The paper proposes the integration of ATM’s connection-oriented switching hardware with the connectionless IP protocol. The proposal is made to exploit the bandwidth and capacity scalability offered by ATM and the connectionless, flexible operation of IP. The idea is eliminate the traditional end-to-end connections in ATM by preserving a cached soft-state of the IP forwarding over time and making local decisions on the type of flow forwarding to be used for the future downstream packets. The paper introduces these basic ideas and delves into the specific details of IP switching, the system structure, flow control semantics and its advantages.
The paper recognizes other IP over ATM integration technologies which tend to obscure the physical layer from IP resulting in the problem of duplication of underlying routing protocol, maintenance and management functions. It points out the explosion in the number of link layer connections between routers that are required when using such technologies in a cloud environment. The paper then introduces the concept of flows which are the logical equivalents of connections in a connection-oriented with the exception that the flow forwarding decisions are purely based on local temporal data of traffic that is cached on the router. Traffic with predominantly short packets will use a connectionless IP forward and longer packets flows will use ATM switching. The two main flow classifications that are performed by the IP switch controller are the port-pair and host-pair flows which influence the forwarding decisions.
The task of integrating ATM under IP is done by replacing the complex ATM software by a more general low-level protocol (GSMP) and building the interface (IFMP) to enable IP to make use of the ATM switching hardware. Flow switches are made from connectionless to virtual circuit flow by binding a free label to the recipient port and routing all further forwarding through the IP switch controller. A downstream node wishing to redirect its flow sends an IFMP message back to the IP switch which then instructs the ATM hardware to make the appropriate direction switch by binding the new label to the output port. In essence IFMP signaling information travels upstream opposite to the direction of data flow. The IFMP redirection message additionally contains the flow identifier which has the header field and lifetime information, the lifetime information is used to compute the refresh rate of the cached flow state. The paper then describes how the lifetime (TTL-time to live) information is subject to preserved propagation by taking a checksum over the header and the lifetime. IFMP ensures the robustness (no drops or corruption) of packet delivery by enforcing adjacency among neighboring nodes and by diminishing the lifetime of inconsistent data. The state information stored at IP is soft because it serves only an advisory purpose and redirection messages can be ignored thus preserving local autonomy. Multicast support and QoS guarantees are then demonstrated followed by a set of host-pair flow experiments. The paper adopts a PPP network model as opposed to a cloud model but does not explain the repercussions of this assumption and the scalability issues that might arise.
The future trends arising from this paper could be development and detailed specification of other integration protocols similar to those quoted in the ‘related work’ section of the paper, which tap the potential throughput achieved from a connection-oriented protocol at the same time allowing the flexibility of a datagram service like IP.
