Graceful insertion and removal approaches for FDDI-II

Abstract

In a large FDDI network, consisting of hundreds of stations, many stations will regularly be inserted and removed. If no mechanisms are provided to do so gracefully, each insertion or removal will cause the ring to re-initialize (resynchronize, and undergo the Claim Process to renegotiate the TTRT). This is particularly undesireable in FDDI-II networks where applications communicating via Isochronous WideBand Channels (WBCsJ are not shielded from these disruptions and real-time constraints cannot afford retransmissions. Furthermore, station insertions and removals alter the ring latency, thereby disrupting all Isochronous WBCs in an FDDI-II network. A mechanism is required which prevents the initiation of the Claim Process and maintains a constant ring latency during the insertion and removal of stations into the ring. Such a mechanism, termed graceful insertion and removal, is described here. The mechanism is designed to support the graceful insertion and removal of stations into the M-ports of concentrators and requires no hardware modification of the end-stations.