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Fiber Optic Communication By

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Presentation on theme: "Fiber Optic Communication By"— Presentation transcript:

1 Fiber Optic Communication By
Engr. Muhammad Ashraf Bhutta

2 Lecture Outlines SDH Overview
Frame structure and multiplex-ing methods Overheads and Pointers

3 SDH Overview Background of SDH Disadvantages of PDH Advantages of SDH
Disadvan-tages of SDH

4 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

5 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.

6 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?

7 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.

8 OAM 4 No universal network management interface
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.

9 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.

10 SDH:high-rate signal is exactly 4 times that
SDH Signals Bit rate(Mb/s) STM-1 or 155M STM-4 or 622M STM-16 or 2.5G STM-64 or 10G SDH:high-rate signal is exactly 4 times that of the next low-rate signal.

11 SDH:4×STM-1=STM-4 ;4×STM-4=STM-16

12 2 Multiplexing methods:
low-rate SDH→high-rate SDH(e.g.:4  STM-1→STM-4). Uses byte interleaved multiplexing method. STM-1 STM-4 Byte interleaved multiplexing

13 Byte interleaved multiplexing

14 PDH 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.: PDH Packing Pkg Alignment PKG a PKG b STM-1

15 3 OAM 4 Compatibility 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.

16 SDH compatibility schematics
PDH, ATM FDDI signals packing SDH network Package package STM-N STM-N packing transmit transmit transmit unpacking PDH, ATM FDDI signals

17 Disadvantages of SDH 2M STM-1 (155M) 34M 140M
1 low bandwidth utilization ratio--- contradiction between efficiency and reliability. 140M 34M 2M 1140M=642M 334M=482M 632M STM-1 (155M) 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.

18 Frame Structure and Multiplexing methods
Multiplexing Procedure Components and functions 140M 34M 2M STM-N

19 STM-N Frame Structure Transmission direction 1 SOH 3 4 AU-PTR
9×270 ×N bytes Transmission direction 1 Transmit left to right up to down SOH 3 4 AU-PTR STM-N payload (including POH) 5 SOH 9 9×N 261×N 270×N columns

20 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.

21 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 Payload Low-rate signals 1 Low-rate signals n loading POH packing STM-N