Sdh

SDH Transport Systems

SYNCHRONIZATION OF DIGITAL SIGNAL :SYNCHRONIZATION OF DIGITAL SIGNAL :

In a set of Synchronous signals, the digital transitions in the signals occur at exactly the same rate. There may be a phase difference between the transitions of the two signals, and this would lie on specified limits.

SDH is a transmission protocol or it is a set of rules for transmitting the data from source to destination via optical fiber.

SYNCHRONOUS SIGNAL:

Requirement Of Synchronous Digital Hierarchy ( SDH )Requirement Of Synchronous Digital Hierarchy ( SDH )

Need for extensive network management capability within the hierarchy.

Standard interfaces between equipment.

Need for inter-working between north American and European systems.

Facilities to add or drop tributaries directly from a high speed signal.

Standardization of equipment management process.

Node View - TJ100MC1

Line Diagram

E1 Tributary Card - TET16/TET21/TET28

E3/DS3 Tributary Card - TE31

TP01

TP01FT

STM-1 Tributary Card - A011

STM-1e/E4 Tributary Card - A1E4

Node view - TJ100MC4

Line Diagram

Tributary Card E1- TET16/TET21/TET28Tributary Card E3/DS3 - TE313 E3/DS3 Tributary Card - TE33Ethernet Tributary Card – ETCEthernet Tributary Card – ETCFTTP01TP01FTSTM1 card Œ A011 or A012STM-1e/E4 Tributary Card - A1E4STM-1e Tributary Card - A012ESTM-4 Tributary Card - A041,A041VLRTR01

TJ100 MC-1 & TJ100 MC-4 can be configured as Regenerator (REG),

Terminal Multiplexers (TMUX),Add-Drop Multiplexers (ADM) and

Digital Cross-Connect (DXC)

SDH Network ElementsSDH Network Elements

The Network Elements of SDH Network :

Regenerator (Reg.)

Terminal Multiplexer (TM)

Add/Drop Multiplexer (ADM)

Digital Cross Connect (DXC)

STM-NSTM-N STM-NSTM-NRegeneratorRegenerator

Regenerator (Reg.)

It mainly performs 3R function:

1R – Reamplification

2R – Retiming

3R – Reshaping

It regenerates the clock and amplifies the incoming distorted and attenuated signal. It derive the clock signal from the incoming data stream.

Regenerator

Terminal Terminal MultiplexerMultiplexer

STM-NSTM-NPDHPDHSDHSDH

Terminal Multiplexer (TM)

It combines the Plesionchronous and synchronous input signals into higher bit rate STM-N Signal.

Terminal Multiplexer

Tributaries Line Interface (aggregate)

1 2 3 45 6 7

123..

1

(Optional)

Add/Drop Multiplexer (ADM)

STM-NSTM-NSTM-NSTM-N

PDHPDH SDHSDH

Add / Drop Add / Drop MultiplexerMultiplexer

Add/Drop Multiplexer

Tributaries

Add / Drop illustration:1 is dropped; 17 is added

12 1

17...

Synchronous Transport Module5 60

1

21 25 34 3

3

5 60

17

21 25 34 3

Drop

Add

Extraction from & insertion into high speed SDH bit streams of Plesiochronous and lower bit rate synchronous signal.

ADM makes possibilities of

Ring structure of network which provides the advantage of automatic back-up path switching in the event of fault.

STM-16STM-4STM-1

140 Mbit/s34 Mbit/s2 Mbit/s

STM-16STM-4STM-1

140 Mbit/s34 Mbit/s2 Mbit/s

Cross - Connect



Digital Cross Connect:A digital cross connect is an equipment which has the capability of interconnecting tributaries

An Agg to Agg connection, a trib to aggregate connection and a tributary to tributary connection is also possible in case of a Digital Cross ConnectTypes – Wideband VT/DS1 level Broadband STS-n/DS3 level &

Narrowband DS0 level

SDH NE: Digital cross connect (DXC)

Ports

Ports

Ports

Ports

25

1

21

PDHATMIP

SDHSDHmultiplexermultiplexer

SDHSDH RegeneratorRegenerator

##Cross-Cross-

connectconnect

SDHSDHmultiplexermultiplexerSDH SDH SDH

PDHATMIP

Regenerator Section

Regenerator Section

Multiplex Section Multiplex Section

Path

TYPICAL LAYOUT OF SDH LAYER

General view of Path Section designations

TopologiesTopologies

Network Configurations

Point to Point

Point to Multipoint

Mesh Architecture

Ring Architecture

SDH Network TopologiesSDH Network Topologies Point-to-Point NetworkPoint-to-Point Network

