SDH

Synchronous• Average frequency of all

clocks in the system is the same.

• No multiplexing stages are needed, any lower order signal can be added to a higher order signal easily.

• No bit stuffing.

Asynchronous.• Each terminal on the

network running on its own clock.

• Uses multiple stages for multiplexing, lower order (e.g. E1-2Mbs) signals are needed to bring up to a range of higher order (e.g.E3-34Mbs) signal for multiplexing.

• Bit stuffing technique is use.

Introduction to Synchronization

PDH

• Older Networks were developed for point to point transmission.

• Supported manual approach to network management & maintenance.

• In PDH signal structures, no place for network management & maintenance functions(i.e.no spare signal capacity for improvement in signal transmission.

PDH cont…

• Development caused interconnection, difficult & unreliable

(Result:Existing standards for point to point communication became unsuitable)

• PDH is stage by stage multiplexing based on 64 Kb/s voice channels with different hierarchies in the

world & approved specs; covered up to 140 Mb/s (1920 voice channels).

PDH cont…

• Lower order signal could not be accessed directly without de-multiplexing & multiplexing again (added cost)

• No common standards available above 140 Mb/s (Result:Vendor Dependency)

• Customer circuits, Speed & B.W. limited.• No proper response to new customer services (Less

efficient, not cost effective, B.W control not possible)

PDH cont…

(HIERARCHIES)

PDH Hierarchies

1. Interfaces Electrical interfaces---only regional standards, no universal standard.2. Three rate hierarchies for PDH: European(2Mb/s) . Japanese (1.5 Mb/s) North American(1.5Mb/s).

3. Optical interfaces---no standards at all, manufacturers develop at their will.

Difficult to inter-connect

Disadvantage of PDH

Multiplexing for PDH: The location of low-rate signals in high-rate signals is not regular nor predictable. So it is impossible to directly add/drop low-rate signals from high-rate signals.

Where did I put

the signals?

Disadvantage of PDH cont..

140Mb/s34Mb/s 34Mb/s

8Mb/s 8Mb/s

2Mb/s

140Mb/s

de-multiplexerde-multiplexer

de-multiplexer multiplexer

multiplexer

multiplexer

Low-rate signals have to be separated from high-rate signals level by level. Multiple levels of multiplexing/de-multiplexing cause signals to deteriorate, it is not suitable for huge-volume transmission.


OAM• OAM function affects the maintenance cost.It is determined by the number of overhead bytes(redundant bytes);• There are VERY few redundant byes available in PDH signals which can be used as OAM purpose, so OAM in PDH is very poor, it is unreliable either.• No universal network management interface. It is hard to set up an integrated network management. No way to form a universal TMN. • PDH is inappropriate to transmit huge-volume signals, so SDH came to play the part.


• SDH (synchronous digital hierarchy) is a standard for telecommunications transport formulated by the International Telecommunication Union (ITU).

• Introduced into the telecommunications network in 1992.

• It's deployed at all levels of the network infrastructure, including the access network and the long-distance trunk network.

Introduction to Synchronous Digital Hierarchy

• It's based on overlaying a synchronous multiplexed signal onto a light stream transmitted over fiber-optic cable.

• SDH is also defined for use on radio relay links, satellite links, and at electrical interfaces between equipment.

Introduction to Synchronous Digital Hierarchy cont…

SDH

Asynchronous

E0 64 kbit/s One 64 kbit/s

E1 2.048 Mbit/s 32 E0

E2 8.448 Mbit/s 128 E0

E3 34.368 Mbit/s 16 E1

E4 139.264 Mbit/s 64 E1

Synchronous

STM-0 51 Mbit/s 21 E1

STM-1 155 Mbit/s 63 E1 or 1 E4

STM-4 622 Mbit/s 252 E1 or 4 E4

STM-16 2.4 Gbit/s 1008 E1 or 16 E4

STM-64 10 Gbit/s 4032 E1 or 64 E4

Transmission Hierarchies

All these factors & deficiencies led to the birth of

S.D.H

Overheads and Pointers

SDH

Overview

Frame structure

and multiplex-

ing methods

Logical parts of SDH

equipment

SDH Principle1

The principle is divided into 4 parts:

1- SDH Overview——To have the basic concept of SDH• What is SDH?• What are the differences?• Advantages and disadvantages of SDH system.

2- Frame structure and multiplexing method of SDH signals The functions of each part in SDH signal frame structure Multiplexing the commonly encountered PDH signals (2Mb/s, 34Mb/s,140Mb/s) into SDH signals?

