| A real-time connection is denied admission to an ATM network if sufficient bandwidth is not available along all suitable paths through the network. This work focuses on methods for admitting high priority connections in such situations. Specifically, bandwidth reallocation and dynamic active channel re-routing are used to admit high priority real-time connections where traditional call admission control techniques would deny admission. A node can select lower priority channels, reallocate their bandwidth to the new higher priority connection being admitted, and reroute those channels so that their Quality of Service requirements and transmission deadlines can still be satisfied. At call admission time, one or more backup channels are established around each potential bandwidth reallocation point (node) of the primary channel, which is likely to select the channel as a victim for bandwidth reallocation. When backup channels have not been established in advance, detouring around a specific port is utilized, if possible, to make the technique more efficient. When reroutes occur, our protocols ensure that the transmitted data are received on time and in sequence, which is essential for real-time communications. SANRoP, a cell-based discrete event simulator, was developed to simulate these protocols in an ATM network in order to determine how well they perform. Three simulation studies were performed to test the suitability of our protocols and algorithms. Our studies indicate that these techniques perform well in a variety of networks experiencing various load conditions. These techniques ensured that no data cells were ever lost or late as a result of the protocols or algorithms. In addition, these techniques were able to admit high priority real-time channels which would otherwise have been denied access to the network because of insufficient resources. |
