Fiber Optic CommunicationBy

Engr. Muhammad Ashraf Bhutta

Lecture Outlines

SDH Overview Frame structure and multiplex-ing methods Overheads and Pointers

Disadvantages of PDH

Disadvan-tageDisadvan-tages of SDHs of SDH

Background of SDH

Advantages of SDH

SDH Overview

Background about SDH emergence What is SDH--Synchronous Digital Hierarchy. Similar to PDH， they are all digital signal transmission system. Why did SDH emerge?1)What we need in info-society: huge volume of info, and digital, integrated, personal.2)What we want the transmission network to be: Broadband---info-highway Standard---universal interface all over the world

Disadvantages of PDH:

1 Interfaces Electrical interfaces---only regional standards, no universal standard. 3 rate hierarchies for PDH:European(2Mb/s) Japanese, North American(1.5Mb/s). Optical interfaces---no standards at all, manufacturers develop at their will.

Multiplexing methods:

Asynchronous 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 Where did I put did I put

the signals?the signals?

140Mb/s34Mb/s 34Mb/s

8Mb/s 8Mb/s

2Mb/s

140Mb/s

de-multiplexerde-multiplexer

de-multiplexer multiplexermultiplexer

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.4 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.

Advantages of SDH:

1 Interfaces Electrical interfaces:standard rate hierarchy(transmission speed level)The basic rate level is called Synchronous Transfer Module(STM-1), the other rate levels are the multiple of STM-1.

Optical interfaces:only scramble the electrical signals.SDH: optical code pattern is scrambled NRZ,PDH: optical code pattern is scrambled mBnB.

SDHSDH Signals Signals Bit rate(Bit rate(Mb/sMb/s))

STM-1STM-1 155.520 155.520 or or 155M155M

STM-4STM-4 622.080622.080 or or 622M622M

STM-16STM-16 2488.3202488.320 or or 2.5G2.5G

STM-64STM-64 9953.2809953.280 or or 10G10G

SDH:high-rate signal is exactly 4 times that of the next low-rate signal.

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

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

STM-1STM-1

STM-1STM-1

STM-1STM-1

STM-1STM-1

STM-4STM-4

Byte interleaved

multiplexing

B1 B2 B3 C1 C2 C3A1 A2 A3

A3B2 B3B1 C1 A2 C2 C3A1

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

PackingPacking PPkkgg

AlignmentAlignment

PKPKG aG a

PKPKG bG b

STM-1STM-1

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

4 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, ATMPDH, ATMFDDI signalsFDDI signals

packingpacking

packagepackage PackagePackage

packingpacking transmittransmit

SDH SDH networknetwork

unpackingunpacking

PDH, ATMPDH, ATMFDDI signalsFDDI signals

SDHSDH compatibility schematics compatibility schematics

transmittransmit transmittransmit

Disadvantages of SDH1 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.

140M140M

34M34M

2M2M

11140M=64140M=642M2M

3334M=4834M=482M2M

63632M2M

STM-1STM-1(155M)(155M)

Components and functions

Multiplexing Procedure

Frame Structure and Multiplexing methods

140M140M

34M34M

2M2M

STM-NSTM-N

STM-N Frame Structure

9×270 ×N bytes9×270 ×N bytes

SOHSOH

SOHSOH

AU-PTRAU-PTR

11

334455

99

STM-N STM-N payloadpayload

(including (including POHPOH))

9×N9×N 261×N261×N270×N 270×N columnscolumns

Transmission Transmission directiondirection Transmit Transmit

left to right left to right up to downup to down

1 Characteristics of SDH signals: 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.

2 Composition 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.

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.

PkgPkg

PkgPkg PkgPkg

PkgPkgPkgPkg

PayloadPayloadPkgPkgLow-rate signals 1

Low-rate signals n

loading

POH

POH

packing

packing

STM-NSTM-N

loading

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 1Low-rate signal 1

Low-rate signal 2Low-rate signal 2

Low-rate signal nLow-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.

According to the value of AU, the receiver can directly drop low-rate signals from STM-N frame. That is to say we can get the “goods” directly from the “carriage” if we know the label of the “goods”. Because the “goods” are placed regularly in the “carriage”, we only need to know the first piece of “goods”.

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 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

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 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(SDH transmission

network)network)

2M

34M TU-PTRPrimary alignmentPrimary 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.

Multiplexing procedures of SDH 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.

