Routing and virtual-path design in ATM networks

The routing of virtual channel connections in an asynchronous transfer mode (ATM) network will have a strong effect on the engineering of ATM virtual paths proposed in ITU-T standards. This paper explores the relative economics of ATM routing schemes, the comparison being between an Internet-like scheme in which routes may use many links (virtual paths) and one in which the choice is limited to the use of single-link and two-link routes, as in most metropolitan telephone (circuit-switched) networks. The specific question studied is "what cost-penalty will be incurred in virtual path design if alternate routes for ATM connections are limited to a maximum of two links in series?" Such a constraint simplifies the routing implementation in ATM networks considerably. The use of virtual channels for ATM connections makes for a basic similarity with circuit-switched networks, suggesting that the knowledge and experience gained with the design and operation of circuit-switched networks should be useful for ATM networks (e.g., ATM virtual paths correspond to trunk-groups in circuit-switched networks). Hence, to study this question, we make use of a well-known network design algorithm for circuit-switched networks, known as the unified algorithm. Our results show that the restriction to two-link routes imposes no penalty on network cost when the offered loads are large enough to ensure moderate connectivity in the network (as is expected in broadband ATM networks), and when virtual-path bandwidth is allocated in units of the bandwidth of the dominant traffic in the network.