Sdh/sonet

SDH T ra nsport Sy st ems

SYNCHRO NIZATIO N O F DIG ITAL S IG NAL :

SYNCHRO NO US SI GNAL :

 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.

Req uir ement O f Synchronou s Di gital Hierar chy ( S DH ) 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/TET28 Tributary Card E3/DS3 - TE31 3 E3/DS3 Tributary Card - TE33 Ethernet Tributary Card РETC Ethernet Tributary Card РETCFT TP01 TP01FT STM1 card ΠA011 or A012 STM-1e/E4 Tributary Card - A1E4 STM-1e Tributary Card - A012E STM-4 Tributary Card - A041,A041VLR TR01

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 Elements

The Network E lement s of SDH Net work :

   

Regenerator (Reg.) Te rmi nal Mu lt iple xe r (TM) Add/Dro p M ulti plexe r (ADM) Digita l Cro ss C onnect (DXC)

Reg enerat or (Re g.)

ST M- N

Re genera tor

ST M- N

It ma inly p er for ms 3R fun ct ion : 1R – Re am pli ficatio n 2R – Re timing 3R – Re sha ping It re ge ner at es th e c loc k a nd am plifie s th e inc oming dis to rt ed an d a tt enu ate d signal. It de riv e the c loc k signal f ro m t he incom ing da ta st re am.

Regenerator

Term inal Multiplexer (TM

PDH SDH

)

Term inal Multiplexer

ST M- N

It com bines th e Ple sio nc hro no us an d s ync hro no us input s ig na ls into hig he r bit r at e ST M- N S igna l.

Terminal Multiplexer

Tributaries

1 2 3

5

6

7

1

2

3

4

1

Line Interface (aggregate)

. . (Optional)

Ad d/Drop M ult iplex er (ADM )

ST M- N

Add / Drop Multiplexer PDH

SDH

ST M-N

Add/Drop Multiplexer

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

Drop

1

Tributaries

2 3 ... 17

1 5 60 21 25 34 3

1

Add

17 5 60 21 25 34 3

Synchronous Transport Module

ADM makes po ssibil it ies of Extraction from & insertion into high speed SDH bit streams of Plesiochronous and lower bit rate synchronous signal. Ring structure of network which provides the advantage of automatic back-up path switching in the event of fault.

Digital Cr os s Co nnect (DXC)

STM- 16 STM- 4 STM- 1

STM-1 6 STM-4 STM-1

140 Mb it/s 34 Mbit/ s 2 Mbit/ s

140 Mbit /s 34 Mbit/ s 2 Mbit/ s

Cro ss - Co nn ec t

Digital Cross Connect (DXC) 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 Connect Types

– Wideband  VT/DS1 level



Broadband  STS-n/DS3 level &



Narrowband  DS0 level

SDH NE: Digital cross connect (DXC) 1

Ports

Ports

Ports

21

Ports 25

TYPI CAL LA YO UT OF SDH LA YE R Gen era l view o f Pa th Se ction de sign at ion s PD H AT M IP

SDH mult iplex er

SDH Regenerator SDH

SDH

Re gen erato r Se cti on

# Crossconnect

SDH

SDH multiplexer

Re gen erato r Se cti on

Mul ti pl ex Se cti on

Mul ti pl ex Se cti on

Path

PDH AT M IP

Topologies

Network Configurations  Point to Point  Point to Multipoint  Mesh Architecture  Ring Architecture

SDH Network Topologies

Re ge ne rato r

Termi nal Mul tipl exer (TM)

Tributaries

Termi nal Mul tipl exer (TM)

Ad d Drop Mul tipl exer (ADM )

Termi na l Mul tipl exe r (TM)

Tributaries

Tributaries

Point-to -P oin t Ne two rk

Tributaries

Ch ain Ne twork

Termi na l Mul tipl exe r (TM)

Ring Network

Add Drop Multiplexer (ADM) Add Drop Multiplexer (ADM)

Add Drop Multiplexer (ADM)

Tr ibut ar ies

Add Drop Multiplexer (ADM)

