SDH Advantages over PDH | Synchronous Digital Hierarchy Advantages over plesiochronous digital hierarchy

 SDH Advantages over PDH | Synchronous Digital Hierarchy Advantages over plesiochronous digital hierarchy

SDH Advantages

 1. Worldwide Standard Bit Rates:

 An international hierarchy shared worldwide and creation of worldwide standard rates above 140 Mbps 

2. Synchronous Clock: 

The SDH system maintains a synchronous clock throughout a defined area. All clocks in the system gets synchronized with a centralized clock known as Primary Rate Clock. 

For example in India BSNL has the Primary Rate clock in the VSNL headquarters Worli, Mumbai. All the clocks in SDH system of BSNL get synchronized with respect to this clock. 

This feature gives of the advantage of avoiding the errors in streams due to different clock speeds. The addition of justification bits such as positive justification, negative justification, justification control bits is not needed at each MUX stage for error identification and correction. 

Byte Interleaving Multiplexing: In SDH system the multiplexing is done by byte interleaving instead of bit interleaving as followed in PDH systems. 

3. Direct Access to Lower Speed Tributaries:

 In PDH to drop a 2mbps stream from say E5 (565 mbps) 4 stages of demultiplexing is necessary, that is from 565 to 140, 140 to 34, 34 to 8, 8 to 2 mbps. 

The needed 2mbps is dropped and for carrying out the transmission of remaining tributaries, again multiplexing is to be done from 2 to 8, 8 to 34, 34 to 140, 140 to 565 mbps, where as in SDH any tributary for example an E1 (2 mbps) stream can be dropped from any stage, even from STM 64 without the necessity of demultiplexing or multiplexing at any stage or disturbing the other tributaries

This maintains the transparency of each bit stream and any bit stream can be dropped from any stage of SDH. For example a 2 Mbps tributary can be dropped even from STM-64, without any necessity of disturbing the other tributaries. 

4. Drop & Insert Mux: 

Individual tributaries of any bandwidth can be dropped or inserted at any multiplexer at any stage, even from STM-64, without any need for demultiplexing. 

5. World Wide Compatibility: 

SDH can transport both E and T hierarchy tributaries without the need of using any additional interfacing equipment. Any tributary of E system or T system can be introduced at any stage of SDH system. 

The tributaries standardized by ITU (T) for introduction to SDH are E1 (2mbps), E3 (34 mbps), E4 (140 mbps), T1 (1.544 mbps), T2 (6.312 mbps), T3 (45 mbps). 

READWhat is SDH? Synchronous Digital Hierarchy

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