Ota000004 Sdh Principle Issue 2

7/30/2019 Ota000004 Sdh Principle Issue 2

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SDH Principle

Confidential Information of Huawei. No Spreading Without Permission

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Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved.

SDH Principle

z Content

SDH Overview...........................................................................Page 1

Frame Structure & Multiplexing Methods.................................Page 9

Overheads & Pointers ...............................................................Page 24


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Page1Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved.

Contents

1. SDH Overview

2. Frame Structure & Multiplexing Methods

3. Overheads & Pointers

z Objectives

Upon completion of this course, you will be able to:

Understand the basic of SDH multiplexing standard

Know the features, applications and advantages of SDH based equipment

z References

SDH Principle Manual

ITU-T G.701, G.702, G.707


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Emergence of SDH

z What is SDH?

Synchronous Digital Hierarchy

It defines a standard frame structure, a specific

multiplexing method, and so on.

z Why did SDH emerge?

Need for a system to process increasing amounts of

information.

New standard that allows interconnecting equipment of

different suppliers.

z SDH is the abbreviation ofSynchronous Digital Hierarchy.

z SDH is a transmission system (protocol) which defines the characteristic of digital signals,

including frame structure, multiplexing method, digital rates hierarchy, and interface code

pattern, and so on.


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Advantages of SDH

z Interfaces

PDH electrical interfaces

Only 3 regional standards:

European (2.048 Mb/s),

Japanese, North American

(1.544 Mb/s)

PDH optical interfaces

No standards, manufacturersdevelop at their will.

SDH electrical interfaces

Universal standards

SDH optical interfaces

Can be connected to different

vendors optical transmission

equipments.

z PDH (Plesiochronous Digital Hierarchy) electrical interfaces

There are only some regional standards: European Series, North American Series and

Japanese Series, instead of universal standards for electrical interface. Each of them has

different electrical interface rate levels, frame structures and multiplexing methods. This

makes it difficult for international interconnection.

z PDH optical interfaces

No universal standards for optical interfaces. All PDH equipment manufacturers use their

own line codes to monitor the transmission performance in the optical links. So equipment

at the two ends of a transmission link must be provided by the same vendor. This causes

many difficulties for network structuring, management and network interconnection.

z SDH electrical interfaces

SDH system provides universal standards for network node interfaces (NNI), including

standards on digital signal rate level, frame structure, multiplexing method, line interface,

etc. So SDH equipment of different vendors can be easily interconnected.

z SDH optical interfaces

Line interfaces (here refers to optical interface) adopt universal standards. Line coding of

SDH signals is only universal scrambling. Therefore the opposite-terminal equipment can be

interconnected with SDH equipment of different vendors via standard descrambler alone.


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140 Mb/s

34 Mb/s 34 Mb/s

8 Mb/s 8 Mb/s

2 Mb/s

140 Mb/s

Not suitable for huge-volume transmission

Headache for network planners

More equipment to achieve this functionality

More equipment More floor space

More power More costs

Demultiplexers Multiplexers

z Multiplexing methods: Level by level

Disadvantages of PDH

z As PDH system adopts asynchronous multiplexing method, the locations of the low-rate

signals are not regular nor fixed when they are multiplexed into higher-rate signals. That is

to say, the locations of the lower signals are unable to be identified from the higher speedsignals. Therefore, low-rate signals can not be directly added/dropped from PDH high-rate

signals. For example, 2Mb/s signals can not be directly added/dropped from 140Mb/s

signals. Here arise two problems:

Adding/dropping low-rate signals from high-rate signals must be conducted level

by level. This not only enlarges the size and increases cost, power consumption

and complexity of equipment, but also decreases the reliability of the equipment.

Since adding/dropping low-rate signals to high-rate ones must go through many

stages of multiplexing and de-multiplexing, impairment to the signals during

multiplexing/de-multiplexing processes will increase and transmission performancewill deteriorate. This is unbearable in large capacity transmission. That's the reason

why the transmission rate of PDH system has not being improved further.

z No universal network management interface in PDH system

Different parts of the network may use different network management systems,

which are obstacles in forming an integrated telecommunication management

system (TMN).


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Advantages of SDH

Lower rate SDH to higher rate SDH

(STM-1STM-4STM-16 STM-64)

4:1

STM-1

A

STM-1

B

STM-1

C

STM-1

D

A

B

D

C

B

A

D

C

B

A

STM-4

One Byte from

STM-1 B

--- Synchronous multiplexing method and

flexible mapping structure

--- Multistage pointer to align PDH loads in

SDH frame, thus, dynamic drop-and-insert

capabilitiesWhat about PDH?

z Multiplexing methods: byte interleaved

z As low-rate SDH signals are multiplexed into the frame structure of high-rate SDH signals

via byte interleaved multiplexing method, their locations in the frame of high-rate SDH

signal are fixed and regular, or say, predictable. Therefore, low-rate SDH signals, e.g.

155Mb/s, (Synchronous Transport Module STM-1 ), can be directly added to or

dropped from high-rate signals, e.g., 2.5Gb/s (STM-16 ). This simplifies the multiplexing

and de-multiplexing processes of signals and makes SDH hierarchy especially suitable for

high rate and large capacity optical fiber transmission systems.

z As synchronous multiplexing method and flexible mapping structure are employed, PDH

low-rate tributary signals (e.g., 2Mb/s ) can also be multiplexed into SDH signal frame

(STM-N). Their locations in STM-N frame are also predictable. So low-rate tributary signals

can be directly added to or dropped from STM-N signals. Note that this is different from

the above process of directly adding/dropping low-rate SDH signals to/from high-rate SDH

signals. Here it refers to direct adding/dropping of low-rate tributary signals, such as

2Mb/s, 34Mb/s, and 140Mb/s, to/from SDH signals. This saves lots of multiplexing/de-

multiplexing equipment (back-to-back equipment), enhances reliability, and reduces signal

impairment, and the cost, power consumption and complexity of the equipment.

Adding/dropping of services is further simplified.


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Advantages of SDH

z OAM function

PDH

In the frame structure of

PDH signals, there are few

overhead bytes used for

OAM.

Weak OAM function

SDH

Abundant overheads bytes

for OAM

Remote & Centralized

Management

Fast circuit provisioning

from centralized point

z PDH OAM function

In the frame structure of PDH signals, there are few overhead bytes used for

operation, administration and maintenance (OAM). The fact that few overhead

bytes are used for the OAM of PDH signals is also a disadvantage for layered

management, performance monitoring, real-time service dispatching, bandwidth

control, and alarm analyzing and locating of the transmission network.

z SDH OAM function

Abundant overhead bits for operation, administration and maintenance (OAM)

functions are arranged in the frame structures of SDH signals. This greatly enforces

the network monitoring function, i.e. automatic maintenance. Some redundancy

bits must be added during line coding for line performance monitoring because

few overhead bytes are arranged in PDH signals. For example, in the frame

structure of PCM30/32 signals, only the bits in TS0 and TS16 time slots are used

for OAM function.

