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1 We bring Light to the Internet ™ SDH and SONET SDH and SONET Transport Technologies Transport Technologies

SDH & PDH DIFF

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Page 1: SDH & PDH DIFF

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We bring Light to the Internet ™

SDH and SONET SDH and SONET

Transport TechnologiesTransport Technologies

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Introduction to Introduction to SDH and SONETSDH and SONET

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• Transmitter, Medium, Receiver

• Network

• Communication Rules – Protocol

Communication BasicsCommunication Basics

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• Voice

• Video & High quality video

• Data

Types of SignalsTypes of Signals

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• Copper - Electrical

• Wireless - Microwave / Radio

• Fiber - Optical

• Satellite*

MediumMedium

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• TDM

• FDM

• WDM

• STDM

Multiplexing TechniquesMultiplexing Techniques

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Transmission TypesTransmission Types

• Asynchronous

• Plesiochronous

• Synchronous

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Transmission ProtocolsTransmission Protocols

• ATM

• Frame Relay

• IP

• TCP

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Types of NetworksTypes of Networks

• LAN, WAN, MAN• GAN• Long Haul• Submarine• Metro• Access

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Network TopologiesNetwork Topologies

• Star Network• Hierarchical• Mesh• Bus• Ring• Hybrid• Private & Public

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Types of CircuitsTypes of Circuits

• Point-to-Point• Multi-Point• 2 and 4 Wire• Digital• Wire, Twisted Pair, Coaxial,

Optical,Wireless

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PDH – PDH – Plesiochronous Digital Plesiochronous Digital

HierarchyHierarchy

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COMPARISION OF SDH / PDH

SDH system has consistent frame structures throughout thehierarchy.

PDH system has different frame structures at different hierarchy levels.

SDHPDH

Digital cross- connections are provided at different signal levels and in different ways on NMS

Physical cross-connections on the same level on DDF are forced if any

The payload is transparentThe payload is not transparent.

The synchronous multiplexing results in simple access to SDH system has consistent frame structures throughout the hierarchy.

Multiplexing / Demultiplexing operations have to be performed from one level to the next level step by step.

The reference clock is synchronized throughout the network.

The reference clock is not synchronized throughout the network

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SDHPDH

G.707 specified the first level of SDH.That is, STM-1, Synchronous Transport Module 1st Order & higher. (STM-1,STM-4,STM-16, STM-64)

G.702 specifies maximum 45Mpbs & 140Mpbs & no higher order (faster) signal structure is not specified

SDH network is designed to be a transport medium for B-ISDN, namely ATM structured signal.

PDH system does not bear capacity totransport B-ISDN signals.

It will transport variety of services.Few services are available

It will transport service bandwidths Sufficient number of OHBs is available

Limited amount of extra capacity for user / management

Byte interleaved synchronous multiplexing.

Bit - by - bit stuff multiplexing

Comparison (Contd.)

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Synchronous Digital Hierarchy

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Contents• Introduction

• SDH frame format and structure

• Payload and Virtual container

• SDH multiplexing Technique

• Function of Section, Multiplex section over head and pointer bytes

• Operations (consolidation and grooming)

• Check your learning

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Bellcore originally proposed SONET - Synchronous Optical NETwork

1985ANSI T1X1 committee agreed the proposal

1986 CCITT SDH standards published: G.707, G.708, G.709

1987 Bellcore submitted SONET to CCITT - much European opposition

History

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History (Contd)

PDH Transmission Rates

Hierarchical Level

American DS-x

European CEPT-x

Japanese Inter-national

0

2

3

4

1

64 64 64 64

84486312

1544 204820481544

63126312

97728139264139264 139264

44736 4473634368 32064

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History (contd)

Note the various differences and hence the standardization problem Compromises Basic rate for SONET increased to 51.840 Mbs to permit more bandwidth for OAM - concession to Europeans - a good move.

Europeans dropped demand for level 2 and 3 rates to be directly supported.

SDH/SONET merged on DS-3 and CEPT-4 rates

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Summary • SONET is a digital hierarchy interface conceived by Bellcore and defined by ANSI for use in North America. • SDH is (a) a network node interface (NNI) defined by CCITT/ITU–TS for worldwide use and partly compatible with SONET; and (b) one of two options for the user-network interface (UNI) (i.e., the customer connection), and formally the U reference-point interface for support of BISDN.