TU-12TU-12

SDH Multiplexing Hierarchy

STM-NSTM-N VC-4VC-4

TUG-2TUG-2

TU-3TU-3

VC-12VC-12 C-12C-12

VC-3VC-3

C-4C-4

C-3C-3

139264kbit/s

34368kbit/s34368kbit/s

2048kbit/s

×N×N

×3×3

×7×7

×3×3

MappingMapping

Pointer Pointer processingprocessingAlign Align adjustmentadjustmentMultiplexingMultiplexing

TUG-3TUG-3

AU-4AU-4AUGAUG

SDH signalSDH signal

PDH signalsPDH signals

140M multiplexing procedures(140M →STM-N)

C4 VC4140M

Rate Adaptation POH To be continued

POH

125us 125us1 260 1 26199

1 1

C4---Container 4: A standard info structure corresponding to 140M,performs bit rate justification.VC4---Virtual Container 4: A standard info structure corresponding toC4, performs real-time performance monitoring of 140M

(continue)(continue)

AU-PTR

AU-4

9

10 270

RSOH

MSOH

AU-PTR

STM-N

1alignment SOH

payload

1

1

11

9

9

270

270xN

125us 125us

125us

1

9

STM-1

AU-4---Administrative Unit 4, a info structure corresponding toVC4, performs pointer alignment.140M—VC4—AU-4—STM-1,One STM-1 can only incorporate one 140M signal.

140M multiplexing procedures

C3 VC3

34M

Rate adaptation POH To be continuedPOH

125us 125us1 84 1 8599

1 1

34M multiplexing procedures

C3---Container 3: A standard info structure corresponding to 34M,performs bit rate justification.VC3---Virtual Container 3: A standard info structure corresponding to C4, performs real-time performance monitoring of 140M

(continue)(continue) TU-3 TUG-3POH

R R

VC4TU-PTR

H1H1H2H2H3H3 FillFill

GapGap

H1H1H2H2H3H3

RR

BIM

125us 125us 125us

11 868611

99 99

1111 8686

11

99

11 261261

×3

TU3---Tributary Unit 3: A standard info structure corresponding toVC3, performs primary alignment.TUG3---Tributary Unit Group 3: A standard info structure corresponding toTU3.34M—VC3—TU3—TUG3； 3 TUG3—VC4—STM-1；One STM-1 can hold 3 34M.

34M multiplexing procedures

C12 TU122M

Rate Adaptation

POH To be continued

125us1 4

9

1

VC12PrimaryAlignment

125us

9

1

125us

9

1

1 4 1 4

POH

PTR

2M multiplexing procedures

2M multiplexing procedures (2M →VC4)

C12--Container 12: A standard info structure corresponding to 2M, performs bit rate justificationfor 2M signals, 4 basic frames constitute a multi-frame.VC12---Virtual Container 12:A standard info structurecorresponding to 2M, performs real-time monitoring.TU12---Tributary Unit 12: A standard info structurecorresponding to VC12, performs primary pointer alignment forVC12.

2M multiplexing procedures (2M →VC4)

TUG29

R R TUG3

186

9

11 1

Byte InterleavedMultiplexing

×3 ×7

(continue)(continue)

125us 125us

ByteInterleavedMultiplexing

2M Multiplexing procedures(2M →VC4)TUG2---Tributary Unit Group 2TUG3---Tributary Unit Group 32M—C12—VC12—TU12； 3TU12—TUG2；7 TUG2—TUG3； 3TUG3—VC4—STM-1。 One STM-1 is able to hold 3×7×3= 63 2M. Multiplexing structure for 2M is 3-7-3.

SDH Multiplexer

C12

C12

C12

C12

STM-1

STM-1

STM-1

STM-1

1#

3#

2#

4#

1#

3#

2#

4#

63 2M

Concept of multi-frame: 4 C12 basic frames make up 1 multi-frame. Both basic frames and multi-frame carry the same 2M signal. One basic frame can hold the info segment of 2M signal during 125us period. One multi-frame holds the info for 2M signal during 500us period.