Tribu tar ies

Add Drop Multiplexer (ADM) Trib utar ies

Add Drop Multiplexer (ADM) Tribu tar ie

Tr ibut ar ies

Tribu tar ies

Exchange

Tribu taries

Add Drop Multiplexer (ADM)

Add Drop Multiplexer (ADM)

Add Drop Multiplexer (ADM)

Exchange

Add Drop Multiplexer (ADM)

STM-4 Rin g

Add Drop Multiplexer (ADM) STM-1

14 0Mbit/ s 2Mb it/s

Add Drop STM-1 Multiplexer (ADM)

2Mbit /s

Exchange

140 Mbit/ s

2Mb it/s

ADM linear route ( Bus )

ADM Ring X

X

X

X

X X

X

X

Tributa rie s

Add /Dro p & Cross Con nect Mux

Add Drop & Cross c on ne ct Mux

STM-N Lin ks

Tr ibut ar ies

Trib utar ies

Add Drop & Cross c onn ec t Mux

Add Drop & Cross con ne ct Mux

Tribu tar ies

Mesh Network

Standard MS Rates : Optical Signals

Electrical Signals

MS Rate

DS0

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

O p tic a l L evel O O O O O O O O O O

C C C C C C C C C C

-

1 3 9 12 18 24 36 48 96 1 92

E le c tric a l L in e R a te L evel ST ST ST ST ST ST ST ST ST ST

S S S S S S S S S S

-

1 3 9 12 18 24 36 48 96 192

5 1 4 6 9 1 1 2 4 9

1 5 6 2 3 2 8 4 9 9

.8 4 0 5 .5 2 6 .5 6 2 .0 8 3 .1 2 4 4 .1 6 .2 4 8 8 .3 7 6 .6 5 3 .2

0 0 0 0 6 0 2 4 8

0 0 0 0

P a y lo a d ra te ( M B ps )

5 1 4 6 9 1 1 2 4 9

0 5 5 0 0 2 8 4 8 6

.1 1 2 0 .3 3 1 .0 0 1 .3 4 2 .0 1 0 2 .6 0 4 .0 0 5 .3 1 0 .7 2 1 .5

6 8 4 6 8 3 7 5 0

O v e rh e a d R a te ( M bps )

8 2 6 2 2

1 5 1 2 3 4 6 8 1 3

.7 2 8 .1 8 4 5 .5 5 0 .7 3 1 .1 0 1 .4 7 2 .2 0 2 .9 4 6 5 .8 3 1 .7

SD H E q u iv a le n t

STM - 1 2 6 4 2 8 4 88 76

STM - 4

STM - 16 STM - 64

Frame Structure

Transport Module STM-1 = 155 Mbit/s STM-4 = 622 Mbit/s STM-16 = 2.5Gbit/s STM-64 = 10Gbit/s Payload

STM-4

STM-n (n >1)

One Section overhead

STM-1 frame structure • 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 Sdh22.exe

Data Rate  Overall 9 rows*270 columns*8000frames/sec*8bits/byte = 155.52Mbps  9 rows*261 columns*8000frames/sec*8bits/byte =150.336Mbps  User Data/ Payload 9 rows*260 columns*8000frames/sec*8bits/byte

STM-1 frame structure

Check your learning section1

STM-1 frame structure 1-3 rows

RSOH

4th row

AU Pointer

5-9 rows

MSOH

9 Columns

PAY LOAD

261 Columns 270 Columns

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.

Byte Interleaved multiplexing

SD H

M U X L in e S ig n a l STM - 4

S T M -3

T rib u ta ry S ig n a ls S T M -1

TU Columns Bytes/ Bandwidth Format Frame

Payload

TU 11 3

27

1.728Mbps DS1

TU 12 4

36

2.304Mbps E-1

TU 2

108

6.912Mbps DS-2

12

SDH Over Heads

STM-1 Section Overhead Y

Y

1* 1*

Y- 1001 SS11 (S unspecified) 1*- All 1’s

Regenerator Section Overhead 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

RSOH (contd..) B1- Bit Interleaved parity (BIP-8) • 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

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

STM Regenerator Section Overhead Regenerator Section Overhead : • Performance monitoring (STM-n signal) • Local orderwire • Data communication channels to carry information for OAM&P • Framing

MS Overhead B2 – Bit Interleaved parity (BIP – 24) • 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

MSOH (contd..) 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 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

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

APS (contd..) Protection Switching is initiated due to : • Signal failure • Signal degradation • In response to commands from a local craft terminal or a remote network manager.

