12-10-2010, 04:32 PM
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SDH Concepts & Principle
Department of Electronics and Telecommunication
Made by :
Siddharth Shetty (748)
Aditya Singh(749)
Aditya Vikram Singh(750)
Sohil Singh(751)
Mayank Wahal(755)
Introduction
It is an international standard networking principle and a multiplexing method. The name of hierarchy has been taken from the multiplexing method which is synchronous by nature. The evolution of this system will assist in improving the economy of operability and reliability of a digital network.
1. Historical Overview
In February 1988, an agreement was reached at CCITT (now ITU-TS) study group XVIII in Seoul, on set of recommendations, for a synchronous digital hierarchy representing a single world wide standard for transporting the digital signal. These recommendations G-707, G-708, G-709 cover the functional characteristic of the network node interface, i.e. the bit rates and format of the signal passing over the Network Node Interface (NNI).
For smooth transformation from existing PDH, it has to accommodate the three different country standards of PDH developed over a time period. The different standards of PDH are given in Fig.1.
The first attempt to formulate standards for Optical Transmission started in U.S.A. as SONET (Synchronous Optical Network). The aim of these standards was to simplify interconnection between network operators by allowing inter-connection of equipment from different vendors to the extent that compatibility could be achieved. It was achieved by SDH in 1990, when the CCITT accepted the recommendations for physical layer network interface. The SONET hierarchy from 52 Mbit per second rate onwards was accepted for SDH hierarchy (Fig.1).
2. Merits of SDH
(i) Simplified multiplexing/demultiplexing techniques.
(ii) Direct access to lower speed tributaries, without need to multiplex/demultiplex the entire high speed signal.
(iii) Enhanced operations, Administration, Maintenance and provisioning capabilities.
(iv) Easy growth to higher bit rates in step with evolution of transmission technology.
(v) Capable of transporting existing PDH signals.
(vi) Capable of transporting future broadband (ATM) channel bit rates.
(vii) Capable of operating in a multi-vendor and multi-operator environment.