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.

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

Cost effective

Manageable

Standardized

International

New generation of multiplexers with directaccess to every single low-speed tributary(e.g. 2 Mbit/s/1.5 Mbit/s), sophisticated signal protection mechanisms

New generation of multiplexers with directaccess to every single low-speed tributary(e.g. 2 Mbit/s/1.5 Mbit/s), sophisticated signal protection mechanisms

Integration of multiplex, cross-connect andline terminal functions as part of a software-controlled network element

Integration of multiplex, cross-connect andline terminal functions as part of a software-controlled network element

Adequate and standardized signal overhead capacity for remote operation, administration and maintenance (OAM)

Adequate and standardized signal overhead capacity for remote operation, administration and maintenance (OAM)

Standardized line signal as a uniform interface for all manufacturers (multi-vendor policy)

Standardized line signal as a uniform interface for all manufacturers (multi-vendor policy)

Uniform multiplexing principle for both existing hierarchies (USA and Europe)Uniform multiplexing principle for both existing hierarchies (USA and Europe)

Introduction to SDH / SONET

Disdvantages of SDH

Abundant Overheads bits

low bandwidth utilization ratio, contradiction between efficiency and reliability

Mechanism of pointer adjustment is complex, it can cause pointer adjustment jitters

Software based Large-scale application of software makes SDH system vulnerable to viruses or mistakes.

Pointer adjustment

Physical Configuration*

MUX MUX

Add/drop

multiplexer

Regenerator Regenerator

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

Section layer

Line layer

Photonic layer

Data link

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

MUX MUX

Add/drop

multiplexer

Regenerator Regenerator

Path

Section

Line

Photonic

Path

Section

Line

Photonic

Section

Line

Photonic

Section

Photonic

Section

Photonic

Commonly Used SONET and SDH Transmission Rates

Transmission Formats and speeds

QUIZ:

No of E1s in STM-1,STM-4,STM-16 and STM-64 ?

Line rate calculation

9

270

Total Frame Capacity: 270 X 9 = 2430 BytesTotal Number of Bits = 2430 X 8 = 19440 BitsTime Period of One Frame = 125 microsecondsBits/Second = 19440/125 X 10 -6 = 155.52 Mbits/Sec = STM-1

4X STM-1 = STM-44XSTM-4 = STM-16

Transmission Formats and speeds

SDH components

SDH Frame is made of the following

– SDH payload

– Pointer

– Path Over head

– Section Overhead» Multiplex section overhead» Regenerator section overhead

Overhead is fixed and is like a

Header. It contains all

information including

Monitoring,O&M functions etc.

Transmission Formats and seeds

SDH Frame

SDH2 34 140

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

270 x N Columns

PO

H

MSOH

Pointer Payload

RSOH

9 Rows

Actual Traffic

261 Bytes1 Byte

Transmission Formats and speeds

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 unidirectional path-switched ring (UPSR) with counter rotating protection path.

Flow of primary and protection traffic from node 1 to node 3

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 Rings

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

Generic configuration of a large SONET network consisting of linear chains and various types of interconnected rings.

Where

OC-3 = STM-1

OC-12 = STM-4

OC-48 = STM-16

OC-192= STM-64

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

SONET /SDH Networks

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 mappedinto an SDH stream?

C-12

VC-12

2 Mb/Sec

Container

Virtual Container

Path Overhead (POH)

How 2 Mb signals are mappedinto an SDH stream?

VC-12

STM-1/4/16

Payload

Pointer

SOHSOH

270

9

TU (Tributary Unit)

Starting address of Payload in VC.

Formation of Synchronous Signal

PointerPhase relation between virtual container (payload) and subordinate frame

Plesiochronous signal

Path overheadAdditional information forend-to-end monitoring

Tributary unit (TU)

Virtualcontainer (VC)

Container (C)

Synchronous Signal

VC11

ITU-T recommendation G.707 and its realization

× n

× 1× 3

× 7

× 1

C2

C11

× 3VC12

× 1

VC4

VC3

C3

VC2

VC3

C12TU12

TU2

TU3TUG3

TUG2

140 Mbit/s

34 Mbit/s(45 Mbit/s)

(6 Mbit/s)

2 Mbit/s

(1.5 Mbit/s)

AU4STM-N

AU3

TU11

C4AUG

Source: TR BM TP 5

AU/G Administrative unit/groupC ContainerSTM Synchronous transport moduleTU/G Tributary unit/groupVC Virtual container

Pointer processing

MultiplexingAligningMapping

Cross-connect level

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)

SOH

SOHPOH

STM-1

VC-4

SDH Multiplexing Structure

STM-1 AU-4

TU-3

AUG-1

TUG-3 VC-3 C-3

VC-4 C-4

TU-12 VC-12 C-12

TUG-2

×1 ×1

×3

×1

×7

×3

139264 kbit/s

34368 kbit/s

2048 kbit/s

Pointer processing

Multiplexing

Mapping

Aligning

AUG-4

AUG-16

AUG-64

STM-4

STM-16

STM-64

×1

×1

×1

×4

×4

×4

Intentionally Left Blank