MSOH (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 regenerators M1 - Remote Error indication • It is used to indicate the MS layer remote error indication (MS-REI)

MSOH (contd..) 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.

SDH Pointers H1

Y

Y

H2 1

1

H3 H3 H3

Use of Pointers H1 & H2 = VC payload pointer • It indicates the starting position of VC H3 = Negative Justification • It is also used for justification 1 = All 1’s • AU pointer is also used for concatenation Y = 1001SS11 (S bits unspecified) • 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 VC3/VC-4 To accomplish this, a process known as byte stuffing is used

Pointers (contd..) •

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. pointer justification.exe

Pointers (contd..) 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

AU – 4 Positive Pointer Justification H1 Y Y

H2 1 1 H3 H3 H3

Points out Start of VC-4

VC-4 Boundary

Positive justification H1 Yopportunity Y H2 1 1 H3 H3 H3 To next Row To next Row Points out Start of VC-4

H1 Y Y

VC-4 Boundary

H2 1 1 H3 H3 H3

Points out Start of VC-4

VC-4 Boundary

AU – 4 Negative Pointer Justification H1 Y Y

H2 1 1 H3 H3 H3

Points out Start of VC-4

VC-4 Boundary

Negative justification opportunity H1 Y Y

H2 1 1

From next row From next row

Points out Start of VC-4

H1 Y Y

VC-4 Boundary

H2 1 1 H3 H3 H3

Points out Start of VC-4

VC-4 Boundary

Multiplexer Section Overhead MS Alarm indication signal



Performance Monitoring of individual STM-1’s



Protection Switching Information



MS Remote Defect Indication (RDI)



Data channels for OAM&P



Pointer to commencement of synchronous payload envelope 

Express order-wire



Path OverHead

TCM – Tandem Connection Monitoring

Path Overhead 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

POH (contd..) C2 – Signal Label • It is defined to indicate the composition or the maintenance of the VC-4 Binary 0000 0000 0000 0001 0000 0010 0000 0011 0000 0100

Hex 00 01 02 03 04

Mapping Unequipped Equipped,non specific TUG structure Locked TU 34 / 45 Mbps into C3 (async)

0001 0010 0001 0011 0001 0100 0001 0101

12 13 14 15

140 Mbps into C4 (async) ATM MAN (DQDB) FDDI

POH (contd..) G1- Path status

FEBE

FERF

UNUSED

• 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..) 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

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 BIP2 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.

STM Path Overhead



Performance Monitoring of STM SPE



Path Status



Path Trace



Signal Label (Unequipped or Equipped)

STM-4 Section OverHead

MAPPING

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)

Container • 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)

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

+

PAYLOAD

=

POH

PAYLOAD

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

Virtual Container • 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 (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.

Tributary Unit • 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 Group • 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)

Administrative Unit • 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

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

SDH Generalised Multiplexing Structure

Mapping of 2Mbps into STM – N signal

A corresponding arrangement is used for demultiplexing

Mapping of 2Mbps into STM – N 2.048 Mbps

1 2 3

(E1)

32

32 Bytes

Stuffing Bytes

C-12

1 23

32

34 Bytes

POH (Lower Order)

VC-12

1 23

32

35 Bytes

Mapping of 2Mbps into STM – N Pointer

TU-12 36 Bytes

TU 12 is arranged Into Matrix of 9 X 4

9 Rows

4 Columns

Mapping of 2Mbps into STM – N TU-12

TU-12

TU-12

9 Rows

4 Columns

4 Columns

4 Columns

Multiplexing

TUG-2

9 Rows

12 Columns

Mapping of 2Mbps into STM – N 7 TUG-2s

Stuffing Bytes

X 7 TUG-2

TUG-3(multiplexing)

TUG 3

86 Columns

84 Columns

Mapping of 2Mbps into STM – N TUG - 3

TUG - 3

TUG - 3 86 Columns

VC - 4

X 3 TUG–3

HOPOH Stuffing Bytes

258 Columns 261 Columns

Mapping of 2Mbps into STM – N 9 rows

POH

VC - 4

Pay Load

261 Columns

AU Pointer

h Row

9 Columns

POH

AU – 4 (Adding Pointer)

Pay Load

261 Columns mapping E1.exe

SYNCHRONIZATION

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.

