两个子层,一个是逻辑链路控制,另一个是媒体访问控制.

OSI其中

AUI——连接单元接口 PMA——物理媒体连接

MAU——媒体连接单元 PLS——物理信令

MDI——媒体相关接口

 

 

 

网络层

编辑

网络层的产生也是网络发展的结果。在联机系统和线路交换的环境中,网络层的功能没有太大意义。当数据终端增多时。它们之间有中继设备相连,此时会出现一台终端要求不只是与惟一的一台而是能和多台终端通信的情况,这就产生了把任意两台数据终端设备的数据链接起来的问题,也就是路由或者叫寻径。另外,当一条物理信道建立之后,被一对用户使用,往往有许多空闲时间被浪费掉。人们自然会希望让多对用户共用一条链路,为解决这一问题就出现了逻辑信道技术和虚拟电路技术。

中继控制层,其主要功能是利用数据链路层所保证的邻接节点间的无差错数据传输功能,通过路由选择和中继功能,实现两个端系统之间的数据传输。为此,网络层还具有多路复用功能,采用统计时分复用原理,将一条数据链路复用为多条逻辑信道,从而实现一个数据终端设备利用一条物理电路同时和多个远程数据通信设备的通信。网络层规定了网路连接的建立和拆除规程以及数据传送规程等。

网络层为建立网络连接和为上层提供服务,应具备以下主要功能:

1.路由选择和中继;

2.激活,终止网络连接;

3.在一条数据链路上复用多条网络连接,多采取分时复用技术;

4.检测与恢复;

5.排序,流量控制;

6.服务选择;

7.网络管理。

 

 

 

传输层

编辑

端开放系统之间的数据传送控制层。主要功能是端开放系统之间数据的收妥确认。同时,还用于弥补各种通信网路的质量差异,对经过下三层之后仍然存在的传输差错进行恢复,进一步提高可靠性。另外,还通过复用、分段和组合、连接和分离、分流和合流等技术措施,提高吞吐量和服务质量。

传输层是两台计算机经过网络进行数据通信时,第一个端到端的层次,具有缓冲作用。当网络层服务质量不能满足要求时,它将服务加以提高,以满足高层的要求;当网络层服务质量较好时,它只用很少的工作。传输层还可进行复用,即在一个网络连接上创建多个逻辑连接。传输层也称为运输层。传输层只存在于端开放系统中,是介于低3层通信子网系统和高3层之间的一层,但是很重要的一层。因为它是源端到目的端对数据传送进行控制从低到高的最后一层。

有一个既存事实,即世界上各种通信子网在性能上存在着很大差异。例如电话交换网,分组交换网,公用数据交换网,局域网等通信子网都可互连,但它们提供的吞吐量,传输速率,数据延迟通信费用各不相同。对于会话层来说,却要求有一性能恒定的界面。传输层就承担了这一功能。它采用分流/合流,复用/介复用技术来调节上述通信子网的差异,使会话层感受不到。

此外传输层还要具备差错恢复,流量控制等功能,以此对会话层屏蔽通信子网在这些方面的细节与差异。传输层面对的数据对象已不是网络地址和主机地址,而是会话层的界面端口。上述功能的最终目的是为会话提供可靠的,无误的数据传输。传输层的服务一般要经历传输连接建立、数据传送、传输连接释放3个阶段才算完成一个完整的服务过程。而在数据传送阶段又分为一般数据传送和加速数据传送两种。

 

 

 

会话层

编辑

会话单位的控制层,其主要功能是按照在应用进程之间约定的原则,按照正确的顺序收、发数据,进行各种形态的对话。会话层规定了会话服务用户间会话连接的建立和拆除规程以及数据传送规程。

会话层提供的服务是应用建立和维持会话,并能使会话获得同步。会话层使用校验点可使通信会话在通信失效时从校验点继续恢复通信。这种能力对于传送大的文件极为重要。会话层,表示层,应用层构成开放系统的高3层,面向应用进程提供分布处理、对话管理、信息表示、检查和恢复与语义上下文有关的传送差错等。为给两个对等会话服务用户建立一个会话连接,应该做如下几项工作:

1.将会话地址映射为运输地址;

2.数据传输阶段;

3.连接释放。

 

 

 

表示层

编辑

数据表示形式的控制层,其主要功能是把应用层提供的信息变换为能够共同理解的形式,提供字符代码、数据格式、控制信息格式、加密等的统一表示。表示层的作用之一是为异种机通信提供一种公共语言,以便能进行互操作。这种类型的服务之所以需要,是因为不同的计算机体系结构使用的数据表示法不同。例如,IBM主机使用EBCDIC编码,而大部分PC机使用的是ASCII码。在这种情况下,便需要表示层来完成这种转换。通过前面的介绍,我们可以看出,会话层以下5层完成了端到端的数据传送,并且是可靠的、无差错的传送。但是数据传送只是手段而不是目的,最终是要实现对数据的使用。由于各种系统对数据的定义并不完全相同,最易明白的例子是键盘——其上的某些键的含义在许多系统中都有差异。这自然给利用其它系统的数据造成了障碍。表示层和应用层就担负了消除这种障碍的任务。

 

 

 

应用层

编辑

OSI参考模型的最高层。其功能是实现应用进程(如用户程序、终端操作员等)之间的信息交换。同时,还具有一系列业务处理所需要的服务功能。应用层一般包括公共应用服务要素(CASE)和特定应用服务要素(SASE>。其中CASE提供应用进程中最基本的服务,向应用进程提供信息传送所必需的、但又独立于应用进程通信的能力。SASE实质上是各种应用进程在应用层中的映射,每一个SASE都针对某一类具体应用,例如文件传送、访问和管理(FTAM)、虚拟终端(VT)、消息处理系统(MHS)、电子数据互换(EDI)和目录查询等。

应用层向应用程序提供服务,这些服务按其向应用程序提供的特性分成组,并称为服务元素。有些可为多种应用程序共同使用,有些则为较少的一类应用程序使用。应用层是开放系统的最高层,是直接为应用进程提供服务的。其作用是在实现多个系统应用进程相互通信的同时,完成一系列业务处理所需的服务。

 

通信协议

 

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科学百科信息科学分类 中国通信学会 通信技术

 

 

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18天前 北大袁萌维护OSI的尊严,火星人与华为战斗在一起

维护OSI的尊严,火星人与华为战斗在一起

    众所周知,开放系统互联(OSI)模型是当今世界互联网的基石。

华为是OSI的忠实维护者。近日,美国政府打压华为毫无道理。这是欺负老实人.

为此,北大火星人科普OSI,与华为战斗在一起。

    注:科普OSI,我们从数据包起步(附件)。

袁萌  陈启清 530

附件:

数据包(英语:Data packet),又称分组,是在分组交换网络中传输的格式化数据单位。

一个数据包(packet)分成两个部分,包括控制信息,也就是头(header),和数据本身,也就是负载(payload)。

我们可以将一个数据包比作一封信,头相当于信封,而数据包的数据部分则相当于信的内容。当然,有时候一个大数据包可以分成多个小数据包,这个和信不同。

 

 

 

 

 

 

OSI模型OSI模型中,数据包是对第三层的数据单位的称呼。

 



 

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19天前 北大袁萌开放系统互联(OSI)发展史,打压华为者最可耻!

开放系统互联(OSI)发展史,打压华为者最可耻!

    当今,美国政客打压华为是搞错了对象。华为是干什么的?简单地说,华为是世界互联网的修理匠,完全                             遵循国际互联网标准OZI

    实质上,打压华为就是跟国际标准OSI过不去,必定自找烦恼。

   记得,上世纪8-90年代,袁萌最喜爱去的地方就是中关村大姐上的电脑书籍商店,去“淘书”,其中开放系统互联(OSI)书籍为“最爱”。

    美国政客打压华为是技术“白痴”,根本不懂OSI

华为是老实人,遵循OSI国际标准做生意,符合互联网的开放性本质。           打压华为者最可耻!

本文附件说明OSI的来历。

袁萌  陈启清  530

附件:

History[edit]

In the late 1970s, the International Organization for Standardization (ISO) conducted a program to develop general standards and methods of networking. A similar process evolved at the International Telegraph and Telephone Consultative Committee (CCITT, from French: Comité Consultatif International Téléphonique et Télégraphique). Both bodies developed documents that defined similar networking models.

In 1983, these two documents were merged to form a standard called The Basic Reference Model for Open Systems Interconnection. The standard is usually referred to as Open Systems Interconnection Reference Model, OSI Reference Model, or simply OSI model. It was published in 1984 by both the ISO, as standard ISO 7498, and the renamed CCITT (now called the Telecommunications Standardization Sector of the International Telecommunication Union or ITU-T) as standard X.200.

OSI had two major components, an abstract model of networking, called the Basic Reference Model or seven-layer model, and a set of specific protocols.

The concept of a seven-layer model was provided by the work of Charles Bachman at Honeywell Information Services. Various aspects of OSI design evolved from experiences with the ARPANET, NPLNET, EIN, CYCLADES network and the work in IFIP WG6.1. The new design was documented in ISO 7498 and its various addenda. In this model, a networking system was divided into layers. Within each layer, one or more entities implement its functionality. Each entity interacted directly only with the layer immediately beneath it, and provided facilities for use by the layer above it.

Protocols enable an entity in one host to interact with a corresponding entity at the same layer in another host. Service definitions abstractly describe the functionality provided to an (N)-layer by an (N-1) layer, where N was one of the seven layers of protocols operating in the local host.

The OSI standards documents are available from the ITU-T as the X.200-series of recommendations.[1] Some of the protocol specifications were also available as part of the ITU-T X series. The equivalent ISO and ISO/IEC standards for the OSI model were available from ISO. Not all are free of charge.[2]

 

 

 

 

 



 

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21天前 北大袁萌华为与北大火星人领跑中国互联网

华为与北大火星人领跑中国互联网

    上世纪80年代后期哦,深圳华为公司成立。

    几乎就在同一时期,袁萌接受北京市高教局聘任组件北京市高校招生计算机辅助管理系统,使用OSI联网标准。19897月,该系统(自编32万条代码)首次投入使用,获得成功。

   199138日,国家教委学生司发文,聘任袁萌担任全全国普通高校招生联网工程总顾问。经过7年艰苦努力,袁萌带领火星人开发团队获得巨大成功。

    这是OSI联网工程在中国第一次成功的实践。

    OSI是什么?请见附件。

袁萌  陈启清  528

附件:

OSI是一个多义词,请在下列义项上选择浏览(共4个义项) 添加义项 

开放系统互联(Open System Interconnection)

根据开放源码促进会

开放源代码促进会

OSI技术(OrdersSourcesIdentification)

 

 

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OSI (开放系统互联(Open System Interconnection) 编辑 讨论

OSIOpen System Interconnection的缩写,意为开放式系统互联。国际标准化组织(ISO)制定了OSI模型,该模型定义了不同计算机互联的标准,是设计和描述计算机网络通信的基本框架。OSI模型把网络通信的工作分为7层,分别是物理层、数据链路层、网络层、传输层、会话层、表示层和应用层。

这是一种事实上被TCP/IP 4层模型淘汰的协议。在当今世界上没有大规模使用。

 

中文名

开放式系统互联

外文名

OSIOpen System Interconnection

   

通信

   

通信协议

目录

1 OSI起源

2 OSI/RM

3 设计目的

4 分层原则

5 OSI/RM分层

6 七层结构

7 总结

8 分层优点

9 比较TCP/IP

 

 

 

OSI起源

196912月,美国国防部高级计划研究署的分组交换网ARPANET投入运行,从此计算机网络发展进入新纪元。ARPANET当时仅有4个结点,分别在美国国防部、原子能委员会、麻省理工学院和加利福尼亚。这4台计算机之间进行数据通信仅有传送数据的通路是不够的,还必须遵守一些事先约定好的规则,由这些规则明确所交换数据的格式及有关同步问题。

ARPANET的实践经验表明对于非常复杂的计算机网络而言,其结构最好是采用层次型的。根据这一特点,国际标准化组织ISO推出了开放系统互联参考模型(Open System Interconnect Reference ModelISO-OSI RM)。该模型定义了不同计算机互联的标准,是设计和描述计算机网络通信的基本框架。开放系统互联参考模型的系统结构共分7层。在该模型中层与层之间进行对等通信,且这种通信只是逻辑上的,真正的通信都是在最底层-物理层实现的,每一层要完成相应的功能,下一层为上一层提供服务,从而把复杂的通信过程分成了多个独立的、比较容易解决的子问题。

OSI在一开始是由ISO来制定,但后来的许多标准都是ISOCCITT联合制定的。 [1] 

 

 

 

OSI/RM

编辑

OSI/RMOpen System Interconnection Reference Model)即开放系统互联基本参考模型。开放,是指非垄断的。系统是指现实的系统中与互联有关的各部分。

世界上第一个网络体系结构由IBM公司提出(1974年,SNA),以后其他公司也相继提出自己的网络体系结构如:Digital公司的DNA,美国国防部的TCP/IP等,多种网络体系结构并存,其结果是若采用IBM的结构,只能选用IBM的产品,只能与同种结构的网络互联。

为了促进计算机网络的发展,国际标准化组织ISO1977年成立了一个委员会,在现有网络的基础上,提出了不基于具体机型、操作系统或公司的网络体系结构,称为开放系统互联模型。

 

 

 

设计目的

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OSI模型的设计目的是成为一个所有销售商都能实现的开放网路模型,来克服使用众多私有网络模型所带来的困难和低效性。OSI是在一个备受尊敬的国际标准团体的参与下完成的,这个组织就是ISO(国际标准化组织)。什么是OSIOSIOpen System Interconnection 的缩写,意为开放式系统互联参考模型。在OSI出现之前,计算机网络中存在众多的体系结构,其中以IBM公司的SNA(Systems Network Architecture,系统网络体系结构)DEC公司的DNA(Digital Network Architecture,数字网络体系结构)最为著名。为了解决不同体系结构的网络的互联问题,国际标准化组织ISO(注意不要与OSI搞混)于1981年制定了开放系统互连参考模型(Open System Interconnection Reference ModelOSI/RM)。这个模型把网络通信的工作分为7层,它们由低到高分别是物理层(Physical Layer),数据链路层(Data Link Layer),网络层(Network Layer),传输层(Transport Layer),会话层(Session Layer),表示层(Presentation Layer)和应用层(Application Layer)。第一层到第三层属于OSI参考模型的低三层,负责创建网络通信连接的链路;第五层到第七层为OSI参考模型的高三层,具体负责端到端的数据通信;第四层负责高低层的连接。每层完成一定的功能,每层都直接为其上层提供服务,并且所有层次都互相支持,而网络通信则可以自上而下(在发送端)或者自下而上(在接收端)双向进行。当然并不是每一通信都需要经过OSI的全部七层,有的甚至只需要双方对应的某一层即可。物理接口之间的转接,以及中继器与中继器之间的连接就只需在物理层中进行即可;而路由器与路由器之间的连接则只需经过网络层以下的三层即可。总的来说,双方的通信是在对等层次上进行的,不能在不对称层次上进行通信。