Chain NetworkChain Network

TerminalMultiplexer

(TM)

TerminalMultiplexer

(TM)Regenerator

Trib

utar

ies

Trib

utar

ies

TerminalMultiplexer

(TM)

TerminalMultiplexer

(TM)

Add DropMultiplexer

(ADM) Trib

utar

ies

Trib

utar

ies

Ring Network

Add DropMultiplexer

(ADM)

Add DropMultiplexer

(ADM)

Add

Drop

Mul

tiple

xer

(ADM

)

Add DropMultiplexer

(ADM)

Add DropMultiplexer

(ADM)

Add DropM

ultiplexer(ADM

)

Trib

utar

ies

Trib

utar

ies

Tributaries Tributaries

TributariesTributaries

TributariesExchange

STM-4 RingSTM-4 Ring

2Mbit/s

140Mbit/s STM-1

Add DropMultiplexer

(ADM)

Add

Drop

Mul

tiple

xer

(ADM

)

Add DropMultiplexer

(ADM)

Add DropMultiplexer

(ADM)

Add DropM

ultiplexer(ADM

)

Exch

ange

Exch

ange

Add DropMultiplexer

(ADM)

STM-1

140Mbit/s

2Mbit/s

2Mbit/s

ADM linear route ( Bus )

ADM Ring

X XX

X X

X X X

Mesh Network

Trib

utar

ies

Trib

utar

ies

TributariesTributaries

Add Drop& Cross connect

Mux

Add

Drop

& Cr

oss

conn

ect

Mux

STM-N Links

Add/Drop& Cross Connect

Mux

Add Drop& Cross connect

Mux

Optical Signals Electrical Signals MS RateDS0 64 Kb/s

DS1 1.544 Mb/s

VT1.5 1.728 Mb/s

VT2 2.304 Mb/s

DS3 44.736 Mb/s

OC-1 STS-1 51.84 Mb/s

OC-3 STS-3 155.52 Mb/s

OC-3c STS-3c 155.52 Mb/s

OC-12 STS-12 622.08 Mb/s

OC-48 STS-48 2488.32 Mb/s

OC-192 STS-192 9953.28 Mb/s

Standard MS Rates :

O C - 1O C - 3O C - 9O C - 1 2O C - 1 8O C - 2 4O C - 3 6O C - 4 8O C - 9 6O C - 1 9 2

S T S - 1S T S - 3S T S - 9S T S - 1 2S T S - 1 8S T S - 2 4S T S - 3 6S T S - 4 8S T S - 9 6S T S - 1 9 2

5 1 .8 4 01 5 5 .5 2 04 6 6 .5 6 06 2 2 .0 8 09 3 3 .1 2 01 2 4 4 .1 6 01 8 6 .2 4 02 4 8 8 .3 2 04 9 7 6 .6 4 09 9 5 3 .2 8 0

5 0 .11 21 5 0 .3 3 64 5 1 .0 0 86 0 1 .3 4 49 0 2 .0 1 61 2 0 2 .6 8 81 8 0 4 .0 3 22 4 0 5 .3 7 64 8 1 0 .7 5 29 6 2 1 .5 0 2

1 .7 2 85 .1 8 41 5 .5 5 22 0 .7 3 63 1 .1 0 44 1 .4 7 26 2 .2 0 88 2 .9 4 41 6 5 .8 8 83 3 1 .7 7 6

-S T M - 1

S T M - 4

S T M - 1 6

S T M - 6 4

O p tica l L e v e l

E lec trica l L e v e l L in e R a te

P ay lo a dra te( M B p s )

O v e rh ea dR a te( M b p s )

S D HE q u iv a len t

Frame Structure

Transport Module

STM-n (n >1)

PayloadOne Section overheadSTM-4

STM-1 = 155 Mbit/sSTM-4 = 622 Mbit/sSTM-16 = 2.5Gbit/sSTM-64 = 10Gbit/s

• 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

Sdh22.exe

D:\Documents and Settings\Administrator\Desktop\Chennai\ANIMATIONS\Click me.exe

Data Rate Overall 9 rows*270

columns*8000frames/sec*8bits/byte = 155.52Mbps

9 rows*261 columns*8000frames/sec*8bits/byte =150.336MbpsUser Data/ Payload 9 rows*260 columns*8000frames/sec*8bits/byte =149.76Mbps

