Real-time transport protocols rely on IP to disseminate audio/video packets from a sender
to one or more receivers. In IP over ATM broadband networks, studies have shown that
the effective bandwidth is reduced by at least 10% and that larger protocol payload sizes
yield higher throughput. However, a dropped cell corrupts the IP packet it belongs to and
reduces the rate successfully-received data, or goodput. This results in quality of service
degradation to multimedia traffic, particularly for intra-frame encoded video raffic that is
sensitive to a packet loss. A key observation for multimedia applications is that achieving
maximum throughput versus reaching optimum goodput is determined by the end-to-end
quality of service requirements. In this report, we derive analytic expressions for the maximum
throughput and packet-loss probability which provides us with a better understanding
of the goodput of real-time transport protocols. We also derive an analytic expression for
optimum PDU that maximizes the goodput with respect to cell-loss probability and number
of ATM switches. We show that optimum PDUs yield higher goodput than the default
MTU for IP over ATM, particularly as the cell-loss probability and/or the number of ATM
switches increase. For reliable multicast, We also derive analytic expressions to the expected
total number of transmissions per packet and to the goodput of reliable multicast.