OSI 标准制定过程中采用的方法是将整个庞大而复杂的问题划分为若干个容易处理的小问题,这就是分层的体系结构办法。在OSI中,采用了三级抽象,即体系结构,服务定义,协议规格说明。

为方便记忆可以将七层从高到低视为:All People Seem To Need Data Processing。每一个大写字母与七层名称头一个字母相对应。

 

 

 

分层原则

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网络中各结点都有相同的层次

不同结点相同层次具有相同的功能

同一结点相邻层间通过接口通信

每一层可以使用下层提供的服务,并向上层提供服务

不同结点的同等层间通过协议来实现对等层间的通信

 

 

 

OSI/RM分层

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对等层实体间通信时信息的流动过程

对等层通信的实质:

对等层实体之间虚拟通信;下层向上层提供服务;实际通信在最底层完成;发送方数据由最高层逐渐向下层传递,到接收方数据由最低层逐渐向高层传递。

协议数据单元PDU

OSI参考模型中,对等层协议之间交换的信息单元统称为协议数据单元(PDUProtocol Data Unit)

而传输层及以下各层的PDU另外还有各自特定的名称:

传输层——数据段(Segment

网络层——分组(数据包)(Packet

数据链路层——数据帧(Frame

物理层——比特(Bit

 

 

 

七层结构

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具体7

数据格式

功能与连接方式

典型设备

应用层 Application

数据ATPU

网络服务与使用者应用程序间的一个接口

终端设备(PC、手机、平板等)

表示层 Presentation

数据PTPU

数据表示、数据安全、数据压缩

终端设备(PC、手机、平板等)

会话层 Session

数据DTPU

会话层连接到传输层的映射;会话连接的流量控制;数据传输;会话连接恢复与释放;会话连接管理、差错控制

终端设备(PC、手机、平板等)

传输层 Transport

数据组织成数据段Segment

用一个寻址机制来标识一个特定的应用程序(端口号)

终端设备(PC、手机、平板等)

网络层 Network

分割和重新组合数据包Packet

基于网络层地址(IP地址)进行不同网络系统间的路径选择

网关、路由器

数据链路层 Data Link

将比特信息封装成数据帧Frame

在物理层上建立、撤销、标识逻辑链接和链路复用 以及差错校验等功能。通过使用接收系统的硬件地址或物理地址来寻址

网桥、交换机

物理层Physical

传输比特(bit)流

建立、维护和取消物理连接

光纤、同轴电缆、

双绞线、网卡、中继器、集线器

1.物理层(Physical Layer

物理层是OSI分层结构体系中最重要、最基础的一层,它建立在传输媒介基础上,起建立、维护和取消物理连接作用,实现设备之间的物理接口。物理层只接收和发送一串比特(bit)流,不考虑信息的意义和信息结构。

物理层包括对连接到网络上的设备描述其各种机械的、电气的、功能的规定。具体地讲,机械特性规定了网络连接时所需接插件的规格尺寸、引脚数量和排列情况等;电气特性规定了在物理连接上传输bit流时线路上信号电平的大小、阻抗匹配、传输速率距离限制等;功能特性是指对各个信号先分配确切的信号含义,即定义了DTE(数据终端设备)和DCE(数据通信设备)之间各个线路的功能;过程特性定义了利用信号线进行bit流传输的一组操作规程,是指在物理连接的建立、维护、交换信息时,DTEDCE双方在各电路上的动作系列。物理层的数据单位是位。

属于物理层定义的典型规范代表包括:EIA/TIARS-232EIA/TIARS-449V.35RJ-45等。

物理层的主要功能:

·为数据端设备提供传送数据的通路,数据通路可以是一个物理媒体,也可以是多个物理媒体连接而成。一次完整的数据传输,包括激活物理连接,传送数据,终止物理连接。所谓激活,就是不管有多少物理媒体参与,都要在通信的两个数据终端设备间连接起来,形成一条通路。

·传输数据。物理层要形成适合数据传输需要的实体,为数据传送服务:

一、保证数据按位传输的正确性;

二、向数据链路层提供一个透明的位传输;

三、提供足够的带宽(带宽是指每秒钟内能通过的比特(BIT)),以减少信道上的拥塞。传输数据的方式能满足点到点,一点到多点,串行或并行,半双工或全双工,同步或异步传输的需要。

完成物理层的一些管理工作,如在数据终端设备、数据通信和交换设备等设备之间完成对数据链路的建立、保持和拆除操作。

物理层的典型设备:光纤、同轴电缆、双绞线、中继器和集线器

2. 数据链路层(Data Link Layer

在物理层提供比特流服务的基础上,将比特信息封装成数据帧Frame,起到在物理层上建立、撤销、标识逻辑链接和链路复用以及差错校验等功能。通过使用接收系统的硬件地址或物理地址来寻址。建立相邻结点之间的数据链路,通过差错控制提供数据帧(Frame)在信道上无差错的传输,同时为其上面的网络层提供有效的服务。

数据链路层在不可靠的物理介质上提供可靠的传输。该层的作用包括:物理地址寻址、数据的成帧、流量控制、数据的检错、重发等。

在这一层,数据的单位称为帧(frame)。

数据链路层协议的代表包括:SDLCHDLCPPPSTP、帧中继等。

链路层的主要功能:

·链路层的功能是实现系统实体间二进制信息块的正确传输

·为网络层提供可靠无错误的数据信息

·在数据链路中解决信息模式、操作模式、差错控制、流量控制、信息交换过程和通信控制规程的问题

链路层是为网络层提供数据传送服务的,这种服务要依靠本层具备的功能来实现。链路层应具备如下功能:

·链路连接的建立,拆除,分离。

·帧定界和帧同步。链路层的数据传输单元是帧,协议不同,帧的长短和界面也有差别,但无论如何必须对帧进行定界。

·顺序控制,指对帧的收发顺序的控制。

·差错检测和恢复。还有链路标识,流量控制等等。差错检测多用方阵码校验和循环码校验来检测信道上数据的误码,而帧丢失等用序号检测。各种错误的恢复则常靠反馈重发技术来完成。

数据链路层的典型设备:二层交换机、网桥、网卡

3.网络层(Network Layer

网络层也称通信子网层,是高层协议之间的界面层,用于控制通信子网的操作,是通信子网与资源子网的接口。在计算机网络中进行通信的两个计算机之间可能会经过很多个数据链路,也可能还要经过很多通信子网。网络层的任务就是选择合适的网间路由和交换结点,确保数据及时传送。网络层将解封装数据链路层收到的帧,提取数据包,包中封装有网络层包头,其中含有逻辑地址信息源站点和目的站点地址的网络地址。

如果你在谈论一个IP地址,那么你是在处理第3层的问题,这是“数据包”问题,而不是第2层的“帧”。IP是第3层问题的一部分,此外还有一些路由协议和地址解析协议(ARP)。有关路由的一切事情都在第3层处理。地址解析和路由是3层的重要目的。网络层还可以实现拥塞控制、网际互连、信息包顺序控制及网络记账等功能。

在网络层交换的数据单元的单位是分割和重新组合数据包(packet)。

网络层协议的代表包括:IPIPXOSPF等。

网络层主要功能是基于网络层地址(IP地址)进行不同网络系统间的路径选择。

网络层为建立网络连接和为上层提供服务,应具备以下主要功能:

·路由选择和中继;

·激活,终止网络连接;

·在一条数据链路上复用多条网络连接,多采取分时复用技术;

·差错检测与恢复;

·排序,流量控制;

·服务选择;

·网络管理;

·网络层标准简介。

网络层典型设备:网关、路由器

4.传输层(Transport Layer

传输层建立在网络层和会话层之间,实质上它是网络体系结构中高低层之间衔接的一个接口层。用一个寻址机制来标识一个特定的应用程序(端口号)。传输层不仅是一个单独的结构层,它还是整个分层体系协议的核心,没有传输层整个分层协议就没有意义。

传输层的数据单元是由数据组织成的数据段(segment)这个层负责获取全部信息,因此,它必须跟踪数据单元碎片、乱序到达的数据包和其它在传输过程中可能发生的危险。

传输层获得下层提供的服务包括:

·发送和接收正确的数据块分组序列,并用其构成传输层数据;

·获得网络层地址,包括虚拟信道和逻辑信道。

传输层向上层提供的服务包括:

·无差错的有序的报文收发;

·提供传输连接;

·进行流量控制。

传输层为上层提供端到端(最终用户到最终用户)的透明的、可靠的数据传输服务,所谓透明的传输是指在通信过程中传输层对上层屏蔽了通信传输系统的具体细节。

传输层协议的代表包括:TCPUDPSPX等。

传输层的主要功能是从会话层接收数据,根据需要把数据切成较小的数据片,并把数据传送给网络层,确保数据片正确到达网络层,从而实现两层数据的透明传送。

传输层是两台计算机经过网络进行数据通信时,第一个端到端的层次,具有缓冲作用。当网络层服务质量不能满足要求时,它将服务加以提高,以满足高层的要求;当网络层服务质量较好时,它只用很少的工作。传输层还可进行复用,即在一个网络连接上创建多个逻辑连接。

传输层也称为运输层。传输层只存在于端开放系统中,是介于低三层通信子网系统和高三层之间的一层,但是很重要的一层。因为它是源端到目的端对数据传送进行控制从低到高的最后一层。

有一个既存事实,即世界上各种通信子网在性能上存在着很大差异。例如电话交换网、分组交换网、公用数据交换网、局域网等通信子网都可互连,但它们提供的吞吐量、传输速率、数据延迟通信费用各不相同。对于会话层来说,却要求有一性能恒定的界面。传输层就承担了这一功能。它采用分流/合流、复用/介复用技术来调节上述通信子网的差异,使会话层感受不到。

此外传输层还要具备差错恢复、流量控制等功能,以此对会话层屏蔽通信子网在这些方面的细节与差异。传输层面对的数据对象已不是网络地址和主机地址,而是和会话层的界面端口。上述功能的最终目的是为会话提供可靠的、无误的数据传输。传输层的服务一般要经历传输连接建立阶段、数据传送阶段、传输连接释放阶段3个阶段才算完成一个完整的服务过程。而在数据传送阶段又分为一般数据传送和加速数据传送两种。传输层服务分成5种类型。基本可以满足对传送质量、传送速度、传送费用的各种不同需要。

5.会话层(Session Layer

这一层也可以称为会晤层或对话层,在会话层及以上的高层次中,数据传送的单位不再另外命名,统称为报文。会话层不参与具体的传输,它提供包括访问验证和会话管理在内的建立和维护应用之间通信的机制。如服务器验证用户登录便是由会话层完成的。

会话层提供的服务可使应用建立和维持会话,并能使会话获得同步。会话层使用校验点可使通信会话在通信失效时从校验点继续恢复通信。这种能力对于传送大的文件极为重要。会话层、表示层、应用层构成开放系统的高3层,面对应用进程提供分布处理,对话管理,信息表示,恢复最后的差错等。会话层同样要担负应用进程服务要求,而运输层不能完成的那部分工作,给运输层功能差距以弥补。主要的功能是对话管理,数据流同步和重新同步。要完成这些功能,需要由大量的服务单元功能组合,已经制定的功能单元已有几十种。

 

会话层的主要功能: [2] 

·会话层连接到传输层的映射;

·会话连接的流量控制;

·数据传输;

·会话连接恢复与释放;

·会话连接管理、差错控制。

为会话实体间建立连接、为给两个对等会话服务用户建立一个会话连接,应该做如下几项工作:

·将会话地址映射为运输地址;

·选择需要的运输服务质量参数(QOS)

·对会话参数进行协商;

·识别各个会话连接;

·传送有限的透明用户数据;

·数据传输阶段。

这个阶段是在两个会话用户之间实现有组织的,同步的数据传输。用户数据单元为SSDU,而协议数据单元为SPDU。会话用户之间的数据传送过程是将SSDU转变成SPDU进行的。

连接释放

连接释放是通过"有序释放""废弃""有限量透明用户数据传送"等功能单元来释放会话连接的。会话层标准为了使会话连接建立阶段能进行功能协商,也为了便于其它国际标准参考和引用,定义了12种功能单元。各个系统可根据自身情况和需要,以核心功能服务单元为基础,选配其他功能单元组成合理的会话服务子集。会话层的主要标准有"DIS8236:会话服务定义""DIS8237:会话协议规范"

6.表示层(Presentation Layer

表示层向上对应用层提供服务,向下接收来自会话层的服务。表示层是为在应用过程之间传送的信息提供表示方法的服务,它关心的只是发出信息的语法与语义。表示层要完成某些特定的功能,主要有不同数据编码格式的转换,提供数据压缩、解压缩服务,对数据进行加密、解密。例如图像格式的显示,就是由位于表示层的协议来支持。

表示层为应用层提供服务包括语法选择、语法转换等。语法选择是提供一种初始语法和以后修改这种选择的手段。语法转换涉及代码转换和字符集的转换、数据格式的修改以及对数据结构操作的适配。 [2] 

7.应用层(Application Layer

网络应用层是通信用户之间的窗口,为用户提供网络管理、文件传输、事务处理等服务。其中包含了若干个独立的、用户通用的服务协议模块。网络应用层是OSI的最高层,为网络用户之间的通信提供专用的程序。应用层的内容主要取决于用户的各自需要,这一层设计的主要问题是分布数据库、分布计算技术、网络操作系统和分布操作系统、远程文件传输、电子邮件、终端电话及远程作业登录与控制等。至2011年应用层在国际上没有完整的标准,是一个范围很广的研究领域。在OSI7个层次中,应用层是最复杂的,所包含的应用层协议也最多,有些还在研究和开发之中。 [2] 

应用层为操作系统或网络应用程序提供访问网络服务的接口。

应用层协议的代表包括:TelnetFTPHTTPSNMPDNS等。

 

 

 

总结

编辑

通过 OSI 层,信息可以从一台计算机的软件应用程序传输到另一台的应用程序上。例如,计算机 A 上的应用程序要将信息发送到计算机 B 的应用程序,则计算机 A 中的应用程序需要将信息先发送到其应用层(第七层),然后此层将信息发送到表示层(第六层),表示层将数据转送到会话层(第五层),如此继续,直至物理层(第一层)。在物理层,数据被放置在物理网络媒介中并被发送至计算机 B 。计算机 B 的物理层接收来自物理媒介的数据,然后将信息向上发送至数据链路层(第二层),数据链路层再转送给网络层,依次继续直到信息到达计算机 B 的应用层。最后,计算机 B 的应用层再将信息传送给应用程序接收端,从而完成通信过程。

OSI 的七层运用各种各样的控制信息来和其他计算机系统的对应层进行通信。这些控制信息包含特殊的请求和说明,它们在对应的 OSI 层间进行交换。每一层数据的头和尾是两个携带控制信息的基本形式。

对于从上一层传送下来的数据,附加在前面的控制信息称为头,附加在后面的控制信息称为尾。然而,在对来自上一层数据增加协议头和协议尾,对一个 OSI 层来说并不是必需的。