SDH Principle

3- Overhead and Pointers• Layered monitoring mechanism of SDH——Overheads• Directly add/drop lower-rate signals in SDH——Pointers

4- Logical composition of SDH equipment• Common network elements of SDH network• Logical function blocks of SDH equipment

SDH Principle Curriculum

Where it can be used

Disadvantages of SDH

Background of SDH

Advantages of SDH

SDH Overview

1. What is SDH.

2. What are the differences.

3. Where it can be used.

4. Advantages & Disadvantages of SDH

Background of SDH

New Digital Hierarchy• 155.52 Mb/s, 622.08 Mb/s, 2488.32 Mb/s etc. Existing PDH and future ATM signals are carried over the SDH system

Very basic functions are same as PDH.• Multiplex low bit rate digital signals to

higher bit rate and transmit large information efficiently.

What is SDH ?

• SDH is a STANDARD for high speed

• High capacity telecommunication networks

• More specifically it is a SYNCHRONOUS DIGITAL TRANSPORT SYSTEM designed for providing a more simple, economic & Flexible telecommunication network infrastructure.

What is SDH ? cont…

What are differences?

Synchronous Network• All network elements work on the same

clock.

Abundant Overhead Bits• To carry large information for Network

Management

Unified Interface and Multiplexing specifications• Common to Europe, North America and

Japan digital hierarchies.• Standard optical interfaces.

What are differences? cont..• Simple multiplexing process

• Easy access to tributary signals in a multiplexed high bit rate signal.

ADD/DROP ----------------- distributionRING ---------------------- survivabilityCROSS CONNECT --------- capacity management

band width management protection route diversity.

• In all traditional N/W application areas, providing

interconnection between three major

telecommunication networks.

Where S.D.H is used?

• Multi-vender Environment

• International Connection

• Realization of highly advanced Network • Management System.

• Fault management.• Configuration management.• Performance management.• Security management.• Accounting management.

What are benefits ?

Interfaces• Electrical interfaces:standard rate hierarchy (transmission speed level).

• Optical interfaces:only scramble the electrical signals.

Advantages of SDH

SDH Signals Bit rate(Mb/s)

STM-1 155.520 or 155M

STM-4 622.080 or 622M

STM-16 2488.320 or 2.5G

STM-64 9953.280 or 10G

• The basic rate level is called Synchronous Transfer Module(STM-1), the other rate levels are the multiple of STM-1.

Advantages of SDH cont…

STM-1155Mb/s

STM-4622Mb/s

STM-162.5Gb/s

STM-6410Gb/s

10Gb/s

¡ Á4 ¡ Á4

¡ Á4

WDM

SDH:4×STM-1=STM-4 ； 4×STM-4=STM-16


Multiplexing methods: • low-rate SDH→high-rate SDH(e.g.:4 STM-1→STM-4). Uses byte interleaved multiplexing method.

STM-1

STM-1

STM-1

STM-1

STM-4

Byte interleaved

multiplexing


Other signals→SDH:Using pointers to align the low-rate signals in SDH frame,so the receivers can directly drop low-rate signals.E.g.:

PDH

Packing Pkg

Alignment

PKG a

PKG b

STM-1


OAM• More bytes in SDH frame structure are used for OAM purpose, about 5% of total bytes. SDH boasts of high capability of OAM.

Compatibility• SDH is compatible with the existing PDH system. SDH allows new types of equipment to be used, allows broadband access, such as ATM.


STM-N STM-N

PDH, ATMFDDI signals

packing

package Package

packing transmit

SDH network

unpacking

PDH, ATMFDDI signalsSDH compatibility schematics

transmit transmit


1. Low bandwidth utilization ratio--- contradiction between efficiency and reliability.

2. Mechanism of pointer adjustment is complex, it can cause pointer adjustment jitters3. Large-scale application of software makes SDH system vulnerable to viruses or mistakes.

140M

34M

2M

1140M=642M

334M=482M

632M

STM-1(155M)

Disadvantages of SDH

Components and functions

Multiplexing Procedure

Frame Structure and Multiplexing methods

140M

34M

2M

STM-N

2

1. Components & Functions

I must understand the functions

of different parts of SDH frame！

9×270 ×N bytes

SOH

SOH

AU-PTR

1

345

9

STM-N payload

(including POH)

9×N 261×N270×N columns

Transmission direction Transmit

left to right up to down

STM-N frame structure

• Block frame in units of bytes(8bit),

• Transmission---from left to right, from top to bottom,

• Frame frequency constant---8000 frames/s, frame period 125us.

