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Fiber Optic CommunicationBy
Engr. Muhammad Ashraf Bhutta
Lecture Outlines
SDH Overview
Frame structure and multiplex-ing methods
Overheads and Pointers
Disadvantages of PDH
Disadvantages of PDH
Disadvan-tageDisadvan-tages of SDHs of SDH
Disadvan-tageDisadvan-tages of SDHs of SDH
Background of SDH
Background of SDH
Advantages 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 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.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
Components and functions
Multiplexing Procedure
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
PayloadPayload
PkgPkgLow-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 processingprocessing
Align Align adjustmentadjustment
MultiplexingMultiplexing
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 1 261
99
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-3
POH
R R
VC4
TU-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)
TUG2
9
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
Section Overhead
OverheadOverhead
Overhead and Pointers
Pointers
Path Overhead
Path Overhead
AU-PTRAU-PTR TU-PTRTU-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 J0J0
B1B1
D1D1
B2B2D4D4
D7D7D10D10
S1S1
B2B2 B2B2 K1K1D5D5
D8D8D11D11
M1M1 E2E2D12D12
D9D9D6D6K2K2
F1F1
D3D3
E1E1
D2D2
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
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