SONET与SDH是什么关系？
1985 年，Bellcore提出SONET（Synchronous Optical Network同步光纤网）标准，美国国家标准协会（ANSI）通过了一系列有关SONET标准。1989年，国际电报电话咨询委员会CCITT接受 SONET概念制定了SDH（Synchronous Digital Hierarchy，同步数字体系）标准，使之成为不仅适于光纤也适于微波和卫星传输的通用技术体制。与SONET有细微差别，SDH/SONET定义了 一组在光纤上传输光信号的速率和格式，通常统称为光同步数字传输网，是宽带综合业务数字网B-ISDN的基础之一。SDH/SONET采用TDM技术，是 同步系统（由主时钟控制，精度10^-9）。两者都用于骨干网传输，是对准同步数字系列PDH （Plesiochronous Digital Hierarchy）的一次革命。SONET多用于北美和日本，SDH多用于中国和欧洲。

STM-1/4/16/64是不是一种速率级别标准？
是,由CCITT制定的SDH optical速率级别。
SDH信号标准速率等级：STM-1为155.52M；STM-4为622.08M；STM-16为2488.32M；STM-64为9553.28M；STM-256为40G。
还有别的STM标准：STM-1，3，4，6，8，12，16，64，256......以STM-1的倍数递增。

OC-192是什么东西的速率标准？对应具体速率是多少？还有其他什么OC速率标准？
OC-192是SONET的optical速率标准，相当于SONET的Electrical STS-192或SDH的optical STM-64，即10Gbps（9553.28M）。其他oc标准还有oc-1，oc-3，oc-9，oc-12，oc-18，oc-24，oc- 36，oc-48，oc-192，oc-768等，以oc-1(51.84 Mbps)的倍数递增。

SONET速率为51.84M-9.953G，也像SDH一样按某种标准分级吗？PDH与WDM的速率上下限分别是多少，像SDH一样按某种标准分级吗？
SDH进行速率分级，有Optical STM-1标准，SONET也进行速率分级，分Electrical STS-1和Optical OC-1。
标准PDH速率小于565Mbps，具体速率与复接等级如下：
基    群：2.048Mb/s       含30路数字电话
二次群：8.448Mb/s       含4个基群
三次群：32.368Mb/s     含4个二次群
四次群：139.264Mb/s   含4个三次群

WDM系统使用不同的波长（在1550nm附近），可以承载多个通路的信息，每条通路速率可以高达2.5Gbps或10Gbps。第一代WDM系统支持4到16个波长，每个波长通路的速率为2.5Gbps；第二代WDM系统现在能支持32到40个波长，预计能达到100个波长；目前已有能支持1Tbps容量（100个10Gbps通路）的WDM实验系统在进行演示。

DWDM实验室水平为：100*10Gb/s（100波，每波10Gb/s），中继距离400km；30*40Gb/s（30波，每波40Gb/s），中 继距离85km；64*5Gb/s（64波，每波5Gb/s），中继距离720km。商用水平为320Gb/s，商用系统的传输能力仅是单根光纤可能传输 容量的1/100。新的DWDM系统现在发展到每根光纤以10Tbps的速度传输。

广域网发展PDH----SDH/SONET----WDM对吗，这些都是使用光纤通信技术吗？PDH/SDH/WDM到底是指一种协议，还是一种传输介质，还是一种传输技术，还是一种传输设备，还是一种....？（工作在7层协议的哪一层？）
PDH--SDH/SONET--WDM是对的，基本上使用光纤通信技术，但不是全部，如SDH还可使用微波和卫星传送。PDH/SDH/WDM规定了光 信号在光纤上传输的速率和格式，其不是一种协议，也不是一种传输介质（介质是光纤），它是一种传输技术，也通指PDH/SDH/WDM上所使用的各种设 备。

同步数字序列SDH 是由一些SDH网元（NE）组成，在光纤上进行同步信息传输、复用和交叉连接的网络。SDH有四个网元：终端复用器TM、再生中继器REG、分扦复用器 ADM、和同步数字交叉连接设备DXC（是一种兼有复用、配线、保护/恢复、监控和网管多种功能的设备，其常用配置：DXC4/4速率为140Mb/s或 155.52Mb/s，DXC4/1速率为2Mb/s)。

注意：SDH是一种物理传输方式，IP是一种网络传输协议，IP ON SDH 即POS是让IP在SDH的网上跑，这三者的概念要分清。

Optical Carrier specifications (in use)

OC-1

OC-1 is a SONET line with transmission speeds of up to 51.84 Mbit/s (payload: 50.112 Mbit/s; overhead: 1.728 Mbit/s) using optical fiber. This base rate is multiplied for use by other OC-n standards. For example, an OC-3 connection is 3 times the rate of OC-1.