Characteristics of SDH signals

1. Payload It is where we put all the information in STM-N

frame structure. All kinds of effective info, such

as 2M, 34M ,140M are first packed before

being stored here. Then they are carried by STM-

N signals over the SDH network.

Composition of SDH signals

If we should consider STM-N signal to be a truck, then info payload would be the carriage of the truck. In order to monitor the transmission status of the goods during transportation, POH are added to each information package.

Pkg

Pkg Pkg

PkgPkg

PayloadPkgLow-rate signals 1

Low-rate signals n

loading

POH

POH

packing

packing

STM-N

loading

Composition of SDH signals cont…

2. Section Overhead• Accomplishes monitoring of STM-N signal streams. To check whether the “goods” in STM-N “carriage” is damaged or not.

• Regenerator Section Overhead(RSOH): monitor the overall STM-N signals.

• Multiplex Section Overhead(MSOH): monitor each STM-1 in STM-N signal.

• RSOH, MSOH and POH set up SDH layered monitoring mechanism.


. SDH Section signal

(SOH)

Low-rate signal 1

Low-rate signal 2

Low-rate signal n

low-rate path signal(POH)

Sections and Paths


3. Administrative Unit Pointer(AU-PTR)

Indicates the location of low-rate signals in STM-N frame(payload), makes the location of low-rate

signals in high-rate signals predictable.


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键入文本键入文本键入文本

键入文本键入文本

键入文本




键入文本




键入文本




键入文本

Sending:AU-PTR indicates the first info package

Receiving:According to the value of AU-PTR, get the first infopackage, through the regularity of byte interleavedmultiplexing, get the other packages

(SDH transmission

network)


2M

34M TU-PTRPrimary alignment

AU-PTRSecondary alignment

• For low-rate signals such as 2M, 34M. We need two-levels of pointers to align. • First, small information “goods” is packed into middle information “goods”. Tributary unit pointer(TU-PTR) is used to align the location of small “goods” in middle “goods”. • Then these middle “goods” are packed into big “goods”, AU-PTR is to align the location of middle info package.


• low-rate SDH→high-rate SDH: byte interleaved multiplexing, 4 into 1.

• PDH signals→STM-N: synchronous multiplexing: 140M→STM-N 34M→ STM-N 2M→STM-N

• Multiplexing is based on the multiplexing route diagram. ITU-T defines several different multiplexing routes, but for any country or region, the method is unique.

2. Multiplexing Procedure of SDH

STM-16 AU-4-16c C-4-16cVC-4-16c

E1: 2.048Mb/s

E4: 139.264Mb/s

STM-4

STM-1

AU-4-4c

AU-4

AU-3

VC-4-4c

VC-4

C-4-4c

C-4

C-3

C-2

C-12

C-11

VC-3

VC-2

VC-12

VC-11

TUG-3

TUG-2

DS1:1.544Mb/s

E3: 34.368Mb/sDS3: 44.736Mb/s

DS2:6.312 Mb/s

VC-3

TU-3

TU-11

TU-12

TU-2

x4

x3

x1

x7x7

x3x3

564.992Mb/s

2259.968Mb/s

VC-n

AU-n

AUG

STM-n Synchronous Transport Module

Administrative Unit Group: One or more AU(s)

Administrative Unit: VC + pointers

Virtual Container: payload + path overhead

STM-64 AU-4-64c VC-4-64c C-4-64c

AUG

x16

x4

x4x64

x16

x4

9039.872Mb/s

Containers of Base Signal (Low Order Payloads)

High Order Payloads

Multiplexing Procedure of SDH cont...

Regenerator Section OH

Multiplex Section OH

9 bytes

3

1

5

261 bytes

VC-4 Payload:C4 or TUG-3 mapped

J1

B3

C2

G1

F2

H4

F3

K3

N1

H1

H2

H3

H1

H2

H3

H1

H2

H3

C-3

Payload

J1

B3

C2

G1

F2

H4

F3

K3

N15 bytes

Higher Order Path OH

AU Pointer

TUG-3 TUG-2/VC12

Muxed

C-3

Payload

J1

B3

C2

G1

F2

H4

F3

K3

N1V

C

1

2

Vx

ptr

Low Order Path OH

Multiplexing /Mapping of Signals cont...