The abundant overheads in SDH signals account for 1/20 of the total bytes in a

frame. It greatly enhances the OAM function and reduces the cost of system

maintenance that occupies most of the overall cost of telecommunication

equipments. The overall cost of SDH system is less than that of PDH system and

estimated to be only 65.8% of that of the later.


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Advantages of SDH

Processing

PDH ATMSDH Ethernet

Pack

SDH NetworkProcessing

PDH ATMSDH Ethernet

Transmit Receive

Container

STM-NSTM-N

Container

Service Signal Flow Model

Unpack

z Compatibility

z SDH has high compatibility, which means that the SDH transmission network and the

existing PDH transmission network can work together while establishing SDH transmission

network. SDH network can be used for transmitting PDH services, as well as signals of

other hierarchies, such as asynchronous transfer mode (ATM) signals and FDDI signals.

z How does the SDH transmission network achieve such compatibility? The basic transport

module (STM-1) of SDH signals in SDH network can accommodate three PDH digital signal

hierarchies and other hierarchies such as ATM, FDDI and DQDB. This reflects the forward

and backward compatibility of SDH and guarantees smooth transitions from PDH to SDH

network and from SDH to ATM.

z How does SDH accommodate signals of these hierarchies? It simply multiplexes the low-

rate signals of different hierarchies into the frame structure of the STM-1 signals at theboundary of the network (e.g. SDH/PDH start point) and then de-multiplexes them at the

boundary of the network (end point). In this way, digital signals of different hierarchies can

be transmitted in the SDH transmission network.


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Comparison between SDH and PDH

z Low bandwidth utilization ratio

In PDH, E4 signal (140Mbits/s) can contain 64 E1 signals.

In SDH, STM-1 (155 Mbits/s) can only carry 63 E1 signals.

z Complex mechanism of pointer justification

z Influence of excessive use of software on system security

z Low bandwidth utilization ratio

One significant advantage of SDH is that system reliability is greatly enhanced

(highly automatic OAM) since many overhead bytes for OAM function are

employed in SDH signals. To transmit the same amount of valid information, PDH

signals occupy less frequency bandwidth (transmission rate) than SDH signals, i.e.

PDH signals use lower rate. In other words, STM-1 occupies a frequency

bandwidth larger than that needed by PDH E4 signals (they have the same amount

of information).

z Complex mechanism of pointer justification

The pointer constantly indicates the location of low-rate signals so that specific

low-rate signals can be properly de-multiplexed in time of "unpacking". However,

the pointer function increases the complexity of the system. Most of all, it

generates a kind of special jitter in SDH system ---- a combined jitter caused by

pointer justification. This jitter will deteriorate the performance of low-rate signals

being de-multiplexed.

z Influence of excessive use of software on system security

One of the features of SDH is its highly automatic OAM, which means that

software constitutes a large proportion in the system. As a result, SDH system is

vulnerable to computer viruses, manual mis-operation and software fault onnetwork layer.


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Contents

1. SDH Overview




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SDH Frame Structure

From ITU-T G.707:

1. One frame lasts for 125microseconds (8000frames/s)

2. Rectangular block structure9 rows and 270 columns(Basic frame: STM-1)

3. Each unit is one byte (8 bits)4. Transmission mode: Byte by

byte, row by row, from left

to right, from top to bottom

Bit rate of STM-1= 9*270*8*8000

1

2

3

4

5

6

7

89

270 Columns

9 rows

Frame = 125 us

z ITU-T defines the frames of STM-N as rectangle block frame structure in unit of byte (8bit).

z The frame structure of STM-N signals is 9 rows 270N columns. The N here is equal to

the N in STM-N, ranging from 1, 4, 16, 64, and 256. The N indicates that this signal is

multiplexed by N STM-1 signals via byte interleaved multiplexing. This explains that the

frame structure of STM-1 signals is a block structure of 9 rows 270 columns. When N

STM-1 signals are multiplexed into STM-N signal via byte interleaved multiplexing, only the

columns of STM-1 signals are multiplexed via byte interleaved multiplexing. While the

number of rows remains constantly to be 9. It is known that signals are transmitted bit-by-

bit in lines. Then what is the sequence of transmission? The principle for SDH signal frame

transmission is: the bytes (8-bit) within the frame structure is transmitted bit-by-bit from

left to right and from top to bottom. After one row is transmitted, the next row will follow.

After one frame is completed, the next frame will start.

z ITU-T defines the frequency to be 8000 frames per second for all levels in STM hierarchy.

That means the frame length or frame period is a constant value of 125us. Constant frame

period is a major characteristic of SDH signals. The constant frame period makes the rates

of STM-N signals regular. For example, the data rate of STM-4 transmission is constantly 4

times as that of STM-1, and STM-16 is 4 times of STM-4 and 16 times of STM-1. Such

regularity of SDH signals makes it possible to directly add/drop low-rate SDH signals

to/from high-rate SDH signals, especially for high-capacity transmission.


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SDH Frame Structure

Frame = 125 us

9

MSOH

AU-PTR Information

Payload

RSOH1

2

3

4

5

6

7

89

270 Columns

9 rows

z Three parts:

SOH

AU-Pointer

Information

Payload

z The frame of STM-N consists of three parts

Section Overhead (including Regenerator Section Overhead ---- RSOH and

Multiplex Section Overhead ---- MSOH)

Administrative Unit Pointer---- AU-PTR

Information Payload


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SDH Frame Structure

Information Payload Also known as Virtual Container level 4 (VC-4) Used to transport low speed tributary signals Contains low rate signals and Path Overhead (POH) Location: rows #1 ~ #9, columns #10 ~ #270

Information Payload Also known as Virtual Container level 4 (VC-4) Used to transport low speed tributary signals Contains low rate signals and Path Overhead (POH) Location: rows #1 ~ #9, columns #10 ~ #270

9

MSOH

AU-PTRPayload

RSOH

270 Columns

HPOH

1

package

package

low rate signal

LPOH, TU-PTR

LPOH, TU-PTR

9 rows

Datapackage

z The Information Payload is a place in the STM-N frame structure to store various

information code blocks to be transmitted by STM-N. It functions as the "wagon box" of

the truck---STM-N. Within the box are packed low-rate signals ---- cargoes to be shipped.

