SDH - BASICS

DIGITAL TRANSMISSION TECHNOLOGIES

PLESIOCHRONOUS DIGITAL HIERARCHY (PDH)

SYNCHRONOUS DIGITAL HIERARCHY (SDH)

MUXMUX

PDH•Almost synchronous signals

SUMMARY OF PDH TRANSMISSION RATES

64 Kbps 2.048 Mbps 8.448 Mbps 34.368 Mbps 139.264 Mbps

Ch 00Ch 01Ch 02Ch 03

Ch 31Ch 30

Ch 28Ch 29

E1

E1

E1

E1

E2

E2

E2

E2

E3

E3

E3

E3

140 Mbps

MUXMUX

MUXMUX

MUXMUX

MUXMUX

x4x4x32x32 x4x4 x4x4

PDH Hierarchy

140

34

34

8

8

2

140

34

34

8

8

2

34 Mbps

8 Mbps

2 Mbps

140 Mbps 140 Mbps

2 Mbps

64 Kbps

64 Kbps

Plesiochronous Drop/Insert

Problems of PDH

• The Plesiochronous Digital Hierarchy had a number of problems:

– Each multiplexing section has to add overhead bits for justification

(higher rate -> more overhead)

– Each part of the world has its own transmission hierarchy (expensive

interconnection equipment)

– Justification (bit stuffing) spreads data over the frame

• add-drop-multiplexers are hard to build

• extract a single voice call -> demultiplex all steps down

• switching of bundles of calls (n * 64 kbit/s) is difficult

• (every switch has to demultiplex down to DS0 level)

– The management and monitoring functions were not sufficient in PDH

– PDH did not define a standard format on the transmission link

• Every vendor used its own line coding, optical interfaces etc.

• Very hard to interoperate

SSynchronousynchronous

DDigitaligital

HHierarchyierarchy

Introduction SDH Frame structure SDH Principles Multiplexing Structure Network Elements Network Topologies Alarms Timing sources Protection Ethernet over SDH Management functions Optical technology SDH Measurements

OUT LINE

INTRODUCTION TO SDH

WHAT IS SDH

Synchronous Digital Hierarchy

The SDH is hierarchically organized set of Digital transport structures which have been standardized by CCITT for Transmission of pay loads in Transmission Networks

SDH - Synchronous Digital Hierarchy A Modular, Layered & Organized Architecture using Synchronous Multiplexing

Technique.

A Standardized hierarchical Set of Digital Transport Structures for transport of suitably Adapted Payloads.

A Set of Improved & Standardized Management Interfaces and Functions, allowing Digital Transmission Systems to inter-work in a multi-vendor environment.

Three major goals:

– Avoid the problems of PDH

– Achieve higher bit rates (Gbit/s)

– Better means for Operation, Administration, and Maintenance

(OA&M)

What is SDH ?

Common standard - Multi vendor.

Better Management – NMS.

Fast provisioning.

Better Network utilization.

Better Network survivability.

Simpler hand over.

Support future services.

SDH FEATURES

SDH FRAME STRUCTURE

1

3

4

5

9

9 bytes 261 bytes

9 rows

AU - POINTER

MULTIPLEX

SECTION

OVERHEAD

REGENERATOR

SECTION

OVERHEAD

270 bytes

STM PAYLOAD

SDH PRINCIPLES

Plesio.signal

C VC AU AUG STM-1

TU TUG VC

TU

AU

POH

+TU-PTR+AU-PTR

+AU-PTR SOH

HIGHER ORDER

CONTAINER TERMINOLOGY

C.. CONTAINER

VC.. VIRTUAL CONTAINER

TU.. TRIBUTARY UNIT

TUG.. TRIB.UNIT GROUP

AU.. ADMINISTRATIVE UNIT

AUG.. ADMINISTRATIVE UNIT GROUP

PTR.. POINTERSOH.. SECTION OVERHEADPOH.. PATH OVERHEAD

CONTAINERS

• The term container C describes a defined network- synchronized transmission capacity.

•Every piece of tributary information is interleaved in containers.