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Data Transmission Rates

A number of transmission rates are defined/possible:

• STS-1, STS-3, STS-9, STS-12, STS-18, STS-24, STS-36, STS-48, STS-192 , STS-768??

• STM-1, STM-3, STM-4, STM-6, STM-8, STM-12, STM-16, STM-64, STM-256??

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Data Transmission Rates(contd)

Optical CarrierOptical CarrierLevelLevel

ElectricalElectricalEquivalent / SDHEquivalent / SDH

Line RateLine Rate(Mb/s)(Mb/s)

OC-1

OC-3

OC-12

OC-24

OC-48

STS-1

STS-3/ STM1

STS-12/STM4

STS-24

STS-48/STM16

51.84

155.52

622.08

1,244.16

2,488.32

*

*

*

OC-192 STS-192/STM64 9,953.28*

OC-768 STS-768/STM256 39813.12

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STM-N Frame Format

• STM - "Synchronous Transport / Transmission Module"

• STM-N general format

• Basic frame STM-1 consists of • 270 x 9 = 2430 octets • 9 x 9 = 81 octets section overhead • 2349 octets payload

• Higher rate frames are derived from multiples of STM-1 according to value of N

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Frame Structure

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Payload details

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Elements of SDH• Container (C) • Virtual Container (VC)

• Tributary Unit (TU)

• Tributary Unit Group (TUG)

• Administrative Unit (AU)

• Administrative Unit Group (AUG)

• Synchronous Transport Module - N (STM – N)

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• Input signals are placed into the containers

• It adds stuffing bytes for PDH signals,which compensates for the permitted frequency deviation between the SDH system and the PDH signal

• C12 (2 Mbps – G.703)• C11 (1.5 Mbps)• C2 (6 Mbps)• C3 (34 / 45 Mbps)• C4 (140 Mbps)

Container

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Container(Contd)ALIGNMENT : It is a process of adopting the incoming PDH signals into containers i.e. PCM 30 or 2Mbps to C12.

ANALOGY

1. Putting 30 mobile phones in one polythene bag 2Mbps or PCM30

2. Packing the above polyethene bag in one carton box along with some packing material. Alignment

3. The above packing material called Stuffing bytes

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Virtual Container

=+POH PAYLOAD PAYLOADPOH

ANALOGY:

Packing C2 carton box with some more packing material and labeled as VC2 box

MAPPING : It is a process from Containers to Virtual containers.

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Mapping is a process used when tributaries are adapted into VCs by adding justification bits and Path overhead information

The 2 Mbps signals are not synchronized to the SDH signal.It imposes no signal structure requirements, so 2 Mbps signals using this mapping do not need to be framed.This allows easy interface with existing PDH systems as variable bit justification occurs as part of this type of 2Mbps mapping.

Mapping (Asynchronous)

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• The rate of 2Mbps signals are synchronized to the SDH signal, but the framing of the 2Mbps signal is not synchronized to SDH signal.It imposes no signal structure requirements, so no need to be framed.

• Variable bit justification does not take place, so 2 Mbps to be mapped must already be synchronized to SDH network.

• Generally used for national networks only.

Bit Synchronous Mapping

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•Here both rate and framing of 2Mbps signal are synchronized to SDH signal.

•Bit justification does not take place.

•Two types

Floating mode :- uses VC-12 pointers.

Locked mode :- avoids using VC-12 pointers. To reduce cost of VC-12 pointer processors.

Byte Synchronous Mapping

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• It adds overheads to a container or groups of tributary units, that provides facilities for supervision and maintenance of the end to end paths

• VCs carry information end to end between two path access points through the SDH system

• VCs are designed for transport and switching sub-SDH payloads• VC12 (C12 + POH)• VC11 (C11 + POH)• VC2 (C2 + POH)• VC3 (C3 + POH)• VC4 (C4 + POH)

Virtual Container

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Virtual Container (contd.)

• At each level, subdivisions of capacity can float individually between the payload areas of adjacent frames. Each subdivision can be readily located by its own pointer that is embedded in the overheads. • The pointer is used to find the floating part of the AU or TU, which is called a virtual container (VC).

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Virtual Container (contd.)

