SDH

SDH / SONET
1. Introduction to SDH/ SONET
• Applications / advantages/ disadvantages
2. Physical Configuration
3. SONET/ SDH Layers
4. Transmission Formats and Speed
5. Optical Interfaces Specifications
6. SONET/ SDH Rings
7. SONET/SDH Networks
 Introduction to SDH / SONET

ITU-T standards is called the Synchronous Digital Hierarchy (SDH)

ANSI standards is called the Synchronous Optical Network (SONET)

Three Important concerns in designing SONET/ SDH*

1. It is a Synchronous network.
• A single clock is used to handle the timing of transmission and
equipment across the entire network.
• Network wise synchronization adds a level of predictability to the
system.
• This predictability , coupled with powerful frame design, enables
individual channels to be multiplexed, thereby improving speed
and reducing cost.
2. Standardization.
• SDH/SONET contains recommendations for the standardization of
fiber optic transmission system equipment sold by different
manufacturers.
 Introduction to SDH / SONET

3. Universal Connectivity.
•SDH/SONET physical specification and frame design include
mechanism that allow it to carry signals from incompatible
tributary systems. This flexibility gives SONET/ SDH a reputation
for universal connectivity.

Applications:
1. Carrier for ISDN and B-ISDN.
2. Carrier for ATM cells.
3. Can support bandwidth on demand.
4. Can be used as the backbone or totally replace other
networking protocols such as SMDS or FDDI.
5. Can replace PDH system,E1, E3 lines.
 Introduction to SDH / SONET
Advantages of SDH

Flexible New generation of multiplexers with direct

access to every single low-speed tributary
(e.g. 2 Mbit/s/1.5 Mbit/s), sophisticated signal protection
mechanisms

Cost effective Integration of multiplex, cross-connect andline terminal functions as

part of a software-controlled network element

Manageable Adequate and standardized signal overhead capacity for remote

operation, administration and maintenance (OAM)

Standardized Standardized line signal as a uniform interface for all manufacturers

(multi-vendor policy)

International
Uniform multiplexing principle for both existing hierarchies (USA and
Europe)
Disdvantages of SDH

Abundant
low bandwidth utilization ratio,
Overheads bits
contradiction between efficiency and
reliability

Pointer Mechanism of pointer adjustment is

adjustment complex, it can cause pointer
adjustment jitters

Software based Large-scale application of software

makes SDH system vulnerable to
viruses or mistakes.
 Physical Configuration*

Add/drop
multiplexer

Regenerator Regenerator

MUX MUX

Section Section Section Section

Line Line

Path
Multiplexer/ Demultiplexer: Multiplexer marks the beginning and end
points of a SDH link. They provide interface between a tributary network and SDH
and either multiplex signals from multiple sources into an STM signal or
demultiplex as STM signal into different destination Signals.

Regenerator: Regenerator extend the length of the links, it takes optical

signal and regenerates. SDH regenerator replaces some of the existing overhead
information with new information. These devices function at the data link layer.

Add/ drop multiplexer: It can add signals coming from different sources
into a given path or remove a desired signal from a path and redirect it without
demultiplexing the entire signal. Instead of relying on timing and bit position
add/drop multiplexer use header information such as addresses and pointers to
identify the individual steams.
Section: It is the optical link connecting two neighbor devices:
•Multiplexer to Multiplexer
•Multiplexer to Regenerator
•Regenerator to Regenerator

Line: It is the portion of the network between two multiplexers:

•STM Multiplexer to add/drop multiplexer
•Two add/drop multiplexers
•Two STM multiplexers

Paths: It is the end to end portion of the network between two STM
multiplexers.

In a simple SDH of two multiplexers linked directly to each other, the

section, line, and path are the same.
 SONET/SDH Layers

Path layer

Line layer

Section layer
Data link

Photonic layer
Physical
 SONET/SDH Layers
Photonic Layer: Corresponds to the physical layer of the OSI model. It
includes physical specifications for the optical fiber channel, the sensitivity of the
receiver, multiplexing functions, and so on. It uses NRZ encoding.

Section Layer: It is responsible for the movement of a signal across a

physical section. It handles framing, scrambling and error control. Section layer
overhead is added to the frame at this layer.

Line Layer: It is responsible for the movement of a signal across a

physical line. Line overhead (Pointers, protection bytes, parity bytes etc) is
added to the frame at this layers. STM multiplexer and add/drop multiplexers
provide line layer functions.

Path Layer: It is responsible for the movement of a signal from its optical
source to its optical destination. At the optical source, the signal is changed
from an electronic form into an optical form, multiplexed with other signals, and
encapsulated in a frame. Path layer overhead is added at this layer. STM
multiplexer provide path layer functions.
 Device Layer Relationship

Path Path
Line Line Line
Section Section Section Section Section
Photonic Photonic Photonic Photonic Photonic

Regenerator Regenerator

MUX MUX

Add/drop
multiplexer
 Transmission Formats and speeds
Commonly Used SONET and SDH Transmission Rates

QUIZ:
No of E1s in STM-1,STM-4,STM-16 and STM-64 ?
 Transmission Formats and speeds

Line rate calculation

270
Total Frame Capacity: 270 X 9 = 2430 Bytes
Total Number of Bits = 2430 X 8 = 19440 Bits
Time Period of One Frame = 125 microseconds
Bits/Second = 19440/125 X 10 -6 = 155.52 Mbits/Sec
= STM-1
4X STM-1 = STM-4
4XSTM-4 = STM-16
 Transmission Formats and seeds

SDH components

 SDH Frame is made of the following

 SDH payload

 Pointer

 Path Over head Overhead is fixed and is like a

Header. It contains all

 Section Overhead information including

 Multiplex section overhead
Monitoring,O&M functions etc.
 Regenerator section overhead
 Transmission Formats and speeds

SDH Frame

2 34 140 SDH

270 x N Columns

1 Byte
RSOH 261 Bytes

Pointer
POH

9 Rows Payload
MSOH
Actual Traffic

STM-1, STM-4, STM-16, STM-64, STM-256

 SONET/ SDH Rings
•SONET and SDH are configured as either ring or mesh architecture.
•So Loop diversity is achieved in case of link or equipment failure.