To monitor the possible impairment to the cargoes (the packed low-rate signals) on a real-

time basis during transmission, supervisory overhead bytes ---- Path Overhead (POH)

bytes are added into the signals when the low-rate signals are packed. As one part of

payload, the POH, together with the information code blocks, is loaded onto STM-N and

transmitted on the SDH network. The POH is in charge of monitoring, administrating and

controlling (somewhat similar to a sensor) the path performances for the packed cargoes

(the low-rate signals).

z What is a path? Let's take the following example. STM-1 signals can be demultiplexed into

63 2Mb/s signals. In other words, STM-1 can be regarded as a transmission path divided

into 63 bypaths. Each bypath, which is equal to a low-rate signal path, transmits

corresponding low-rate signals. The function of the Path Overhead is to monitor the

transmission condition of these bypaths. The 63 2Mb/s paths multiplex and form the path

of STM-1 signals that can be regarded as a "section" here. Paths refer to corresponding

low-rate tributary signals. The function of POH is to monitor the performance of these

low-rate signals transmitted via the STM-N on the SDH network. This is consistent with the

analogy in which the STM-N signal is regarded as a truck and the low-rate signals are

packed and loaded onto the truck for transmission.


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SDH Frame Structure

Functions: Fulfills the section layer OAM

9

270 Columns

9 rows

Types of Section Overhead

1. RSOH monitors the regeneratorsection

2. MSOH monitors the multiplexingsection

Location:1. RSOH: rows #1 ~ #3,

columns #1 ~ #92. MSOH: rows #5 ~ #9,

columns #1 ~ #9

1

2

3

5

6

7

89

MSOH

AU-PTR Information

Payload

RSOH

Section OverheadSection Overhead

z The Section Overhead (SOH) refers to the auxiliary bytes which is necessary for network

operation, administration and maintenance (OAM) to guarantee normal and flexible

transmission of Information Payload. For example, the Section Overhead can monitor the

impairment condition of all "cargoes" in STM-N during transmission. The function of POH

is to locate the certain impaired cargo in case impairments occurred. SOH implements the

overall monitoring of cargoes while the POH monitors a specific cargo.

z The Section Overhead is further classified into Regenerator Section Overhead (RSOH) and

Multiplex Section Overhead (MSOH). They respectively monitor their corresponding

sections and layers. Then, what's the difference between RSOH and MSOH? In fact, they

have different monitoring domains. For example, if STM-16 signals are transmitted in the

fiber, the RSOH monitors the overall transmission performance of STM-16 while the MSOH

monitors the performances of each STM-1 of the STM-16 signals.

z RSOH, MSOH and POH provide SDH signals with monitoring functions for different layers.

For a STM-16 system, the RSOH monitors the overall transmission performance of the

STM-16 signal; the MSOH monitors the transmission performances of each STM-1 signal;

and the POH monitors the transmission performances of each packaged low-rate tributary

signal (e.g. 2Mb/s) in STM-1. Through these complete monitoring and management

functions for all levels, you can conveniently conduct macro (overall) and micro (individual)

supervision over the transmission status of the signal and easily locate and analyze faults.


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SDH Frame Structure

9

MSOH

AU-PTR Information

Payload

RSOH

270 Columns

9 rows4

Function:Indicates the first byte of VC4

Location:row #4, columns #1 ~ #9

J1

AU-PTRAU-PTR

z The Administrative Unit Pointer within column 9 N of row 4 of the STM-N frame is 9

N bytes in total. What's the function of AU-PTR? We have mentioned before those low-

rate tributaries (e.g. 2Mb/s) could be added/dropped directly from high-rate SDH signals.

Because the locations of low-rate signals within a high-rate SDH frame structure are

predictable, i.e. regular. The predictability can be achieved via the pointer overhead bytes

function in the SDH frame structure. The AU-PTR indicates the exact location of the first

byte of the information payload within the STM-N frame so that the information payload

can be properly extracted at the receiving end according to the value of this location

indicator (the value of the pointer). Let's make it easier. Suppose that there are many

goods stored in a warehouse in unit of pile. Goods (low-rate signals) of each pile are

regularly arranged (via byte interleaved multiplexing). We can locate a piece of goods

within the warehouse by only locating the pile this piece of goods belongs to. That is to

say, as long as the location of the first piece of goods is known, the precise location of any

piece within the pile can be directly located according to the regularity of their

arrangement. In this way you can directly carry (directly add/drop) a given piece of goods

(low-rate tributary) from the warehouse. The function of AU-PTR is to indicate the location

of the first piece of goods within a given pile.

z In fact, the pointer is further classified into higher order pointer and low order pointer. The

higher order pointer is AU-PTR while the lower order pointer is TU-PTR (Tributary Unit

Pointer). The function of TU-PTR is similar to that of AU-PTR except that the former

indicates smaller "piles of goods".


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SDH Multiplexing Features

z SDH Multiplexing includes:

Low to high rate SDH signals (STM-1 STM-N)

PDH to SDH signals (2M, 34M & 140M STM-N)

Other hierarchy signals to SDH Signals (IP STM-N)

z Some terms and definitions:

Mapping

Aligning

Multiplexing

z SDH multiplexing includes three types: multiplexing of lower-order SDH signals into higher-

order SDH signals and multiplexing of low-rate tributary signals (e.g. 2Mb/s, 34Mb/s and

140Mb/s) into SDH signals ----STM-N, and other hierarchy signals to SDH Signals.

The second type of multiplexing from Low to high rate SDH signals is conducted

mainly via byte interleaved by multiplexing four into one, e.g. 4STM-1-->STM-4

and 4STM-4-->STM-16. after the multiplexing, the rate of the higher-level STM-

N signals is 4 times that of the next lower-level STM-N signals. During the byte

interleaved multiplexing, the information payload, pointer bytes of each frame are

multiplexed via interleaved multiplexing based on their original values.

The second type of multiplexing is mostly used for multiplexing of PDH signals into

the STM-N signals.

The last one is other hierarchy signals e.g. IP or ATM signals to SDH Signals.


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AU-4

TU-3TUG-3 VC-3 C-3

VC-4 C-4

TU-12 VC-12 C-12

TUG-2

3

1

7

3

E4 signal

E3 signal

E1 signal

Multiplexing

Mapping

Aligning

STM-1 AUG-11

1

AUG-4

AUG-16

AUG-64

STM-4

STM-16

STM-64

1

1

1

4

4

4

Go to glossary

C-4-4cVC-4-4cAU-4-4c1

C-4-16cVC-4-16cAU-4-16c1

C-4-64cVC-4-64cAU-4-64c1

SDH Multiplexing Structure

z ITU-T defined a complete multiplexing structure, through which digital signals of three

PDH hierarchies can be multiplexed into STM-N signals.

This multiplexing structure includes some basic multiplexing units: C - Container,

VC - Virtual Container, TU - Tributary Unit, TUG - Tributary Unit Group, AU -

Administrative Unit, and AUG - Administrative Unit Group. The suffixes of these

multiplexing units denote their corresponding signal levels.

The multiplexing route used in a country or an area must be unique. The route on

the slide is the most usual and adopted in most of countries.

z Low-rate tributaries are multiplexed into STM-N signals through three procedures:

mapping, aligning and multiplexing.

