Resource Reservation Protocol (RSVP) is a protocol that hosts can use to request specific QoS parameters through the network for a particular application data stream. A host can request guaranteed service through a network. If all routers have RSVP support enabled and there is sufficient unreserved bandwidth, a reservation is established throughout the network. In case of insufficient bandwidth, the reservation fails and notifies the hosts. At that point, hosts can send traffic without a reservation, or drop the connection.

RSVP can be enabled per network region on the network region form. If RSVP is enabled, endpoints including IP telephones and media processors attempt to establish a reservation for each call. If the reservation fails, Avaya endpoints still try to place a call but lower the DiffServ priority of the call to the better-than-best-effort (BBE) DSCP that is defined on the network region form. By default, this value is 43.

If RSVP is enabled on a network region, it is very important that it also be enabled on associated routers. If not, all RSVP reservations fail, and all voice traffic in that region is marked with the BBE DSCP, which generally receives degraded service versus the EF (DSCP 46) DiffServ Code Point.