Presentation on theme: "Fiber Optic Communication By"— Presentation transcript:
1Fiber Optic Communication By Engr. Muhammad Ashraf Bhutta
2Lecture Outlines SDH Overview Frame structure and multiplex-ing methodsOverheads and Pointers
3SDH Overview Background of SDH Disadvantages of PDH Advantages of SDH Disadvan-tages of SDH
4Background about SDH emergence What is SDH--Synchronous Digital Hierarchy. Similar toPDH，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-highwayStandard---universal interface all over the world
5Disadvantages 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.
6Multiplexing methods: Asynchronous Multiplexing for PDH:The location of low-rate signals in high-rate signals is notregular nor predictable. So it is impossible to directlyadd/drop low-rate signals from high-rate signals.Wheredid I putthe signals?
7Low-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.
8OAM 4 No universal network management interface OAM function affects the maintenance cost.It is determinedby the number of overhead bytes(redundant bytes);There are VERY few redundant byes available in PDHsignals which can be used as OAM purpose, so OAM in PDHis very poor, it is unreliable either.4 No universal network management interfaceIt is hard to set up an integrated networkmanagement. No way to form a universal TMN.PDH is inappropriate to transmit huge-volume signals, soSDH came to play the part.
9Advantages 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.
10SDH:high-rate signal is exactly 4 times that SDH SignalsBit rate(Mb/s)STM-1or 155MSTM-4or 622MSTM-16or 2.5GSTM-64or 10GSDH:high-rate signal is exactly 4 times thatof the next low-rate signal.
14PDH Pkg Packing PKG a PKG b 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.:PDHPackingPkgAlignmentPKG aPKG bSTM-1
153 OAM 4 Compatibility More bytes in SDH frame structure are used for OAM purpose, about 5% of total bytes. SDH boastsof high capability of OAM.4 CompatibilitySDH is compatible with the existing PDH system.SDH allows new types of equipment to be used,allows broadband access, such as ATM.
17Disadvantages of SDH 2M STM-1 (155M) 34M 140M 1 low bandwidth utilization ratio--- contradictionbetween efficiency and reliability.140M34M2M1140M=642M334M=482M632MSTM-1(155M)2 Mechanism of pointer adjustment is complex, it cancause pointer adjustment jitters3 Large-scale application of software makes SDH systemvulnerable to viruses or mistakes.
18Frame Structure and Multiplexing methods Multiplexing ProcedureComponents and functions140M34M2MSTM-N
19STM-N Frame Structure Transmission direction 1 SOH 3 4 AU-PTR 9×270 ×N bytesTransmission direction1Transmitleft to rightup to downSOH34AU-PTRSTM-N payload(including POH)5SOH99×N261×N270×N columns
201 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 framestructure. All kinds of effective info, such as 2M, 34M ,140M are first packed before being stored here. Thenthey are carried by STM-N signals over the SDH network.
21If we should consider STM-N signal to be a truck, then info payload would be the carriage of the truck. In order tomonitor the transmission status of the goods duringtransportation, POH are added to each information package.PkgPayloadLow-rate signals 1Low-rate signals nloadingPOHpackingSTM-N