Section Overhead

Overhead

Overhead and Pointers

Pointers

Path Overhead

AU-PTR TU-PTR

3

Overhead

SOH

RSOH MSOH

POH

VC4POH

VC12 POH

(HPOH)(LPOH)

OVERHEAD

STM-N RSOH

STM-1MSOH

VC4HO-POH

VC12LO-POH

Layered Monitoring

A1 A1 A1 A2 A2 A2 J0B1D1

B2D4D7D10S1

B2 B2 K1D5D8D11

M1 E2D12D9D6K2

F1D3

E1D2

AU-PTR

* *

*

RSOH

MSOH

Bytes reserved for domestic useMarked bytes are not scrambled

1 2 3 4 5 6 7 8 9123456789

* * * ****

SOH (Section Over Head)

SDH Networking

I want to master the common NEs and the functions of logical blocks

• TM: Terminal Multiplexer

• ADM: Add/Drop

Multiplexer

• REG: Regenerator

• DXC: Digital Cross Connect

Network Element

Common NEs in SDH Network

TM ADM REG DXC

TMSTM-N

2M 34M 140M STM-M Note: (M<N)

(Optical Interface)

(Tributary Interface)

Application of TM in chain network

TMTM ADM

• Multiplexing, cross-connectionw

TM (Terminal Multiplexer)

ADMSTM-N

2M 34M 140M

(Optical interface)

(Tributary Interface)

Application of ADM in chain network

TMTM ADM

STM-N ew

• Multiplexing, cross-connection

(Optical interface)

STM-M Note: (M<N)

ADM (Add/Drop Multiplexer

REGSTM-N

TMTM REG

STM-N ew

ADMADM

• Regeneration, amplification and relaying

(Optical interface)(Optical interface)

Application of REG in chain network

REG (Regenerator)

DXC

• Core function is cross-connection

• Used at hub station

(Optical interface)(Optical interface)

DXC (Digital Cross Connect)

•Chain Network

•Star Network

•Ring Network

Basic Networks

A B C D E

• All the nodes are connected one after another

• Both ends open

• Not easy to provide protection

Chain Network

A

• A special node connected directly with

other nodes

• No direct connection with other nodes

• Easy and flexible to manage

E

DC

B

Star Network

A

• Connect the end nodes of chain network

• Easy to provide protection

• Widely used network

C

B E

D

Ring Network

Protection

• SDH need to be highly reliable.• Down-time should be minimal (less than 50 msec)• So systems must repair themselves (no time for manual intervention)

• Upon detection of a failure (dLOS, dLOF, high BER)the network must reroute traffic (protection switching)from working channel to protection channel

• The Network Element that detects the failure (tail-end NE)initiates the protection switching

• The head-end NE must change forwarding or to send duplicate traffic• Protection switching is unidirectionalProtection switching may be revertive (automatically revert to working channel)

head-end NE tail-end NE

working channel

protection channel

What is Protection?

Head-end and tail-end NEs have bridges (muxes)Head-end and tail-end NEs maintain bidirectional signaling channel

Signaling is contained in K1 and K2 bytes of protection channel• K1 – tail-end status and requests• K2 – head-end status

head-end bridge tail-end bridgeworking channel

protection channel signaling channel

How Does it works ?

Types of Protection?

• Linear 1+1 Protection (SNCP)• Linear 1+N Protection• Two Fiber or Four Fiber Protection• Unidirectional & Bidirectional Protection• UPSR & BLSR (MS-SPRing)

• Simplest form of protection

• Can be at STM-n level (different physical fibers) or at STM/VC level (called Sub Network Connection Protection)

working channel

protection channel

extra traffic

Linear 1+1 Protection

• In order to save BW we allocate 1 protection channel for every N working channels

working channels

protection channel

Linear 1+N Protection

• 1 + 1 protection

• 1 : n protection

Bridge Switching

XWorking Line/Path

Protection Line/Path

Working Line/Path

Protection Line/PathX

Line : STM-N line, Path : VCn path

1+1 & 1+ N Protection

• Ring based protection is popular • Full protection against physical fiber cuts• Simpler and less expensive than mesh topologies• Protection at line (multiplexed section) or path

layer

2 fibers in opposite directions

Two Fiber & Four Fiber

• Unidirectional routingworking channel B-A same direction (e.g. clockwise) as A-Bmanagement simplicity: A-B and B-A can occupy same timeslotsInefficient: waste in ring BW and excessive delay in one direction

