SDH的帧结构

这个图你得会画

STM-4，N=4

STM-1 速率:

STM-4 速率:

...

它们的帧周期都是

STM-N帧由270*N列和9行字节组成。

SDH帧结构: 段开销、信息净负荷和管理单元指针。

  • 信息净负荷(payload): 用来传各种业务信息
  • 段开销: 传附加字节，用来维持网络运行，方便管理、维护

传输方式: 从左到右，从上到下

OH(overhead): 开销，overhead cost or expense.

RSOH(Regeneration Section Overhead): 再生段开销

AU4P(AU-4 Pointers)(Administrative Unit Group of level 4 Pointers): 管理单元指针

MSOH(Multiplex Section Overhead): 复用段开销

净负荷 | 有效载荷: payload

你可以试着理解一下，但维基百科上都没写清楚，似乎不需要你理解

THE SDH MULTIPLEX SECTION( MS n ) TRANSPORT LAYER

The MSn layer, where n denotes the multiplex level 1, 4, 16, 64 or 256.

The multiplex section specific OverHead (MS-OH) is used to transfer OAM information.

OAM(Operations, administration and management)

THE SDH REGENERATOR SECTION( RS n ) LAYER

It has dedicated Regenerator Section OverHead (RS-OH) to provide the capability to check the connectivity, monitor the performance, and communicate with the regenerators located between two network elements.

Forward Error Correction (FEC) can be used to correct bit errors that occur due to the extended range of the optical signals.

STM-N有 个A1，A1连续排列

STM-N有 个E1，E1连续排列

定帧字节: A1 和 A2

A1 and A2 for frame alignment

用来判定STM-*，以及识别一帧的起始位置。

如果连续5帧都搜不到A1、A2，将产生R OOF(报警)，持续3ms后，又会产生LOF(loss of frame 报警)，此时它会向下游设备发送全”1“信号。下游设备如果接收到全1，会产生AIS(报警)

再生段追踪字节: J0

J0 for identification

...

数据通信通路(Data Communication Channel)字节: D1~D12

D1 ... D3 and D4 ... D12 provide data communication channels

传输网管信息(OAM, Operations, administration and management)

公务联络字节: E1、E2

E1 and E2 are engineer order wires

提供 1 个 64kb/s 的数字电话通路

使用者通路字节: F1

F1 is a user channel

...

奇偶效验字节: B1、B2

B1 and B2 for performance monitoring

B1 用于监测再生段

B2 用于监测复用段

自动保护倒换(APS, Auto protection switching)字节: K1、K2

K1 and K2 for protection switching control and remote defect indication

属于自愈环技术(后路不通，自动走前路)

切换时间 < 50 ms

这里的multiplex section remote defect indication = 复用段远端接收缺陷指示 = MS-RDI

同步状态字节: S1

S1 for synchronization status

复用段远端误码块指示字节: M1

M1 for remote error indication

这里的multiplex section remote error indication = MS-REI

通道开销 分为

  • 高阶通道开销(HP-POH)
  • 低阶通道开销(LP-POH)

开销 = additional bytes

POH属于净负荷(payload)

Reference:

https://en.wikipedia.org/wiki/STM-1

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