A robust real-time transport protocol for multimedia information retrieval in an ATM network

Interactive multimedia services require on-demand and real-time delivery of information to the subscriber over networks. The need for preserving the temporal properties of certain media imposes quality of service (QoS) requirements on the network. In this paper, we propose a deadline priority scheduling protocol to switch multimedia traffic from media servers (MS) to users. Users retrieve data from MSs in the form of large packets by placing data requests which carry a time deadline parameter with their access multiplexer (AM). Each AM queues the data requests from its customers based on their deadlines. In order to schedule a data transaction, each AM submits its most urgent data request to the appropriate MS. An MS accepts the most urgent data request that it receives. The AM whose request has been accepted instructs the corresponding MS to begin transmitting as soon as it finishes its current transaction. The receiving MS begins transmitting the requested data when it finishes its current transaction. The received data is stored in the user's line card for subsequent playout or download to the user terminal. The proposed scheduling protocol is robust in the sense that it guarantees collision free delivery of the data even if the local clocks of AMs and MSs drift. The performance of the protocol is evaluated in terms of meeting the QoS requirements. Simulation results on the link utilization are also presented.