Dual-mode routing: a generic framework for IP over ATM integrated routing

Design issues for an integrated routing architecture for IP and ATM are outlined. Two separate aspects of this integration are: (1) a common routing architecture for IP and ATM (layer integration) and (2) integrating best-effort (BE) and QoS routing architecture (service integration). Whereas the first level of integration is highly recommended, we show that the second level of integration is not desirable because BE and QoS traffic have, in terms of routing, contradictory requirements. Four criteria are proposed, namely, route refreshing vs. route pinning, hop by hop vs. explicit routing, pre-computed routes vs. on-demand route computation and stable vs resource related metrics. A fifth alternative is whether or not to integrate in the routing architecture the capability to compute shortcut paths, that are bypassing layer 3 (L3) nodes and using only layer 2 (L2) devices. Using this framework, we conclude that BE traffic flows are well served by a combination of route refreshing, hop by hop routing pre-computed routes and static routing metrics while QoS routing is built on route pinning, explicit routing, on-demand route computation and resource related metrics. Finally, the ability to compute L2 shortcuts in an L2/L3 integrated routing architecture is an added value simplifying the overall network design and optimising the efficacy of the forwarding path