• The AU pointer locates a higher-order VC, and the TU pointer locates a lower-order VC. For example, an AU–3 contains a VC–3 plus a pointer, and a TU–2 contains a VC–2 plus a pointer.

• A VC is the payload entity that travels across the network, being created and dismantled at or near the service termination point.

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• It adds pointers to the VCs

• This pointer permits the SDH system to compensate for phase differences within the SDH network and also for the frequency deviations between the SDH networks

• TUs acts as a bridge between the lower order path layer and higher order path layer

• TU12 (VC12 + pointer)• TU2 (VC2 + pointer) • TU3 (VC3 + pointer)

Tributary Unit

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• It defines a group of tributary units that are multiplexed together

• As a result, a TU group could contain one of the following combinations

• Three TU-12s (TUG – 2)

• Seven TUG-2s (TUG – 3)

Tributary Unit Group

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• It adds pointer to the HO Virtual containers(similar to the tributary unit) • AU - 3 (VC-3 + pointer)• AU - 4 (VC-4 + pointer)

Administrative Unit Group

• It defines a group of administrative units that are multiplexed together to form higher order STM signal

Administrative Unit

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Synchronous Transport Module – n• It adds section overhead (RSOH & MSOH) to a number of AUGs that adds facilities for supervision & maintenance of the multiplexer & regenerator sections

• This is the signal that is transmitted on the SDH line

• The digit “n” defines the order of the STM signal

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STM-1 frame structure

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SDH Multiplexing ProcessSDH Multiplexing Process

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• As indicated in the figure, the STM – n signal is multiples of frames consisting of 9 rows with 270 bytes in each row

• The order of transmission of information is first from left to right and then from top to bottom

• The first 9 bytes in each row are for information and used by the SDH system itself.This area is divided into 3 parts

Regenerator Section Overhead(RSOH) Multiplex Section Overhead(MSOH) Pointers

STM-1 frame structure (contd..)

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SDH Generalised Multiplexing Structure

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Mapping of 2Mbps into STM – N signal

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• Stuffing bytes are added in the container one at the head and the other at the tail of each frame

• The lower order POHs are added at the head of each frame in the VC12

• Adding of pointers takes place at the head of each frame in the TU12

• Three parallel TU12s are multiplexed to form a TUG-2

• Seven TUG-2s are multiplexed to form a TUG-3

• Multiplexing of three TUG3s with stuffing bytes at the header forms the input to VC4

Mapping of 2Mbps into STM – N signal

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• Higher order path over heads are added at this level, which is the input to AU4

• The location of the starting byte J1(VC-4) is written in pointer bytes H1 and H2. This process is defined as pointer processing

• AUG, performs the function of concatenation in case of higher order STMs

• In STM-1,virtually there is no difference between AUG and AU-4

• AUG is attached with SOH, to form an STM-1 (1st order of Synchronous Transport module)

Mapping of 2Mbps into STM – N signal

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2.048 Mbps(E1)

1 2 3 32

32 Bytes

1 2 3 32VC-1235 Bytes

POH (Lower Order)

1 2 3 32C-1234 Bytes

Stuffing Bytes

Mapping of 2Mbps into STM – N signal

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TU-12

36 Bytes

Pointer

9 Rows

4 Columns

TU 12 is arranged Into Matrix of 9 X 4

Mapping of 2Mbps into STM – N signal

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TUG-2 9 Rows

12 Columns

9 Rows

4 Columns 4 Columns 4 Columns

TU-12 TU-12 TU-12

Multiplexing

Mapping of 2Mbps into STM – N signal

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7 TUG-2s

Stuffing Bytes

86 Columns 84 Columns

TUG 3

X 7 TUG-2 TUG-3(multiplexing)

Mapping of 2Mbps into STM – N signal

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HOPOH

VC - 4

258 Columns

Stuffing Bytes

261 Columns

TUG - 3 TUG - 3 TUG - 3

86 Columns

X 3 TUG–3

Mapping of 2Mbps into STM – N signal

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261 Columns

AU – 4 (Adding Pointer)

PO

H Pay LoadAU Pointer

9 Columns

4 th Row

Pay LoadP

OH

VC - 4

261 Columns

9 rows

Mapping of 2Mbps into STM – N signal

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PAY LOAD

RSOH

MSOH

AU Pointer

261 Columns

270 Columns

9 Columns

1-3 rows

5-9 rows

4th row

STM-1 frame structure

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SDH Over HeadsSDH Over Heads

