N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 5 - SONET, WDM, DWDM and B-ISDN Tchnologies                                                                  Slide 1 of 76 _________________                                                                                  __________

Objectives:

This module provides an introduction to the optical communications basics, optical communications standards and optical transmission technologies. The information transmission through an optical fiber changed the communications industry. An optical fiber has more data transmission capability than a copper and a coaxial cable. The optical fibers carry light rays. The light rays operate at Tera Hz. The transmission wavelengths used for single-mode fibers are in micrometers range. Potentially an optical fiber is capable of carrying a Tera bps. Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) are a set of standards for a fiber optic transmission medium specifically designed for broadband data applications. SONET is transport interface that allows a network to transport various kinds of services. SONET is the North American optical fiber standard that supports transmission rates up to 2.488 G bits per sec on a single fiber. The basic starting rate for SONET is 51.84 M bps. SONET’s equivalent European optical transmission standard is Synchronous Digital Hierarchy (SDH). CCITT recommended an international standard based on OC-3 (155.520 M bps) that allowed European industry to multiplex 34 M bps signal. The rates hierarchies for SONET and SDH are different. Both hierarchies come together at OC-3 level. SONET standards are based on ANSI standards and SDH standards are based on CCITT-ITU recommendations. Wave Division Multiplexing (WDM) and Dense Wave Division Multiplexing (DWDM) optical transmission technologies allow multiple waves to carry data simultaneously over a single fiber, hence increasing the fiber throughput. A single fiber is capable of carrying data up to 10 G bps. WDM doubles the fiber transmission capability by enabling to transmit two wavelengths simultaneously. DWDM technology allows multiple wavelengths simultaneously through a fiber. At present DWDM equipment is available off-the-shelf for 16 wavelengths through a fiber. The laboratory results have demonstrated 80 wavelengths through a fiber. The CCITT has also selected ATM as a target architecture for basic transport within Synchronous Optical Network (SONET) / Synchronous Digital Hierarchy (SDH). SONET has been widely used in carriers’ core network and Metropolitan Area Networks. SONET has built-in diagnostics mechanism to detect transmission facilities failures. This module also introduces B-ISDN, an enhancement to N-ISDN standards for broadband communications. Adaptation Layers in ATM are as a result of B-ISDN. B-ISDN is a broadband network in which ATM and SONET transport is used to provide services based on connection orientation, end-to-end timing relation, Constant bit rate and variable bit rate service characteristics. Case studies of the application of this technology have been included in the module to reinforce the value of this technology for wide area networking.

The objective of this module is to cover:

1.0   Optical transmission basics

2.0   Optical transmission hierarchy

3.0   SONET and SDH standards

4.0   SONET signaling rates

5.0   SONET architecture

6.0   SONET Rings

7.0   B-ISDN

8.0   Wave Division Multiplexing (WDM)

9.0   Dense Wave Division Multiplexing (DWDM)

10.0  Future optical communications networks

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