OC-3 / STM-1x

OC-3 is a network line with transmission speeds of up to 155.52 Mbit/s (payload: 148.608 Mbit/s; overhead: 6.912 Mbit/s, including path overhead) using fiber optics. Depending on the system OC-3 is also known as STS-3 (electrical level) and STM-1 (SDH).

When OC-3 is not multiplexed by carrying the data from a single source, the letter c (standing for concatenated) is appended: OC-3c.

OC-3c

OC-3c ("c" stands for "concatenated") concatenates three STS-1(OC-1) frames into a single OC-3 look alike stream. The three STS-1 (OC-1) streams interleaved with each other such that the first column is from the first stream, the second column is from the second stream, and the third is from the third stream. Concatenated STS(OC) frames carry only one column of path overhead because they cannot be divided into finer granularity signals. Hence, OC-3c can transmit more payload to accommodate a CEPT-4 139.264 Mbit/s signal. The payload rate is 149.76 Mbit/s and overhead is 5.76 Mbit/s.

OC-12 / STM-4x

OC-12 is a network line with transmission speeds of up to 622.08 Mbit/s (payload: 601.344 Mbit/s; overhead: 20.736 Mbit/s).

OC-12 lines are commonly used by ISPs as WAN connections. While a large ISP would not use an OC-12 as a backbone (main link), it would for smaller, regional or local connections. This connection speed is also often used by mid-sized (below Tier 2) internet customers, such as web hosting companies or smaller ISPs buying service from larger ones.

OC-24

OC-24 is a network line with transmission speeds of up to 1244.16 Mbit/s (payload: 1202.208 Mbit/s; overhead: 41.472 Mbit/s). Implementations of OC-24 in commercial deployments are rare.

OC-48 / STM-16x / 2.5G Sonet

OC-48 is a network line with transmission speeds of up to 2488.32 Mbit/s (payload: 2405.376 Mbit/s; overhead: 82.944 Mbit/s).

With usually cheap interface prices and being faster than OC-3, OC-12 connections, and even surpassing gigabit Ethernet, OC-48 connections are used as the backbones of many regional ISPs. Interconnections between large ISPs for purposes of peering or transit are quite common. As of 2005, the only connections in widespread use that surpass OC-48 speeds are OC-192 and 10 gigabit Ethernet.

OC-48 is also used as transmission speed for tributaries from OC-192 nodes in order to optimize card slot utilization where lower speed deployments are used. Dropping at OC-12, OC-3 or STS-1 speeds are more commonly found on OC-48 terminals, where use of these cards on an OC-192 would not allow for full use of the available bandwidth.

OC-96

OC-96 is a network line with transmission speeds of up to 4976.64 Mbit/s (payload: 4810.752 Mbit/s; overhead: 165.888 Mbit/s). Implementations of OC-96 in commercial deployments are rare, if ever used at all.

OC-192 / STM-64x / 10G Sonet

OC-192 is a network line with transmission speeds of up to 9953.28 Mbit/s (payload: 9621.504 Mbit/s; overhead: 331.776 Mbit/s).

A standardized variant of 10 gigabit Ethernet (10GbE), called WAN-PHY, is designed to inter-operate with OC-192 transport equipment while the common version of 10GbE is called LAN-PHY (which is not compatible with OC-192 transport equipment in its native form). The naming is somewhat misleading, because both variants can be used on a wide area network.

As of 2005, OC-192 connections are most common for use on backbones of large ISPs.

OC-768 / STM-256x

OC-768 is a network line with transmission speeds of up to 39,813.12 Mbit/s (payload: 38,486.016 Mbit/s; overhead: 1,327.104 Mbit/s).

On October 23, 2008, AT&T announced the completion of upgrades to OC-768 on 80,000 fiber-optic wavelength miles of their IP/MPLS backbone network. OC-768 SONET interfaces have been available with short-reach optical interfaces from Cisco since as early as 2006. Infinera made a field trial demonstration data transmission on a live production network involving the service transmission of a 40 Gbit/s OC-768/STM-256 service over a 1,969 km terrestrial network spanning Europe and the U.S. In November 2008, an OC-768 connection was successfully brought up on the TAT-14/SeaGirt transatlantic cable, with the longest hop being 7,500km.

