Time-lined TCP for the TCP-friendly delivery of streaming media

This paper introduces time-lined TCP (TLTCP). TLTCP is a protocol designed to provide TCP-friendly delivery of time-sensitive data to applications that are loss-tolerant, such as streaming media players. Previous work on unicast delivery, of streaming media over the Internet proposes using UDP and performs congestion control at the user level by regulating the application's sending rate. TLTCP, on the other hand is intended to be implemented at the transport level, and is based on TCP with modifications to support time-lines. Instead of treating all data as a byte stream TLTCP allows the application to associate data with deadlines. TLTCP sends data in a similar fashion to TCP with the deadline for a section of data has elapsed; at which point the now obsolete data is discarded in favor of new data. As a result, TLTCP supports TCP-friendly delivery of streaming media by retaining much of TCP's congestion control functionality. We describe an API for TLTCP that involves augmenting the recvmsg and sendmsg socket calls. We also describe how streaming media applications that use various encoding schemes like MPEG-1 can associate data with deadlines and use TLTCP's API. We use simulations to examine the behavior of TLTCP under a wide range of networks and workloads. We find that it indeed performs time-lined data delivery and under most circumstances the bandwidth is shared equally, among completing TLTCP and TCP flows. Moreover those scenarios under which TLTCP appears to be unfriendly are those under which TCP flows competing only with other TCP flows do not share bandwidth equitably.