A Session Admission Control (SAC) for negotiating admission control in a multi-services communications network including multicast services is described. The module distributes the admission process between a centralized decision function (SAC-PDP) and a distributed decision function (SAC-M) in a fashion that solves admission control scaling problems. The mechanism for interaction between the SAC-PDP and SAC-M is defined. Mechanisms are defined for the SAC-PDP to discover or learn the network capacity against which the admission control decisions will be made. Systems are also described for incorporating SAC-M in multicast replication points in the network, allowing multicast replication points to participate in the admission control process.