Optical Carrier specifications (unused)

Note: All of the following OC lines are theoretical. None of these are currently in use.

OC-384

Will be able to provide transmission speeds of around 19.8912 Gbit/s.

OC-1536

Will be able to provide transmission speeds of around 79.62624 Gbit/s. It is unknown if such standards will be implemented in the near future. As of 2007, the majority of work beyond 40 Gbit/s is focusing on 100 gigabit Ethernet, in the IEEE's Higher Speed Study Group.

OC-3072

Will be able to provide transmission speeds of around 159.25248 Gbit/s

OC-7144F

Will be able to provide transmission speeds of around 301.33598 Gbit/s

SONET   技术原理

8.6 SONET  
     SONET(同步光纤网)一种光纤技术，其数据传输速率可以高达1 G b p s以上。S O N E T增长
的很快，越来越多的电话公司都将它纳入了服务范围。该标准是由B e l l c o r e和电信工业解决
方案联盟( AT I S )开发的，在1 9 8 4年被提交给A N S I，成为一个开放的、灵活的和廉价的光纤传
输标准。在1 9 8 6年，I T U - T开始开发类S O N E T的传输和速度建议，但是最终形成的标准却叫
做同步数字序列( S D H )，该标准主要在欧洲使用。现在， S O N E T的数据传输速率已经可以高
达2 . 4 8 8 G b p s，并且承诺在将来可以达到1 3 . 2 7 1 G b p s。
    

      S O N E T的一个优点是它是非专有的，所以可以从众多的厂家购买点到点的网络设备。SONET可以连接到AT M、I S D N和其他设备的接口上，为这些设备提供高速通信。S O N E T的另外一个优点是它可以在很长的距离上提供高速的数据传输，例如在两个城市或者州之间。S O N E T在以下方面尤其有用：
          在两个相距很远的网络之间提供高速的数据连接(例如，在大学校园和私有公司发起的研究中心之间提供高速的数据传输)。
          在两个相距很远的站点之间举行视频会议。
          远程教学。
          高质量的音频和视频播放。
          复杂图形的高速传输，例如，通过卫星拍摄得到的地形学地图和图像。

8.6.1 通信介质和特性

       S O N E T高速通信使用的通信介质是单模光纤电缆和T 载波通信(从T- 3开始)。主要的传输
方法发生在物理层，这使得其他一些传输技术，如AT M、F D D I和S M D S等，可以运行在
S O N E T之上。S O N E T和使用固定信元长度的技术最为兼容(例如，AT M和S M D S )，和使用可
变帧长的技术兼容性要差一些。
       S O N E T的基本速率为5 1 . 8 4 M b p s ,即光纤载波级别1 ( O C - 1 )，其电子方面的级别称为同步传输信号级别1 ( S T S - 1 )。从该速率开始，便可以将信号切换到特殊类型服务所需要的更高速率
上。当前可用的速率范围如表8 - 2所示。未来的S O N E T传输速度有望达到S T S级别2 5 6，速率
为1 3 . 2 7 1 G b p s。O C - 3、O C - 1 2和O C - 4 8是现在最常用的选择。(通过项目练习8 - 3，收集一些通过R B O C提供的S O N E T服务方面的信息。)

       等价的S T S说明的是S O N E T用来进行传输的路径数量，例如S T S - 1使用一条路径，
而S T S - 9使用9条路径。下载I T U - T的版本S D H和S O N E T十分相似，但是S D H的基本速率是1 5 5 . 5 2 M b p s，而不是5 1 . 8 4 M b p s，称为同步传输模型级别1 ( S T M - 1 )。表8 - 3给出的是S D H的光纤传输速率。
 
8.6.2 SONET网络拓扑和故障恢复

      S O N E T在环型拓扑中传输，提供的故障恢复方法有三种(具体实现哪种方法取决于WAN

提供商使用的体系结构)：单向路径交换、自动保护交换和双向路径交换。在单向路径交换中，
光纤环只有一个。数据信号在环上沿两个方向传输。接收结点决定接受哪个信号。如果在一
个路径上有断口，在另外一个路径上的信号仍然可以达到目的结点。沿另外一条路径发送的
数据提醒接收节点当前只有一个路径是通的。
 在自动保护交换中，如果在S O N E T网络上的某一个点检测到了故障，则把数据定向到另
 第三种故障恢复方法是双向路径交换，提供的故障恢复率最高，可以高达9 9 %。它使用双环
技术，所以在任何时候总有两个路径可以到达某个节点(见图8 - 1 5 )。数据在两个环上都进行发送，
但是方向相反。如果在其中的一条路径上有断口，另外一条路径上的数据仍然可以畅通无阻。