STM-1 frame structure

Check your learning section1

PAY LOAD

RSOH

MSOH

AU Pointer

261 Columns

270 Columns

9 Columns

1-3 rows

5-9 rows

4th row

STM-1 frame structureSTM-1 frame structure

Check your learning section2

SDH Multiplexing Process

STM-N Frame

• Is got by Byte Interleaved Multiplexing of

Lower Order Frame.

• For Example STM-4 is got by Multiplexing 4 STM-1

Frames.

S D H

M U X

T rib u ta ryS ig n a lsS T M -1

L in e S ig n a l

S T M -3

Byte Interleaved multiplexing

STM - 4

TU Format

Columns Bytes/Frame

Bandwidth Payload

TU 11 3 27 1.728Mbps DS1

TU 12 4 36 2.304Mbps E-1

TU 2 12 108 6.912Mbps DS-2

SDH Over Heads

STM-1 Section Overhead

Y Y 1* 1*

Y- 1001 SS11 (S unspecified)

1*- All 1’s

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 OverheadRegenerator Section Overhead

• 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..)RSOH (contd..)

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..)RSOH (contd..)

Regenerator Section Overhead :

• Performance monitoring (STM-n signal)

• Local orderwire

• Data communication channels to carry information for OAM&P

• Framing

STM Regenerator Section Overhead

• 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)

MS OverheadMS Overhead

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 Protn.• 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..)MSOH (contd..)

Automatic Protection SwitchingAutomatic 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

Protection Switching is initiated due to :

• Signal failure

• Signal degradation

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

APS (contd..)APS (contd..)

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 regeneratorsM1 - Remote Error indication• It is used to indicate the MS layer remote error indication (MS-REI)


S1 Synchronization status message byte (SSMB)• Bits 5 to 8 of this S1 byte are used to carry the synchronization messages0000 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.


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 PointersSDH 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

• 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..)Pointers (contd..)

pointer justification.exe

D:\Documents and Settings\Administrator\Desktop\Chennai\ANIMATIONS\pointer justification.exe

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 stuffingNegative 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..)Pointers (contd..)

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

Points outStart of VC-4


VC-4 Boundary

To next RowTo next Row

Positive justification opportunity

AU – 4 Positive Pointer AU – 4 Positive Pointer JustificationJustification

Points outStart of VC-4


VC-4 Boundary

From next row

From next row

Negative justification opportunity

H1 Y Y H2 1 1

H2 1 1H1 Y Y

H1 Y Y H2 1 1

H3 H3 H3

H3 H3 H3


AU – 4 Negative Pointer AU – 4 Negative Pointer JustificationJustification

MS Alarm indication signalPerformance Monitoring of individual STM-1’sProtection Switching InformationMS Remote Defect Indication (RDI)

Data channels for OAM&PPointer to commencement of synchronous payload envelopeExpress order-wire

Multiplexer Section Overhead

Path OverHeadPath OverHead

TCM – Tandem Connection Monitoring

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 OverheadPath Overhead

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

POH (contd..)POH (contd..)

Binary Hex Mapping0000 0000 00 Unequipped0000 0001 01 Equipped,non specific0000 0010 02 TUG structure0000 0011 03 Locked TU0000 0100 04 34 / 45 Mbps into C3 (async)0001 0010 12 140 Mbps into C4 (async)0001 0011 13 ATM0001 0100 14 MAN (DQDB)0001 0101 15 FDDI

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..)POH (contd..)FEBE FERF UNUSED

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..)POH (contd..)

VC12 path overhead

BIP-2 (Bits 1 and 2). The Bit Interleaved Parity (BIP) bits are used to provide an error monitoring function for the VC-12 path.

REI (Bit 3). The Remote Error Indication (REI) bit is used to communicate detected BIP-2 errors back to the VC-12 path originator.

RFI (Bit 4). Remote Fail Indicator (RFI). Not used in present applications.

Signal label (Bits 5 to 7). These bits are used to indicate the payload mapping and equipped status.