•The following containers are distinguished:

Designation Signal to be transmitted

C-11 1,544 kbit/s

C-12 2048 kbit/s

C-2 6312 kbit/s

C-3 44,736 kbit/s or 34,368 kbit/s

C-4 139264 kbit/s

VIRTUAL CONTAINERS

• Apath overhead is added to each container.This unit is called a virtual container

•POH carries information on supervision and maintenance of a path switched in the network.

•POH ensures reliable transport of the container from signal source to destination.

•All containers transmitted in one larger container are termed as LO containers.

•Those containers that are transmitted directly are termed as HO containers.

•The following VCs are distinguished:

VC-11, VC-12, VC-2 LO Containers

VC-3, VC-4 HO Containers

TRIBUTARY UNIT

• The tributary unit TU is termed as the component of the higher – order container inside which the embedded LO VC can vary plus the corresponding pointer.

•The following TU are distinguished :

TU –11 , TU – 12 , TU – 2 , TU – 3 .

TRIBUTARY UNIT GROUP

•Before being interleaved in the higher order container, the TU are combined into a group , ie,byte interleaved. Such a group is called a TUG.

•The following TUG have been defined:

TUG – 2 , TUG – 3

ADMINISTRATIVE UNIT

• The component of the STM-1 frame within which the VC is able to float is termed as administrative unit.

• The corresponding pointer is called the AU-pointer.

• It is possible to transmit the following AU in the STM-1 frame:

1 X AU – 4

3 X AU – 3 ADMINISTRATIVE UNIT GROUP

• Several AU are byte-interleaved to one AU group (AUG).

Circuit Layer Network

Multiplex Section Layer

Regenerator Section Layer

Physical Medium Layer

VC-11

VC-3

VC-12 VC-2 VC-3

VC-4

Circuit Layer

Path Layer

TransmissionMedia Layer

Section Layer

Higher OrderPath Layer

Lower OrderPath Layer

SDH Network - A Layered Model

SDHSDH

MUXMUX

SDH SDH

MUX MUX

SDH SDH

MUXMUX

1 63. . . . . .

SDHSDH

MUXMUX

1 63. . . . . .

TMNConfigControlSecurityStatistics

DiagnosticSoftware upload

MasterClock

Synchronous Technology

STM1/4/16/64

SDH Interfaces

45 Mbps34 Mbps6 Mbps

1.5 Mbps

FDDI

MAN

ISDN-B

STM-1

Any Speed (TU-n)

One Step Multiplexing

ISDN

LAN

2 Mbps

ATM

140 Mbps

SDH Transport RatesSignal Level

STM-1

STM-4

STM-16

STM-64

Rate (Mbps)

155.52

622.08

2488.32

9953.28

Capacity Voices63 E13 E31 E4

252 E112 E3 4 E4

1008 E148 E316 E44032 E1192 E364 E4

189014401920

756057607680

30240230403072012096092160

122880

Multiplexing Structure

• Line Terminal Mux ( LTM )

• Add Drop Mux ( ADM )

• SDH Regenerator

• Synchronous Digital Cross Connect ( SDXC )

BASIC SDH NETWORK ELEMENTS

Terminal Multiplexer

Add/Drop Multiplexer

Regenerator

Digital Cross Connect DXC

TYPICAL NETWORK TOPOLOGIES

Point to Point

Rings

Mesh

POINT TO POINT

TERMINAL

MULTIPLEXER

TERMINAL

MULTIPLEXER

WORKING PATH

PROTECTION PATH

TRIBUTARY SIDE LINE SIDE TRIBUTARY SIDE

RING TOPOLOGY

ADM

ADM ADM

ADM

TRIBUTARY SIDE TRIBUTARY SIDE

TRIBUTARY SIDE

TRIBUTARY SIDE

EASTWEST

EAST

WEST

WESTEAST

WEST

EAST

MESH TOPOLOGY

ALARMS

LOS/LOFRS-TIM

BIP Err.

"1"AIS

MS-AIS "1"

MS-BIP Err.