SDH mapping is a procedure by which tributaries are adapted into virtual

containers at the boundary of an SDH network, e.g. E1 into VC-12.

SDH aligning is a procedure to add TU-PTR or AU-PTR into the VC-12, VC-3 or VC4.

The pointer value constantly locates the start point of VC within the TU or AU. So

that the receiving end can correctly separate the corresponding VC.

SDH multiplexing, a relatively simple concept, is the procedure by which the TUs

are organized into the higher order VC or the AUs are organized into STM-N via

byte interleaving.


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From 140Mb/s to STM-N

140M Rate adaptationAdd HPOH

C4

9

1 260125s

1

Next

Mapping

VC4

1

9

125s1 261

H

P

O

H

z From 140Mb/s to C4

First, the 140Mb/s PDH signals are adapted via bit rate justification (bit stuffing

method) into C-4, which is a standard information structure used to accommodate

140Mb/s PDH signals. After being processed via bit rate justification techniques,

service signals of various rates involved in SDH multiplexing must be loaded into a

standard container corresponding to the rate level of the signal: 2Mb/s---C-12,

34Mb/s---C-3 and 140Mb/s---C-4. The main function of a container is for bit rate

justification. The frame structure of C-4 is block frame in unit of bytes, with the

frame frequency of 8000-frame per second.

z From C4 to VC4

A column of path overhead bytes (higher-order path overhead VC-4-POH) shall be

added in front of the C-4 block frame during multiplexing in order to monitor the

140Mb/s path signals. Then the signals become a VC-4 information structure. The

virtual container, a kind of information structure whose integrity is always

maintained during transmission on the SDH network, can be regarded as an

independent unit (cargo package). It can be flexibly and conveniently

added/dropped at any point of the path for synchronous multiplexing and cross-

connection processing. Now you might get the idea that VC-4 is in fact the

information payload of the STM-1 frame. The process of packing PDH signals into

C and adding the corresponding path overhead to form the information structure

of VC is called mapping.


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Add

AU-PTRAdd

SOH

Aligning

AU-PTR AU-4

10 270

X1

AUG-1

Multiplexing

AUG-N

1 270

RSOH

MSOH

Info

PayloadAU-PTR

9

STM-1

Add

SOH

One STM-1 frame can load onlyone 140Mbit/s Signal

1 270N

RSOH

MSOH

Info

PayloadAU-PTR

9

STM-N

z From VC4 to AU4

By adding an Administrative Unit Pointer --- AU-PTR before the VC-4, the signal is

changed from VC-4 into another information structure--- Administrative Unit AU-4.

The function of AU-PTR is to indicate the location of the higher order VC within the

STM frame. Under the pointer function, the higher order VC is allowed to "float"

within the STM frame, i.e. the frequency offsets and phase differences to a certain

degree between VC-4 and AU-4 are tolerable. Because the AU-PTR is outside of

the payload area and co-located with the section overhead instead. This

guarantees that the AU-PTR can be accurately found in the corresponding location.

Then the VC-4 can be localized by the AU pointer and disassembled from STM-N

signals.

z From AU4 to AUG (N)

One or more AUs with fixed locations within the STM frame form an AUG ----

Administrative Unit Group. The location of the first byte of the VC-4 with respect

to the AU-4 pointer is given by the pointer value. The AU-4 is placed directly in the

AUG.

z From AUG (N) to STM-N

The last step is to add corresponding SOH to AU-4 to form STM-N signals. During

being multiplexed, the N AUGs are one-byte interleaved into this structure andhave a fixed phase relationship with respect to the STM-N.


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34M RateAdaptation

Add LPOH

C3

1 84

9

125s

1 1

9

VC3

L

P

O

H

125s1 85

Next

Mapping

z From 34Mb/s to C3

Similarly, 34Mb/s signals are first adapted into the corresponding standard

container -- C-3 through bit rate justification.

z From C3 to VC3

After adding corresponding POH, the C-3 is packed into VC-3 with the frame

structure of 9 rows 85 columns.


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1st

align

Fill

gap3

86

TU-3

1

H1

H2

H3

1

9

1 86

1

9

H1

H2

H3

R

TUG-3

Multiplexing

HP

O

H

R R

VC-4

9

1

1 2613

Sameprocedure

as 140M

Aligning

z From VC3 to TU3

For the convenience of locating VC-3 at the receiving and separating it from the

high-rate signals, a three-byte pointer, TU-PTR (Tributary Unit Pointer), is added to

the VC-3 frame. Then what is the function of a tributary pointer? The TU-PTR is

used to indicate the specific location of the first byte of the lower order VC within

the tributary unit TU. It is similar to an AU-PTR that indicates the location of the

first byte of the VC-4 within the STM frame. Actually, the operating principles of

these two kinds of pointers are similar.

z From TU3 to TUG3

The TU-3 frame structure is imcomplete. First fill the gap to form the frame

structure of TUG3.

z From TUG3 to C4, VC4 and STM-N

Three TUG-3 can be multiplexed into the C-4 signal structure via byte interleaved

multiplexing method. The TUG-3 is a 9-row by 86-column structure. Two columns

of stuffed bits are added to the front of the composite structure of 3 TUG-3 to

form a C-4 information structure.

The last step is to multiplex C-4 into STM-N. This is similar to the process of

multiplexing 140Mb/s signals into STM-N signals: C-4-->VC-4-->AU-4-->AUG--

>STM-N.


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From 2Mb/s to STM-N

2MNext

page

125s

1 4

C12

1

9

4LPOH

VC12

1

1

9

RateAdaptation

AddLPOH

Add

TU-PTR

Aligning

TU12

1 4

1

9

TU-PTRMapping

z At present, the most frequently used multiplexing method is multiplexing of 2Mb/s signals

into STM-N signals. It is also the most complicated method of multiplexing PDH signals

into SDH signals.

z From 2Mb/s to C12

First, the 2Mb/s signal shall be adapted into the corresponding standard container

C-12 via rate adaptation.

z From C12 to VC12

To monitor on a real-time basis the performance of each 2Mb/s path signal during

transmission on SDH network, C-12 must be further packed ---- adding

corresponding path overhead (lower order overhead)---- to form a VC-12

information structure. The LP-POH (lower order path overhead) is added to the

notch in the top left corner of each basic frame. Since the VC can be regarded as

an independent entity, dispatching of 2Mb/s services later is conducted in unit of

VC-12.

z From VC12 to TU12

For correct aligning of VC-12 frames in the receiving end, a four-byte TU-PTR is

added to the four notches of the VC-12 multi-frame. Then the information

structure of the signal changes into TU-12 with 9 rows4 columns. The TU-PTR

indicates the specific location of the start point of the first VC-12 within the multi-

frame.


