SDH Presentation

BY AYODEJI MORAKINYO BIMONTHLY PRESENTATION 1BY AYODEJI MORAKINYO BIMONTHLY PRESENTATION 1

SYNCHRONOUS DIGITAL

HIERARCHY (SDH)

…At the Speed of Ideas

By Ayodeji Morakinyo

BY AYODEJI MORAKINYO BIMONTHLY PRESENTATION 2

Agenda

Introduction

Comparisons between STM-1 and STM-4 & PDH and SDH

The SDH Frame

The Virtual Container and Tributary Units

Faults, Errors & Alarms

Principles of Partitioning & Layering and Network Sync

Equipment Protection

The Cons of SDH Technology


First approved in 1988, SDH is a high speed and high

capacity optical transport system capable of creating simple,

flexible and economic infrastructures in telecommunication

networks. It is primarily used to carry telephony traffic.

In North America (Canada, USA, etc), SONET is the

equivalent of SDH. The differences are found only in the

terminologies used & the lowest signal level.

The SDH channel range or frequency is between

4GHz to 13GHz frequency bands for LH transmission.

Introduction


vPDH Equipment

PDH Equipment

ATM Equipment

PDH Equipment

PDH Equipment

ATM Equipment

ATM VP

ATM VP140Mbit/s

2Mbit/s

45Mbit/s

34Mbit/sSTM-4

STM-4

STM-1

STM-16

STM-1

6

STM-1

6

STM-16

STM-1

STM-4

STM

-4

STM-4


Lowest level SDH signal is called Synchronous Transport

Module level 1 (STM-1) operating at basic rate 155.52Mbps. STM-

1 can be seen as an SDH frame.

STM-N Frame

MUX

Signal A

Signal B

Signal C

Signal D

STM-1 frame

STM-4STM-4

* STM-1 frames multiplexed must have the same:

frame, bit rate and synchronisation.


9 r

ow

s

270 columns

Comparison between STM-1 and STM-4

4 X 270 columns = 1080

In STM-1, 9 columns are used for section overhead.

In STM-4, 36 columns are used for section overhead.

9 r

ow

s

1080 columns

STM-1 STM-4


N rows X M columns X 8 bits/byte X 2frequency

Therefore,

9X 270 X 8 X 2(4000)frames/sec = 15552000bit/s

Because, the human voice frequency is between 300 & 3400Hz

And with the consideration of band guard, we obtain: 4KHz

Therefore, the frequency utilized is 4000Hz

So, approximately, we have:

155.52Mbit/s


Higher SDH rates are obtained by multiplexing the base

rate. From STM-1 to higher data rates.

So, there we can have:

STM-N Bit rate

STM-1 155.52Mbps

STM-4 622.08Mbps

STM-16 2488.32Mbps

STM-64 9953.28Mbps

STM-N X 4

STM-4NWhere: N=1, 4,16


Comparison between PDH & SDH

Unlike PDH, SDH has the advantage of allowing both

system monitoring and management in terms of tributary

access, cost effectiveness, and equipment vendor variability.

It allows for upgrades from the basic rate of 155.52Mbps to

622.08Mbps and so on.

STM-1

STM-4

STM-16

STM-64

155.52Mbit/

s …

...

9953.28M

bit/s


Plesiochronous Digital

Hierarchy

(PDH)


PDH SDH

Provision is made for system

monitoring only i.e. no spare

signal capacity.

Allows both system monitoring and

management functions e.g.

maintenance can be performed

remotely from the network

management station. Hence, response

to customers request is swifter.

Only same vendor equipment

are used throughout the

network

Multi-vendor interoperability.

Different vendor-supplied equipment

can be utilized on the network. Hence,

upgrading is easier to perform.

Structure is comparatively rigid. Flexible Architecture.

It is capable of accommodating future

applications with a variety of

transmission rate.


Synchronous Digital

Hierarchy

(SDH)


The SDH Frame

A frame is a variable-length data packet that can be

transported in a network.

An SDH frame is one of a particular signal capacity (or

STM level) that can be transmitted along an optical link in a

synchronous transport network.

RSOH

Virtual container

PO

H

payload or customer traffic

MSOH

155.52Mbit/s

is the signal

capacity for

STM-1 data

frame

SOH


SOH

9 columns

POH

1 column

Actual capacity of VC

Finding the actual capacity of the container (VC):

270 columns – (9 + 1) columns = 260 columns

Hence, 9rows X 260columns X 8bits/byte X 2(4000)

Actual capacity of VC payload = 149.76Mbit/s


SDH

Terminal

Mux

SDH

DXC

SDH

Terminal

Demux

Transport Nodes

Regenerators

Regenerators: examples are optical amplifiers like LOFA

Transport Nodes: examples are DXCs, Muxes and Demuxes.


The SDH frame comprises the section overhead (SOH)

which is responsible for the transmission of the payload and the

payload (or customer traffic) itself.