• Bidirectional routingA-B and B-1 are opposite in directionboth using shortest routespatial reuse: timeslots can be reused in other sections

A

BA-B

B-A

A

B

B-AA-B

C

B-C

C-B

Unidirectional & Bidirectional Protection

Of all the possible combinations, only a few are in use

Unidirectional Path Switched Ringsprotects tributariesextension of 1+1 to ring topology

Bidirectional Line Switched Rings (two-fiber and four-fiber versions)called Multiplex Section Shared Protection Ring in SDHsimultaneously protects all tributaries in STMextension of 1:1 to ring topology

Path switching

Line switching

Two-fiber

Four-fiber

Unidirectional

Bidirectional

UPSR

BLSR

UPSR & BLSR (MS-SPRing)

SDH/SONET Optical Ring

Working Ring(WR)

Fiber Cut

ProtectionRing(PR)

X 2:1 Switch1:2 Bridge

UPSR

BLSR/2F: Bidirectional Line Switched Ring /N-Fiber

SDH/SONET Optical Ring

Working Channel

Fiber Cut

Protection Channel

Node 4

Node 3

Node 1T2,1

Node 2

T2,1 T1,4

XLooping

Looping

BLSR (MS-SP Ring)

• Working channel is in one directionprotection channel in the opposite direction

• Two-fiber versionhalf of OC-N capacity devoted to protectiononly half capacity available for traffic

• Four-fiber versionfull redundant OC-N devoted to protectiontwice as many NEs as compared to two-fiber

Example

recovery from unidirectional fiber cut

UPSR & BLSR (MS-SPRing) cont…

NGSDH(Next Generation

SDH)

SDH legacy technology is improving and adopting data-friendly features.Three technologies are central to Next-Generation SDH.• Virtual Concatenation: VCAT• Link Capacity Adjustment Scheme: LCAS• Generic Framing Procedure: GFP

Next Generation SDH

Purpose of GFP

• New ITU-T standard, G.7041 describes a Generic Framing Procedure (GFP) which may be used for efficiently mapping client signals into and transporting them over SONET/SDH or G.709 links.

Generic Framing Procedure (GFP) OverviewGFP defines a mapping of client data signals into SDH payloads in order to allow SDH to transport non-TDM traffic more efficiently. GFP defines two types of client signals:

Frame-mapped GFP for PDU-oriented signals such as IP/ PPP or Ethernet MAC.

Transparent-mapped GFP for block-oriented signals such as Fiber Channel.

Benefits of GFPGFP provides major benefits. It gives one uniform mechanism to transport any data type over SDH.

Purpose of GFP

VCAT

Payloads that don’t fit into standard VT/VC sizes can be accommodatedby concatenating of several VTs / VCs

For example, 10 Mbps doesn’t fit into any VT or VCso w/o concatenation we need to put it into an STS-1 (48.384 Mbps)the remaining 38.384 Mbps can not be used

We would like to be able to divide the 10 Mbps among 7 VT1.5/VC-11 s = 7 * 1.600 = 11.20 Mbps or

5 VT2/VC-12 s = 5 * 2.176 = 10.88 Mbps

Concatenation

• Virtual Concatenation (VCAT G.707 ) payload split over multiple STSs / STMsfragments may follow different routesrequires support only at path terminationsrequires buffering and differential delay alignment

Virtual Concatenation

VCAT is an inverse multiplexing mechanism (round-robin)VCAT members may travel along different routes in SONET/SDH network

Intermediate network elements don’t need to know about VCAT(unlike contiguous concatenation that is handled by all intermediate nodes)

…

H4

Virtual Concatenation

Using VCAT increases efficiency to close to 100% !

Rate Mb/s w/o VCAT efficiency with VCAT efficiency

10 STS-1 21% VT2-5v

VC-12-5v

92%

100 STS-3c

VC-4

67% STS-1-2v

VC-3-2v

100%

1000 STS-48c

VC-4-16c

42% STS-3c-7v

VC-4-7v

95%

Efficiency Comparison

Link Capacity Adjustment Scheme

• LCAS is defined in G.7042• LCAS extends VCAT by allowing dynamic BW changes.

Benefits of LCAS• The use of LCAS provides an effective way for the Service Provider to change

the bandwidth• allocated. Provisioning quickly the right bandwidth at any time is a major

operations management goal of Service Providers.

LCAS

THANKS

Any Question?

Documents

SDH