News & Events
Article Published in CommsDesign
January 6, 2005 - A wide variety of user services are supported by metro networks to provide customers with bandwidth requirements to meet their growing demands. Several types of low-rate services such as voice and data enter the network edge through service adapters and are multiplexed together into virtual tributaries for switching and transport over Sonet. Virtual tributaries (VTs) are commonly used for grooming applications where sub STS-1 level signals are generated from a number of sources operating at various rates and combined into a higher-speed, channelized data pipe. Some end users, for example, may demand T1 rate services of 1.544-Mbit/s mapped into VT1.5 virtual tributary types while others may require an E1 rate service of 2.048 Mbit/s mapped into a VT2 virtual tributary type.
This article will look inside Sonet and focus on VT management and processing during transport through the network. Operations such as interleaving, pointer processing, tributary alignment for switching, overhead processing, and support for protection mechanisms including unidirectional path switched rings (UPSR) will be discussed. Finally, a virtual tributary switch application will be provided to tie in all the concepts discussed.
Understanding Sonet VTs: A Tutorial
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