Transformer Tunnels: A Framework for Providing Route Specific Adaptations

This research work was supported in part by DARPA under contract numbers DAAH04-95-1-0596 and DAAG55-97-1-0322, NSF grant numbers CCR 95-09620, IRIS 95-09816 and Sponsors of WINLAB.

In a network using links with diverse properties, a packet flow that is fine tuned for some links (by selecting a proper packet size, transmission rate, encryption method, etc.) may be inappropriate for other links. Ability to change the flow properties over segments of the network allows flows with different characteristics to coexist; making it possible to adapt to diverse link properties. Application-specific adaptation mechanisms (such as proxies) do not force adaptations on every packet flowing over the link and are therefore insufficient for this purpose. We propose the concept of transformer tunnels that force adaptations on all the packets flowing through them. Transformer tunnels can coexist with proxies because the adaptations provided by both are independent of each other. Transformer tunnels provide adaptations by means of transformation functions. By attaching various transformation functions to such tunnels, we can efficiently fine tune the flow properties. We also provide an API for developing transformation functions. We have implemented transformer tunnels and have used them in our wireless network. In this paper, we present the effects on mobile hosts that use this mechanism to transform flows over the last-hop link for reducing losses during handoffs, and for improving the link utilization.