A bandwidth allocation protocol for MPEG VBR traffic in ATM networks

Abstract

A periodic allocation protocol, called anticipated traffic allocation protocol (ATAP) for real time VBR traffic is proposed. The main objective of this protocol is to dynamically allocate the available bandwidth to real-time VBR sources, i.e. to be more efficient than the CBR allocation and at the same time more secure that the "walk-in" allocation. The ATAP unit is located at the network entry node between the real-time encoder and the applied bandwidth allocation protocol in the network, the fast reservation protocol FRP/DT. This reservation protocol cannot satisfy the real-time requirements, since the source would have to wait at least a round trip delay to reserve a required bandwidth increase. Hence, the ATAP proposes to anticipate and allocate the bandwidth one period in advance. This permits the encoder to adjust its coding bit rate according to the network loading condition. Doing so, a congestion will gracefully degrade the subjective quality of the signal, instead of "blindly" loosing cells at the network entry node. A minimum bit rate negotiated at the connection set-up is always guaranteed to assure the connection continuity in the case of the case of bandwidth reservation refusal. On the network side, the ATAP interacts with the FRP/DT. Reservation failures are used as congestion indicators to control the entering traffic and to adjust the cell priority. A simulation analysis investigates the performance of the ATAP and its interaction with the FRP/DT for two real MPEG VBR audio sequences under different bit rate anticipation approaches.