MS-REI

MS-RDI

AU-AIS

AU-LOP

AIS

"1"

HP-UNEQ

HP-TIM

HP-BIP Err.

HP-REI

HP-RDI

"1"AIS

TU-AIS

TU-LOP

LOM

HP-PLM

LP-UNEQ

LP-TIM

LP-BIP Err.

LP-REILP-RDI

LP-PLM

"1"

"1"

"1"

AIS

AIS

RegeneratorSection

MultiplexSection

Higher OrderPath

Lower OrderPath

(J0)

(B1)

(K2)

(B2)

(M1)

(K2)

(C2)

(J1)

(B3)

(G1)

(G1)

(H4)

(C2)

(V5)

(J2)

(V5)

(V5)

(V5)

(V5)

Alarm Test at STM-N port

CLOCK SUPPLY HIERARCHY STRUCTURE

• If synchronization is not guaranteed, this can result in considerable degradation in network functionality and even total failure. To avoid such scenarios, all NEs are synchronized to a central clock.

• This central clock is generated by a high-precision, primary reference clock (PRC) unit conforming to ITU-T recommendation G.811.

• This clock signal must be distributed throughout the entire network.

• A hierarchical structure is used, in which the signal is passed on by the subordinate synchronization supply units (SSU) and synchronous equipment clocks (SEC). The synchronization signal paths can be the same as those used for SDH communications.

TIMING SOURCES

AUTOMATIC PROTECTION SWITCHING

LINEAR PROTECTION

RING PROTECTION

FOR POINT TO POINT CONNECTIONS

FOR RING CONNECTIONS

PROTECTION SCHEMES 1+1 Protection

1:1 Protection

1:N Protection

PROTECTION SCHEMES MULTIPLEX SECTION SHARED PROTECTION RING (MS-SPRING)

SUB NETWORK PROTECTION (SNC)

LINEAR PROTECTION SCHEMES• In 1+1 protection scheme the working channel is permanently bridged to the W & P path.

• In 1:1 protection scheme the working channel is not permanently bridged to the W & P path and extra traffic is possible on the Protection path.

• In 1:n protection scheme for n working channels 1 backup path is provided.

MULTIPLEX SECTION SHARED PROTECTION RING (MS-SPRING)

• For MS shared protection rings, the working channels carry the normal traffic signals to be protected while the protection channels are reserved for protection of this service.

• Protection channels may be used to carry extra traffic when not being used for protection of normal traffic.

• Normal traffic signals are transported bi-directional over spans.

• The pair of tributaries (incoming and outgoing) only uses capacity along the spans between the nodes where the pair is added and dropped.

• Switch action by using the APS bytes (K1 and K2 bytes in the MSOH of the protection section).

SUB NETWORK PROTECTION

• SNC protection is a linear protection scheme which can be applied on an individual basis to VC-n signals.

• Sub network connection protection is a dedicated protection mechanism that can be used on any physical structure (i.e. meshed, rings, or mixed). It may be applied at any path layer in a layered network.

• SNC protection operates in a unidirectional protection switching manner.

• 1+1 Uni-directional protection switching is generally used. In this architecture, there is no APS channel required.

SUB NETWORK PROTECTION

ETHERNET OVER SDH

The Status TodaySDH/ SONET - is the deployed technology in the core network with huge investments in capacity!

Ethernet - is the dominant technology of choice at LANs and well known at all enterprises worldwide!

Data traffic is still growing, but only at a slower speed than expected

All network topologies focusing on an IP/Ethernet ONLY approach are shifted to long-term future.

Bring SDH/SONET and Ethernet together!

Customer needs Ethernet

Typical Ethernet Traffic

Connections

100

25

50

75

Mbit/s

time1 2 3 4

Ethernet Packet

Problem: How can we efficiently transport Ethernet over an existing SDH/SONET network?

Example: For 10M available SDH - Containers are...

VC-12 ...too small !

