Michael J. Andrews and David Cyganski
Convergent Technology Center
ECE Department, WPI
Worcester, MA 01609-2280
Current efforts to make networked real-time multimedia data distribution a practical reality have focused primarily on the development of means to exploit the TCP protocol. However, much of the Internet is sufficiently slow or congested as to force most multimedia applications to use large ``streaming buffers'' to accommodate the highly non-deterministic nature of this communications channel. Some users may prefer to trade full reliability and corresponding fidelity for a variable quality, but low latency and properly paced transmission.
XUDP (eXtended User Datagram Protocol) is a transport layer protocol that provides an alternative, semi-reliable, method for transmitting real-time, multimedia data over an internet. Through a process of ``timed obsolescence,'' an application can deliberately specify a time to discard any given data parcel for which all comprising UDP datagrams have not been received. This allows placement of a value on the preservation of the timing relationships between sequential multimedia data parcels which is higher than the value given to reliable but un-timely delivery. XUDP is currently implemented as a user-space daemon, operating above UDP through Berkeley sockets, taking advantage of UDP's fast payload checksum and multiplexing ability. It offers full flow-control with a number of TCP-like optimizations and a sockets-like API.
Keywords: multimedia data transport, internetworking, loss-tolerant, transport-layer protocol