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From 2Mb/s to STM-N

X 3

1 12

TUG-2

1

9

X 7

Multiplexing

R R

TUG-3

1 86

1

9

MultiplexingSameprocedure

as 34M

z From TU12 to TUG2

Three TU-12 forms a TUG-2 via byte interleaved multiplexing. The TUG-2 has the

frame structure of 9 rows by 12 columns.

z From TUG2 to TUG3

Seven TUG-2 can be multiplexed into a TUG-3 information structure via byte

interleaved multiplexing. Note that this information structure formed by the 7

TUG-2 is 9-row by 84-column. Two rows of fixed stuff bits shall be added in front

of the structure. The TUG-3 is a 9-row by 86-column structure with the first two

columns of fixed stuff.

z From TUG3 to C4, VC4 and STM-N

The procedures of multiplexing the TUG-3 information structure into STM-N are

the same as mentioned before.


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Questions

z What are the main parts of SDH Frame structure?

z What is the transmission rate of STM-4? How to

calculate it ?

z The frame of STM-N consists of three parts

Section Overhead (including Regenerator Section Overhead ---- RSOH and

Multiplex Section Overhead ---- MSOH)

Administrative Unit Pointer---- AU-PTR

Information Payload with POH

z There are 9 rows and 270N columns in the STM-N frame, which will be transmitted 8000

times per second. Here the value of N equals to 4 for STM-4.

9 (rows) X 270 X 4 (columns) X 8 (bits) X 8000 (frame/second) = 622080000

bits/second. It is so called 622 Mbits/s


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Contents

1. SDH Overview




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Overheads

Overheads

Section

Overhead(SOH)

Path

Overhead(POH)

Regenerator

Section Overhead

(RSOH)

Multiplex Section

Overhead

(MSOH)

High Order Path

Overhead

(HPOH)

Low Order Path

Overhead

(LPOH)

z As mentioned before, the functions of overhead are to implement layered monitoring

management for SDH signals. The monitoring is classified into section layer monitoring and

path layer monitoring. The section layer monitoring is further classified into regenerator

section layer monitoring and multiplex section layer monitoring while the path layer

monitoring is further classified into higher order path layer and lower order path layer.

Thus the layered monitoring for STM-N is implemented. For example, in a STM-16 system,

the regenerator section overhead monitors the overall STM-16 signal while the multiplex

section overhead further monitors each of the 16 STM-1. Furthermore, the higher order

path overhead monitors the VC-4 of each STM-1 and the lower order path overhead can

monitor each of the 63 VC-12 in the VC-4. Hence the multistage monitoring functions

from 2.5Gb/s to 2Mb/s are implemented.


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Overheads

E2M1S1

D12D11D10

D9D8D7

D6D5D4

K2K1B2B2B2

AU-PTR

D3D2D1

XXF1E1B1

XXJ0A2A2A2A1A1A1

HPOH:VC-3/4

N1

K3

F3

H4

F2

G1

C2

B3

J1

RSOH

MSOH

987654321 10

9

8

7

6

5

4

3

2

1

Media dependent bytes (Radio-link, Satellite)X Reserved for National use

Huawei propriety bytes LPOH: VC-11/12

K4N2J2V5

z Then, how are these monitoring functions implemented? They are implemented via

different overhead bytes.

z The overhead of each layer, including RSOH, MSOH, HPOH, and LPOH consists of some

different bytes for different OAM function. Especially, several overhead bytes e.g. K1 and

K2 bytes are very important for maintenance and troubleshooting. According to ITU-T

recommendation, there are some overhead bytes reserved for national use.


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A1 and A2 Bytes

z Framing Bytes

Indicate the beginning of the STM-N frame

Bytes are unscrambled

A1 = f6H (11110110), A2 = 28H (00101000)

STM-N: (3XN) A1 bytes, (3XN) A2 bytesSTM-N STM-N STM-N STM-N STM-N STM-N

Finding frame head

z Like a pointer, the function of the frame bytes is alignment. The first step is to properly

extract each STM-N frame from the received continuous signal stream at the receiver. The

function of the bytes A1 and A2 is to locate the start of the STM-N frame. So the receiver

can align and extract the STM-N frame from the information stream via these two bytes

and further align a specific lower-rate signal within the frame via the pointers.

z How does the receiver align the frames via the A1 and A2 bytes? The A1 and A2 have

fixed value, i.e. fixed bit patterns: A1: 11110110 (f6H) and A2: 00101000(28H). The

receiver monitors each byte in the stream. After detecting 3N successive f6H bytes

followed by 3N 26H bytes (there are three A1 and three A2 bytes within an STM-1 frame),

the receiver determines that an STM-N frame starts to be received. By aligning the start of

each STM-N frame, the receiver can identify different STM-N frames and disassemble them.

z STM-N signals shall be scrambled before being transmitted via the line so that the receiver

can extract timing signals from the line. But the A1 and A2 framing bytes shall not be

scrambled for the receiver to properly align them. Thus it is convenient to extract the

timing from the STM-N signals and disassemble the STM-N signals at the receiver.


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A1 and A2 BytesFrame

Next

process

Find

A1,A2

OOF

LOF

N

Y

AIS

over 3ms

over 625s(5 frames)

z If the receiver doesn't receive A1 and A2 bytes within five or more successive frames

(625us), i.e. it can't identify the start of five successive frames (identify different frames), it

will enter out-of-frame status and generate out-of-frame alarm ---- OOF. If the OOF keeps

for 3ms, the receiver will enter loss-of-frame status ---- the equipment will generate loss-

of-frame alarm ---- LOF. Meanwhile, an AIS signal will be sent downward and the entire

services will be interrupted. Under LOF status, if the receiver stays in normal frame

alignment status again for successive 1ms or more, the equipment will restore the normal

status.


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D1 ~ D12 Bytes

z Data Communications Channel (DCC) Bytes

RS-DCC D1 ~ D3 192 Kbit/s (3x64 Kbit/s)

MS-DCC D4 ~ D12 576 Kbit/s (9x64 Kbit/s)

NMT

DCC channel

NE NE NENE

OAM Information: Operation, Administration andmaintenance

z One of the features of SDH is its highly automatic OAM function which can conduct

commands issue and performance auto poll to the networks element via NMT Network

Management Terminals. SDH has some functions which are not possessed by PDH

systems, such as real-time service allocation, alarm fault location and on-line performance

testing. Where are these OAM data arranged to transmit? The data used for OAM

functions, such as sent commands and checked alarm performance data, are transmitted

via D1-D12 bytes within the STM-N frame. Thus the D1-D12 bytes provide a common data

communication channel accessible to all SDH network elements. As the physical layer of

the embedded control channel (ECC), the D1-D12 bytes transmit OAM information among

the network elements and form a transmission channel of the SDH management network

(SMN).

z The DCC has a total rate of 768kb/s that provides a powerful communication base for SDH

network management. D1, D2 and D3 are regenerator section DCC bytes (DCCR) with a

rate of 364kb/s192kb/s and are used to transmit OAM information among

regenerator section terminals. D4-D12 are multiplex section DCC bytes (DCCM) with a sum

rate of 964kb/s=576kb/s and are used to transmit OAM information among multiplex

section terminals.