2.176 Mbit/s

VC-3 ... inefficient20%

48.38 Mbit/s

OR

Customer 3 = 100M

Customer 2 = 60M

Customer 1 = 10M

VC Nomenclature

VC-nVirtual Container n

n=4, 3, 2, 12, 11

Defines the type of virtual containers, which will be virtually concatenated.

-XNumber of

virtuallyconcatenated

containers

All X Virtual Containers form together the

“Virtual Concatenated Group” (VCG)

vIndictor for

Virtual Concatenation

v = virtual concatc = contiguous concat

Virtual Concatenated Group (VCG) of X VC-n containers!

STM-16

VirtualConcatenation

VC-4-7v

AU-4 Pointers

MSOH

RSOH

VC-4-5 VC-4-6 VC-4-7 VC-4-8

VC-4-9 VC-4-10 VC-4-11 VC-4-12

VC-4-13 VC-4-14 VC-4-15 VC-4-16

VC-4-1 VC-4-2 VC-4-3 VC-4-4

Pointers

MSOH

RSOH VC-4-1 VC-4-2 VC-4-3 VC-4-4

VC-4-5 VC-4-6 VC-4-7 VC-4-8

VC-4-9 VC-4-10 VC-4-11 VC-4-12

VC-4-13 VC-4-14 VC-4-15 VC-4-16

The blocks can start at any position in the payloadThe block consists of distributed VC-nsEach container has it‘s own pointer

SDH - Virtual Concatenation

C-12-5v

C-12-12v

C-12-46vC-3-2v

C-3-4v

C-3-8vC-4-6v

C-4-7v

NewSDH

92%

98%

100%100%

100%

100%89%

95%

C-4-64v 100%

Ethernet

ATM

ESCON

Fibre Channel

Fast Ethernet

Gigabit Ethernet

data

10 Mbit/s

25 Mbit/s

200 Mbit/s

400 Mbit/s800 Mbit/s

100 Mbit/s

1 Gbit/s

10 Gb Ethernet 10 Gbit/s

efficiency

100M Ethernet STM-1= 64 x VC-12

VC-12-5v

VC-12-46v

2x 10M Ethernet VC-12-5v

8x E1 Services

Example:

More services integrated- by using VC!

MANAGEMENT FUNCTIONS• The functions of a TMN are : operation,administration, maintenance, and provisioning (OAM&P). This includes monitoring of network performance and checking of error messages.

•SDH includes a management layer where the communication is through the data communication channel (DCC) time slots (D1 – D12) in the interface rate.

•Channels D1 to D3 with a capacity of 192 kbps (DCCp) are used for SDH-specific NE management. Channels D4 to D12 with a capacity of 576 kbps (DCCm) can be used for non SDH-specific purposes.

Laptop computer

Ring 1Ring 2

LCT

EMS EMS

NMS

EMS – Elementary management system

NMS – Network management system

LCT – Local craft terminal

An optical fiber is made of very thin glass rods composed of two parts:the inner portion of the rod or core and the surrounding layer or cladding.Light injected into the core of a glass fiber will follow the physical path of that fiber due to the total internal reflection of the light between the core and the cladding. A plastic sheathing around the fiber provides the mechanical protection.

OPTICAL FIBRE

TYPES OF FIBRE

• Multimode fiber, due to its large core, enables different paths (multi-modes) to transmit the light along the link.

MULTIMODE FIBER

• The primary advantages of multimode fiber are it’s ease of coupling to light sources and to other fibers, connectorization and splicing.

• The disadvantage is it’s relative higher attenuation and/or low bandwidth.

SINGLE MODE FIBER • The reduced core diameter limits the light to propagation of only one mode, eliminating modal dispersion completely.• The advantage of single mode fiber is its higher performance with respect to bandwidth and attenuation.

MULTIMODE FIBER

SINGLE MODE FIBER

Connector Types

• Straight physical contact (PC)• Slanted (angled) physical contact (APC)• Straight air gap

Straight physical contact (PC)

The fiber ends are pressed together in the connector. There is no air gap left to cause reflections. The return loss is 30 – 55 dB.

This is the most common connector for single mode fibers

(for example FC/PC, ST, SC/PC, DIN, HMS, E 2000 connectors).

