A local area network (LAN) segment is a computer sub-network which includes multiple stations in the same physical area communicating by forwarding messages on a shared LAN media. Stations on different LAN segments in the same physical area often communicate through a shared LAN switching fabric, which selectively forwards messages received over the fabric to the destination LAN segment. Stations on different LAN segments in different physical areas, in contrast, often communicate over a backbone network which interconnects multiple LAN switches on the edge of the network. In such an arrangement, each LAN switch selectively forwards messages received over the backbone network to the destination LAN segment.
Communication on LAN segments, and communication between LAN segments over LAN switches, is broadcast-oriented. A station desiring to communicate with another station on the same LAN segment does not need to know where the destination station is located on the segment. Instead, the source station relies on the broadcast capability of the LAN media to propagate all messages to all stations on the segment. An interface on the intended destination station captures the message. Other interfaces on the segment ignore the message. Similarly, if a message propagated on a LAN segment is destined for a station on a different LAN segment associated with the same LAN switch, the LAN switch interconnecting the two segments will typically capture and propagate the message on a switching fabric connecting the two segments. In turn, an interface on the LAN switch associated with the intended destination LAN segment captures and propagates the message on the segment. Other interfaces on the LAN switch ignore the message. Again, there is no requirement that the source station know where the intended destination station resides within the network for successful communication. Rather, communication between the stations on different LAN segments over the LAN switch is "seamless" because the stations can communicate as if they are on the same LAN segment.
In contrast, communication over backbone networks is not always broadcast-oriented. One widely-used backbone technology is asynchronous transfer mode (ATM). Communicating over an ATM network requires that point-to-point or point-to-multipoint virtual connections be established between switches on the edge of the network. Thus, it is necessary for complete connectivity in ATM backbone networks to configure every source switch with virtual connections to every destination switch. Such configuration has generally required either manual configuration by a network administrator or implementation of ATM signaling procedures. Additional configuration has been required to maintain connectivity in the event an established link fails. As a result of these configuration and maintenance requirements, performance of ATM backbone networks has been hindered.
ATM's configuration demands have become even greater with the advent of virtual local area networks (VLANs). A VLAN is an aggregate of LAN segments which are part of the same logical group, but not necessarily the same physical group. By limiting the flow of messages across VLAN boundaries in an ATM network, VLANs can conserve network bandwidth and enhance network security. However, VLANs can at the same time lessen network robustness by requiring configuration of additional overlay virtual connections.
Robustness problems in ATM networks have been further exacerbated by using configuration services which by necessity or design give microprocessors, rather then custom logic, a primary role in message forwarding.
Accordingly, there is a need for more efficient services for configuring and maintaining connectivity in ATM networks.
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