•SONET/SDH rings are commonly called self-healing rings. Means

automatic switching to standby link on failure or degradation of the link.

Three main features of SONET/SDH rings:

1. There can be either two or four fibers running between the nodes on a
ring.
2. Operating signal signals can travel either clockwise only (unidirectional
ring) or in both directions around the ring (which is called bidirectional
ring).
3. Protection switching can be performed either via line-switching or a path
switching scheme.
• Line switching moves all signal channels of an entire STM-N
channel to a protection fiber.
• Path switching can move individual payload channels within a
STM-N channel to another path.
 SONET/ SDH Rings

Following two architectures have become popular for SONET and

SDH Networks:

1. Two fibers, unidirectional, path-switched ring (two-

fiber UPSR)
2. Two fiber or four fiber, bidirectional, line switched
ring( two fiber or four fiber BLSR)\

(They are also referred to as unidirectional or

bidirectional self healing ring , USHRs or BSHRs)
 SONET/ SDH Rings

Generic two fiber Flow of primary and protection

unidirectional path-switched traffic from node 1 to node 3
ring (UPSR) with counter
rotating protection path.
 SONET/ SDH Rings

Architecture of a four-fiber bidirectional line-switched ring (BLSR).

 SONET/ SDH Rings

Reconfiguration of a four-fiber BLSR under transceiver or line failure.

 SONET /SDH Networks
SONET/SDH equipment allows the configuration of a variety of network
architectures, as shown in next slide. For example
•Point-to-point links
•Linear chains
•UPSRs
•BLSRs
•Interconnected rings

Each of the individual rings has its own failure recovery mechanisms and
SONET/SDH network management procedures.

An important SONET/SDH network element is the add/drop multiplexer

(ADM). This piece of equipment is a fully synchronous, byte-oriented
multiplexer that is used to add and drop subchannels within an OC-N signal.

The SONET/SDH architectures also can be implemented with multiple

wavelengths. For example, Fig in next slide, will show a dense WDM
deployment on an OC-192 trunk ring for n wavelengths
 SONET /SDH Networks

Where
OC-3 = STM-1
OC-12 = STM-4
OC-48 = STM-16
OC-192= STM-64

Generic configuration of a large SONET network consisting of linear

chains and various types of interconnected rings.
 SONET /SDH Networks

Functional concept of an add/drop multiplexer for SONET/SDH applications.

 SONET /SDH Networks

Dense WDM deployment of n wavelengths in an OC-192/ STM-64 trunk ring.

Mapping

 Is the procedure through which signals are packed

inside an SDH frame

 PDH signal passes through the following steps before

emerging as an SDH Signal

 Container (C-X)
 Virtual Container (VC-X)
 Tributary Unit (TU-X)
 Tributary Unit Group (TUG-X)
 Administrative Unit (AU-4)
 STM Signal
 How 2 Mb signals are mapped
into an SDH stream?

Container
2 Mb/Sec C-12

Path Overhead (POH)

Virtual Container

VC-12
 How 2 Mb signals are mapped
into an SDH stream?

Payload VC-12
Starting address of
Payload in VC.

Pointer

TU
(Tributary Unit)

SOH
STM-1/4/16 SOH
9
270
Formation of Synchronous Signal

Plesiochronous signal

Container (C)

Path overhead
Additional information for
end-to-end monitoring

Virtual
container (VC)

Pointer
Phase relation between
virtual container (payload)
and subordinate frame

Tributary
unit (TU)
Synchronous Signal
ITU-T recommendation G.707 and its
realization

STM-N ×n ×1
AUG AU4 VC4 C4 140 Mbit/s
×1
×3
TUG3 TU3 VC3

34 Mbit/s
AU3 VC3 C3 (45 Mbit/s)
AU/G Administrative unit/group ×7
C Container
STM Synchronous transport module ×1
TU/G Tributary unit/group
VC Virtual container TUG2 TU2 VC2 C2 (6 Mbit/s)
Pointer processing ×3
Multiplexing TU12 VC12 C12 2 Mbit/s
Aligning
Mapping

Cross-connect level TU11 VC11 C11 (1.5 Mbit/s)

Source: TR BM TP 5
SDH Overheads

 An overhead is like a delivery notice with the parcel

which contains information about the contents,
Condition, type, address, postal date, weight etc. of the
parcel.
 In the SDH a distinction is made between Section
Overhead (SOH) and Path Overhead (POH)
STM-1
SOH

SOH
POH VC-4
 SDH Multiplexing Structure

×1 Mapping
STM-64 AUG-64
Aligning
×4
×1 Multiplexing
STM-16 AUG-16
×4 Pointer processing
×1
STM-4 AUG-4

×4
×1 ×1
STM-1 AUG-1 AU-4 VC-4 C-4 139264 kbit/s

×3

×1 34368 kbit/s
TUG-3 TU-3 VC-3 C-3

×7
TUG-2

×3 TU-12 VC-12 C-12 2048 kbit/s