当数据在各层间传送时,每一层都可以在数据上增加头和尾,而这些数据已经包含了上一层增加的头和尾。协议头包含了有关层与层间的通信信息。头、尾以及数据是相关联的概念,它们取决于分析信息单元的协议层。例如,传输层头包含了只有传输层可以看到的信息,传输层下面的其他层只将此头作为数据的一部分传递。对于网络层,一个信息单元由第三层的头和数据组成。对于数据链路层,经网络层向下传递的所有信息即第三层头和数据都被看作是数据。换句话说,在给定的某一 OSI 层,信息单元的数据部分包含来自于所有上层的头和尾以及数据,这称之为封装。

例如,如果计算机 A 要将应用程序中的某数据发送至计算机 B ,数据首先传送至应用层。 计算机 A 的应用层通过在数据上添加协议头来和计算机 B 的应用层通信。所形成的信息单元包含协议头、数据、可能还有协议尾,被发送至表示层,表示层再添加为计算机 B 的表示层所理解的控制信息的协议头。信息单元的大小随着每一层协议头和协议尾的添加而增加,这些协议头和协议尾包含了计算机 B 的对应层要使用的控制信息。在物理层,整个信息单元通过网络介质传输。

计算机 B 中的物理层收到信息单元并将其传送至数据链路层;然后 B 中的数据链路层读取计算机 A 的数据链路层添加的协议头中的控制信息;然后去除协议头和协议尾,剩余部分被传送至网络层。每一层执行相同的动作:从对应层读取协议头和协议尾,并去除,再将剩余信息发送至上一层。应用层执行完这些动作后,数据就被传送至计算机 B 中的应用程序,这些数据和计算机 A 的应用程序所发送的完全相同

一个 OSI 层与另一层之间的通信是利用第二层提供的服务完成的。相邻层提供的服务帮助一 OSI 层与另一计算机系统的对应层进行通信。一个 OSI 模型的特定层通常是与另外三个 OSI 层联系:与之直接相邻的上一层和下一层,还有目标联网计算机系统的对应层。例如,计算机 A 的数据链路层应与其网络层,物理层以及计算机 B 的数据链路层进行通信。

 

 

 

分层优点

编辑

1)人们可以很容易的讨论和学习协议的规范细节。

2)层间的标准接口方便了工程模块化。

3)创建了一个更好的互连环境。

4)降低了复杂度,使程序更容易修改,产品开发的速度更快。

5)每层利用紧邻的下层服务,更容易记住各层的功能。

OSI是一个定义良好的协议规范集,并有许多可选部分完成类似的任务。

它定义了开放系统的层次结构、层次之间的相互关系以及各层所包括的可能的任务。是作为一个框架来协调和组织各层所提供的服务。

OSI参考模型并没有提供一个可以实现的方法,而是描述了一些概念,用来协调进程间通信标准的制定。即OSI参考模型并不是一个标准,而是一个在制定标准时所使用的概念性框架。

 

 

 

比较TCP/IP

 

TCP/IP模型实际上是OSI模型的一个浓缩版本,它只有四个层次:

1.应用层,对应着OSI的应用层、表示层、会话层

2.传输层,对应着OSI的传输层

3.网络层,对应着OSI的网络层

4.网络接口层,对应着OSI的数据链路层和物理层

OSI模型的网络层同时支持面向连接和无连接的通信,但是传输层只支持面向连接的通信;TCP/IP模型的网络层只提供无连接的服务,但是传输层上同时提供两种通信模式。

 



 

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21天前 北大袁萌学微积,用华为,为国争光

学微积,用华为,为国争光

    标志语“学微积,用手机”,我们提出已经有一年了。

当今,华为手机物美价廉,据此,我们将标志语给为“学微积,用华为”,为国争光。

袁萌  陈启清  528



 

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22天前 北大袁萌华为人注重基础探究,火星人被北大踹到南太平洋里去了

华为人注重基础探究,火星人被北大踹到南太平洋里去了 

526日,中央电视台“面对面”节目专题采访华为董事长兼CEO任正非先生,他说:华为非常重视基础教育与研究,公司聘用700多名数学家,800多名物理学家,120名化学家,年平均工资110万,…

  相对而言,火星人专长于互联网与人工智能技术,北大方正盗窃火星人远程通信源代码,事后,安中运作,促使北京大学把火星人开发团队踹到南太平洋里去了,喝盐水度日。好惨啦!

袁萌  陈启清  527



 

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22天前 北大袁萌北大火星人与华为的一丝因缘

北大火星人与华为的一丝因缘

    回顾往事,1995526日,北大方正集团职工袁庭球盗窃火星人源代码。事后,北大方正随即将其开除。

袁萌得知此之后,随即前往北京市公安局要求放人,当场表示:北大火星人愿意聘用袁庭工程师,因为袁庭是一个技术人才。

二十多年过去了。

现在,袁庭球担任了华为中央研究院副院长。

  这大概就是北大火星人与华为之间的一丝因缘。

事实证明,北大方正坏事做绝,袁庭球工程师是个好样的!

袁萌  陈启清 526



 

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23天前 北大袁萌北大火星人从1G走到4G

北大火星人从1G走到4G

   近日,我们接连发表博客科普短文,提及世界 互联网发展、演

的时间表。

    那么。什么是1G2G3G4G呢?怎么划分互联网的“G”?请看本文附件。

注:1995526日,北大方正盗窃火星人远程通信软件源代码,其中包含互联网“滑动窗口”协议模块的程序实现。

袁萌  陈启清  527

附件:

What is 5G?

Evolution beyond mobile internet

From analogue through to LTE, each generation of mobile technology has been motivated by the need to meet a requirement identified between that technology and its predecessor (see Table 1). For example, the transition from 2G to 3G was expected to enable mobile internet on consumer devices, but whilst it did add data connectivity, it was not until 3.5G that a giant leap in terms of consumer experience occurred, as the combination of mobile broadband networks and smartphones brought about a significantly enhanced mobile internet experience which has eventually led to the app-centric interface we see today. From email and social media through music and video streaming to controlling your home appliances from anywhere in the world, mobile broadband has brought enormous benefits and has fundamentally changed the lives of many people through services provided both by operators and third party players.

Generation Primary services Key differentiator

Weakness (addressed by subsequent generation)

1G Analogue phone calls Mobility Poor spectral efficiency, major security issues

2G Digital phone calls and messaging

Secure, mass adoption

Limited data rates – difficult to support demand for internet/e-mail

3G Phone calls, messaging, data Better internet experience

Real performance failed to match hype, failure of WAP for internet access

3.5G Phone calls, messaging, broadband data

Broadband internet, applications

Tied to legacy, mobile

 specific architecture and protocols

4G All-IP services (including voice, messaging)

Faster broadband internet, lower latency

?

Table 1: Evolution of technology generations in terms of services and performance Source: GSMA Intelligence

More recently, the transition from 3.5G to 4G services has offered users access to considerably faster data speeds and lower latency rates, and therefore the way that people access and use the internet on mobile devices continues to change dramatically. Across the world operators are typically reporting that 4G customers consume around double the monthly amount of data of non-4G users, and in some cases three times as much. An increased level of video streaming by customers on 4G networks is often cited by operators as a major contributing factor to this.

The Internet of Things (IoT) has also been discussed as a key differentiator for 4G, but in reality the challenge of providing low power, low frequency networks to meet the demand for widespread M2M deployment is not specific to 4G or indeed 5G.



 

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24天前 北大袁萌Understanding5G

Understanding 5G

ANALYSIS Understanding 5G: Perspectives on future technological advancements in mobile

December 2014

© GSMA Intelligence gsmaintelligence.com • info@gsmaintelligence.com • @GSMAi

GSMA Intelligence  Understanding 5G

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Contents

Executive summary ............................................................................................................................ 3

Introduction .........................................................................................................................................4

What is 5G? .......................................................................................................................................... 5

Potential 5G use cases....................................................................................................................... 8

The implications of 5G for mobile operators ...............................................................................11

Continuing development of mobile technologies: what 5G isn’t ...........................................14

Conclusions: enabling innovation through industry-wide collaboration .............................15

Appendix A: Current 5G industry activity ...................................................................................18

Appendix B: LTE opportunities and challenges .........................................................................21

GSMA Intelligence  Understanding 5G

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Executive summary

5G offers enormous potential for both consumers and industry

As well as the prospect of being considerably faster than existing technologies, 5G holds the promise of applications with high social and economic value, leading to a ‘hyperconnected society’ in which mobile will play an ever more important role in peoples lives.

The GSMA will work for its members and with its partners to shape 5G

As the association representing the mobile industry, the GSMA will play a significant role in shaping the strategic, commercial and regulatory development of the 5G ecosystem. This will include areas such as the definition of roaming and interconnect in 5G, and the identification and alignment of suitable spectrum bands. Once a stable definition of 5G is reached, the GSMA will work with its members to identify and develop commercially viable 5G applications. This paper focuses on 5G as it has developed so far, and the areas of technological innovation needed to deliver the 5G vision.

There are currently two definitions of 5G

Discussion around 5G falls broadly into two schools of thought: a service-led view which sees 5G as a consolidation of 2G, 3G, 4G, Wi-fi and other innovations providing far greater coverage and always-on reliability; and a second view driven by a step change in data speed and order of magnitude reduction in end-to-end latency. However, these definitions are often discussed together, resulting in sometimes contradictory requirements.

Sub-1ms latency and >1 Gbps bandwidth require a true generational shift

Some of the requirements identified for 5G can be enabled by 4G or other networks. The technical requirements that necessitate a true generational shift are sub-1ms latency and >1 Gbps downlink speed, and only services that demand at least one of these would be considered 5G use cases under both definitions.

Achieving sub-1ms latency is a hugely exciting challenge that will define 5G

Delivering 1ms latency over a large scale network will be challenging, and we may see this condition relaxed. If this were to happen, some of the potential 5G services identified may no longer be possible and the second view of 5G would become less clear. This paper looks at some of the challenges that must be overcome to deliver 1ms latency.

At the same time 4G will continue to grow and evolve

Technologies such as NFV/SDN and HetNets are already being deployed by operators and will continue to enable the move towards the hyper-connected society alongside developments in 5G. Considerable potential also remains for increasing 4G adoption in many countries, and we expect 4G network infrastructure to account for much of the $1.7 trillion the world’s mobile operators will invest between now and 2020. Operators will continue to focus on generating a return on investment from their 4G (and 3G) networks by developing new services and tariffing models that make most efficient use of them.

GSMA Intelligence  Understanding 5G

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Introduction

Objectives of this report

The purpose of this report is to take a step toward clarifying what ‘5G’ really means in the technological sense, by: reducing 5G to its fundamental core (including acknowledging what it is arguably not); expanding on some of the use case scenarios that 5G might enable; and discussing conceivable implications for operators in terms of network infrastructure and commercial opportunities. This can only be achieved by framing the discussion around 5G in a broader context alongside existing network technologies and those currently in development.

In summary, there are three key questions that this report will ask:

1. What is (and what isn’t) 5G? 2. What are the real 5G use cases? 3. What are the implications of 5G for mobile operators?

Notes on terminology

GSMA Intelligence’s definition of 4G includes the following network technologies: LTE, TD-LTE, AXGP, WiMAX, LTE-A, TD-LTE-A, LTE with VoLTE and WiMAX 2.

Due to the commonality of operator definitions classifying LTE and TD-LTE as 4G technologies, we follow this convention. This differs from the ITU’s strict definition of transitional versus true 4G. Also, where we use the term ‘LTE’ in this document it incorporates all LTE variants (LTE, TD-LTE, AXGP, LTE-A and TD-LTE-A). Finally, for simplicity we do not consider WiMAX in this analysis, so where the term ‘4G’ is used it incorporates all LTE variants but not WiMAX (a transitional 4G technology) or WiMAX 2 (a true 4G technology). Therefore for the purpose of this report the terms ‘4G’ and ‘LTE’ are interchangeable.

GSMA Intelligence  Understanding 5G

5

What is 5G?

Evolution beyond mobile internet

From analogue through to LTE, each generation of mobile technology has been motivated by the need to meet a requirement identified between that technology and its predecessor (see Table 1). For example, the transition from 2G to 3G was expected to enable mobile internet on consumer devices, but whilst it did add data connectivity, it was not until 3.5G that a giant leap in terms of consumer experience occurred, as the combination of mobile broadband networks and smartphones brought about a significantly enhanced mobile internet experience which has eventually led to the app-centric interface we see today. From email and social media through music and video streaming to controlling your home appliances from anywhere in the world, mobile broadband has brought enormous benefits and has fundamentally changed the lives of many people through services provided both by operators and third party players.

Generation Primary services Key differentiator

Weakness (addressed by subsequent generation)

1G Analogue phone calls Mobility Poor spectral efficiency, major security issues

2G Digital phone calls and messaging

Secure, mass adoption

Limited data rates – difficult to support demand for internet/e-mail

3G Phone calls, messaging, data Better internet experience

Real performance failed to match hype, failure of WAP for internet access

3.5G Phone calls, messaging, broadband data

Broadband internet, applications

Tied to legacy, mobile

 specific architecture and protocols

4G All-IP services (including voice, messaging)

Faster broadband internet, lower latency

?

Table 1: Evolution of technology generations in terms of services and performance Source: GSMA Intelligence

More recently, the transition from 3.5G to 4G services has offered users access to considerably faster data speeds and lower latency rates, and therefore the way that people access and use the internet on mobile devices continues to change dramatically. Across the world operators are typically reporting that 4G customers consume around double the monthly amount of data of non-4G users, and in some cases three times as much. An increased level of video streaming by customers on 4G networks is often cited by operators as a major contributing factor to this.

The Internet of Things (IoT) has also been discussed as a key differentiator for 4G, but in reality the challenge of providing low power, low frequency networks to meet the demand for widespread M2M deployment is not specific to 4G or indeed 5G. As Table 1 suggests, it is currently unclear what the opportunity or ‘weakness’ that 5G should address is.

GSMA Intelligence  Understanding 5G

6

Two views of 5G exist today:

View 1 – The hyper-connected vision: In this view of 5G, mobile operators would create a blend of pre-existing technologies covering 2G, 3G, 4G, Wi-fi and others to allow higher coverage and availability, and higher network density in terms of cells and devices, with the key differentiator being greater connectivity as an enabler for Machine-to-Machine (M2M) services and the Internet of Things (IoT). This vision may include a new radio technology to enable low power, low throughput field devices with long duty cycles of ten years or more.

View 2 – Next-generation radio access technology: This is more of the traditional ‘generation-defining’ view, with specific targets for data rates and latency being identified, such that new radio interfaces can be assessed against such criteria. This in turn makes for a clear demarcation between a technology that meets the criteria for 5G, and another which does not.

Both of these approaches are important for the progression of the industry, but they are distinct sets of requirements associated with specific new services. However, the two views described are regularly taken as a single set and hence requirements from both the hyper-connected view and the next-generation radio access technology view are grouped together. This problem is compounded when additional requirements are also included that are broader and independent of technology generation.

