TRAFFIC MANAGEMENT FOR AN ATM SWITCH WITH PER-VC QUEUING - CONCEPT AND IMPLEMENTATION

The services to be supported by an asynchronous transfer mode (ATM)-ba sed multiservice network differ significantly in terms of their traffi c characteristics and required quality of service. During the last few years it has been broadly accepted that efficient use of transmission capacity is not possible unless these differences are reflected in th e way the related traffic streams are handled within the ATM layer. To address this need, the ATM Forum and ITU-T [1, 3] have specified diff erent real-time and non-real-time ATM-layer service categories. This a rticle first discusses the requirements for traffic management in a sw itch supporting all these service categories from the service provider s' and users' points of view. The first generation of ATM switches. ty pically equipped with small cell buffers, only satisfies the requireme nts for the real-time service categories (CBR, rt-VBR). Statistical mu ltiplexing, if supported at all, is limited to connections with low pe ak cell rates. Larger cell buffers and new traffic control functions a re required to support non-real-time service categories (nrt-VBR, ABR, UBR). In the second part of this article a switch architecture which is scalable from small to large system sizes is presented. It provides the required buffering and additional functions for the non-realtime service categories with the aid of a statistical multiplexing unit (SM U), a module which can also be used as an optional addition to a conve ntional ATM switch. The focus is on the functional description of two novel yet key components of the SMU, namely the buffer management and cell scheduling functions. The buffer management function provides per -VC queuing and achieves an optimal utilization of the large cell buff er shared by connections of different service categories. The two-stag e cell scheduling function supports traffic shaping on the VC and VP l evels, and Weighted Fair Queuing within groups of connections. The ove rall concept supports high link utilization, fairness. and throughput guarantees, and enables a migration from today's ATM networks to a ful ly integrated multiservice network. Finally, implementation aspects ar e discussed to show the feasibility of the concept for very high bit r ates.