Centralized Call Admission Control and Load Balancing for Voice Over IP

In this paper, we will present two methods for call admission control and load balancing for voice-over-IP services. Both approaches employ a centralized database function referred to as Call Control Database (CCDB) that keeps track of the voice occupancy levels across the IP network. The first method employs an accounting-based strategy in the sense that the voice gatekeepers explicitly declare the bandwidth requirement of each admitted call. This strategy enables the "accounting" of voice bandwidth occupancy on each network link within the administrative domain so as to facilitate the control actions. The second method on the other hand employs a measurement-based strategy, in the sense that the IP routers play a direct role in monitoring link occupancies and assisting in call control decisions. In particular, each router provides periodically updated traffic measurements (based on the existing RMON capabilities), for each network link emanating from it. These measurements are used to estimate the link utilizations, and thereby initiate call control actions. The methodologies to be described are suitable for packetized voice services over any IP network that supports the Diffserv capability, such that voice traffic can be isolated from data traffic. In addition, the network may optionally support MPLS explicit routing; this will allow a graceful and efficient implementation of call admission control and load balancing. With suitable functional enhancements, the methods will also work in conjunction with OSPF routing to provide call admission control, but without load balancing across multiple paths.