Implementation and Evaluation of Late Data Choice for TCP in Linux

Real-time delivery of time-dependent data over the Internet is challenging. UDP has often been used to transport data in a timely manner, but its lack of congestion control is often criticized. This criticism is a reason that the vast majority of applications today use TCP. The downside of this is that TCP has problems with the timely delivery of data. A transport protocol that adds congestion control to an otherwise UDP-like behaviour is DCCP For this protocol, late data choice (LDC) [8] has been proposed to allow adaptive applications control over data packets up to the actual transmission time. We find, however, that application developers appreciate other TCP features as well, such as its reliability. We have therefore implemented and tested the LDC ideas for TCP. It allows the application to modify or drop packets that have been handed to TCP until they are actually transmitted to the network. This is achieved with a shared packet ring and indexes to hold the current status. Our experiments show that we can send more useful data with LDC than without in a streaming scenario. We can therefore claim that we achieve a better utilization of the throughput, giving us a higher goodput with LDC than without.