Pr im ar y Refe ren ce Cl ock ( PRC ) Strat um 1

SYNCHRONIZATION HIERARCHY

DIGI TAL EX CHANGE Str atum 1

TRANSMISSION

Digit al Exch an ge Str atum 2

NE TWORK

Digit al Exch ang e Str atum 2

Digit al Exc han ge Stratu m 2

Trans missio n Ne twork

Digita l Excha ng e Stratu m 3

Di gita l Excha nge Str atum 3

Digita l Excha ng e Stratum 3

Digita l Excha ng e Str atum 3

Digita l Excha ng e Stratum 3

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 HIERARCHY STRUCTURE

•

•

•

•

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 1 2 3 4

Accuracy Skip Rate Notes 2.523/Year PRC 10*10-11 11.06/Day Electronic Switch Sys 1.6*10-8 4.6*10-6 132.48/Hour DCS PBX, CPE 3.2*10-5 15.36/Min

SYNCHRONIZATION All network elements are synchronised to a central clock ➄The central clock is generated by a high precision primary clock(prc)-G.811 (10x10-11 ) ➄Clock is distributed throughout the network,this signal is passed on to the Sub-ordinate Synchronization units (ssu) and synchronous equipment clock (sec)

Primary

Secondary

Selector

Internal Clock

Auotmatic Switch Timing Signal Generator (TSG)

Internal Diagram of BITS

S1 S ynchronizatio (S SM B)

n stat us mess age b yte

• 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 and a PRC clock source: . Configuration of network elements for clock distribution . Clock distribution behavior when a fault occurs During 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

TYPI CAL LA YO UT OF SDH LA YE R Gen era l view o f Pa th Se ction de sign at ion s PD H AT M IP

SDH mult iplex er

SDH Regenerator SDH

SDH

Re gen erato r Se cti on

# Crossconnect

SDH

SDH multiplexer

Re gen erato r Se cti on

Mul ti pl ex Se cti on

Mul ti pl ex Se cti on

Path

PDH AT M IP

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.

The ad vantag e of the alarm s moni tori ng are illustrat ed as follow s :  Com plet e f ailur e of a con nec tion re sults, fo r exa mple , in a LOS ala rm ( los s o f s ign al) in t he re ceiving n et wo rk e lement .  This alar m trigg er s a c omplet e c hain of sub se que nt messa ges in t he for m of AIS .  The t ran sm itt in g side is inf or med o f t he f ailur e by the r et urn of a n RDI alar m (r em ote d efe ct indic ation ).  The a lar m m ess age s a re tr an smit te d in defin ed by tes in t he TOH o r PO H.

Types of Alarms  Equipment Alarms  Facility Alarms

Wh at is dif fere nc e bet ween a De fect a nd a Failure?



A defe ct is a de te ction of an alar m such as los s of signa ls, los s of fr ame s. AIS los s of exc ess ive err or s.



A fail ure is a def ec t tha t per sist s be yon d a maxi mum time alloc at ed. It is us ed to ac ce ss to integ rat e Aut om atic Pro te ction Switch ing ( 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

Lo ss O f S ignals ( L OS ) :

 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.

@ RSOH OOF

LOF

TIM(J0)

DCC Fail

Out of Fra me ( OO F ) :  This situation occurs when 4, or in some implementations, 5 consecutive SDH frames are received with invalid framing patterns(A1 and A2 bytes)  The maximum time to detect OOF is therefore 625Ms  The OOF clears when consecutive SDH frames are received with valid framing patterns

Loss O f Fram e ( LO F ) :

 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 AI S :

This This

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

The 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 and H3 bytes pointer bytes plus all bytes of associated VC-4) Removal Removal of AU-4 path AIS is detected when three consecutive valid AU pointers are received with normal NDF’s

TU-12 AIS :

 This is sent downstream to alert the Lower Order Path Terminating Equipment(LOPTE) of a detected TU-12 LOP state or a received TU-12 path AIS  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 v4 plus all bytes of associated VC)  The TU-12 AIS detected by the LOPTE when all 1’s pattern is received in bytes v1 and v2 or three consecutive multiframes.  Removal of TU-12 is detected when three consecutive valid TU12 pointers are received with normal NDF’s

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.