5G technology requirements

As a result of this blending of requirements, many of the industry initiatives that have progressed with work on 5G (see Appendix A) identify a set of eight requirements:

1-10Gbps connections to end points in the field (i.e. not theoretical maximum) • 1 millisecond end-to-end round trip delay (latency) • 1000x bandwidth per unit area • 10-100x number of connected devices • (Perception of) 99.999% availability • (Perception of) 100% coverage • 90% reduction in network energy usage • Up to ten year battery life for low power, machine-type devices

Because these requirements are specified from different perspectives, they do not make an entirely coherent list – it is difficult to conceive of a new technology that could meet all of these conditions simultaneously.

Equally, whilst these eight requirements are often presented as a single list, no use case, service or application has been identifed that requires all eight performance attributes across an entire network simultaneously. Indeed some of the requirements are not linked to use cases or services, but are instead aspirational statements of how networks should be built, independent of service or technology – no use case needs a network to be significantly cheaper, but every operator would like to pay less to build and run their network. It is more likely that various combinations of a subset of the overall list of requirements will be supported ‘when and where it matters’.

GSMA Intelligence  Understanding 5G

7

Finally, while important in their own right, six of these requirements are not generationdefining attributes. These are considered below:

Perceived 99.999% availability and 100% geographical coverage:

These are not use case drivers, nor technical issues, but economic and business case decisions. 99.999% availability and 100% coverage are achievable using any existing technology, and could be achieved by any network operator. Operators decide where to place cells based on the cost to prepare the site to establish a cell to cover a specific area balanced against the benefit of the cell providing coverage for a specific geographic area. This in turn makes certain cell sites and coverage areas - such as rural areas and indoor coverage - the subject of difficult business decisions.

Whilst a new generation of mobile network technology may shift the values that go in to the business model that determines cell viability, achieving 100% coverage and 99.999% availability will remain a business decision rather than a technical objective. Conversely, if 100% coverage and 99.999% availability were to be a 5G ‘qualifying criteria’, no network would achieve 5G status until such time as 100% coverage and 99.999% availability were achieved.

Connection density (1000x bandwidth per unit area, 10-100x number of connections):

These essentially amount to ‘cumulative’ requirements i.e. requirements to be met by networks that include 5G as an incremental technology, but also require continued support of pre-existing generations of network technology. The support of 10-100 times the number of connections is dependent upon a range of technologies working together, including 2G, 3G, 4G, Wi-fi, Bluetooth and other complementary technologies. The addition of 5G on top of this ecosystem should not be seen as an end solution, but just one additional piece of a wider evolution to enable connectivity of machines. The Internet of Things (IoT) has already begun to gain significant momentum, independent of the arrival of 5G.

Similarly, the requirement for 1,000 times bandwidth per unit area is not dependent upon 5G, but is the cumulative effect of more devices connecting with higher bandwidths for longer durations. Whilst a 5G network may well add a new impetus to progression in this area, the rollout of LTE is already having a transformational effect on the amount of bandwidth being consumed within any specific area, and this will increase over the period until the advent of 5G. The expansion of Wi-fi and integration of Wi-fi networks with cellular will also be key in supporting greater data density rates.

Meeting both of these requirements will have significant implications for OPEX on backhaul and power, since each cell or hotspot must be powered and all of the additional traffic being generated must be backhauled.

Reduction in network energy usage and improving battery life:

The reduction of power consumption by networks and devices is fundamentally important to the economic and ecological sustainability of the industry. A general industry principle for minimising power usage in network and terminal equipment should pervade all generations of technology, and is recognised as an ecological goal as well as having a

GSMA Intelligence  Understanding 5G

8

significant positive impact on the OPEX associated with running a network. At present it is not clear how a new generation of technology with higher bandwidths being deployed as an overlay (rather than a replacement) on top of all pre-existing network equipment could result in a net reduction in power consumption.

Some use cases for M2M require the connected device in the field to lie dormant for extended periods of time. It is important that innovation in how these devices are powered and the leanness of the signaling they use when becoming active and connected is pursued. However, this requirement is juxtaposed with 5G headline requirements on data rate – what is required for mass sensor networks is very occasional connectivity with minimal throughput and signaling load. Work to develop such technology predates the current 5G requirements and is already being pursued in Standards bodies.

These six requirements should be and are being pursued by the industry today using a range of techniques (some of which are covered later in the paper) but these amount to evolutions of existing network technology and topology or opportunities enabled by changing hardware characteristics and capabilities. These will in turn open business opportunities for operators and third parties. However, none of these business opportunities exist today – they are constrained by limitations greatly governed by economics, and much of these six requirements are motivated by improving the economic viability of those opportunities, rather than filling technological gaps that explicitly prohibit these opportunities, regardless of the amount they might cost to enable.

Thus in the strictest terms of measurable network deliverables which could enable revolutionary new use case scenarios, the potential attributes that would be unique to 5G are limited to sub-1ms latency and >1 Gbps downlink speed.

Potential 5G use cases

Imagining the mobile services of the next decade

As with each preceding generation, the rate of adoption of 5G and the ability of operators to monetise it will be a direct function of the new and unique use cases it unlocks. Thus the key questions around 5G for operators are essentially:

a. What could users do on a network which meets the 5G requirements listed above that is not currently possible on an already existing network? b. How could these potential services be profitable?

Figure 1 illustrates the latency and bandwidth/data rate requirements of the various use cases which have been discussed in the context of 5G to date. These potential 5G use cases and their associated network requirements are described below.

GSMA Intelligence  Understanding 5G

9

Delay

1ms

10ms Disaster alert

Automotive ecall

Monitoring sensor networks

Personal cloud

Wireless cloud based office

Video streaming

First responder connectivity

Bi-directional remote controlling

Real time gaming

Autonomous driving

Augmented Reality

Virtual Reality

Tactile internet

Multi-person video call

Device remote controlling

100ms

1,000ms

<1 Mbps 1 Mbps 10 Mbps 100 Mbps >1 Gbps

Fixed Nomadic On the go

Services that could be enabled by 5G

Services that can be delivered by legacy networks

Bandwidth throughput

M2M connectivity

Figure 1: Bandwidth and latency requirements of potential 5G use cases Source: GSMA Intelligence

Virtual Reality/Augmented Reality/Immersive or Tactile Internet

These technologies have a number of potential use cases in both entertainment (e.g. gaming) and also more practical scenarios such as manufacturing or medicine, and could extend to many wearable technologies. For example, an operation could be performed by a robot that is remotely controlled by a surgeon on the other side of the world. This type of application would require both high bandwidth and low latency beyond the capabilities of LTE, and therefore has the potential to be a key business model for 5G networks.

However, it should be pointed out that VR/AR systems are very much in their infancy and their development will be largely dependent on advances in a host of other technologies such as motion sensors and heads up display (HUD). It remains to be seen whether these applications could become profitable businesses for operators in the future.

Autonomous driving/Connected cars

Enabling vehicles to communicate with the outside world could result in considerably more efficient and safer use of existing road infrastructure. If all of the vehicles on a road were connected to a network incorporating a traffic management system, they could potentially travel at much higher speeds and within greater proximity of each other without risk of accident - with fully-autonomous cars further reducing the potential for human error.

GSMA Intelligence  Understanding 5G

10

While such systems would not require high bandwidth, providing data with a commandresponse time close to zero would be crucial for their safe operation, and thus such applications clearly require the 1 millisecond delay time provided in the 5G specification. In addition a fully ‘driverless’ car would need to be driverless in all geographies, and hence would require full road network coverage with 100% reliability to be a viable proposition.

Wireless cloud-based office/Multi-person videoconferencing

High bandwidth data networks have the potential to make the concept of a wireless cloud office a reality, with vast amounts of data storage capacity sufficient to make such systems ubiquitous. However, these applications are already in existence and their requirements are being met by existing 4G networks. While demand for cloud services will only increase, as now they will not require particularly low latencies and therefore can continue to be provided by current technologies or those already in development. While multi-person video calling - another potential business application - has a requirement for lower latency, this can likely be met by existing 4G technology.

Machine-to-machine connectivity (M2M)

M2M is already used in a vast range of applications but the possibilities for its usage are almost endless, and our forecasts predict that the number of cellular M2M connections worldwide will grow from 250 million this year to between 1 billion and 2 billion by 2020, dependent on the extent to which the industry and its regulators are able to establish the necessary frameworks to fully take advantage of the cellular M2M opportunity.

Typical M2M applications can be found in ‘connected home’ systems (e.g. smart meters, smart thermostats, smoke detectors), vehicle telemetric systems (a field which overlaps with Connected cars above), consumer electronics and healthcare monitoring. Yet the vast majority of M2M systems transmit very low levels of data and the data transmitted is seldom time-critical. Many currently operate on 2G networks or can be integrated with the IP Multimedia Subsystem (IMS) – so at present the business case for M2M that can be attached to 5G is not immediately obvious.

A true requirement for a generational shift?

Thus many of the services that have been put forward as potential ‘killer apps’ for 5G do not require a generational shift in technology, and could be provided via existing network technologies. Only applications that require at least one of the key 5G technical requirements – sub-1ms latency and >1 Gbps downlink speed – can be considered true next generational business cases.

Of these two requirements, reducing latency to sub-1ms levels may provide the greatest technical challenge (see page 12). Meanwhile, as discussed in more detail in Appendix B, operators are already making a considerable amount of progress in increasing the data speeds of their existing networks by adopting LTE-A technologies (see Figure 2). While it is important to note that although many of the use cases and services discussed in this section do not strictly require 5G, they could offer an enhanced user experience on a 5G network. However this amounts to an incremental benefit that is more difficult to market than a genuine new service, and not a core component of any 5G business case.

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3.5G/DC-HSPA+

4G/LTE

4G/LTE Cat. 4

4G/LTE Advanced

5G*

1,000 Mbps

10,000 Mbps

150 Mbps

100 Mbps

42.2 Mbps

Figure 2: Maximum theoretical downlink speed by technology generation, Mbps (*10 Gbps is the minimum theoretical upper limit speed specified for 5G) Source: GSMA Intelligence

The implications of 5G for mobile operators

The progress from initial 3G networks to mobile broadband technology has transformed industry and society by enabling an unprecedented level of innovation. If 5G becomes a true generational shift in network technology, we can expect an even greater level of transformation. There are varying implications of providing an increased level of connectivity or developing a new radio access network (RAN) to deliver a step change in per connection performance, or a combination of the two. This means that the final design of a 5G network could be any one of a range of options with differing radio interfaces, network topologies and business capabilities.

While a shift to 5G would be hugely impactful, the industry will need to overcome a series of challenges if these benefits are to be realised, particularly in terms of spectrum and network topology.

5G spectrum and coverage implications

While there are a number of spectrum bands which could potentially be used in meeting some of the 5G requirements identified to date, there is currently a substantial focus on higher frequency radio spectrum.  As discussed in Appendix A, operators, vendors and academia are combining efforts to explore technical solutions for 5G that could use frequencies above 6GHz and reportedly as high as 300 GHz. However, higher frequency bands offer smaller cell radiuses and so achieving widespread coverage using a traditional network topology model would be challenging.

It is widely accepted that ‘beam-forming’ - the focussing of the radio interface into a beam which will be usable over greater distances – is an important part of any radio interface definition that would use 6GHz or higher spectrum bands. This however means that the beam must be directed at the end user device that is being connected. Since the service being offered is still differentiated from fixed line connections on the basis

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of ‘mobility’, the beam itself will have to track the device. This is innovation that could make 5G an expensive technology to deploy on large scale, since each cell may have to support several hundred individual beams at any one time and track the end users that are connected via these beams in three dimensional space.

High-order MIMO (Multi-Input, Multi-Output) is another method for increasing bandwidth that is often discussed. This is where an array of antennae is installed in a device and multiple radio connections are established between a device and a cell. However, high- order MIMO can have issues with radio interference, so technology is required to help mitigate this problem. This tends to focus on a need for the radio network to adjust its beam to take into account the specific orientation of the antenna at any given time.

All of this is incremental research and development over and above that currently being conducted for 4G. The use of bands higher than 6GHz will likely require operators to invest in an entirely new RAN since it will have fundamentally different masthead requirements. Given the level of infrastructure required to achieve the desired network topology, operators may be forced to rethink their existing business models. New technology is rarely a cheap option, and the nature of the new technology that is required in the radio network makes it very power-intensive, hence counter to the stated requirement for significant reduction in overall network power consumption.

That said, vendors are researching ways to include beam forming and MIMO technology in mobile devices. As a result, the process of identifying and aligning internationally around common bands for 5G will have a clear dependency on the technology that can be identified to overcome band usage in high frequencies for wide area coverage.

Can 1 millisecond latency be achieved?

Achieving the sub-1ms latency rate identified as a technical requirement for 5G necessitates a new way of thinking about how networks are structured, and will likely prove to be a significant undertaking in terms of technological development and investment in infrastructure.

Despite the inevitable advances in processor speeds and network latency between now and 2020, the speeds at which signals can travel through the air and light can travel along a fibre are governed by fundamental laws of physics. Subsequently services requiring a delay time of less than 1 millisecond must have all of their content served from a physical position very close to the user’s device. Industry estimates suggest that this distance may be less than 1 kilometre, which means that any service requiring such a low latency will have to be served using content located very close to the customer, possibly at the base of every cell, including the many small cells that are predicted to be fundamental to meeting densification requirements. This will likely require a substantial uplift in CAPEX spent on infrastructure for content distribution and servers.

If any service requiring 1 millisecond delay also has a need for interconnection between one operator and another, this interconnectivity must also occur within 1 kilometre of the customers. This could well be the case in a service such as social networking content pushed into augmented reality. Today, inter-operator interconnect points are relatively sparse, but to support a 5G service with 1 millisecond delay, there would likely need to be

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interconnection at every base station, thus impacting the topological structure of the core network. Roaming customers would need to have visited network contextual roaming capabilities, and have content relevant to their applications available directly from the visited network, posing challenges for the existing roaming model.

In the most extreme case, it would make sense for a single network infrastructure to be implemented, which would be utilised by all operators. This would mean all customers could be served by a single content source, with all interaction and interconnect with localised context also being served from that point at the base station. This would also imply that only one radio network would be built, and then shared by all operators.

Figure 3: Latency performance for LTE compared to latency requirement for 5G  Source: GSMA

Such a model would considerably reduce CAPEX in the network build (since rather than say four operators building four parallel networks, only a single network would be built) but would require unprecedented levels of co-operation between operators. It would also impact the nature of inter-operator competition, shifting focus to services rather than data rate and coverage differentiation. It would also make spectrum auctions somewhat irrelevant, since only one radio network being built would mean there would only be one bidder and one license per market.

Once this is all realised, it is likely that requirements for sub-1ms delay will be relaxed or possibly removed entirely from 5G, rather than industry committing to the massive upheaval and resource acquisition that would be implied. If this were to happen, it may draw into question the viability of coupling services such as augmented and virtual reality, immersive internet and autonomous driving with mobility. However, if those services were removed from the expected service set, the justification for the technological view of 5G would also become questionable.