RDI (Bit 8). The Remote Defect Indicator (RDI) bit is used to indicate certain detected TU path alarms to the VC-12 path originator.

Performance Monitoring of STM SPE Path Status Path Trace Signal Label (Unequipped or Equipped)

STM Path Overhead

STM-4 Section OverHeadSTM-4 Section OverHead

MAPPING

Elements of SDHElements 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)

• 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)

ContainerContainer

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.

• 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 ContainerVirtual Container

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).

• 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.

• 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)



Tributary UnitTributary Unit

• 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 GroupTributary Unit Group

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

Administrative UnitAdministrative Unit

Synchronous Transport Module – nSynchronous 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

SDH Generalised Multiplexing SDH Generalised Multiplexing StructureStructure

Mapping of 2Mbps into STM – N signalMapping of 2Mbps into STM – N signal

A corresponding arrangement is used for demultiplexing

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 – NMapping of 2Mbps into STM – N

TU-12

36 Bytes

Pointer

9 Rows

4 Columns

TU 12 is arranged Into Matrix of 9 X 4


TUG-2 9 Rows

12 Columns

9 Rows

4 Columns 4 Columns 4 Columns

TU-12 TU-12 TU-12

Multiplexing


7 TUG-2s

Stuffing Bytes

86 Columns 84 Columns

TUG 3

X 7 TUG-2 TUG-3(multiplexing)


HOPOHVC - 4

258 Columns

Stuffing Bytes

261 Columns

TUG - 3 TUG - 3 TUG - 3

86 Columns

X 3 TUG–3


261 Columns

AU – 4 (Adding Pointer)

POH Pay LoadAU Pointer

9 Columns

4 th Row

Pay LoadPOH

VC - 4

261 Columns

9 rows


D:\Documents and Settings\Administrator\Desktop\Chennai\ANIMATIONS\mapping E1.exe

SYNCHRONIZATION

Synchronization is the means of keeping all of the digital equipment in your network operating at the same rate.In terms of synchronous networks (SDH/SONET), this means that all network elements must be oriented towards a single clock. In SDH and SONET, higher bit rates and synchronization are the major Advances compared to older transmission technologies. This is the only way to assure uniform standardization at all hierarchy levels and represents a major challenge for system manufacturers and network operators.

Synchronization

Primary Reference Clock ( PRC )

Stratum 1

DIGITAL EXCHANGEStratum 1

TRANSMISSION NETWORK

Digital ExchangeStratum 2



Transmission Network






SYNCHRONIZATION HIERARCHY

The network illustrates the digital network synchronization hierarchy,with all clocks normally operating at the same frequency as the reference source. A large network can comprise the interconnection of many such clusters of nodes, each operating plesiochronous.

Clock Hierarchies

CLOCK SUPPLY HIERARCHYCLOCK SUPPLY HIERARCHY STRUCTURESTRUCTURE

• S1 Clk : Cesium / Rubidium atomic clk. Accurate upto 0.00001ppm. Loses 1sec every 3000yrs.• S2 Clk : Accurate to 0.016ppm. <255 slips in 1st 86 days after loosing S1 link. 1st slip can’t occur within first 7 days.• S3 Clk : Accurate upto 4.6ppm. <255 slips in 1st 24hrs after loss of reference. 1st slip can’t occur <6mins after reference loss.• S4 Clk : No guarantee.

Stratum Accuracy Skip Rate Notes1 10*10-112.523/Year PRC

2 1.6*10-811.06/Day Electronic Switch Sys

3 4.6*10-6 132.48/Hour DCS

4 3.2*10-5 15.36/Min PBX, CPE

All network elements are synchronised to a central clock

The central clock is generated by a high precision primary clock(prc)-G.811 (10x10-11 )

Clock is distributed throughout the network,this signal is passed on to the Sub-ordinate Synchronization units (ssu) and synchronous equipment clock (sec)

SYNCHRONIZATIONSYNCHRONIZATION

Selector Internal Clock

Auotmatic Switch

Timing Signal Generator (TSG)

Primary Secondary

Internal Diagram of BITS

S1 Synchronization status message byte (SSMB)

• Synchronization Status Messaging is the transmission of synchronization quality messages between NEs.•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.