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STM-1 Section Overhead

Y Y 1 1

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A1 & A2 – Framing Bytes

• These two bytes indicate the beginning of the STM-N frame

J0 – Regenerator Section Trace

• It’s used to transmit a Section Access Point Identifier so that a section receiver can verify its continued connection to the intended transmitter

• Identifies by a number in the individual STM – 1s of a higher order STM - n

Regenerator Section Overhead

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• This is a parity code (even parity), used to check for transmission errors over a regenerator section

• Its value is calculated over all bits of the previous STM-N frame after scrambling, then placed in the B1 byte of STM-1 before scrambling E1 – Engineering Order wire • This byte is allocated to be used as a local order wire channel for voice communication between regenerators

• This byte functionality is available at both multiplexers and Regenerators

B1- Bit Interleaved parity (BIP-8)

RSOH (contd.)

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• Each bit in BIP will indicate the parity of all respective bits in the previous frame.

Ex :

Transmitted signal = 01100100

10000110

10100100

BIP calculation = 01000110

Bit Interleaved parity (BIP)

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• Regenerator section BIP is calculated over the entire signal including all RSOH,MSOH,VC-4 POH and payload of the previous frame..The result is placed in B1 for a STM-1.

• MS BIPs are calculated over the previous STM-1 frame,minus RSOH, and placed in the B2 bytes.

• Path BIP’ are calculated over the previous frame, minus RSOH and MSOH and are found in the B3 byte of every STM-1.

BIP (contd…)

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F1 – User Channel

• This byte is set aside for the user’s purposes

D1 to D3 – Data Communication Channel

• These three bytes form a 192 kbps DCC for Operation & management of the SDH System

• Network management system sends / receives provisioning, security, status / control alarm and performance monitoring command / response by way of DCC

RSOH (contd.)

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• This is used to determine if a transmission error has occurred over a multiplex section. It is even parity, and is calculated over all bits of the MS Overhead and the STM-N frame (except the regenerator section) of the previous STM-N frame before scrambling

• The value is placed in the three B2 bytes of the MS Overhead before scrambling. These bytes are provided for all STM-1 signals in an STM-N signal

B2 – Bit Interleaved parity (BIP – 24)

Multiplex Section Overhead

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D4 to D12 – Data Communication Channel• These nine bytes form a 576 kbps DCC for Operation & management of the multiplexers on a SDH line

• Network management system sends / receives provisioning, security, status / control alarm and performance monitoring command / response by way of DCC

K1 & K2 – Multiplex Section Protection

• These two bytes are used for MSP signaling between multiplex level entities for bi-directional automatic protection switching and for communicating Alarm Indication Signal (AIS) and Remote Defect Indication (RDI) conditions

MSOH (contd.)

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K1 Byte Allocation

..Unused1001

..Manual switch1000

..Signal degrade, low priority1010

..Signal degrade, high priority1011

..Signal fail, low priority1100

..Signal fail, high priority1101

..Forced switching1110

HighLockout of protection1111

PriorityCondition,state or external request

Bits

1234

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..Do not revert0001

..Reverse request0010

LowNo request0000

..Unused0011

..Exercise0100

..Unused0101

..Wait to restore0110

..Unused0111

PriorityCondition,state or external request

Bits

1234

K1 Byte Allocation

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K1 Byte Allocation

Working channel091001

Working channel081000

Working channel101010

Working channel111011

Working channel121100

Working channel131101

Working channel141110

Extra Traffic channel151111

Requesting switch actionChannel no.

Bits

5678

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Working channel010001

Working channel020010

Null channel000000

Working channel030011

Working channel040100

Working channel050101

Working channel060110

Working channel070111

Requesting switch actionChannel no.

Bits

5678

K1 Byte Allocation

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6708

09

10

11

12

13

14

15

Channel no.

1000

1001

1010

1011

1100

1101

1110

1111

Bits

1234

Working channel

Working channel

Working channel

Working channel

Working channel

Working channel

Working channel

Extra traffic channel

Requesting switch action

K2 Byte Allocation

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Working channel010001

Working channel020010

Null channel000000

Working channel030011

Working channel040100

Working channel050101

Working channel060110

Working channel070111

Requesting switch actionChannel no.