LTE – min 10ms

4ms 4ms 1-2ms 5-10ms if in the same country as the customer

Core Network

Internet

5G service sub-1ms

<0.5ms <0.5ms

Content

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Continuing development of network technologies: what 5G isn’t

To further enhance the mobile broadband experience for customers, operators are continuing to develop their 4G networks through the deployment of LTE-Advanced technologies. Many are also deploying technologies such as network function virtualisation (NFV), software defined networks (SDN), heterogeneous networks (HetNets) and low power, low throughput (LPLT) networks. These allow different network upgrade paths and expansion of coverage through integration of broader wireless technologies, as well as potentially having a positive effect in the total cost of ownership of the network.

The term 5G is sometimes used to encapsulate these technologies. However, it is important to clarify that these technological advancements are continuing independently of 5G. While these are areas that will have significant impact on the mobile industry over the coming years, explicitly including them under the term 5G has the potential to adversely affect progress in the industry between now and the realisation of 5G as a commercial service.

A summary of these technologies follows:

Network Function Virtualisation (NFV) and Software Defined Networks (SDN)

NFV is a network architecture concept that enables the separation of hardware from software or ‘function’, and has become a reality for the mobile industry due to the increased performance of ‘common, off-the-shelf’ (COTS) IT platforms. SDN is an extension of NFV wherein software can perform dynamic reconfiguration of an operator’s network topology to adjust to load and demand, e.g. by directing additional network capacity to where it is needed to maintain the quality of customer experience at peak data consumption times. A number of operators have built or are building part or all of their LTE networks using NFV and SDN as the basis.

These technologies in combination can potentially reduce operator CAPEX as they offer a cheaper and simpler network architecture that is easier to upgrade, while OPEX is also reduced through power savings as network capacity is only provided when and where it is needed. However, shifting from existing structures to IT-based soft functions will bring new complexities for operators in terms of network provisioning and management, as well as requiring a new skill set within operator staff.

Heterogeneous Networks (HetNets)

HetNet refers to the provision of a cellular network through a combination of different cell types (e.g. macro, pico or femto cells) and different access technologies (i.e. 2G, 3G, 4G, Wi-fi). By integrating a number of diverse technologies depending on the topology of the coverage area, operators can potentially provide a more consistent customer experience compared to what could be achieved with a homogenous network.

Small cell deployments are a key feature of the HetNet approach as they allow considerable flexibility as to where they are positioned, however, the use of more cells brings implications in terms of power supply and backhaul, especially when they are located in remote areas. Wi-fi can also play a significant role in HetNets, both in terms of data offload and roaming.

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HetNet technology has typically been developed in relation to data networking, but recently voice has been brought under the scope as well, not least because of support for Wi-fi calling being available in Apple’s iPhone 6 which was released in September 2014.

Conclusions: enabling innovation through industry-wide collaboration

The many initiatives and discussions on 5G going on around the world by governments, vendors, operators and academia demonstrate the continuing ethos of collaboration and innovation across the industry. In these debates we must ensure that we continue to coordinate with aligned goals to maintain momentum in completing the definition of 5G.

The key 5G considerations at this stage are:

When 5G arrives will be determined by what 5G turns out to be

As discussed earlier, there are currently two differing views of what 5G is. The first view makes its implementation somewhat intangible – 5G will become a commercial reality when sufficient industry voices say so, but this will be something that is difficult to measure by any recognisable metric. The second approach is more concrete in that it has a distinct set of technical objectives, meaning that when a service is launched that meets those objectives it will count as the advent of 5G.

 

As the requirements identified for 5G are a combination of both visions, in some cases the requirement set is self-contradictory – for example, it would not be possible to have a new RAN with beam forming and meet a requirement for power reduction, because beam forming uses a lot more power than today’s RAN. As a result, there must be an established answer to the question of what 5G is before there can be an answer to the question of when it will arrive.

The case for a new RAN should be based on its potential to improve mobile networks

The principal challenge in the 5G specification is the sub-1ms latency requirement, which is governed by fundamental laws of physics. If, as discussed above, this challenge proves too much and the requirements for sub-1ms delay are removed from 5G, the need for a new RAN would be questioned. Whether a new air interface is necessary is arguably more of a question of whether one can be invented that significantly improves mobile networks, rather than on a race to the arbitrary deadline of 2020.

This raises the question of where the industry should go next. Without a new air interface, the ‘5G’ label makes less sense, as the industry would need to shift to the evolutionary view of 5G - with the new networks building on LTE and Wi-fi by adding new functionalities and architecture.

5G should not distract from more immediate technological developments

Technologies such as multiple-carrier LTE-A, NFV/SDN, HetNets and LPLT networks will form an important part of the evolution of mobile networks. Each has the potential to offer tangible benefits to operators within the next few years, and so the industry should not risk losing focus on the potential benefits of these technologies in the short and

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medium term. Also, the term ‘5G’ should always be associated with the definition of new radio technology. Everything else is the net result of other forms of innovation.

LTE remains very important and will continue to evolve

There remains considerable potential for future LTE growth, which still only accounts for 5% of the world’s mobile connections. LTE penetration as a percentage of connections is already as high as 69% in South Korea, 46% in Japan and 40% in the US, but LTE penetration in the developing world stands at just 2%. Hence there is still a substantial opportunity for operators to generate returns on their investment in LTE networks.

LTE technology will also continue to develop, with operators already making a considerable amount of progress in increasing the data speeds of their existing networks by adopting multiple-carrier LTE-A technologies. Therefore, while there remain monetisation and interconnect issues around LTE, these advancements will enable operators to offer many of the services that have been put forward in the context of 5G long before 5G becomes a commercial reality.

The industry should make full use of governmental interest and resources

As detailed in Appendix A, there is a considerable level of governmental interest worldwide in the subject of 5G, not to mention a substantial amount of funding available for research and development in the field. It is important that the industry leverages this and effectively channels the focus and resource into something meaningful for both operators and their customers. This should be implemented in a coordinated framework to avoid a fragmented vision of 5G for different parts of the world.

5G is an opportunity to develop a more sustainable operator investment model

If previous generations of mobile technology have taught us anything, it is it that, as with each preceding generation, 5G will unlock value in ways we cannot and will not anticipate. Services that were initially expected to have a negligible impact became hugely popular (e.g. SMS), while those expected to be the ‘next big thing’ have been slow to gain traction (e.g. video calling). Through the development of 5G, we as an industry can expect a paradigm shift in the way that all of the stakeholders in the mobile ecosystem play their role. Regulators especially can use this as an opportunity to create healthier environments that stimulate continuing investment in next generation technology.

 

Some of the business cases that have worked well for 3G and 4G technologies may not be the right ones for 5G. By actively conceiving and exploring 5G business cases at an earlier stage, operators will have greater potential to shape the new paradigm.

The GSMA will continue to work with its members to shape the future of 5G

Whichever form 5G eventually takes, the GSMA, as the association representing the mobile industry, looks forward to contributing to the development of a 5G ecosystem through collaboration and thought leadership. The GSMA’s focus is on:

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working with its operator members to identify and develop commercially viable 5G applications • collaborating in the work being undertaken in terms of research, development and definition of 5G technologies by industry groups such as 3GPP, NGMN and ITU-R, and contributing to the various working groups in these areas • identifying requirements around roaming and interconnect • driving the development of the regulatory framework for 5G by identifying suitable spectrum bands for its operation, and working with governments around the world to ensure international alignment within those bands • creating a forum for relevant parties to discuss 5G through e.g. GSMA boards and committees, industry workshops, Mobile World Congress etc.

The successful shift to next generation networks can only be achieved through strong industry-wide collaboration. The GSMA will continue communicating through subsequent papers to influence the strategic direction of 5G development, as the business case and technical requirements for 5G become clearer. In order to realise the immense opportunity that 5G represents for the industry, the GSMA will do all it can to ensure that the next generation of telecommunications deliver innovation and consumer benefits in an economically viable way.

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Appendix A: Current 5G industry activity

Since 2012, a number of initiatives have been established to define and develop 5G and there have also been a considerable number of statements from interested parties such as governments and infrastructure vendors. Having fallen behind Eastern Asia and North America in terms of mobile technological advancement due to a relatively slow rollout and adoption of 4G networks, European governments are particularly keen to get ahead of the curve in the 5G space and there have been a number of announcements from Neelie Kroes, European Commission (EC) Vice President for Digital Agenda, on the subject going back to Mobile World Congress 2013. The governments of Japan, South Korea and China have also been particularly active in driving the 5G agenda.

Meanwhile, vendors such as Ericsson, Huawei, NSN and Samsung all began research and development towards 5G in 2013, and this year mobile operators have also begun making announcements regarding their own 5G laboratory trials. A summary of the key parties, milestones and targets is below.

ITU-R launched “IMT for 2020 and beyond” setting the stage for “5G”

Japan, Korea and China working on 5G requirements

Neely Kroes press conference in Barcelona launched 5G PPP (5G public private partnership)

EU project METIS starts work on defining 5G

Samsung, NSN, Huawei, Ericsson have all started developments toward 5G

NTT Docomo announced “experimental trials” for 5G using higher frquency bands

2012 2013 2014 2020

Figure 4: Timeline of key events in 5G developments  Source: GSMA Intelligence

ITU Radiocommunication Sector (ITU-R)

The ITU-R plays a key role in in the global management of the radio-frequency spectrum and satellite orbits as well as being the body that defined the criteria for previous generations of technology – the IMT-2000 family of technologies correlates directly to 3G, whilst the intent was that IMT-Advanced technologies would be 4G. However, for 4G the relationship between ITU-R IMT definitions and specific ‘G’s became broken. IMTAdvanced only identifies two technologies as meeting the criteria laid out by ITU-R for 4G – LTE-A and WiMAX2. Operators and equipment vendors blurred this definition by marketing LTE, WiMAX and even HSPA+ as ‘4G’. LTE and WiMAX are in fact included in the IMT-2000 technology group, and so, if the association between ITU-R IMT groups and ‘generations’ were to be maintained, LTE and WiMAX would be 3rd Generation, rather than 4th.

In early 2012, ITU-R began a programme to develop “IMT-2020” (International Mobile Telecommunications 2020), setting the stage for the 5G research activities that have since emerged across the world. In 2015, the organisation plans to finalise its “Vision” of

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the 5G mobile broadband connected society. This view of the horizon for the future of mobile technology will be key in setting the agenda for the World Radiocommunication Conference (WRC) 2015, where discussions regarding additional spectrum will take place in support of the future growth of the industry.

NGMN Alliance

The NGMN (Next Generation Mobile Networks) Alliance is a forum made up of 24 mobile operators and various other mobile industry ecosystem companies including network and handset vendors, and research institutes. NGMN began working on identifying requirements for 5G standards in Q4 2013 and plans to present a white paper detailing end-to-end requirements for 5G at its industry conference in March 2015. The paper is intended to support the standardisation and subsequent availability of 5G from 2020.

The NGMN Alliance has positioned itself as the lead organisation driving the 5G agenda, although is yet to make any public statement on what the requirements it defines might be.

European Commission

The EC’s 5G research activities began in November 2012 with the co-funding of METIS (Mobile and wireless communications Enablers for the Twenty-twenty (2020) Information Society), a consortium of 29 partners spanning vendors, operators, the automotive industry and academia focused on the next generation of mobile and wireless communications systems for year 2020. A year later METIS published its five key 5G scenarios, 12 test cases and seven Key Performance Indicators for 5G, associated with technical requirements. The project is due to release its final report in April 2015.

In December 2013, the EC went further and announced a joint 5G research and innovation project with the private sector - The 5G Infrastructure Public Private Partnership (5G PPP) - with collective funding of ¤4.2 billion, of which ¤700 million will come from the commission itself, reflecting its desire to seize the initiative in 5G development. 5G PPP will facilitate research into solutions, architectures, technologies and standards for 5G infrastructure, and aims to ensure that at least 20% of 5G standards essential patents (SEP) are developed and owned by European organisations, while ensuring that European vendors retain at least 35% of global market share in the supply of future network infrastructure.

National governments

Outside of Europe, the majority of 5G research appears to be confined to Eastern Asia, with China, Japan and South Korea all working independently on defining 5G requirements. China’s 5G initiative, named ‘IMT-2020’, is a combination of three government agencies and has established eight working groups with the aim of promoting the development of 5G technologies in the country.

Meanwhile, Japan’s ‘2020 and Beyond Ad Hoc’ (20B AH) group was established by the Association of Radio Industries and Businesses (ARIB) in September 2013 to study the concept, function and architecture of mobile communications systems going into the next

 

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decade, as well as the services and applications those systems could offer. The country has set an ambitious target of having commercial 5G services available in time for the 2020 Olympic Games in Tokyo.

Equally ambitious 5G targets have been set in South Korea. The country’s ‘5G Forum’ group’s website states that “The 5G technology is expected to be commercialised by 2020 with 1,000-time speed of current LTE data transfer.” The Korean Ministry of Education, Science and Technology has allocated $1.6 billion of funding to the project.

Individual operators and vendors

More ambitious yet is South Korean market leader, SK Telecom, who announced last July that it had signed an agreement with Ericsson to develop 5G technology in time to demonstrate a network at the 2018 Winter Olympics in Pyeongchang. Earlier that month, the vendor had already demonstrated a 5Gbps data throughput speed in laboratory trials, in the 15 GHz frequency band.

Again the majority of research and innovation at the operator and vendor level is taking place in Eastern Asia, with both Huawei and Samsung having reportedly achieved latencies of less than 5 milliseconds in laboratory trials. Japan’s NTT DoCoMo has also begun conducting extensive “experimental trials” of potential 5G technologies across multiple frequency bands. The operator has partnered with various vendors to test technologies in a number of spectrum bands, including Alcatel-Lucent (3-6 GHz), Fujitsu (3-6 GHz), NEC (5 GHz), Ericsson (15 GHz), Samsung (28 GHz) and Nokia (70 GHz).

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Appendix B: 4G opportunities and challenges

LTE is still in the early stages of its lifecycle

Historically, cellular technologies have adhered to an approximate 20-year cycle from launch to peak penetration, with around ten years between the launch of each new technology (see Figure 5). The first commercial LTE networks went live in 2009 and based on historical precedent we would not expect the technology to reach a peak level of connections until around 2030.

1980 1990

1G – AMPS (19 years)

9 years

2G – GSM (18 years)

3G – WCDMA (19 years)

4G – LTE (18 years)

2000 2010 2020 2030

Launch Peak

10 years

9 years

Today

Figure 5: Evolution of mobile technology by generation, 1980 onwards  Source: GSMA Intelligence

In reality, the adoption of LTE is proceeding at a faster rate than its predecessor technologies (see Figure 6), yet we still do not expect LTE connections to peak until well into the next decade. The technology is still at an early stage in its lifecycle, with networks currently confined to just 110 of the world’s 237 mobile markets. Hence LTE still represents a considerable growth opportunity for the industry – at present, only around a third of the world’s mobile operators (293) have live LTE networks. Assuming all known future network launches go ahead as planned, 158 countries will soon have at least one LTE operator – yet this still leaves one third of the world’s mobile markets as untapped territory for LTE services.