8.6.3 SONET分层和OSI模型

      S O N E T使用了四个协议层(见图8 - 1 6 )。其中最底层为光子层，与O S I模型中物理层对应。
该层处理信号的转换和传输。被传输的电信号需要转换成光信号，然后再放到光纤电缆上，
在接收端，需要将接收到的光信号再还原为电信号。该层还监视着信号传输方面的问题，包
括光脉冲的形状，传输的能量级别以及传送信号的波长等。

     第二层叫做路段层(Section layer)。该层负责对数据进行封装，保证数据以正确的顺序进
行发送，同时保证每一个帧的定时和检查传输中出现的错误。
     再上面一层为线路层，该层监视传输中出现的问题，如果出现问题则进行故障恢复。同
时该层还负责信号的同步和交换，保证整个帧都到达其目的地。
     最上面的一层为路径层，用以将信号映射到通信信道上。例如，它可以将AT M信号映射
到一个信道而将I S D N信号映射到另外一个信道。该层还保证从源到目的地的信道的可靠性。

8.6.4 SONET帧

      STS-1帧是S O N E T帧的最为基本的组装块(见图8 - 1 7 )。S T S - 1帧长9 0个字节。它由虚拟支

流( V T )构成，使用什么虚拟支流的类型取决于应用程序的需求。每个V T都是一个独立的数据
封装。V T决定了如何将一个载波信号映射到S O N E T帧中。例如，已经定义了映射T- 1 ( V T 1 . 5 )
和T- 3 ( V T 6 )通信的V T。V T从设计上保证了异步和同步信号的传输。除了承载多个V T之外， S T S - 1帧还包含一个开销比特的前导。该开销比特包含差错检验和该帧的其他传输维护信息。

Controlling Radio Network Controller (CRNC)
A role an RNC can take with respect to a specific set of Node B’s. This represents the RNC functions that deal with control of subtending Node Bs. There is only one Controlling RNC for any Node B. The Controlling RNC has the overall control of the logical resources of its node B’s.

Drift Radio Network Controller (DRNC)
This represents RNC functions that deal with control of functions during soft handover when the RNC is downstream from the serving RNC and has control over at least 1 Node B who has soft handover leg(s).

Generic Radio Network Controller (GRNC)
This represents the RNC functions that are not covered by any of the other three types. This also relates to global functions such as transit or ATM functions.

Hard Handover
This is a category of handover procedures where all the old radio links in the UE are abandoned before the new radio links are activated.

Iu
Interface reference point between the RNS and the Core Network. (See also Iu-CS and Iu-PS.)

Iu-CS
Interface between the RNC and the circuit switched side of the Core Network, typically the MSC.

Iu-PS
Interface between the RNC and the packet switched side of the Core Network, typically the SGSN.

Iub
Interface between the RNC and the Node B. It is considered as a reference point.

Iur
Interface between two RNSs. While this interface logically represents a point to point link between RNSs, the physical realisation may not be a direct link. It is also considered as a reference point.

Node B Application Part (NBAP)
NBAP is used for setting up Radio Access Bearers (RAB) in the Radio Network Layer over the Iub.

Radio Access Network Application Part (RANAP)
Radio Network Signalling over the Iu.

Radio Network Subsystem Application Part (RNSAP)
Radio Network Signalling over the Iur between the SRNC and DRNC.

Serving Radio Network Controller (SRNC)
This represents the RNC functions that are used during an active call or data session.

Soft Handover
Soft handover is a category of handover procedures where the radio links are added and abandoned in such manner that the UE always keeps at least one radio link to the UTRAN. This typically involves multiple Node Bs.

Softer Handover
This is a type of soft handover that involves one or more cells of the same Node B.

Universal Mobile Telephone System (UMTS)
This represents the third generation mobile phone system that incorporates both Wideband CDMA for the FDD mode in the paired spectrum and Time Division – CDMA for the TDD mode in the unpaired spectrum.