Presentation on theme: "Fiber Optic Communication By Engr. Muhammad Ashraf Bhutta."— Presentation transcript:
Fiber Optic Communication By Engr. Muhammad Ashraf Bhutta
Lecture Outlines SDH Overview Frame structure and multiplex-ing methods Overheads and Pointers
Disadvantages of PDH Disadvan- tages of SDH Disadvan- tages 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 did I put the signals?
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.
SDH Signals Bit rate(Mb/s) STM or 155M STM or 622M STM or 2.5G STM or 10G SDH:high-rate signal is exactly 4 times that of the next low-rate signal.
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.: PDHPDH Packing PkgPkgPkgPkg Alignment PK G a PK G b STM-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.
Disadvantages of SDH 1 low bandwidth utilization ratio--- contradiction between efficiency and reliability. 2 Mechanism of pointer adjustment is complex, it can cause pointer adjustment jitters 3 Large-scale application of software makes SDH system vulnerable to viruses or mistakes. 140M 34M 2M 1 140M=64 2M 3 34M=48 2M 63 2M STM-1 STM-1(155M)
Components and functions Multiplexing Procedure Frame Structure and Multiplexing methods 140M 34M 2M STM-N
STM-N Frame Structure 9×270 ×N bytes SOH SOH AU-PTR STM-N payload (including POH) (including POH) 9×N261×N 270×N columns Transmission direction Transmit left to right up 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 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.Pkg PkgPkg PkgPkg Payload Pkg Low-rate signals 1 Low-rate signals n loading POH packing STM-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 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.
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”.
Sending: AU-PTR indicates the first info package Receiving: According to the value of AU-PTR, get the first info package, through the regularity of byte interleaved multiplexing, get the other packages (SDH transmission network) network)
2M 34M TU-PTR Primary alignment AU-PTR Secondary 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.
140M multiplexing procedures (140M →STM-N) C4 VC4 140M Rate Adaptation POH To be continued POHPOH 125us 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) AU-PTR AU RSOH MSOH AU-PTR STM-N 1 alignment SOH payload xN 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
C3VC3 34M Rate adaptation POH To be continued POHPOH 125us M 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) TU-3TUG-3 POHPOH R VC4 TU- PTR H1H2H3 FillGap H1H2H3 R BIM 125us ×3 TU3---Tributary Unit 3: A standard info structure corresponding to VC3, 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 TU12 2M Rate Adaptation POH To be continued 125us VC12 Primary Alignment 125us POH PTR 2M multiplexing procedures
2M multiplexing procedures (2M →VC4) C12--Container 12: A standard info structure corresponding to 2M, performs bit rate justification for 2M signals, 4 basic frames constitute a multi-frame. VC12---Virtual Container 12:A standard info structure corresponding to 2M, performs real-time monitoring. TU12---Tributary Unit 12: A standard info structure corresponding to VC12, performs primary pointer alignment forVC12.
2M Multiplexing procedures (2M →VC4) TUG2---Tributary Unit Group 2 TUG3---Tributary Unit Group 3 2M—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
SDH Multiplexer C12 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 VC3TU3 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 and Pointers Pointers Path Overhead AU-PTRTU-PTR
Overhead SOH RSOH MSOH POH VC4 PO H VC12 POH POH (HPOH) (LPOH)
SOH(take STM-1 as an example ) A1A1A1A2A2A2J0 B1 D1 B2 D4 D7 D10 S1 B2B2K1 D5 D8 D11 M1E2 D12 D9 D6 K2 F1 D3 E1 D2 AU-PTR ** * RSOH MSOH Bytes reserved for domestic use Marked bytes are not scrambled *******
STM-N Signal stream 1) Framing bytes:A1,A2 to locate the frame heads
Frame Head? Next process Found A1,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 channel NM 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
Bit Interleaved parity
B1 working mechanism: SDHEquipmentSendingSDHEquipmentReceiving Detect B1 Insert B1 STM-N If error blocks occurred produce: RS-BBE performance event
5) Bit interleaved Parity B2 byte monitor the error blocks of MSSDHEquipmentSendingSDHEquipmentReceiving Detect B2 Insert B2 STM-N If error blocks occurred produce: MS-BBE performance event
SDH SDHEquipmentSender EquipmentReceiver STM-N Error blocks found produce: MS-BBE performance event Send M1 byte M1 received produce: MS-REI performance 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 back MS-RDI Giving MS-AIS Found K2(b6-b8) Producing MS-RDI