Rerouting Methods

In ATM-based wireless networks, fast, seamless, and distributed handoff is a critical issue. Handoff call management plays a major role in supporting acceptable levels of QoS in Personal Communication Systems.

Some of the important concerns in performing such connection rerouting are

• limiting handoff latency;

• maintaining an efficient route;

• limiting disruption of continuous media traffic;

• limiting network switch update rates due to rerouting.

Limiting handoff latency is essential, particularly in microcellular networks where handoffs may occur frequently, and users may suddenly lose contact with the previous wireless AP. The process of maintaining an efficient route can also potentially lead to disruptions in user traffic that are intolerable for continuous media applications such as packetized audio and video. Thus, it is important to achieve a suitable trade-off between the goals of maintaining an efficient route and limiting disruption to continuous media traffic while maintaining low handoff latency at the same time. In order to not overload the switch, this must be done while keeping the switch updates due to connection rerouting, low.

Connection rerouting procedures for ATM-based wireless networks include handoff schemes, which are Switched Virtual Circuit (SVC)-based and PVC-based schemes.

Connection rerouting involves the location of the COS. A COS is defined to be the farthest switch from the fixed endpoint that is also the point of divergence between the new and old routes connecting the mobile and fixed endpoint.

Four general approaches toward connection rerouting are proposed:

• Optimistic handoff approach

• Ordered handoff approach

• Predictive handoff approach

• Chaining handoff approach.

The goal of an optimistic handoff scheme is to perform simple and fast handoffs with the optimistic view that disruption to user traffic will be minimal. The COS simply reroutes data traffic through a different path to the new BS with the connection from the source to the COS remaining unmodified.

The goal of an ordered approach is to provide ordered lossless data delivery during handoffs. The incremental and multicast-based rerouting schemes fall into this category.

However, complex protocols with resynchronization mechanisms and buffering at the BS are necessary to ensure lossless connection rerouting.

In predictive approaches to connection rerouting, the key idea is to predict the next BS of the mobile endpoint and perform advance multicasting of data to the BS. This approach requires the maintenance of multiple connection paths to many or all the neighbors of the current BS of the mobile endpoint.

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