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).

@ HOPOH TIM(J1)

PLM(C2)

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

LOM(H4)

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

Lo ss O f P oint er (LO P )

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 M ultifram e (LO M )



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)

TIM/PLM(J2)

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

Som e SDH alarm s : SDH MUX

STM-1

SDH MUX

MS-REI

SDH MUX

RF I

Ca bl e Cut

STM-1

Ex cess ive Err ors

SDH REG EN STM-1

Ca bl e Cut STM-1

STM-1

Loss of Signal

SDH MUX

Los s of Sign al SDH MUX

Los s of Fr ame SDH MUX

SDH REG EN

Z

RF I

SDH REG EN

STM-1

MS -AIS

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

Schem es

 Linear Protection (1+1,1:1,1:N)  Ring protection: Unidirectional (UPSR/SNCP, MSP) Bi-directional (2FMSSP, 4FMSSP)

1+1 P rotect ion  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 P rotect ion SDH Multiplexer

SDH Multiplexer

Multiplex Section

Working Section Protection Section

SDH Multiplexer

SDH Multiplexer

Working Section Fault Protection Section

1+1 Card Protection

1+1 Protected Linear Link

1:1 Prot ec tion(Ded icate d P rote ction)  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: N P rote ction

 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 Card Protection

1:N Protected Linear Network

Path Protection working path

B VC-n

C path protection switching within 30 ms

A

D

protection path

VC-n

E

Unidirectional Operation

Bidirectional Operation

Unidirectional Path Switched Ring/SNCP

UP SR/S N CP  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

UP SR/ SNCP

 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

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 condition F

A

Tributary Tributary B

E

ADM

C

D One Fiber

2 Fiber MSSP - Fault F

A

Tributary Tributary B

E

ADM

C

D

2F M SSP Node A

Node B

Node C

Fiber 1

Fiber 2 working protection

Node F

Node E

Node D

2F MS SP

Node A

Node B

Node C

Fiber 1

Fiber 2 MS Protection Switching within 50 ms

Node F

Node E

Node D

2F MSS P (M ultiplexer S ec tion S hared Prot ec tion)  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

4F MSSP

4 Fiber MSSP - Normal A

F

Tributary Tributary

E

B

ADM

C

D

4 Fiber MSSP (Span Switch) - Fault A

F

Tributary Tributary B

E

C Working Fiber 1+2

D

Protection Fiber 3+4

4 Fiber MSSP (Ring Switch) - Fault A

F

Tributary B

Tributary

C Working Fiber 1+2

E

D Protection Fiber 3+4

NODE A

NODE D

NODE B

NODE C

NODE E

NODE F

STS-n NODE A

NODE D

NODE B

NODE C

NODE E

NODE F

STS-n

NODE A

NODE D

NODE B

NODE C

NODE E

NODE F

NODE A

NODE D

NODE B

NODE C

NODE E

NODE F

NODE A

NODE D

NODE B

NODE C

NODE E

NODE F

NODE A

NODE D

NODE B

NODE C

NODE E

NODE F

4F MSS P  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

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.

COMBINATIONS PROTECTIONS Protected Add/ Drop With MSP on 1 Pair of Tribs

Dual trib to aggreagate with MSP on 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

Advant age 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.

Advant age of SDH (Cont d.): 

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.

Advant age of SDH (Cont d.): 

Software and configuration information can be downloaded to network elements.

 

Reliability of ring networks using path protection.



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



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

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

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 the hierarchy.

Physical cross-connections on the Digital cross- connections are same level on DDF are forced if any provided at different signal levels and in different ways on NMS

Comparison (Contd.) 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,STM16,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.