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E1 and E2 Bytes

z Orderwire Bytes

E1 RS Orderwire Byte Used between regenerators

E2 MS Orderwire Byte Used between multiplexers

Digital telephone channel

E1-RS, E2-MS

E1 and E2

NE NE NENE

z E1 is part of the RSOH and may be accessed at regenerators. E2 is part of the MSOH and

man be accessed at multiplex section terminations. Each of these two bytes provides a

64kb/s orderwire channel for voice communication, i.e. voice information is transmitted via

these two bytes.

z The orderwire provides a convenient communication function during maintenance and

troubleshooting.


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B1 Byte

z Bit interleaved Parity Code (BIP-8) Byte

A parity code (even parity)

Used to check the transmission errors over the RS

B1 BBE is represented by RS-BBE (performance event)

Tx

2#STM-N

Rx

1#STM-N Calculate B

1#STM-N

2#STM-N

Calculate B

A1 00110011

A2 11001100A3 10101010

A4 00001111

B 01011010

BIP-8

B1 = B

STM-NB1

B

Compare B & B RS-BBE

z This B1 byte is allocated for regenerator section error monitoring (Byte B1 is located in the

regenerator section overhead). What is the mechanism for monitoring? First, we'll discuss the BIP-8

parity.z Suppose that a signal frame is composed of 4 bytes: A1=00110011, A2=11001100, A3=10101010

and A4=00001111. The method of providing BIP-8 parity to this frame is to divide it into 4 block

with 8 bits (one byte) in a parity unit (each byte as a block because one byte has 8 bits, the same as

a parity unit) and to arrange these blocks. Compute the number of "1" over each column. Then fill a

1 in the corresponding bit of the result (B) if the number is odd, otherwise fill a 0. That is, the value

of the corresponding bit of B makes the number of "1" in the corresponding column of A1A2A3A4

blocks even. This parity method is called BIP-8 parity. In fact this is an even parity since it guarantees

that the number of "1" is even. B is the result of BIP-8 parity for the A1A2A3A4 block.

z The mechanism for B1 byte is: the transmitting equipment processes BIP-8 even parity over all bytes

of the previous frame (1#STM-N) after scrambling and places the result in byte B1 of the currentframe (2#STM-N) before scrambling. The receiver processes BIP-8 parity over all bits of the current

frame (1#STM-N) before de-scrambling and compares the parity result and the value of B1 in the

next frame (2#STM-N) after de-scrambling. The different bit means the error block. According to the

number of different bits, we can monitor the number of error blocks occurred in 1#STM-N frame

during transmission.

z If the B1 of the receive end has detected error blocks, the number of error blocks detected by the

B1 will be displayed in receive end performance event RS-BBE (Regenerator Section Background

Block Error). When the error bits detected by the receive end exceed a given threshold, the

equipment will report corresponding alarms. When the error bit ratio (EBR) is greater than 10E-6,

the given alarm is B1-SD. When the error bit ratio (EBR) is greater than 10E-3, B1-EXC (anothername B1-OVER) will be given.


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B2 Byte

z Bit interleaved Parity Code (MS BIP-24) Byte

BIP-24 is used to check the bit errors over the MS

B2 BBE is represented by MS-BBE (performance event)

The working mechanism of B2 is same as B1

z B2 is similar to B1 in operation mechanism except that it monitors the error status of the

multiplex section layer. The B1 byte monitors the transmission error of the complete STM-

N frame signal. There is only one B1 byte in an STM-N frame. There are N*3 B2 bytes in anSTM-N frame with every three B2 bytes corresponding to an STM-1 frame. The B2

monitoring adopts BIP-24 (three bytes) method, which can at most monitor 24 error

blocks one time.

z Since error performance of higher rate signals is reflected via error blocks, the error status

of STM-N signals is actually the status of error blocks. As can be seen from the BIP-24

parity method, each bit of the parity result is corresponding to a bit block. So three B3

bytes can at most monitor 24 error blocks from an STM-N frame that occur during

transmission (The result of BIP-24 is 24 bits with each bit corresponding to a column of

bits ---- a block).

z If the B2 of the receive end has detected error blocks, the number of error blocks detected

by the B2 will be displayed in this end performance event MS-BBE (Multiplex Section

Background Block Error). At the same time, M1 will be used to report to the transmit end

that error blocks have been detected, and the transmit end will report MS-FEBBE

(Multiplex Section Far End Background Block Error) performance event and MS-REI

(Multiplex Section Remote Error Indication) alarm. When the error bits detected by the

receive end exceed a given threshold, the equipment will report corresponding alarms.

When the error bit ratio (EBR) is greater than 10E-6, the given alarm is B2-SD. When the

error bit ratio (EBR) is greater than 10E-3, B2-EXC will be given.


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M1 Byte

z Multiplexing Section Remote Error Indication Byte

A return message from Rx to Tx ,when Rx find B2 bit errors

Value is the same as the count of BIP-24xN (B2) bit errors

Tx generate corresponding performance event MS-FEBBE

Tx Rx

Traffic

Generate

MS-FEBBE

MS-REI

Find B2 bit errors

Generate MS-BBE

Return M1

z If the B2 of the receive end has detected error blocks, the number of error blocks detected

by the B2 will be displayed in this end performance event MS-BBE (Multiplex Section

Background Block Error). At the same time, M1 will be used to report to the transmit

end that error blocks have been detected, and the transmit end will report MS-FEBBE

(Multiplex Section Far End Background Block Error) performance event and MS-REI

(Multiplex Section Remote Error Indication) alarm.

z This is a message returned to its transmit end by the receive end so that the transmit end

can get the receiving error status of the receive end. For STM-N levels this byte conveys

the count (in the range of [0, 255]) of interleaved bit blocks that have been detected in

error by the BIP-24N (B2). For rates of STM-16 and above, this value shall be truncated to

255.


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K1 and K2 (b1-b5) Bytes

AutomaticProtection

Switching (APS)bytes

Transmitting APS protocolUsed for network multiplexing

protection switch function

P

WTR

WTR P

I

I

I I

P

S

S P

z Two bytes are allocated for APS signaling for the protection of the multiplex section. For

the bit assignments for these bytes and the bit-oriented protocol, please refer to G.783,

G.841 (10/98).