0

3,500

3,000

2,500

2,000

1,500

1,000

500

5,000

4,000

4,500

2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020

2G

3G

4G LTE

Mobile connections (in millions)

Figure 6: Total cellular connections, global, by technology generation  Source: GSMA Intelligence

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In terms of coverage, we expect LTE networks to reach 26% of the world’s population by the end of 2014 (see Figure 7), although the technology will account for only 6% of global connections at that time, illustrating the considerable growth potential for LTE even in regions with widespread networks such as the Americas, Europe and Oceania, where we expect coverage to increase from around three in five people on average in 2014 to more than four in five by 2020.

An expected proliferation of launches will also bring coverage to more than two thirds of the population of Asia by that time, while almost one in five Africans will also be covered by LTE networks, more than double the current proportion. Thus globally we expect that LTE coverage will rise from a quarter now to more than 60% of the world’s population by 2020 – meaning that 4.9 billion people will potentially have access to the technology.

20% 30% 40% 60% 70% 80% 90% 100%

World

Africa

Americas

Asia

Europe

Oceania

0%

2014

2020

Figure 7: LTE network coverage forecasts, as a % of population by region  Source: GSMA Intelligence

Opportunities for further evolution of LTE

As a technology, LTE continues to develop. Operators are already making a considerable amount of progress in increasing the data speeds of their existing networks by adopting dual-carrier LTE-A technologies, which can achieve theoretical downlink speeds of up to 300 Mbps. As of October 2014, some 22 operators had already launched LTE-A, and we are aware of firm commitments by a further 47 to implement the technology. All in all 15 countries across the world now have live LTE-A networks, and this figure will increase to 35 assuming that all currently planned networks successfully make it to the commercial launch stage.

LTE-A should be able to meet mobile broadband demand (in terms of speed) for several years to come and will provide operators with increasing opportunities to develop attractive and profitable 4G services. In addition, 3GPP is also working on optimising congestion control for more efficient use of M2M on LTE networks.

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LTE is driving increasing CAPEX levels

Given the potential that remains for increasing 4G adoption in many countries, we expect to see considerable further investment in the technology. We forecast that the world’s mobile operators will invest $1.7 trillion in network infrastructure over the period 20142020 (see Figure 8), much of which will be in 4G networks. This outlay is a considerable uplift on the estimated $878 billion invested over the period 2009-2013 and underlines the industry’s commitment to meeting the exponentially increasing demand for mobile broadband services as well as connecting ‘the next billion people’ to the internet.

$150,000

$100,000

$50,000

$300,000

$200,000

$250,000

$0

2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

(in millions)

Figure 8: Total mobile operator CAPEX forecast, annual, in million US$  Source: GSMA Intelligence

The monetisation challenge that remains for LTE

The rapid migration towards LTE in the world’s most advanced mobile markets has driven a surge in data usage, with 4G users typically consuming twice as much data per month as other users. However, while the introduction of LTE has led to an uplift in ARPU in some instances, the impact on revenue varies widely depending on the market. For example, in South Korea KT reported an LTE ARPU of KRW 44,300 ($41.91) in Q2 2014, 31.8% greater than their blended ARPU for the same period. Operators in the US are seeing similar trends with Verizon Wireless – the largest LTE operator globally with 53.7 million 4G connections in Q2 2014 – announcing that its Q2 2014 ARPA (average revenue per account) was up 4.7% on a year earlier to $159.73 (based on an average of 2.8 connections per account).

However, in regions such as Europe, the migration towards LTE is at a significantly earlier stage and while they have reported similar trends in terms of data consumption, mobile operators in these regions are not yet seeing the same positive impact on revenue from LTE as witnessed in ‘digital pioneer’ markets such as South Korea, the US and Japan. In many cases, European operators are pricing 4G at the same price as 3G from the outset, while those that initially charged a premium for 4G are having to re-evaluate in the face of strong competition. Hence, the most significant challenge around LTE for many operators remains the monetisation of the networks that they have invested heavily

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in. While operators are transitioning their tariff structures to become increasingly datacentric, the continued decline in voice and SMS revenues is in many cases yet to be offset by corresponding increases in data revenues.

Thus, operators must seek to manage the change in usage patterns and pricing to minimise any cannibalisation of voice and SMS revenues and to ensure that margins are protected and future investment in LTE and other network technologies remains viable.

LTE interconnect and roaming issues

Interconnect is another area where LTE still has significant challenges to overcome. The GSMA has made progress in this area through the definition of IP eXchange (IPX), a technology with an all-IP core that can provide an improved interconnection which enhances the richness and quality of LTE data roaming. IPX allows the data roaming experience to be managed from end-to-end and manipulated in real time, which is useful for providing services requiring particular attributes e.g. high bandwidth, low latency.

However, the wider adoption of voice over LTE (VoLTE) has been constrained by the absence of a standard IP-based interconnect technology for voice, largely due to operator concerns about being unable to effectively manage and bill VoLTE traffic in the same way as traditional voice calls. Reaching an agreed technical standard for VoLTE interconnect is crucial, as voice services must provide a consistent experience for customers over any network, anywhere in the world. Hence the GSMA will continue to work towards the goal of delivering a seamless VoLTE interconnect and roaming service for consumers while protecting the commercial interests of operators.

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                         Authors

Dan Warren  Senior Director, GSMA Technology Calum Dewar  Lead Analyst, GSMA Intelligence

Other GSMA contributors to this report:

Hyunmi Yang Chief Strategy Officer Javier Albares Head of Corporate Strategy Elisa Balestra  Corporate Strategy Manager Scott Burcher  Senior Analyst, GSMA Intelligence Matthew Bloxham  Senior Director - Head of Policy Research, Government & Regulatory Affairs Wladimir Bocquet  Senior Director - Spectrum Policy, Government & Regulatory Affairs

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About GSMA Intelligence

GSMA Intelligence is the definitive source of global mobile operator data, analysis and forecasts; and a publisher of authoritative industry reports and research.

Our data covers every operator group, network and MVNO in every country worldwide — from Afghanistan to Zimbabwe. It is the most accurate and complete set of industry metrics available, comprising tens of millions of individual data points, updated daily.

 

GSMA Intelligence is relied on by leading operators, vendors, regulators, financial institutions and third-party industry players, to support strategic decision-making and long-term investment planning. The data is used as an industry reference point and is frequently cited by the media and by the industry itself.

For more information, visit gsmaintelligence.com/about/

Whilst every care is taken to ensure the accuracy of the information contained in this material, the facts, estimates and opinions stated are



 

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24天前 北大袁萌世界5G技术研发之十年

世界5G技术研发之十年

    十年前,美国宇航局启动了5G研发的大门。

十年之前,2013116日,华为宣布,投入巨资研发5G技术。此时,北大火星人“无穷小放飞互联网”行动正处在高潮之中,华为进军5G消息极大地鼓舞了火星人o

5G是大势所趋,谁也阻挡不了。

袁萌  陈启清  525

附件:世界5G技术研发之十年

History of 5G

In April 2008, NASA partnered with Geoff Brown and Machine-to-Machine Intelligence (M2Mi) Corp to develop 5G communications technology.[77] 

In 2008, the South Korean IT R&D program of "5G mobile communication systems based on beam-division multiple access and relays with group cooperation" was formed.[78]

In August 2012, New York University founded NYU WIRELESS, a multi-disciplinary academic research centre that has conducted pioneering work in 5G wireless communications.[79][80][81]

On 8 October 2012, the UK's University of Surrey secured £35M for a new 5G research centre, jointly funded by the British government's UK Research Partnership Investment Fund (UKRPIF) and a consortium of key international mobile operators and infrastructure providers, including Huawei, Samsung, Telefonica Europe, Fujitsu Laboratories Europe, Rohde & Schwarz, and Aircom International. It will offer testing facilities to mobile operators keen to develop a mobile standard that uses less energy and less radio spectrum while delivering speeds faster than current 4G with aspirations for the new technology to be ready within a decade.[82][83][84][85]

On 1 November 2012, the EU project "Mobile and wireless communications Enablers for the Twenty-twenty Information Society" (METIS) starts its activity towards the definition of 5G. METIS achieved an early global consensus on these systems. In this sense, METIS played an important role of building consensus among other external major stakeholders prior to global standardization activities. This was done by initiating and addressing work in relevant global fora (e.g. ITU-R), as well as in national and regional regulatory bodies.[86]

Also in November 2012, the iJOIN EU project was launched, focusing on "small cell" technology, which is of key importance for taking advantage of limited and strategic resources, such as the radio wave spectrum. According to Günther Oettinger, the European Commissioner for Digital Economy and Society (2014–2019), "an innovative utilization of spectrum" is one of the key factors at the heart of 5G success. Oettinger further described it as "the essential resource for the wireless connectivity of which 5G will be the main driver".[87] iJOIN was selected by the European Commission as one of the pioneering 5G research projects to showcase early results on this technology at the Mobile World Congress 2015 (Barcelona, Spain).

In February 2013, ITU-R Working Party 5D (WP 5D) started two study items: (1) Study on IMT Vision for 2020 and beyond, and; (2) Study on future technology trends for terrestrial IMT systems. Both aiming at having a better understanding of future technical aspects of mobile communications towards the definition of the next generation mobile.[88]

On 12 May 2013, Samsung Electronics stated that they had developed a "5G" system. The core technology has a maximum speed of tens of Gbit/s (gigabits per second). In testing, the transfer speeds for the "5G" network sent data at 1.056 Gbit/s to a distance of up to 2 kilometers with the use of an 8*8 MIMO.[89][90]

In July 2013, India and Israel agreed to work jointly on development of fifth generation (5G) telecom technologies.[91]

On 1 October 2013, NTT (Nippon Telegraph and Telephone), the same company to launch world's first 5G network in Japan, wins Minister of Internal Affairs and Communications Award at CEATEC for 5G R&D efforts[92]

On 6 November 2013, Huawei(华为) announced plans to invest a minimum of $600 million into R&D for next generation 5G networks capable of speeds 100 times faster than modern LTE networks.[93]

In April 2019, South Korea became the first country to adopt 5G.[94] Just hours later, Verizon launched its 5G services, and disputed South Korea's claim of becoming the world's first country with a 5G network, because allegedly, South Korea's 5G service was initially launched for just 6 South Korean celebrities so that South Korea could claim the title of having the world's first 5G network.[95] In fact, the three main Korean telecommunication companies (SK Telecom, KT and LG Uplus) added more than 40,000 users to their 5G network on the launch day.[96]

 

 



 

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25天前 北大袁萌第五代移动通信技术(5G)

第五代移动通信技术(5G

  当前,,百度一下“5G”,搜索到的结果使人一头雾水。

北大火星人最关心5G技术的发展,因为,它提倡“学微积,用手机”。

本文附件把5G完全说明白了。

袁萌  陈启清 525

附件:

规范发布时间

20194

使用于 电信

第五代移动通信技术(英语:5th generation mobile networks5th generation wireless systems,简称5G)是最新一代蜂窝移动通信技术,是4GLTE-A WiMax)、3GUMTSLTE)和2GGSM)系统后的延伸。5G的性能目标是高数据速率、减少延迟、节省能源、降低成本、提高系统容量和大规模设备连接。Release-15中的5G规范的第一阶段是为了适应早期的商业部署。Release-16的第二阶段将于20204月完成,作为IMT-2020技术的候选提交给国际电信联盟(ITU)。[1]

ITU IMT-2020规范要求速度高达20 Gbit/s,可以实现宽信道带宽和大容量MIMO[2] 第三代合作伙伴计划(3GPP)将提交5G NR(新无线电)作为其5G通信标准提案。5G NR可包括低频(FR1),低于6 GHz和更高频率(FR2),高于2.4 GHz和毫米波范围。然而,在早期部署中,在4G硬件(非独立)上使用5G NR软件的速度和延迟只比新4G系统稍好一点,估计要好15%到50%。[3][4][5] 独立eMBB部署的仿真显示,在FR1范围内,吞吐量提高了2.5倍,在FR2范围内提高了近20倍。[6]

当前,提供5G无线硬件与系统的公司有:三星、高通、思科、诺基亚、爱立信、联发科技、瞻博网络、中兴。[7][8][9][10][11][12][13]

目录

1

概述

2

规格

3

基站及覆盖范围

4

技术创新

5

部署

6

争议

6.1

健康问题

6.2

间谍活动

6.3

实际需求

7

参考资料

概述

与早期的2G3G4G移动网络一样,5G网络是数字蜂窝网络,在这种网络中,供应商覆盖的服务区域被划分为许多被称为蜂窝的小地理区域。表示声音和图像的模拟信号在手机中被数字化,由模数转换器转换并作为比特流传输。蜂窝中的所有5G无线设备通过无线电波与蜂窝中的本地天线阵和低功率自动收发器(发射机和接收机)进行通信。收发器从公共频率池分配频道,这些频道在地理上分离的蜂窝中可以重复使用。本地天线通过高带宽光纤或无线回程连接与电话网络和互联网连接。与现有的手机一样,当用户从一个蜂窝穿越到另一个蜂窝时,他们的移动设备将自动“切换”到新蜂窝中的天线。

5G网络的主要优势在于,数据传输速率远远高于以前的蜂窝网络,最高可达10 Gbit/s,比当前的有线互联网要快,比先前的4G LTE蜂窝网络快100倍。[14][15] 另一个优点是较低的网络延迟(更快的响应时间),低于1毫秒,而4G30-70毫秒。[15] 由于数据传输更快,5G网络将不仅仅为手机提供服务,而且还将成为一般性的家庭和办公网络提供商,与有线网络提供商竞争。以前的蜂窝网络提供了适用于手机的低数据率互联网接入,但是一个手机发射塔不能经济地提供足够的带宽作为家用计算机的一般互联网供应商。

 

5G网络通过在30300 GHz的毫米波波段内或附近[14],使用更高频率的无线电波来实现这些更高的数据速率,而以前的蜂窝网络使用700 MHz3 GHz之间的微波频带中的频率。一些5G供应商将使用微波频段中的第二个低频范围,低于6 GHz,但这不会有新频率的高速度。由于毫米波频段的带宽更为丰富,5G网络将使用更宽的频道与无线设备进行通信,频率最高可达400 MHz,而4G LTE的频率为20 MHz,可以每秒传输更多数据(比特)。OFDM调制技术是利用多个载波在频率信道中进行传输,从而同时并行地传输多个比特的信息。