Relations between info structures

E1 C12 VC12 TU12

E3 C3 VC3 TU3

E4 C4 VC4

Summary STM-N frame structure and functions of different parts of the frame Methods for multiplexing PDH into STM-N frames 140M multiplexed into STM-N frames 34M multiplexed into STM-N frames 2M multiplexed into STM-N frames

Section Overhead

Overhead

Overhead and Pointers

Pointers

Path Overhead

AU-PTR TU-PTR

OverheadOverhead

SOHSOH

RSOHRSOH MSOHMSOH

POHPOH

VC4VC4POHPOH

VC12VC12 POHPOH

(HPOH) (LPOH)

Layered monitoring

STM-N RSOH

STM-1MSOH

VC4HO-POH

VC12LO-POH

SOH(take STM-1 as an example)

A1A1 A1A1 A1A1 A2A2 A2A2 A2A2 J0J0B1B1D1D1

B2B2D4D4D7D7D10D10S1S1

B2B2 B2B2 K1K1D5D5D8D8D11D11

M1M1 E2E2D12D12D9D9D6D6K2K2

F1F1D3D3

E1E1D2D2

AU-PTRAU-PTR

** **

**

RSOHRSOH

MSOHMSOH

Bytes reserved for domestic useBytes reserved for domestic use

Marked bytes are not scrambledMarked bytes are not scrambled

1 2 3 4 5 6 7 8 91 2 3 4 5 6 7 8 9112233445566778899

** ** ** ********

STM-N STM-N STM-N STM-N STM-N STM-N

Signal streamSignal stream

1) Framing bytes:A1,A2 to locate the frame heads

Frame Frame Head?Head?

Next Next processprocess

FoundA1,A2?

Give OOF

Generate LOF

N

Y

Insert AIS

Over 3ms

2) DCC Data Communication Channel bytes:D1—D12 An info channel for OAM between NE-NE D1-D3 is in Regenerator section(DCCR), D4-D12 is in Multiplex section(DCCM),

OAM info includes: performance monitoring, alarms inquiry, command issue,etc.

DCC channelNM

UTP

3) Order wire bytes: E1,E2 Each provides a 64kb/s order wire digital telephone. E1is for RS order wire E2 is for MS order wire E2can not be used by a REGs

4) Bit interleaved parity byte:B1 Performs real-time monitoring over the signal stream

A1 00110011A2 11001100A3 10101010A4 00001111

B 01011010

BIP-8

Bit Interleaved parity

B1 working mechanism:

SDHSDHEquipmentEquipment

SendingSending

SDHSDHEquipmentEquipmentReceivingReceiving

Detect B1Detect B1Insert B1Insert B1

STM-NSTM-N

If error blocks occurredIf error blocks occurredproduce: RS-BBEproduce: RS-BBEperformance eventperformance event

5) Bit interleaved Parity B2 byte monitor the error blocks of MS

SDHSDHEquipmentEquipment

SendingSending

SDHSDHEquipmentEquipmentReceivingReceiving

Detect B2Detect B2Insert B2Insert B2

STM-NSTM-N

If error blocks occurredIf error blocks occurredproduce: MS-BBEproduce: MS-BBEperformance eventperformance event

SDHSDHEquipmentEquipment

SenderSender

SDHSDHEquipmentEquipment

ReceiverReceiver

STM-NSTM-N

Error blocks foundError blocks foundproduce: MS-BBEproduce: MS-BBEperformance eventperformance event

Send M1Send M1bytebyte

M1 receivedM1 receivedproduce: MS-REIproduce: MS-REIperformance eventperformance event

6) Multiplex section Remote Error Indication byte:M1 Sent from receiver to sender Informs the sender: the error blocks detected by receiver through B2

7) Automatic Protection Switching(APS) bytes---K1,K2

Carries APS protocol for MSP switching

MS Remote Defect Indication byte: K2(b6-b8)=111, indicates that all “1” signals have been received, receiver will give MS-AIS alarm K2(b6-b8)=110, indicates that MS-RDI has been received, which means the counter-part has received signal deterioration, such as MS-AIS, RLOF etc.

K2 Detection

Sending backMS-RDI

GivingMS-AIS

FoundK2(b6-b8)

ProducingMS-RDI

111

110

SDHSDHEquipmentEquipment

SenderSender

SDHSDHEquipmentEquipment

ReceiverReceiver

STM-NSTM-N

Find K2(111)Find K2(111)produce: MS-AISproduce: MS-AIS

alarm eventalarm event

Sending back K2Sending back K2(110)(110)

Receive K2(110)Receive K2(110)produce: MS-RDIproduce: MS-RDI

alarm eventalarm event

8) Synchronous Status byte S1(bit5~8) For synchronous status indication The smaller the value of S1, the higher the

quality of synchronous clock!

2 Path Overhead2 Path Overhead

VC4VC4POHPOH

VC12VC12 POHPOH

(HPOH) (LPOH)

Classification: Lower-order POH--VC12 Higher-order POH---VC4 Difference: VC-4 macro, VC-12 micro VC-4 includes VC-12