QL settings for use with SSM

Example: Ring synchronization

Figs. A,B,C give a simple example of ring synchronization using four network elements anda PRC clock source:. Configuration of network elements for clock distribution. Clock distribution behavior when a fault occursDuring normal operation, the complete ring is clocked by the PRC, which is directly connected to NE 1 (clock input T3). This NE cannot derive a clock from the data inputs and is not configured initially as a clock port. This prevents possible clock loops.The other three network elements derive the clock from the incoming data signals. The best clock source is always used (here, PRC). The output signals have this clock quality, so PRC is indicated in the S1 byte. To avoid clock loops, ªDon't Use for Synchronizationº (DNU) is indicated in the S1 byte in the opposite direction.At NE 4, PRCs are present at both data ports. In this case according to the clock derivation table determining the priority in case of identical clock priority, the clock from NE 3 is used.

What happens to the ring in case of a fault ? In this case, NE 3 no longer receives a valid synchronization signal from NE 2, so it operates in holdover mode (Fig. B) since an alternative clock source is not yet available. This is also indicated in the S1 byte (SEC) towards NE 4.NE 4 now receives a signal with PRC quality from NE 1 in the reverse direction. According to the clock derivation table, NE 4 takes the synchronization clock from the reverse direction (NE 1).The same applies to NE 3, which uses the clock from NE 4 from the reverse direction (Fig. C).Despite the disruption, all of network elements still use the PRC clock.

Errors & Alarms

PDHATMIP

SDHSDHmultiplexermultiplexer

SDHSDH RegeneratorRegenerator

##Cross-Cross-

connectconnect

SDHSDHmultiplexermultiplexerSDH SDH SDH

PDHATMIP

Regenerator Section

Regenerator Section

Multiplex Section Multiplex Section

Path

TYPICAL LAYOUT OF SDH LAYER

General view of Path Section designations

The advantage of the alarms monitoring are illustrated as follows :

Complete failure of a connection results, for example, in a LOS alarm (loss of signal) in the receiving network element.

This alarm triggers a complete chain of subsequent messages in the form of AIS.

The transmitting side is informed of the failure by the return of an RDI alarm (remote defect indication).

The alarm messages are transmitted in defined bytes in the TOH or POH.

Numerous alarm and error messages are built into SDH. They are known as defects and anomalies, respectively. They are coupled to network sections and the corresponding overhead information.

Types of Alarms

Equipment Alarms

Facility Alarms

What is difference between a Defect and a Failure?

A defect is a detection of an alarm such as loss of signals, loss of frames. AIS loss of excessive errors.

A failure is a defect that persists beyond a maximum time allocated. It is used to access to integrate Automatic Protection Switching ( APS ).

Equipment Alarms• Card Failure• Card Mismatch• Card Missing• DCN Failure• Fan Failed• Disk 90% full• Derived Voltage high/low• I/p Voltage on PSU high/low• LAN port down• Memory usage exceeded• SW download failed• Temperature too high

Facility Alarms• AIS E1/MS/P/STM• LOS• LOF• OOF• LOM• LFD• RDI MS/P• REI MS/P• RFI P• LOP MS/P• TIM RS/MS/P• PLM P

Cont..

• Signal Degrade• Signal Fail• Timing Reference Failed• Forced Switch Active• Forced Switch to channel• Manual Switch Active• Manual Switch to channel• Laser Bias Voltage high/low• Derived I/p voltage high/low

LOS

Signal Degrade

Signal Fail

Loss Of Signals ( LOS ) :Loss Of Signals ( LOS ) :

It could be due to cut cable, excessive attenuation of the signal or an equipment fault.

The LOS state will clear when 2 consecutive framing patterns are received and no LOS condition is detected.

OOF

LOF

TIM(J0)

DCC Fail

@ RSOH

Out of Frame (OOF ) :Out of Frame (OOF ) :

This situation occurs when 4, or in some This situation occurs when 4, or in some implementations, 5 consecutive SDH frames are implementations, 5 consecutive SDH frames are received with invalid framing patterns(A1 and A2 received with invalid framing patterns(A1 and A2 bytes) bytes)

The maximum time to detect OOF is therefore 625MsThe maximum time to detect OOF is therefore 625Ms

The OOF clears when consecutive SDH frames are The OOF clears when consecutive SDH frames are received with valid framing patterns received with valid framing patterns

Loss Of Frame ( LOF ) :Loss Of Frame ( LOF ) :

The LOF occurs when the OOF state exists for a specified time in msecs

If OOFs are intermittent,the timer is not reset to zero until an “in frame” state persists continuously for specified time in msecs