毫米波会被大气中的气体吸收,并且比微波辐射的范围更小,因此蜂窝的大小更小;5G蜂窝将有一个城市街区那么大,而以前的蜂窝网络可能横跨好几公里。电磁波也很难穿过建筑物的墙壁,需要多个天线来覆盖一个蜂窝。[14] 毫米波天线比以前的蜂窝网络中使用的大型天线要小,只有几英寸长,所以5G蜂窝将被安装在电话杆和建筑物上的许多天线覆盖,而不是一个基站塔。[15] 另一种用来提高数据传输速率的技术是大规模MIMO技术。[14] 每个蜂窝将有多个天线与无线设备进行通信,每个天线通过一个独立的频道,由设备中的多个天线接收,这样多个数据流将同时并行传输。在一种称为波束赋形的技术中,基站计算机将不断计算无线电波到达每个无线设备的最佳路径,并将组织多个天线以相控阵的形式协同工作,产生到达设备的毫米波束。[14][15] 更小、更多的蜂窝使得5G网络基础设施比以前的蜂窝网络每平方千米覆盖更昂贵。部署当前仅限于都市地区,那里每个手机都有足够的用户来提供足够的投资回报,而且人们对这项技术是否能够到达偏乡区域存在疑问。[14]

新的5G无线设备也具有4G LTE功能,因为新的网络使用4G与蜂窝创建连接,此外在5G无法到达的地方也会使用4G[16]

5G的高数据传输速率和低延迟被认为在不久的将来会有新的用途。[16] 一种应用是实际的虚拟现实和增强现实。另一种应用是物联网中快速的机器对机器的交互。例如,道路上车辆中的计算机可以通过5G连续不断地相互通信,也可以连续不断地与道路通信。[16]

规格[编辑]

下一代移动网络联盟(Next Generation Mobile Networks Alliance)定义了5G网络的以下要求:

10Gbps的数据传输速率支持数万用户;

1Gbps的数据传输速率同时提供给在同一楼办公的许多人员;

支持数十万的并发连接以用于支持大规模传感器网络的部署;

频谱效率应当相比4G被显著增强;

覆盖率比4G有所提高;

信令效率应得到加强;

延迟应显著低于LTE

下一代移动网络联盟认为,5G应会在2020年陆续推出,以满足企业和消费者的需求。除了简单的提供更快的速度,他们预测5G网络还需要满足新的使用案例需求,如物联网(网络设备建筑物或Web访问的车辆)、广播类服务,以及在发生自然灾害时的生命线通信。

基站及覆盖范围[编辑]

基站类型

部署环境

用户数量

输出功率(mW

最远覆盖范围

Femto cell

家用, 商用

4 - 8 (家用), 16 - 32 (商用)

10 - 100(户外), 0.2 - 1(户外)

10

Pico cell

大型购物商场, 机场, 火车站,摩天大楼等公共区域

64 - 128

100 - 250 (户外), 1 - 5 (户外)

10

Micro cell

128 - 256

5 - 10 (仅限户外)

100余米

Metro cell

超出 250

10 - 20 (仅限户外)

100

Wi-Fi (对比)

家用, 商用

低于 50

20 - 100 (户外), 0.2 - 1000 (户外)

10余米

技术创新[编辑]

5G4G相比的技术创新如下:[17]

5G将采用512-QAM1024-QAM更高的数据压缩密度调制/解调制器,当前4G使用256-QAM64-QAM的调制以压缩传输数据,因此频谱效率每Mbps/100MHz的利用效率更高提高更多传输速率。

5G将采用28GHz毫米波通信,比如当前4G使用700MHz900MHz1800Mhz2600Mhz等低频段,虽然电波衍射能力比较高但是在低频上频谱资源就却相当有限,在高频的毫米波大多是军用战斗机雷达或测速照相等少数设备,频谱宽度更高,而且更容易找到连续频谱,使空白频谱非常容易获取。

波束指向配合多输入多输出(Multi-input Multi-output ; MIMO)相控数组天线,MIMO多输入多输出利用电磁波的空分复用和路径不同多天线系统提高传输速率,类似在军用领域的技术将延伸出的商用技术版本。

波束自适应和波束成形,能够提高特定方向的波瓣优化传输距离。[18]

新材料将使用GaN氮化镓或是GaAs砷化镓材料的RF射频天线和功率放大器,此材料的RF射频天线能在更高的频段有更高的能源效率,设备会比较省电。[19][20][21]

为了适应工业物联网、无人驾驶汽车、商用无人机等新技术的应用,网络延迟时间将降低到1毫秒以下。[22]

部署[编辑]

本条目需要更新。 (2019428)

请更新本文以反映近况和新增内容。完成修改时,请移除本模板。

主条目:全球5G商用网络列表

由于5G技术将可能使用的频谱是28GHz60GHz,属极高频(EHF),比一般电信业现行使用的频谱(如2.6GHz)高出许多。虽然5G能提供极快的传输速度,能达到4G网络的40倍,而且时延很低,但信号的衍射能力(即绕过障碍物的能力)十分有限,且发送距离很短,[23]这便需要增建更多基站以增加覆盖。

华为在2013116日宣布将在2018年前投资6亿美元对5G的技术进行研发与创新,并预告在2020年用户会享受到20Gbps的商用5G移动网络。201458日,日本电信营运商NTT DoCoMo正式宣布将与EricssonNokia、三星等六间厂商共同合作,开始测试凌驾现有4G网络1000倍网络承载能力的高速5G网络,传输速度可望提升至10Gbps。预计在2015年展开户外测试,并期望于2020年开始运作。[24]

2013513日,韩国三星电子宣布,已成功开发第5代移动通信(5G)的核心芯片实现,[25]这一技术预计将于2020年开始推向商业化。[26]该芯片技术可在28GHz超高频段以每秒1Gb以上的速度传送数据,且最长传送距离可达2公里。与韩国当前4G技术的传送速度相比,5G技术要快数百倍。通过这一技术,下载一部1GB的高清(HD)电影只需十秒钟。2015年诺基亚与加拿大Wind Mobile通信营运商成功测试5G。在2018年冬季奥运期间,韩国推出了5G试验网络,计划于2020年实行大规模商用。[23]201683日,澳大利亚电信宣布将于2018年在黄金海岸进行5G试验。[27]

华为20164月份宣布率先完成中国IMT-20205G)推进组第一阶段的空口关键技术验证测试,在5G信道编码领域全部使用极化码,20161117日国际无线标准化机构3GPP87次会议在美国拉斯维加斯召开,中国华为主推PolarCode(极化码)方案,美国高通主推LDPC方案,法国主推Turbo2.0方案,最终短码方案由极化码胜出,之前长码由LDPC胜出,底层规格确立。

2016年高通公司发表全球首个5G基带芯片X50,骁龙X50 5G调制解调器使用28GHz毫米波通信,下行速率达到5Gbps为当前最快的量产形芯片X16使用在S835处理器的1Gbps5倍之多,X50基带可能在2018年初量产。[28][29]高通进一步的解释是,利用毫米波波长短的特点,形成狭窄的定向波束,发送和接收更多能量,从而克服传播/路径损耗的问题并在空间中重复使用。此外,在视距路径受阻时,非视距(NLOS)路径(如附近建筑的反射)能有大量能量以提供替代路径。按照高通的规划,骁龙X50 5G平台将包括调制解调器、SDR051毫米波收发器和支持性的PMX50电源管理芯片。[30]

2019年手机芯片大厂联发科在世界移动通信大会(MWC 2019),展示该公司第一款 5G 调制解调器芯片M70的传输速度,当前正与客户紧密合作,预期 2020 年市场上将推出搭载联发科技芯片的 5G 终端设备。[31]

201943日,韩国于当地时间(UTC+923时启动5G网络服务并成为第一个5G国家。三家韩国电信公司(SK TelecomKTLG Uplus)在发布当天表示使用5G网络的用户已超过40,000[32] [33][34] [35]

争议[编辑]

健康问题[编辑]

2018年以来,一些团体以健康问题为由,反对部署5G[36] 最终因未无足够的证据[37]说服监管机构或专业协会(如:美国国家癌症研究所)或证明5G对人体有害。[38]

间谍活动[编辑]

因担心海外间谍组织借此从事间谍活动,美国已敦促其盟国禁止使用由中方所提供的5G设备。当前,澳大利亚、日本等国家已禁止其运营商在5G网络建设中采购中方设备。[39] [40][41] [42]

部分国家虽针对潜在的安全隐患作出警告并成功说服其运营商停止采购,但并未正式禁止使用。[42][43][44]

实际需求[编辑]

华为创始人任正非在20184月接受新华社采访时表示:“科学技术的超前研究不代表社会需求已经产生,5G就是媒体炒作过热了,我不认为现在5G有这么大的市场空间”[45]

网易创始人丁磊在2019年两会期间表示:“我不认为5G的高速会对当前的媒体平台有重大的改变,全世界都一样……它只是个速度的增加而已,其实你现在手机速度也够快了,不管是WIFI4G,都差不多够快了。我觉得(日常使用)基本上完全可以满足。”[46]

参考资料[编辑]

^ TELCOMA GLOBAL | 5g Technology Introduction. telcomaglobal.com. [2018-09-13].

^ Understanding massive MIMO and what it means for 5G. enterpriseiotinsights.com. [2019-01-21].

^ Dave. 5G NR Only 25% to 50% Faster, Not Truly a New Generation. wirelessone.news. [2018-06-25].

^ Factcheck: Large increase of capacity going from LTE to 5G low and mid-band. wirelessone.news. [2019-01-03].

^ Teral, Stephane. 5G best choice architecture (PDF). ZTE. 2019-01-30 [2019-02-01].

^ Predicting real-world performance of 5G NR mobile networks and devices. Qualcomm. 2018-03-07 [2019-01-03].

^ Japan allocates 5G spectrum, excludes Chinese equipment vendors. South China Morning Post.

^ Huawei Launches Full Range of 5G End-to-End Product Solutions. huawei.

^ Japan allocates 5G spectrum to carriers, blocks Huawei and ZTE gear. VentureBeat. April 10, 2019.

^ Samsung signals big 5G equipment push, again, at factory. January 4, 2019.

^ Nokia says it is the one-stop shop for 5G network gear | TechRadar. www.techradar.com.

^ 5G radio – Ericsson. Ericsson.com. February 6, 2018.

^ 5G MediaTek modem and SoC coming this year. Pocketnow.

^

跳转至:

14.0 14.1 14.2 14.3 14.4 14.5 Nordrum, Amy; Clark, Kristen. Everything you need to know about 5G. IEEE Spectrum magazine. Institute of Electrical and Electronic Engineers. 27 January 2017 [23 January 2019].

^

跳转至:

15.0 15.1 15.2 15.3 Hoffman, Chris. What is 5G, and how fast will it be?. How-To Geek website. How-To Geek LLC. 7 January 2019 [23 January 2019]. doi:  请检查|doi= (帮助).

^

跳转至:

16.0 16.1 16.2 Segan, Sascha. What is 5G?. PC Magazine online. Ziff-Davis. 14 December 2018 [23 January 2019].

^ 高通专注于用实际行动为5G铺路. Qualcomm. 2016-12-29.

^ 5G Small Cell | 5G Network Development. Qualcomm. 2018-10-02 [2019-04-08] (英语).

^ GaN打造的功率放大器为5G铺路 - RF技术 - 电子工程世界网. www.eeworld.com.cn. [2019-04-08].

^ ALLISON GATLIN. 矽原料竞争者悄悄触及苹果、谷歌和特斯拉的晶片市场. 2016-07-18.

^ 三星最新信息. Samsung tw. [2019-04-08] (中文(台湾).

^ Jo Best. The race to 5G: Inside the fight for the future of mobile as we know it. [2019-01-09].

^

跳转至:

23.0 23.1 还没到来的5G手机网络是什么样?. 新浪网 sina.com.hk. 2015-12-07.

^ 超越 LTE 千倍速度,NTT DoCoMo 测试 5G 网路,预计 2020 年推出. T客邦. 2014-05-12.

^ 三星电子研发出5G核心技术 互联网档案馆的存档,存档日期2013-06-22.,亚太日报,2013514

^ 东网透视:5G五年后面世 1秒下载1GB片,东网港澳,20151011

^ Mike Wright. Preparing for the arrival of 5G. Telstra. 2016-08-03.

^ 万南. 高通发布全球首款5G基带:28GHz毫米波、峰值5Gbps. 快科技. 2016-10-18.

^ Qualcomm Snapdragon. Meet Snapdragon X50 – Qualcomm Technologies' First 5G Modem. 2016-10-17 –通过YouTube.

^ 张里欧. 高通谈5G不是只有快 28GHz频段毫米波首度展出. 2016-02-29.

^ 财讯快报. 联发科MWC秀出第一款5G数据机晶片M70 终端设备2020年上市. 2019-02-26.

^ US dismisses South Korea’s launch of world-first 5G network as ‘stunt’ - 5G - The Guardian. amp.theguardian.com.

^ 5G 4 3 . The Asia Business Daily.

^ South Korea to seize on world's first full 5G network. Nikkei Asian Review.

^ 综述:韩国大众开始使用5G手机网络-新华网. www.xinhuanet.com. [2019-04-08].

^ ABOUT US. americansforresponsibletech.org be. Americans for Responsible Technology. [April 6, 2019].

^ 5G Mobile Technology Fact Check (PDF). asut. 2019-03-27 [2019-04-07].

^ Cell Phones and Cancer Risk. [April 6, 2019]. However, although many studies have examined the potential health effects of non-ionizing radiation from radar, microwave ovens, cell phones, and other sources, there is currently no consistent evidence that non-ionizing radiation increases cancer risk in humans.

^ White House mulls executive order to ban Huawei and ZTE equipment in U.S.. December 27, 2018.

^ U.S. shifts to require strict 5G security from allies, not Huawei bans. VentureBeat. April 8, 2019.

^ Huawei would reportedly sell 5G chips to Apple, if U.S. ban isn’t an issue. VentureBeat. April 8, 2019.

^

跳转至:

42.0 42.1 Hunter, Kirsty Needham, Fergus. China takes Australia's Huawei 5G ban to global trade umpire. The Sydney Morning Herald. April 14, 2019.

^ 楽天は中国系机器使わず、ソフトバンクも暗に认める. April 10, 2019 –通过jp.reuters.com.

^ UN says US fears over Huawei’s 5G are politically motivated. Engadget.

^ 华为,下一步如何作为?——对话任正非-新华网.

^ 丁磊:5G的高速在短期内不会对生活有重大改变-中新网.