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K2 (b6 ~ b8) Byte

z Rx detects K2 (b6-b8) = "111

Generate MS-AIS alarm

z Tx detects K2 (b6-b8) = "110"

Generate MS-RDI alarm

Generate

MS-AIS

Start

Detect

K2 (b6-b8)

Return

MS-RDI

Generate

MS-RDI

111

110

z This is an alarm message, returned to the transmit end (source) by the receive end (sink),

which means that the receive end has detected an incoming section defect or is receiving

the Multiplex Section Alarm Indication Signal (MS-AIS). That is, when the receive end

detects receiving deterioration, it returns an Multiplex Section Remote defect

Indication (MS-RDI) alarm signal to the transmit end so that the later obtains the status of

the former. If the received b6-b8 bits of the K2 is 110, it means that this signal is an MS-

RDI alarm signal returned by the opposite end. If the received b6-b8 bits of the K2 is 111,

it means that this signal is an MS-AIS alarm signal received by current end. Meanwhile, the

current end is required to send out MS-RDI signal to the opposite end, i.e. insert 110 bit

pattern into the b6-b8 of the K2 within the STM-N signal frame to be sent to the opposite

end. Not all deterioration results in returning MS-RDI. Current end equipment returns MS-

RDI only upon receiving R-LOS, R-LOF, and MS-AIS alarm signals.


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S1 Byte

z Synchronization Status Message Byte (SSB): S1

b1 ~ b4 Value indicates the external clock ID (Extended SSM)

b5 ~ b8 Value indicates the sync. Level (Standard SSM)

G.813 (Sync. Equipment Timing Clock)1011

Do not use for sync (DNU).1111

SSU-B (G.812 local)1000

SSU-A (G.812 transit)0100

G.811 PRC0010

Quality unknown (existing sync. Network)0000

Descriptionbits 5 ~ 8

z We can use the extended SSM for clock protection. In this case, the different value of bits

1 ~ 4 of byte S1 indicates the different clock source.

z Bits 5 to 8 of byte S1 are allocated for Synchronization Status Messages. Table 3-1 gives

the assignment of bit patterns to the four synchronization levels agreed to within ITU-T.

Two additional bit patterns are assigned: one to indicate that quality of the

synchronization is unknown and the other to signal that the section should not be used for

synchronization. The remaining codes are reserved for quality levels defined by individual

Administrations. Different bit patterns, indicating different quality levels of clocks defined

by ITU-T, enable the equipment to determine the quality of the received clock timing signal.

This helps to determine whether or not to switch the clock source, i.e. switch to higher

quality clock source. The smaller the value of S1 (b5-b8), the higher the level of clock

quality.


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Path Overheads

N1

K3

F3

H4

F2

G1

C2

B3

J1 VC-n Path Trace Byte

Path BIP-8

Path Signal Label

Path Status

Path User Channel

TU Multiframe Indication

Path User Channel

AP Switching

Network Operator

Higher Order Path Overhead

1 2 3 4 5 6 7 8 9 10

1234567

89

R S O H

M S O H

A U P T R

z The Section Overhead is responsible for section layer OAM functions while the Path

Overhead for path layer OAM functions. Like transporting the cargoes loaded in the

container: not only the overall impairment status of the cargoes (SOH) but also the

impairment status of each cargo (POH) shall be monitored.

z According to the "width" of the monitored path (the size of the monitored cargo) , the

Path Overhead is further classified into Higher Order Path Overhead and Lower Order Path

Overhead. In this curriculum the Higher Order Path Overhead refers to the monitoring of

VC-4 level paths within the STM-N frame. The Lower Order Path Overhead implements the

OAM functions for VC-12 path level, i.e. monitoring the transmission performance of

2Mb/s signals within the STM-N frame.

z The Higher Order Path Overhead, consisting of 9 bytes, is located in the first column of theVC-4 frame.


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J1 Byte

Next

process

Detect J1

Match

HP-TIM

YN

z Path trace byte

The first byte of VC-4

User-programmable (HUAWEI SBS)

The received J1 should match the

expected J1

z The AU-PTR pointer indicates the specific location of the start of the VC-4 within the AU-4,

i.e. the location of the first byte of the VC-4, so that the receive end can properly extract

VC-4 from the AU-4 according to the value of this AU-PTR. The J1 is the start of the VC-4,

so the AU-PTR indicates the location of the J1 byte.

z The J1 byte is used to transmit repetitively a Higher Order Path Access Point Identifier so

that a path receiving terminal can verify its continued connection to the intended

transmitter (this path is under continued connection). This requires that the J1 bytes of the

received and transmit ends match. The default transmit/receive J1 byte values of the

equipments provided by Huawei Company are HuaWei SBS. Of course the J1 byte can

be configured and modified according to the requirement.

z The received J1 should match or be same with the expected J1. If not, HP-TIM alarm willbe generated, which perhaps interrupts the service within the VC4 sometimes.


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B3 Byte

Nextprocess

Verify B3

YNCorrect

HP-BBE

z Path bit parity

Even parity code

Used to detect bit errors

Mechanism is same as B1 and B2

z The B3 byte is allocated for monitoring the transmission error performance of VC-4. Its

monitoring mechanism is similar to that of the B1 and B2 except that it is used to process

BIP-8 parity for the VC-4 frame.

z Once the receive end detects error blocks, the number of error blocks will be displayed in

the performance monitoring event ---- HP-BBE (Higher Order Path Background Block

Error) of the received end. At the same time, G1 (b1-b4) will be used to report to the

transmit end that error blocks have been detected, and the transmit end will report HP-

FEBBE (Higher-order Path Far End Background Block Error) performance event and

HP-REI (Higher-order Path Remote Error Indication) alarm.

z When the error bits detected by the receive end exceed a given threshold, the equipment

will report corresponding alarms. When the error bit ratio (EBR) is greater than 10E-6, thegiven alarm is B3-SD. When the error bit ratio (EBR) is greater than 10E-3, B3-EXC will be

given.


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C2 Byte

Detect C2

00H

HP-UNEQMatch

HP-SLMNext

process

Insert AIS

downward

N Y

NY

z Signal label byte

The received C2 should match

with the expected C2

Specifies the mapping type in

the VC-n

00 H Unequipped

02 H TUG structure

13 H ATM mapping

z The C2 is allocated to indicate the composition of multiplexing structure and information

payload of the VC frame, such as equipped or unequipped status of the path, the type of

loaded services and their mapping method. For example, C2=00H indicates that this VC-4

path is unequipped. Then the payload TUG-3 of the VC-4 is required to be inserted all "1" -

--- TU-AIS and the higher order path unequipped alarm ---- HP-UNEQ appears in the

equipment. C2=02H indicates that the payload of the VC-4 is multiplexed via a TUG

structure multiplexing route. In China, the multiplexing of 2Mb/s signals into VC-4 adopts

the TUG structure. To configure the multiplexing of 2Mb/s signals for Huawei equipments,

the C2 is required to be configured as TUG structure.

z The received C2 should match or be same with the expected C2. If not, HP-SLM alarm will

be generated, which interrupts the service within the VC4 sometimes.


