Admission Control

RETHER incorporates a distributed admission control scheme that is guaranteed to be free of race conditions. The admission decision at a node is postponed until it receives the token, because the token carries the most up-to-date information about all active real-time and their bandwidth reservations. Since only one node holds the token at a time, mutual exclusion is automatic. A disadvantage with this scheme is that bandwidth reservation requests are delayed due to the waiting for the token to arrive before the admission decision can be made.

RETHER intends to support both real-time and non-real-time traffic on the same Ethernet segment. To prevent starvation for non-real-time traffic, only a fixed fraction of the total raw bandwidth is set aside for real-time connections. The reserved bandwidth for non-real-time traffic minimizes unnecessary timeouts for existing network protocols such as NFS, and places an upper bound on the token inter-arrival time as seen by NRT nodes. This bound is critical to a timer-based mechanism for detecting and recovering from disastrous failure scenarios.