SOH is the signal capacity contained in each SDH frame to

transport virtual containers between adjacent nodes.

SOH = RSOH + MSOH

SDH Frame = SOH + POH + Payload

SOH bytes occupy the first 9 columns of an STM-1 frame.


RSOH is the regenerator section overhead. It is

responsible for the transmission of the frame between

regenerators (e.g. from amplifier to amplifier, from amplifier to

demux or from DXC to amplifier).

The RSOH bytes and their functions include:

�parity BIP-8 check (B1 byte)

�frame alignment pattern (A1, A2 bytes)

�STM-1 identification (J0 byte)

�user channel (F1 byte)

�datacom channel (D1, D2, D3 bytes)

�voice channel (E1 byte)

RSOH


MSOH is the multiplexer section overhead and it

manages the transmission between transport nodes (e.g. from

mux to DXC and from DXC to demux).

Some MSOH bytes and their functions are:

�parity check (B2 byte)

�alarm information (S1 byte)

�automatic protection switching (K1,K2 bytes)

�payload pointers (H1,H2,H3 bytes)

�datacom channel (D4 – D12 bytes)

�voice channel (E2 byte)

MSOH


POH is the path overhead and it manages the transmission

of the virtual container between the mux (where the frame is

assembled) and the demux (where it is disassembled).

POH bytes and functions:

�path trace message (J1 byte)

�parity check (B3 byte)

�user channel (F2,F3 bytes)

�alarm & performance information (G1,N1 bytes)

�virtual container structure (C2 byte)

�automatic protection switching (K3 byte)

�multi-frame indication for TUs (H4 byte)

POH


The Virtual Container and Tributary Units

The virtual container (VC) is the part of the STM-N

frame that contains the customer traffic. It is designed to

carry 139Mbps actual payload and possesses the ability to

float relative to the STM frame.

The VC can be

divided into tributary

units (TUs)

TU-2 TU-3 TU-12

Tributary Units


A tributary unit is a low order signal that can be

multiplexed through the tributary channel. It represents

a mini-frame and fixed numbers of TUs can be mapped

into a VC.

Mapping here refers to the process of inserting

signals into the virtual container.

Payload capacity provided for each TU is always

slightly greater than that required by it. For example, a

49.54Mbps TU-3 may be mapped with a 44.736Mbps

capacity.


TU frame is similar to the SDH frame on the basis that

it comprises the TU-SOH, TU-POH and low rate tributary

signal.

TU-SOH

TU-POH

Low rate tributary signal

Tri

bu

tary

Un

it


Tributary Unit Data Rate Number of Columns

TU-3 49.54Mbps 86

TU-2 6.912Mbps 12

TU-12 2.304Mbps 4

TU-11 1.728Mbps 3

Tributary Unit Group (TUGs) are intermediate

multiplexing levels derived from the smaller tributary units.

TUG-2 = TU-2 + TU-12 + TU-11

TUG-3 = TU-3 + TU-2

AUG = TUG-2 + TUG-3


TUs have two operating modes:

1.Locked Mode: where the TUs are locked in the VC and they

do not require payload pointers . Also in this mode, the TU

structure does not have a POH. Hence, it is suitable where no

sync problems exist.

2.Floating Mode: is the most utilized mode. Here, the TU’s

virtual container is allowed to float w.r.t the TU frame. This

mode also has two types: the async mode and the byte sync

mode.

No POH


Why should use TUs?

�Designed to fit neatly into the virtual container

�Allows direct access to lower level tributaries

�Provides efficient transport, add-drop & cross-connection

capabilities with minimum delay

�Cross-connects & add-drop elements do NOT have to

demux to gain access to smaller tributaries.


When transmission errors occur in SDH, they are

detected by the BIP bytes and communicated back

upstream via the REI signal.

REI means Rate Error Indication. It is a signal that is

sent upstream when an error occurs at the far of the frame

block.

In the event of a serious fault, an alarm is generated

[e.g. loss of signal (LOS), frame (LOF) or pointer (LOP)]. A

Remote Detection Indication (RDI) message is sent back to

the transmitting end. NEs downstream are also alerted via

an AIS (Alarm Indication Signal)

Pry

Sec

Faults, Errors & Alarms


Again, when such major failures occur, the NE will

switch transmission from the line where the fault occurs to the

back-up line. This is initiated by the Multiplexer Section

Protection (MSP).

SDH networks are designed to recover from failure

conditions using protection switching (K1,K2) bytes. To create

the back-up line, the transmission lines are duplicated between

NEs.

Other kinds of errors:

Interruption of line Server signal failure (SSF)

No input signal

Failure of an NE

LOP


Partitioning Concept: entails representing the physical

implementation as links and sub-networks, starting from the

smallest (indivisible) sub-network or matrix .

Any sub-network may also be partitioned into a number

of smaller sub-networks interconnected by links.

Layering Concept: entails the provision of transport layer by

layer such that each network layer provides transport and uses

transport from the layer below.