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VC-12VC-12VC-12VC-12

K4N2J2V51

9

1 4

500s VC-12 multi-frame

Low Order Path Overheadz V5

Indicated by TU-PTR

Error checking, Signal Label and

Path Status of VC-12

b1 - b2 Error Performance

Monitoring (BIP-2)

b3 Return Error detected in

VC-12 (LP-REI)

b8 Return alarm detected in

VC-12 (LP-RDI)

Path Overheads

z The LPOH here refers to the path overhead of the VC-12 that monitors the transmission

performance of the VC-12 path level, i.e. monitors the transmission status of 2Mb/s PDH

signals within the STM-N frame. Where is the LPOH located within the VC-12? The lower

order POH is located in the first byte of each VC-12 basic frame. An LP-POH consists of

four bytes denoted V5, J2, N2 and K4. Usually, V5 byte is the most important in LPOH.

z The V5 provides the functions of error checking, signal label and path status of the VC-12

paths. So this byte has the functions of the G1, B3 and C2 bytes within the higher order

path overhead. If the V5 (b1b2) of the receive end have detected error blocks, the number

of error blocks detected by the V5 (b1b2) will be displayed in this end performance event

LP-BBE (Lower-order Path Background Block Error). At the same time, V5 (b3) will be

used to report to the transmit end that error blocks have been detected, and the transmit

end will report LP-FEBBE (Lower-order Path Far End Background Block Error)

performance event and LP-REI (Lower-order Path Remote Error Indication) alarm.

When the error bits detected by the receive end exceed a given threshold, the equipment

will report corresponding alarms. When the error bit ratio (EBR) is greater than 10E-6, the

given alarm is BIP-SD. When the error bit ratio (EBR) is greater than 10E-3, BIP-EXC will be

given.

z Bit 8 of the V5 is allocated for the VC-12 Path Remote Defect Indication. An LP-RDI (Lower

Order Path Remote Defect Indication) is sent back to the source if either a TU-12 AIS signal

or signal failure condition is being detected by the sink. Notes: In this curriculum, RDI iscalled remote deterioration indication or remote defect indication.


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Pointers

Pointers

Administrative

Unit Pointer(AU-PTR)

Tributary

Unit Pointer(TU-PTR)

Bytes indicated

AU-PTR VC-4 J1TU-PTR VC-3 J1

VC-12 V5

z The function of the pointers is aligning via which the receiver can properly extract the

corresponding VC from the STM-N and then disassemble the VC and C packages and

extracts the lower rate PDH signals, i.e. directly drop lower rate tributary signals from the

STM-N signal.

z What is aligning? Aligning is a procedure by which the frame offset information is

incorporated into the Tributary Unit or the Administrative Unit, i.e. via the Tributary Unit

Pointer (or Administrative Unit Pointer) attached to the VC to indicate and determine the

start of the lower order VC frame within the TU payload ( or the start of the higher order

VC frame within the AU payload). When relative differences occur in the phases of the

frames and make the VC frames "float", the pointer value will be justified to ensure that it

constantly and properly designates the start of the VC frame. For a VC-4, its AU-PTR

indicates the location of the J1 byte while for a VC-12; its TU-PTR indicates the location of

the V5 byte. The TU pointer or AU pointer provides a method of allowing flexible and

dynamic alignment of the VC within the TU or AU frame because these two pointers are

able to accommodate differences, not only in the phases of the VC and the SDH, but also

in the frame rates.


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AU-PTR

RSOH

MSOH

MSOH

RSOH

H1YYH2FF H3H3H3

H1YYH2FFH3H3H3

0 --- 1--- --- --- --- --- --- --- --- --- --- 86

696 --- 697 --- --- --- --- --- --- --- --- 782

1 9 270

1

4

9

1

4

9

125s

250s

522 --- 523 --- --- --- --- --- --- --- --- 608

435 --- 436 --- --- --- --- --- --- --- --- 521

Negative

justification

Positive

justification

0 --- 1 --- --- --- --- --- --- --- --- --- --- 86

435 --- 436 --- --- --- --- --- --- --- --- 521

87 --- 88 --- --- --- --- --- --- --- --- --- 173

87 --- 88 --- --- --- --- --- --- --- --- --- 173

z The AU-PTR, located in row 4 of columns 1 to 9 within the STM-1 frame, is used to

indicate the specific location of the fist byte J1 of the VC-4 within the AU-4 payload so

that the receiver can properly extract the VC-4. The AU-4 pointer provides a method of

allowing flexible and dynamic alignment of the VC-4 within the AU-4 frame. Dynamic

alignment means that the VC-4 is allowed to "float" within the AU-4 frame. Thus, the

pointer is able to accommodate differences, not only in the phases of the VC-4 and the

SOH, but also in the frame rates. The pointer contained in H1 and H2 designates the

location of the byte where the VC-4 begins. The last ten bits (bits 7-16) of the pointer

word carry the pointer value.


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TU-PTR

VC3

H1

H2

H3

TU POINTERS

V4V3V2V1

VC-

12

VC-

12

VC-

12

VC-

12

1 4

1

9

TU POINTERS

TU Multi-frame 500s

z The TU pointer is used to indicate the specific location of the first byte V5 of the VC-12

within the TU-12 payload so that the receiver can properly extract the VC-12. The TU

pointer provides a method of allowing flexible and dynamic alignment of the VC-12 within

the TU-12 multi-frame. The TU-PTR is located in the bytes denoted V1, V2, V3 and V4

within the TU-12 multi-frame.

z The TU pointer of TU3 consists of H1, H2 and H3. Their function is similar to that of AU-

PTR.


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Questions

z Which byte is used to report the MS-AIS and MS-

RDI?

z What is the mechanism for R-LOF generation?

z Which byte implements the RS (MS/HP) error

monitoring?

z K2 byte is used to monitor the status of MS, which might generate MS-AIS or MS-RDI

alarm.

z If the receiver doesn't receive A1 and A2 bytes within five or more successive frames

(625us), i.e. it can't identify the start of five successive frames (identify different frames), it

will enter out-of-frame status and generate out-of-frame alarm ---- OOF. If the OOF keeps

for 3ms, the receiver will enter loss-of-frame status ---- the equipment will generate loss-

of-frame alarm ---- LOF. Meanwhile, an AIS signal will be sent downward and the entire

services will be interrupted. Under LOF status, if the receiver stays in normal frame

alignment status again for successive 1ms or more, the equipment will restore the normal

status.

z The BIP-8 parity.


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Summary

z SDH Overview

z Frame Structure & Multiplexing Methods

z Overheads & Pointers

z The focus is the mechanism for the bytes to monitor alarms and performances.


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SDH Principle Page-47

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Ota000004 Sdh Principle Issue 2

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