As the framing bytes are there in Regenerator section overhead(RSOH) this alarm is sometimes known as RS-LOF

@ MSOH

AIS/RDI(K1,K2)

DCC Fail

Timing Reference Signal Fail(S1)

REI(M1)

MS-AIS :

This alarm is sent by a Regenerator Section Terminating equipment(RSTE) to alert the downstream Multiplex section Terminating Equipment(MSTE) of detected LOS or LOF state

It is indicated by an STM-N signal containing valid RSOH and a scrambled all 1’s pattern in the rest of the frame

The MS-AIS is detected by the MSTE when bits 6 to 8 of the received k2 byte are set to “111” for 3 consecutive frames

Removal is detected by the MSTE when bits 6 to 8 of the received k2 byte are set with a pattern other than “111” in bits 6 to 8 of k2

AU-4 AIS :

This is sent by MSTE(Multiplex Section Terminating This is sent by MSTE(Multiplex Section Terminating Equipment) to alert the downstream higher order path Equipment) to alert the downstream higher order path terminating equipment (HOPTE) of a detected LOP state or terminating equipment (HOPTE) of a detected LOP state or a received AU path AIS a received AU path AIS

The AU-4 path AIS is indicated by transmitting an all 1’s The AU-4 path AIS is indicated by transmitting an all 1’s pattern in the entire AU-4(I.e an all 1‘s pattern in H1,H2 pattern in the entire AU-4(I.e an all 1‘s pattern in H1,H2 and H3 bytes pointer bytes plus all bytes of associated VC-and H3 bytes pointer bytes plus all bytes of associated VC-4) 4)

Removal of AU-4 path AIS is detected when three Removal of AU-4 path AIS is detected when three consecutive valid AU pointers are received with normal consecutive valid AU pointers are received with normal NDF’sNDF’s

TU-12 AIS :

This is sent downstream to alert the Lower Order Path This is sent downstream to alert the Lower Order Path Terminating Equipment(LOPTE) of a detected TU-12 LOP Terminating Equipment(LOPTE) of a detected TU-12 LOP state or a received TU-12 path AISstate or a received TU-12 path AIS

TU-12 path AIS is indicated by transmitting an all 1’s pattern TU-12 path AIS is indicated by transmitting an all 1’s pattern in the entire TU-12 (I.e all 1’s in pointer bytes v1,v2,v3and in the entire TU-12 (I.e all 1’s in pointer bytes v1,v2,v3and v4 plus all bytes of associated VC) v4 plus all bytes of associated VC)

The TU-12 AIS detected by the LOPTE when all 1’s pattern The TU-12 AIS detected by the LOPTE when all 1’s pattern is received in bytes v1 and v2 or three consecutive multi-is received in bytes v1 and v2 or three consecutive multi-frames.frames.

Removal of TU-12 is detected when three consecutive valid Removal of TU-12 is detected when three consecutive valid TU-12 pointers are received with normal NDF’sTU-12 pointers are received with normal NDF’s

If the received signal contains bit errors, the receiving network element detects and reports BIP errors. Since this is not the same as a complete failure of the connection, the alarm here is referred to as an anomaly that is indicated back in the direction of transmission. The return message is called a REI (Remote Error Indication).

REI & RDI:

If network is failed due to fault in network connection itself, breakup in path or fault in terminal equipment then RDI (Remote Defect Indication) alarm will appear.

@ HOPOHTIM(J1)

PLM(C2)

REI,RDI,PLM,TIM,AIS,LOP(G1)

LOM(H4)

IEC,TC-REI/OEI/API/RDI/ODI(N1)

Loss Of Pointer (LOP )Loss Of Pointer (LOP )

The LOP state occurs when ‘n’ consecutive invalid pointers are received or ‘n’ New Data Flags(NDF) are received(other than in a concatenation indicator)

The LOP state is cleared when 3 equal valid pointers or 3 consecutive AIS indications are received.This alarm is very rare in steady state because the pointer is either valid or is all 1s

An AIS indication is all 1’s pattern in the pointer bytes.Concatenation is indicated when the pointer bytes are set to “1001XX1111111111” I.e NDF enabled(H1 and H2 bytes for AU LOP; v1 and v2 bytes for TU LOP)

Loss Of Multiframe (LOM )Loss Of Multiframe (LOM )

The LOM state occurs on SDH LOVCs & SONET VTs.