 

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26天前 北大袁萌世界互联网发展的时间表

世界互联网发展的时间表

专注远距离数据通讯的北大火星人从历史中走来, 

上世纪90年代初,北大火星人是国内远程数据通讯的领跑者。

   不了解历史就是文盲。请见附件。

袁萌 陈启清  524

附件:

Internet history timeline

Early research and development:

1965: NPL network planning starts

1966: Merit Network founded

1966: ARPANET planning starts

1967: NPL network packet switching pilot experiment

1969: ARPANET carries its first packets

1970: Network Information Center (NIC)

1971: Tymnet switched-circuit network

1972: Merit Network's packet-switched network operational

1972: Internet Assigned Numbers Authority (IANA) established

1973: CYCLADES network demonstrated

1974: Telenet commercial packet-switched network

1976: X.25 protocol approved

1978: Minitel introduced

1979: Internet Activities Board (IAB)

1980: USENET news using UUCP

1980: Ethernet standard introduced

1981: BITNET established

Merging the networks and creating the Internet:

1981: Computer Science Network (CSNET)

1982: TCP/IP protocol suite formalized

1982: Simple Mail Transfer Protocol (SMTP)

1983: Domain Name System (DNS)

1983: MILNET split off from ARPANET

1985: First .COM domain name registered

1986: NSFNET with 56 kbit/s links

1986: Internet Engineering Task Force (IETF)

1987: UUNET founded

1988: NSFNET upgraded to 1.5 Mbit/s (T1)

1988: OSI Reference Model released

1988: Morris worm

1989: Border Gateway Protocol (BGP)

1989: PSINet founded, allows commercial traffic

1989: Federal Internet Exchanges (FIXes)

1990: GOSIP (without TCP/IP)

1990: ARPANET decommissioned

1990: Advanced Network and Services (ANS)

1990: UUNET/Alternet allows commercial traffic

1990: Archie search engine

1991: Wide area information server (WAIS)

1991: Gopher

1991: Commercial Internet eXchange (CIX)

1991: ANS CO+RE allows commercial traffic

1991: World Wide Web (WWW)

1992: NSFNET upgraded to 45 Mbit/s (T3)

1992: Internet Society (ISOC) established

1993: Classless Inter-Domain Routing (CIDR)

1993: InterNIC established

1993: AOL added USENET access

1993: Mosaic web browser released

1994: Full text web search engines

1994: North American Network Operators' Group (NANOG) established

Commercialization, privatization, broader access leads to the modern Internet:

1995: New Internet architecture with commercial ISPs connected at NAPs

1995: NSFNET decommissioned

1995: GOSIP updated to allow TCP/IP

1995: very high-speed Backbone Network Service (vBNS)

1995: IPv6 proposed

1996: AOL changes pricing model from hourly to monthly

1998: Internet Corporation for Assigned Names and Numbers (ICANN)

1999: IEEE 802.11b wireless networking

1999: Internet2/Abilene Network

1999: vBNS+ allows broader access

2000: Dot-com bubble bursts

2001: New top-level domain names activated

2001: Code Red I, Code Red II, and Nimda worms

2003: UN World Summit on the Information Society (WSIS) phase I

2003: National LambdaRail founded

2004: UN Working Group on Internet Governance (WGIG)

2005: UN WSIS phase II

2006: First meeting of the Internet Governance Forum

2010: First internationalized country code top-level domains registered

2012: ICANN begins accepting applications for new generic top-level domain names

2013: Montevideo Statement on the Future of Internet Cooperation

2014: NetMundial international Internet governance proposal

2016: ICANN contract with U.S. Dept. of Commerce ends, IANA oversight passes to the global Internet community on October 1st

Examples of Internet services:

1989: AOL dial-up service provider, email, instant messaging, and web browser

1990: IMDb Internet movie database

1995: Amazon.com online retailer

1995: eBay online auction and shopping

1995: Craigslist classified advertisements

1996: Hotmail free web-based e-mail

1997: Babel Fish automatic translation

1998: Google Search

1998: Yahoo! Clubs (now Yahoo! Groups)

1998: PayPal Internet payment system

1999: Napster peer-to-peer file sharing

2001: BitTorrent peer-to-peer file sharing

2001: Wikipedia, the free encyclopedia

2003: LinkedIn business networking

2003: Myspace social networking site

2003: Skype Internet voice calls

2003: iTunes Store

2003: 4Chan Anonymous image-based bulletin board

2003: The Pirate Bay, torrent file host

2004: Facebook social networking site

2004: Podcast media file series

2004: Flickr image hosting

2005: YouTube video sharing

2005: Reddit link voting

2005: Google Earth virtual globe

2006: Twitter microblogging

2007: WikiLeaks anonymous news and information leaks

2007: Google Street View

2007: Kindle, e-reader and virtual bookshop

2008: Amazon Elastic Compute Cloud (EC2)

2008: Dropbox cloud-based file hosting

2008: Encyclopedia of Life, a collaborative encyclopedia intended to document all living species

2008: Spotify, a DRM-based music streaming service

2009: Bing search engine

2009: Google Docs, Web-based word processor, spreadsheet, presentation, form, and data storage service

2009: Kickstarter, a threshold pledge system

2009: Bitcoin, a digital currency

2010: Instagram, photo sharing and social networking

2011: Google+, social networking

2011: Snapchat, photo sharing

2012: Coursera, massive open online courses

 

 

 



 

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26天前 北大袁萌互联网是什么?

互联网是什么?

   回顾往事,1990年初,袁萌从中国人民大学调入北京大学,即被校方指派替代北大计算系马希文教授参与规划、建设中关村地区高校校园网(含中科院)的筹备组。这是中国互联网建设的开始。

   但是,正确的互联网概念是什么?含混不清是不行的。请见附件。

袁萌  陈启清  524

附件:互联网的正确概念

互联网(英语:Internet)是指21世纪之初网络与网络之间所串连成的庞大网络。这些网络以一些标准的网络协议相连,连接全世界几十亿个设备,形成逻辑上的单一巨大国际网络。[1]它是由从地方到全球范围内几百万个私人的、学术界的、企业的和政府的网络所构成,通过电子,无线和光纤网络技术等等一系列广泛的技术联系在一起。这种将计算机网络互相联接在一起的方法可称作“网络互联”,在这基础上发展出覆盖全世界的全球性互联网络称互联网,即是互相连接一起的网络。互联网并不等同万维网(WWW),万维网只是一个基于超文本相互链接而成的全球性系统,且是互联网所能提供的服务其中之一。互联网带有范围广泛的信息资源和服务,例如相互关系的超文本文件,还有万维网的应用,支持电子邮件的基础设施,点对点网络,文件共享,以及IP电话服务。

 



 

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27天前 北大袁萌为实现《北京共识》的宏伟目标,,北大火星人将不懈努力之

为实现《北京共识》的宏伟目标,,北大火星人将不懈努力之

大家知道,《北京共识》强调,要将人工智能平台和基于数据的学习分析作为构建终身学习系统的关键技术,实现人人皆学、处处能学、时时可学。确保人工智能技术使每个人不分性别、不分健康状况、不分社会或经济地位、不分民族或文化背景、不分地域,都能享受优质教育和学习机会。

试想,实现《北京共识》强调的上述宏伟目标,如果不采用电子化教材(学微积,用手机),不采用“知识共享”策略,那是绝对实现不了的。

为达此目的,北大火星人将不懈努力之。

袁萌  陈启清   522

附件:

《北京共识》提出,各国要制定相应政策,推动人工智能与教育、教学和学习系统性融合,利用人工智能加快建设开放灵活的教育体系,促进全民享有公平、有质量、适合每个人的终身学习机会。

《北京共识》强调,要将人工智能平台和基于数据的学习分析作为构建终身学习系统的关键技术,实现人人皆学、处处能学、时时可学。确保人工智能技术使每个人不分性别、不分健康状况、不分社会或经济地位、不分民族或文化背景、不分地域,都能享受优质教育和学习机会。

《北京共识》倡议,要支持对与新兴人工智能技术发展相关的前沿问题进行前瞻性研究,探索利用人工智能促进教育创新的有效战略和实践,以期在人工智能与教育领域构建具有共同价值观的国际共同体。

此次大会得到国际社会积极响应。斯洛文尼亚副总理兼教育、科学和体育部部长耶尔奈伊皮卡洛,联合国教科文组织执行局主席李炳铉,总干事代表、教育助理总干事斯蒂芬妮亚贾尼尼出席大会并致辞。

此次大会由中国教育部、联合国教科文组织、中国联合国教科文组织全国委员会、北京市人民政府共同主办。

 

2017年有什么大会什么的大会国家大会有哪些

 

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最近更新:05-2020:18

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28天前 北大袁萌中国人工智能发展之始端

中国人工智能发展之始端

回顾以往,上世纪1979年秋天,清华大学、北航、中国人民大学、北邮、北京科技大学、武大、浙大、中南科技大学、社科院等单位的代表开会决定组建中国人工智能学会。

  袁萌是中国人工智能    学会发起人之一,经过学会理事会选举,袁萌担任学会第一届副秘书长、第二、三届秘书长,时间长达15年。

    1881年,中国人工智能学会(国家一级学会)正式成立。

   请见本文附件。

袁萌  陈启清  521

附件:

国际人工智能与教育大会于2019516-18日在北京召开。国家主席习近平向大会致贺信。开幕式上,孙春兰副总理宣读习近平主席贺信并致辞。来自全球100多个国家、10余个国际组织的约500位代表汇聚一堂,共同探讨全球教育的未来发展之路,并通过成果文件《北京共识》。

此次大会有哪些主要内容?产生哪些成果?教育小微带你来了解↓↓↓

 

大会举行期间,在“通过人工智能促进可持续发展目标实现的新兴政策与战略”主题的部长论坛环节,教育部部长陈宝生以《中国的人工智能教育》为题做主旨发言,分享了走向智能时代中国教育的思考和探索。

 

大会期间,教育部副部长孙尧、田学军、钟登华分别参加了相关活动,他们都说了哪些观点?一起看看↓↓↓

教育部副部长孙尧在“促进人工智能在教育领域应用的公平性、包容性和透明性”为主题的全体会议环节,做主旨发言,与参会人士交流和探讨了教育扶贫话题。

孙尧表示,教育扶贫承载着阻断贫困代际传递的重大使命,中国教育部坚持精准扶贫精准脱贫的基本方略,深入推进扶智育人教育脱贫攻坚行动,着力构建较为完善的教育扶贫制度体系,着力实施补短兜底的教育扶贫工程项目,着力落实精准到人的学生资助体系,着力推动量身定制的教育扶贫倾斜政策,着力探索“高校品牌”的特色扶贫路径,全力打好教育脱贫攻坚战。

孙尧表示,脱贫攻坚战已进入决战决胜的关键时期,我们将以习近平主席关于扶贫的重要论述为指引,狠抓工作落实,深入推进“人工智能+教育扶贫”,持续拓展教育脱贫攻坚方式,提升教育脱贫攻坚精准度,加大教育脱贫攻坚力度,巩固提升教育脱贫攻坚成果,坚决打赢教育脱贫攻坚战。

教育部副部长、中国联合国教科文组织全国委员会主任田学军在闭幕式致辞中提出,人类正加速迎来、日益走近智能时代,新情况新课题层出不穷,迫切需要国际社会采取负责任态度、坚持人文理念、秉持合作精神。此次大会能够取得圆满成功、成果超出预期,关键在于与会代表展现出了坚定的责任担当、深切的人文关怀以及积极的合作精神。

田学军表示,中国愿意进一步密切与教科文组织和广大会员国合作,落实《北京共识》,继续围绕人工智能与教育搭建国际交流平台,携手共建更加包容、更加公平、更加优质的现代化教育,为全面实现2030年可持续发展目标,为推动构建人类命运共同体做出应有贡献。

教育部副部长钟登华在“展望人工智能时代教育的未来”为主题的主题会议环节,做主题发言,分享了近年来中国政府推动智能教育发展的认识与行动。

钟登华指出,人类社会的发展离不开科技的创新和教育的进步,以人工智能为代表的新一代信息技术的快速发展,将会对传统的教育理念、教育体系和教学模式产生革命性影响,从而进一步释放教育在推动人类社会发展过程中的巨大潜力。近年来,在《新一代人工智能发展规划》《高等学校人工智能创新行动计划》《中国教育现代化2035》等政策文件的指引下,一些地区和学校在提升信息素养、推广智能学伴、构建智能化校园、改革评价方式、促进交叉融合等方面开始了人工智能与教育教学融合的探索。

钟登华表示,智能时代的中国教育发展,将呈现几个新特征:教育改革创新将注入人机协同、共创分享的新动力;教育科学研究将进入交叉融合、集智创新的新阶段;教育发展目标将聚焦更加公平、更有质量的新标准;教育治理体系将面临社会伦理、数据安全的新挑战。他希望,通过多种方式加强与世界各国的交流与合作,在联合国教科文组织的引领下,共同开展相关科学研究,进行理论创新与实践探索,分享发展经验和创新成果,为实现全纳、公平、可持续的优质教育,实现全人类的共同利益贡献力量。

 

会议通过成果文件《北京共识》,主要内容有哪些?一起来看↓↓↓

《北京共识》提出,各国要制定相应政策,推动人工智能与教育、教学和学习系统性融合,利用人工智能加快建设开放灵活的教育体系,促进全民享有公平、有质量、适合每个人的终身学习机会。

《北京共识》强调,要将人工智能平台和基于数据的学习分析作为构建终身学习系统的关键技术,实现人人皆学、处处能学、时时可学。确保人工智能技术使每个人不分性别、不分健康状况、不分社会或经济地位、不分民族或文化背景、不分地域,都能享受优质教育和学习机会。

《北京共识》倡议,要支持对与新兴人工智能技术发展相关的前沿问题进行前瞻性研究,探索利用人工智能促进教育创新的有效战略和实践,以期在人工智能与教育领域构建具有共同价值观的国际共同体。

此次大会得到国际社会积极响应。斯洛文尼亚副总理兼教育、科学和体育部部长耶尔奈伊皮卡洛,联合国教科文组织执行局主席李炳铉,总干事代表、教育助理总干事斯蒂芬妮亚贾尼尼出席大会并致辞。

此次大会由中国教育部、联合国教科文组织、中国联合国教科文组织全国委员会、北京市人民政府共同主办。

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2017年有什么大会什么的大会国家大会有哪些

 

微言教育

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2019年全国学前教育宣传月来了,活动重点看过来!

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29天前 北大袁萌BeijingConsensus(北京共识)

Beijing Consensus(北京共识)

  Int'l conference on AI, education concludes with Beijing Consensus

   Source: Xinhua| 2019-05-18 23:28:10|

  

  

  

   BEIJING, May 18 (Xinhua) -- The International Conference on Artificial Intelligence (AI) and Education concluded in Beijing Saturday.

   Nearly 500 representatives from over 100 countries and more than 10 international organizations jointly discussed the future development of global education and passed an outcome document, the Beijing Consensus.

   Themed "Planning Education in the AI Era: Lead the Leap," the conference covers topics such as policy-making for education, course development, as well as promotion of educational equality and inclusiveness.

   Various countries should make corresponding policies to promote integration of AI and education, build open and flexible educational systems, and facilitate universal accessibility to fair and quality lifelong learning opportunities, according to the Beijing Consensus.

   The Beijing Consensus also proposes to support research on frontier issues related to emerging AI technologies, as well as to explore effective strategies and practices on facilitation of educational innovation.

   The conference, which started Thursday, aims to introduce the application of artificial intelligence technology in the field of education of China to the world in an intuitive and vivid way.

  

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1月前 北大袁萌高举《北京共识》旗帜,火星人“对簿”北京大学

高举《北京共识》旗帜,火星人“对簿”北京大学

   1995526 北大方正盗窃火星人源代码(智慧产物)。事后,方正暗中运作,1997228日,北京大学召开校长办公会决定把火星人一脚踹到南太平洋里面。

经过二十多年长途游泳如今回到大陆北京,高举《北京共识》旗帜,与北大“对簿”互联网。

敬请关注。

袁萌  陈启清  519



 

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