| In the layering architecture of a packet-switched internetwork, the “transport layer” provides the end-to-end data transport service between applications across the network. On the Internet, the most popular computer internetwork, TCP is the most extensively used transport-level protocol. Years of enhancement and fine tuning has made it very efficient and robust. TCP is also congestion adaptive, which contributes significantly to the tremendous growth of the Internet. Therefore, TCP demonstrates that one transport protocol can cover a large percentage of applications.; The Internet is now increasingly used for real-time multimedia applications. For multi-participant applications such as audio/video broadcasting, multicast is needed to make efficient utilization of the network resources. In addition, many applications are record-based, such as database and storage applications. TCP, as it is designed, does not well support these applications. Consequently, UDP has been used. However, UDP provides basically no transport level services, so on top of UDP (or IP directly), there have been a proliferation of application-specific real-time transport protocols, and a large number of reliable multicast protocols. However; none of these has achieved the desired effectiveness and efficiency, and neither has achieved sufficient maturity and acceptance.; We have designed three extensions to TCP: real-time extension TCP-RTM, framing extension TCP-Framing, and multicast extension TCP-SMO. We have implemented these extensions in a Linux kernel, and we have conducted both testbed-based experiments and public Internet experiments. The resulting performance measurement data have been quantitatively analyzed, and they show that these extensions are both effective and efficient for the targeted applications. We conclude that a small number of low-cost extensions to a conventional connection-oriented reliable transport protocol allow it to support real-time, multicast and record based applications, and we can unify the transport layer of a packet-switched internetwork by using a single transport protocol. |