LOM is detected by checking the 7 & 8 bit of H4 Byte.

LOM is recovered when an error free H4 sequence is found in 4 consecutive VC – n frames.

@LOPOH

REI,RDI,RFI,PLM,AIS,LOP(V5)

AIS,TC-REI/OEI/API/RDI/ODI(N2)

TIM/PLM(J2)

RFI

Lossof

FrameMS-REI

Lossof

Signal

MS-AISLossof Signal

RFI Z

SDHREGEN

SDHREGEN

SDHREGEN

SDHMUX

SDHMUX

SDHMUX

SDHMUX

SDHMUX

SDHMUX

STM-1STM-1

STM-1 STM-1

STM-1STM-1

Cable Cut

Cable Cut

Excessive Errors

Some SDH alarms :

PROTECTION SCHEMES

Failure Events According to ATIS Causes

1) Fiber cable dig-ups 2) Fiber cable non-dig-ups 3) Digital cross-connects 4) Synchronization timing 5) Internal power components

Protection Schemes

Linear Protection (1+1,1:1,1:N)

Ring protection:

Unidirectional (UPSR/SNCP, MSP) Bi-directional (2FMSSP, 4FMSSP)

In 1+1 protection, for each of the working unit(Which can be either unit or path)there will be a corresponding protection unit

Both the units will be carrying data all the time ,the receiving end will select the better of the two signals

In case of failure,there will be a switching from working to protection

Even if the fault in the working unit is rectified ,there will be no automatic switching from protection unit back to working unit

This is called Non-Revertive type(because there is no automatic reversion from working to protection even when the working unit is functioning properly)

1+1 Protection1+1 Protection

Protection Section

Working Section

Multiplex SectionSDH Multiplexer SDH Multiplexer

Protection Section

Working SectionSDH Multiplexer SDH Multiplexer

Fault

1+1 Protection1+1 Protection

1+1 Card Protection

1+1 Protected Linear Link

Even in 1:1 protection, for each of the working unit(Which can be either unit or path)there will be a corresponding protection unit

Only working unit will be carrying data all the time,in case of the failure in the protection unit there will be a switching to the protection unit

Once the fault in the working unit is rectified there will be a switching from protection unit back to the working unit

This is called Reversion type(because there is an automatic reversion from protection back to the working once the working unit is restored)

1:1 Protection(Dedicated Protection)1:1 Protection(Dedicated Protection)

1:N protection is very similar to 1:1 protection,except the fact that for N working units there will be one protection unit

This is also called revertive protection,because as soon as the fault in the working unit is rectified there will be an automatic reversion from working to protection

1: N Protection1: N Protection

1:N Card Protection

1:N Protected Linear Network

Path Protection

A

B C

D E

path protectionswitching

within 30 ms

VC-n

working path

protection path

VC-n

Unidirectional Operation

Bidirectional Operation

Unidirectional Path Switched Ring/SNCP

UPSR/SNCP

In Uni-directional rings,signal is being carried in only one direction that is either clockwise or anti-clockwise

Only in case of failure there will be a switching in the other direction also

In the above example let us assume that there is an interruption in the circuit between A and B.Direction y is unaffected by this fault , an alternative path must however,be found for direction X

The connection is therefore switched to the alternative path in the Network elements A and B

The other network elements(C and D) switch through the back up path

A simpler method is to use the so-called path switched ring Traffic is transmitted simultaneously over both the working

line and the protection line If there is an interruption, the receiver (in this case

A)switches to the protection line and immediately takes up the connection

UPSR/SNCP

Advantages of UPSR/SNCP

• Unidirectional protection switching is a simple scheme to implement and does not require a protocol.

• Unidirectional protection switching can be faster than bidirectional protection switching because it does not require a protocol.