Bits

1234

K2 Byte Allocation

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1: n architecture

1+ 1 architecture

1

0

MSP switch architectureBit 5

K2 Byte Allocation

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Future use000

Future use001

Future use010

Future use011

Future use100

Future use101

MS FERF110

MS AIF111

StatusBits 678

K2 Byte Allocation

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Automatic Protection Switching•APS is the capability of a transmission system to detect a failure on a working facility and to switch to a standby facility to recover the traffic.

•Only the Multiplex Section in SDH is protected in this automatic fashion.

•MS protection mechanism is coordinated by K1 and K2 bytes.

•Path protection is managed at a higher level by network management functions

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Protection Switching is initiated due to :

• Signal failure

• Signal degradation

• In response to commands from a local craft terminal or a remote network manager.

Two modes of APS are provided

• 1+1 Protection

• 1:N protection

APS (contd…)

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1+1 Protection switching

Normal condition

One signal is chosen per

pair

Failure condition

The best signal is chosen

Near End Far End

DestinationSource

Working

Protection

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1: N Protection switching

Normal condition

Protection on channel empty

Failure condition

Protection channel

contains failed line

Near End Far End

Source Destination

Working

Protection

Protection

Near End Far End

Working

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E2 – Engineering Order wire

• This byte is allocated to be used as a local order wire channel for voice communication between multiplexers• This byte is not accessible at the regenerators

M1 - Remote Error indication

• It is used to indicate the MS layer remote error indication (MS-REI)

MSOH (contd.)

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S1 Synchronization status message byte (SSMB)• Bits 5 to 8 of this S1 byte are used to carry the synchronization messages

0000 Quality unknown (existing sync. network)

0010 G.811 PRC (Primary Reference Clock)

0100 G.812 transit SSU-A (Synchronisation Supply Unit - A)

1000 G.812 local SSU-B (Synchronisation Supply Unit – B)

1011 G.813 Option 1 SEC (Synchronous Equipment Timing Clock)

1111 Do not use for synchronization. This message may be emulated by equipment failures and will be emulated by

Multiplex Section AIS signal.

MSOH (contd.)

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H1 Y Y H2 1 1 H3 H3 H3

H1 & H2 = VC payload pointer

H3 = Negative Justification

1 = All 1’s

Y = 1001SS11 (S bits unspecified)

SDH Pointers Use of Pointers• It indicates the starting position of VC• It is also used for justification• AU pointer is also used for concatenation• SDH provides payload pointers to permit differences in the phase and frequency of the Virtual Containers (VC-n) with respect to the STM-N frame

• Lower-order pointers are also provided to permit phase

differences between VC-12/VC-2 and the higher-order

VC-3/VC-4

To accomplish this, a process known as byte stuffing is used

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• The value of the pointer has a range of 0 to 782

For example, • If the VC-4 Payload Pointer has a value of 0, then the VC-4 begins in the byte adjacent to the H3 byte of the Overhead;

• If the Payload Pointer has a value of 87 (since each row of the payload has 86 positions), then the VC-4 begins in the byte adjacent to the K2 byte of the overhead in the byte of the next row

• The pointer value, which is a binary number, is carried in bits 7 through 16 of the H1-H2 pointer word.

Pointers (contd.)

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Positive Pointer Justification• When the data rate of the VC is too slow in relation to the rate of the STM-1 frame, positive stuffing must occur. An additional byte is stuffed in, allowing the alignment of the container to slip back in time. This is known as positive stuffing

Negative Pointer Justification• Conversely, when the data rate of the VC is too fast in relation to the rate of the STM-1 frame, that negative stuffing must occur. Because the alignment of the container advances in time, the payload capacity must be moved forward. Thus, actual data is written in the H3 byte, the negative stuff opportunity within the Overhead; this is known as negative stuffing

Pointers (contd.)