The layer providing transport is called a SERVER while the

one using transport is termed a CLIENT.

Principles of Partitioning & Layering and Network Sync


Transit part sub-

network in a

national part

sub-network

Local part sub-

network in a

national part

sub-network

National part

sub-networkInternational part

sub-network

PARTITIONING CONCEPT


LAYERING CONCEPT

PDH or ATM VP Layer Network

VC - 11 VC - 12 VC- 2 VC -3

VC - 4

Multiplexer

section

Regenerator

Section

Pa

th L

ay

er

Se

ctio

n L

ay

er

Low

ord

er

Hig

h o

rde

r

High and low order

path layers handle the

termination and

generation of POH


The partitioning concept is vital for defining:

•The network structure within a layer network

•Administrative boundaries between network operators

jointly providing connections within a single layer network

The layering concept allows:

•Simple modelling of networks that contain multiple

transport technologies

•Independent design and operation of each network layer


Network Synchronization

SDH networks are used to transport PDH and ATM signals

hence, they must be able to convey data in both synchronous

and asynchronous modes.

Clock Types

1. Primary Reference Clock (PRC): ensures that NEs are

synchronously clocked or timed. PRC can be doubled or

tripled on different sites for safety purpose with one

acting as the master clock and the others as slave e.g.

Rubidium-clock or GPS: 10-11/day frequency shift.

2. Synchronous Supply Unit (SSU): is used for refreshing sync

signals after 20 NEs. The transit mode is 10-8/day. Local

mode is 10-9 /day.


3. Synchronous Equipment Clock (SEC): is the lowest level of

clocking obtainable in SDH networks. The frequency drift is at

10-8

/day.

PRC

SSU

SEC


1. Equipment Protection Switching (EPS): the matrix, clock,

control and power parts are protected via EPS (1+1) while

all electrical I/O boards are optically protected via the EPS

(1:N).

In EPS (1+1) protection mechanism, one working

equipment is protected by another redundant one so that

if the working equipment fails, the faulty one can be

exchanged. Its’ mode is non-revertive.

Equipment 1

Equipment 2

Equipment Protection


In EPS (1:N), N working pieces of equipment are

protected by just one equivalent. During normal operation

without equipment failure, the protecting equipment is

inactive. However, it may also be used to transfer extra

traffic (low priority line).

Equipment 1

Equipment 2

Equipment N

Equipment P

…


Tx

Rx

Rx

Tx

Rx

Tx

Tx

Rx

High Priority Line

MS

Low Priority Line

EPS (1:N) mode is revertive.

*Traffic is sent back to the working channel when the fault

has been rectified; once the wait-to-restore time(5-12mins)

has elapsed*


2. Multiplex Section Protection (MSP): provides

equipment protection in the NE, line protection between

adjacent multiplex elements and all optical I/O boards inside

NE are optically protected via MSP(1+1).

Node A Node B

SOH

Normal Traffic Channel

Protection Channel

SOH

Normal Traffic Channel

Protection Channel

STM-16 Fibre

Normal Channel

AU: 1-8

Protection Channel

AU: 9-16

MS-SPRING


Network Restoration: is an alternative to network protection in

which DXC together with SDH network manager provide support for

path restoration, MSP & SNCP as well as SNCP protection &

restoration combined.

DXC

A

NE

B

NE

C

DXC

D

NE

F

NE

E

DXC

A

NE

B

NE

C

DXC

D

NE

F

NE

E

VC-n

VC-n

VC-n

VC-n

Few seconds later . . .


1. Fixed Circuits causes data traffic limitation

SDH provisions dedicated P-to-P circuits between ring

nodes hence, each has fixed allocation of BW that limits the

maximum burst traffic data transfer rate. This is the

disadvantage for data traffic because it is inherently bursty.

2.Waste of BW for meshing

Mesh creation results in inefficient BW usage since

meshes in metro networks require ease of deployment,

maintenance and upgrading.

The Cons…


In conclusion, SDH transport network saves the customer the

hassles of labour-intensive maintenance and provides the

advantage of using different vendor equipment on the same

network.

SDH offers more flexibility and relatively economic solutions.

SDH is therefore customer friendly and

as a result, helps in attaining one the

objectives of Alcatel-Lucent.


END OF PRESENTATION

MERCI MERCI MERCI MERCI

BEAUCOUP!BEAUCOUP!BEAUCOUP!BEAUCOUP!


Acronyms

ATM = Asynchronous Transfer Mode

BIP-8 = Bit Interleaved Polarity Eight

BW = Bandwidth

Demux = Demultiplexer

DXC = Digital Cross-connect

I/O = Input/output

LOFA = Light Optical Fibre Amplifier

MUX = Multiplexer

NE = Network Element

P-to-P = Point to Point

SNCP = Sub-network Connection Protection

SONET = Synchronous Optical Network

VP = Virtual Path

Documents

SDH Presentation