• Under multiple failure conditions there is a greater chance of restoring traffic by protection

Unidir. MS Dedicated Protection Ring - normal State

Unidir. MS Dedicated Protection Ring - failed State

MSSP• In this type bandwidth is segregated in to three ways

• Working Traffic

• Extra Traffic

• Non Pre-emptible unprotected Traffic (NUT)

2F Multiplexer Section Shared Protection

2 Fiber MSSP – Normal condition2 Fiber MSSP – Normal condition

A F

B

C D

E

ADM

TributaryTributary

One Fiber

2 Fiber MSSP - Fault2 Fiber MSSP - Fault

A F

B

C D

E

ADM

TributaryTributary

Node A

Node D

Node B Node C

Node ENode F

workingprotection

Fiber 1

Fiber 2

2F MSSP2F MSSP

Node A

Node D

Node B Node C

Node ENode F

MS ProtectionSwitching

within 50 ms

Fiber 1

Fiber 2

2F MSSP2F MSSP

In this network connection between network elements are bi-directional.the overall capacity of the network can be split up for several paths each with one bi-directional working line

While for unidirectional rings,an entire virtual ring is required for each path

If a fault occurs between neighboring elements A and B,network element B triggers protection switching and controls network element A by means of the k1 and k2 bytes in the SOH

2F MSSP (Multiplexer Section Shared Protection)2F MSSP (Multiplexer Section Shared Protection)

4F MSSP

4 Fiber MSSP - Normal4 Fiber MSSP - Normal

A F

B

C D

E

ADM

TributaryTributary

4 Fiber MSSP (Span Switch) - Fault4 Fiber MSSP (Span Switch) - Fault

A F

B

C D

ETributary

Tributary

Protection Fiber 3+4Working Fiber 1+2

4 Fiber MSSP (Ring Switch) - Fault4 Fiber MSSP (Ring Switch) - Fault

A F

B

C D

ETributary

Tributary

Protection Fiber 3+4Working Fiber 1+2

NODE A NODE B

NODE D NODE E NODE F

NODE C

NODE A NODE B


NODE C

STS-n

STS-n

NODE A NODE B


NODE C

Even greater protection is provided by bi-directional rings with 4 fibers

Each pair of fibers transports working and protection channels

This results in 1:1 protection, i.e.100% redundancy This improved protection is coupled with relatively high

costs

4F MSSP4F MSSP

Advantages of MSSP

• With bidirectional protection switching operation, the same equipment is used for both directions of transmission after a failure.

• With bidirectional protection switching, if there is a fault in one path of the network, transmission of both paths between the affected nodes is switched to the alternative direction around the network. No traffic is then transmitted over the faulty section of the network and so it can be repaired without further protection switching.

• Bidirectional protection switching is easier to manage because both directions of transmission use the same equipments along the full length of the trail.

Protected Add/ Drop With MSP on 1 Pair of Tribs

COMBINATIONS PROTECTIONS

Dual trib to aggreagate with MSPon aggregates and MSP on 2 tribs

Protected Add/Drop with Card Protection on 1 Trib

Unprotcted Trib to Trib with Card Protection on 2 Tribs

Protected Trib to Trib with cp on 1 trib and MSP on 2 tribs

Node Element Ring

Types of Traffic Matrix

Advantage of SDH :

The SDH is based on global international standard.

Faster provision of services by remoter control.

In service performance monitoring of signals.

Possibility of control of circuit routing by customers.

Easier management of bandwidth.

Remote test access and maintenance from a central location.

Optical Transmission interfaces.

It will allow existing PDH hierarchies to be transported in the SDH.

Reduced amount of equipment in the network and hence savings on accommodation and power consumption.

Greater equipment reliability due to advanced electronic circuitry and 1+1 protection.

Improved protection facilities for transmission failures.

Advance network management features.

Single stage multiplexing into the higher bit rates.

Cross connect functionality can be distributed around the network.

Advantage of SDH (Contd.):

Software and configuration information can be downloaded to network elements.

Reliability of ring networks using path protection.

Implementation of new broadband services such as ATM is made easier.

There are cost saving and increased revenue to the network operation.

Equipment from different manufacturer can be connected together in the same network.

Advantage of SDH (Contd.):

COMPARISION OF SDH / PDH

PDH SDH

The reference clock is not synchronized throughout the network

The reference clock is synchronized throughout the network.

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

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

PDH system has different frame structures at different hierarchy levels.

SDH system has consistent frame structures throughout thehierarchy.

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

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

PDH SDH

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

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)

PDH system does not bear capacity to transport B-ISDN signals.

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

Limited amount of extra capacity for user / management

It will transport service bandwidths Sufficient number of OHBs is available

Bit - by - bit stuff multiplexing Byte interleaved synchronous multiplexing.

Comparison (Contd.)

Sdh

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