Slanted (angled) physical contact (APC)

In these connectors the ends of the fibers are slanted.Again no air gap is left. This gives the best return loss(60-80 dB).

These connectors are used for high-speed telecom and CATV links (for example FC/APC, SC/APC, E 2000-HRL connectors).

Straight air gap

Inside these connectors there is a small air gap between the two fiber ends. Their return loss is less than 14 dB andthe reflection is fairly high.

Straight air gap connectors, for example ST connectors, are used for multimode fibers.

FACTORS AFFECTING OPTICAL TRANSMISSION

Attenuation Light absorption.Scattering,Bending losses

Dispersion Modal dispersion.Chromatic dispersion.

Loss mechanism

Bandwidth Limitation

Measurements on optical fiber systems• End-to-End Optical Link Loss

• Rate of attenuation per unit length

• Attenuation contribution to splices, connectors, couplers (events)

• Length of fiber or distance to an event

• Linearity of fiber loss per unit length (Attenuation discontinuities)

• Reflectance or Optical Return Loss

TRANSMITTER PARAMETERS

MEAN LAUNCHED POWER

EXTINCTION RATIO

EYE PATTERN MASK

The mean launched power is the average power of a pseudo-random data sequence coupled into the fibre by the transmitter.

The Extinction ratio (EX) is defined as:

EX = 10 log A/B

where A is the average optical power level for a logical "1" and B is the average optical power level for a logical "0".

General transmitter pulse shape characteristics including rise time, fall time,pulse overshoot, pulse undershoot, and ringing, all of which should be controlled to prevent excessive degradation of the receiver sensitivity, are specified in the form of a mask of the transmitter eye diagram

RECEIVER PARAMETERS

Receiver sensitivity is defined as the minimum acceptable value of average received power at to achieve a 1 × 10-10 BER.

RECEIVER SENSITIVITY

Receiver overload is the maximum acceptable value of the received average power at point R for a 1 × 10-10 BER.

RECEIVER OVERLOAD

RECEIVER REFLECTANCE Reflections from the receiver back to the cable plant are specified by the maximum permissible reflectance of the receiver.

Different families of optical testers

• Optical Laser source

• Optical power meter

• Optical attenuator

• Optical talk set

• Optical time domain reflectometer

OPTICAL LASER SOURCE AND POWER METER

• A light source is a device used as a continuous and stable source (CW) for attenuation measurements.

• The power meter’s main function is to display the incident power on the photodiode.

Talk sets

Talk sets transmit voice over installed fiber cable, allowing technicians splicing or testing the fiber to communicate, even when they are in the field.

Visual Fault Locators

Visual Fault Locators are red light lasers which visually locate faults, up to around 5 kilometers.By sending visual light, the operator can easily see breaks and important bends in the fiber, as the light escapes out. This function makes them useful for continuity testing of patch cords, jumpers, or short sections of fiber.

OTDR

• An OTDR (Optical Time Domain Reflectometer) is a fiber optic tester characterizing fibers and optical networks. The aim of this instrument is to detect, locate and measure events at any location in the fiber link.

• One of the main benefits of the OTDR is that it can fully test a fiber from only one end.

Functional Tests Parametric Tests

Error-free Transmission (via all Paths through NE)

Optical Power ( transmitter )

Protection Switching test Optical Sensitivity and overload

( receiver )

Order wire calling Electrical tributaries Line rate tolerance

Automatic Laser Shutdown

Ethernet testing

Summary of Typical TestsSDH Measurements

Functional Tests

Functional Tests Instrument used

Error-free Transmission (via all Paths through NE)

SDH Analyser

Protection Switching test SDH Analyser

Order wire calling

Automatic Laser Shutdown

Ethernet testing Ethernet traffic generator / PCs

Parametric Tests Instruments used

Optical Power ( transmitter ) Optical power meter

Optical Sensitivity and overload

( receiver )

Optical power meter, Optical attenuator,SDH Analyser

Electrical tributaries Line rate tolerance SDH Analyser

Parametric Tests