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H1 Y Y H2 1 1

H2 1 1H1 Y Y

H1 Y Y H2 1 1

H3 H3 H3

H3 H3 H3

H3 H3 H3

Points outStart of VC-4 VC-4 Boundary

AU-4 Pointer Positive justification

Points outStart of VC-4

Points outStart of VC-4 VC-4 Boundary

VC-4 Boundary

To next RowTo next Row

Positive justification opportunity

AU – 4 Positive Pointer Justification

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Points outStart of VC-4

Points outStart of VC-4 VC-4 Boundary

VC-4 Boundary

From next row

From next row

Negative justification opportunity

AU-4 Pointer Negative justification

H1 Y Y H2 1 1

H2 1 1H1 Y Y

H1 Y Y H2 1 1

H3 H3 H3

H3 H3 H3

Points outStart of VC-4 VC-4 Boundary

AU – 4 Positive Pointer Justification

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Path OverHead

TCM – Tandem Connection Monitoring

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J1- Path trace

• Starting point of VC• It is used to transmit repetitively a path access

point identifier, similar to J0

B3 – Path Bit Interleaved Parity – BIP- 8

• Error Monitoring over the previous VC-4 frame.• Even parity is used to monitor path errors

Path Overhead

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C2 – Signal Label• It is defined to indicate the composition or the maintenance of the VC-4

POH (contd.)

FDDI150001 0101

MAN (DQDB)140001 0100

ATM130001 0011

140 Mbps into C4 (async)120001 0010

34 / 45 Mbps into C3 (async)040000 0100

Locked TU030000 0011

TUG structure020000 0010

Equipped,non specific010000 0001

Unequipped000000 0000

MappingHexBinary

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G1- Path status

• It is defined to send back the path status and performance to where the path is generated

F2,F3 – Path User Channels

• It is assigned for user communication purposes between path elements by the network operator

H4 – Multi frame Indicator

• H4 byte provides the multiframe information

POH (contd.)

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K3 – Automatic protection switching(APS) channel

• (b1-b4) are assigned for APS signaling for protection at the VC-4/3 path labels

N1 – Network operator Byte

• The tandem connection monitoring function is currently not used

POH (contd.)

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Benefits of SDHBenefits of SDH

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Pointers, Mux/Demux

Reduced back to back multiplexing

Optical Interconnect

Multi Point Configuration

Grooming

Enhanced OAM

Enhanced Performance monitoring

Benefits of SDH

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Operations

Managing capacity in the network involves such operations as the following:

a. protection, for circuit recovery in milliseconds

a. restoration, for circuit recovery in seconds or minutes

a. provisioning, for the allocation of capacity to preferred routes destinations for each type of traffic

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Operations ( contd)

a. consolidation, or the funneling of traffic from unfilled bearers onto fewer bearers in order to reduce waste of traffic capacity

b. grooming, or the sorting of different traffic types from mixed payloads into separate

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Consolidation and Grooming

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Routing Function of a Typical ADM

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SDH Network ElementsSDH Network Elements

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SDH Network elements

Terminal multiplexer

Regenerator

Add / Drop Multiplexer

Cross – connect

Wide-band Digital cross connect

Broad band Digital cross connect

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Terminal Multiplexer STM –1

E1 VC STM-N

E3 STM-1

STM-1

E1

E3

STM-N

STM-N STM-N

Regenerator

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STM-N

STM-N STM-N

STM-N TU AU-4

STM-N E1 E4

STM-N 2 Mbps 140 Mbps

STM-N STM-N

Add / Drop Multiplexer

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TU – 12 Switch Matrix

TU-12 TU-12 TU-12 ` TU-12

STM-N STM-1 E1 E4

STM-N STM-1 2 Mbps 140 MbpsSTM-N

Wide Band Digital Cross Connect

Transparent Switch Matrix

AU-4 AU-4 AU-4 ` AU-4

STM-N STM-N E1 E4

STM-N STM-1 2 Mbps 140 MbpsSTM-N

Broad Band Digital Cross Connect

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TopologiesTopologies

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Network Configurations

Point to Point

Point to Multipoint

Mesh Architecture

Ring Architecture

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PTE PTERegen

Point to Point

Point to Multi point

PTE ADM PTERegenRegen

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ADM

ADM

ADM

ADM

Ring Architecture

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Mesh Topology

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G.811

G.812

G.812

Under definition (G.81s)

Primary Reference Clock (PRC)

Slave clock (transit node)

Slave clock (local node)

SDH network-element clock

Related CCITT recommendation

Clock type

Synchronization