| Popis: |
Currently, the ATM Forum’s Wireless ATM (WATM) working group is in the process of developing a set of new specifications for ATM mobility. The work encompasses the definition of a new 25 Mbps air-interface, suitable location management and a fast handoff scheme. To date, most of the working group contributions have focussed on extensions to existing signalling specifications with little regard for the type of Quality of Service (QOS) which could be achieved during handoff. The working group considers WATM to be a direct extension to the standard ATM specification with uniformity of end-to-end QOS. In this paper we advocate an alternative approach. We argue that large-scale mobility requirements, limited radio resources, and fluctuation network conditions make the delivery of hard QOS guarantees in the wireless domain very difficult. To address this challenge, we are implementing a QOS-aware middleware platform called “mobiware” which operates between the application and radio ATM link layers. At the heart of the mobiware platform lies a QOS controlled handoff algorithm which exploits the inherent scalability of audio and video flows. Implicit in the term “QOS controlled” is the notion that audio and video flows can be represented as multi-layer scalable flows and adapted during handoff to meet fluctuating network conditions based on a user-supplied QOS adaptation policy. Novel aspects of the mobiware QOS controlled handoff signalling algorithm include the use of mobile-soft-state to represent mobile flows, aggregation techniques for bundling and transporting mobile flows to and from mobile devices, and re-routing and QOS re-negotiation anchor points which limit the impact of small scale mobility on the wireline network. |
