Multiple-ring Architecture and Its Fddi Applications

This paper discusses a networking concept referred to as Multiple-Ring Architecture (MRA). In FDDI reliability applications, MRA is an attractive alternative to the popular dual homing architecture for the following reason. Unlike the requirement of several reliable concentrators needed in the dual homing architecture, the MRA only requires several routing interfaces at each backbone node (i.e., at each router node); different fiber cables and networks share the same set of routers, creating a set of highly fault tolerant networks of low overall cost and complexity. 1 MULTIPLE-RING ARCHITECTURE An important consideration in the design of a computer network is the reliability and availability of communication paths among all nodes of the network. Implementing some form of network redundancy can improve in reliability; however, the resulting system cost and complexity also increase. Generally, it is desirable to maximize the number of links and nodes that must fail in order to disrupt the operation of the network, subject to fixed cost constraints. This paper presents a networking concept, which we refer to as Multiple-Ring Architecture (MRA), that is closely related to the multiplechannel ring network mentioned in [1]. We use the ring topology [e.g., a Fiber Distributed Data Interface (FDDI) token ring] to illustrate the main concept, though the MRA is applicable to many other types of network topologies. Suppose that one would like to use a number of links to connect stations. A simple ring configuration shown in Fig. 1 will satisfy this need; however, such a simple ring is vulnerable to link failures. To increase the reliability of the network, its nodes can be dual homed with the cost of two additional concentrators (CONs) as well as many additional links (see N Fig. 2). Generally, there is a trade-off in reliability and cost in network design. As an alternative to dual homing, the MRA shown in Fig. 3 can offer some reliability with lower cost. The MRA is accomplished by requiring each station that is connected to multiple rings to be able to route the traffic among different rings. Such a station can be fulfilled by a modern router or a gateway, which is capable of directing the traffic from one ring to another when a link is congested or disconnected either by system mal-function or by scheduled outage. Therefore, network management (e.g., taking a station out of the ring for service) can be simplified with the MRA, whose required number of links is only slightly more than that of the simple ring network. Fig. 1 Simple Ring Configuration Fig. 2 Dual Homing Architecture Fig. 3 Multiple-Ring Architecture CON CON