Performance evaluation of transport layer protocols for transmitting real-time data over diffserv networks

In this paper, we discuss transport layer protocols to support real-time data transmission overnetworks using Differentiated Services (Diffserv) where bandwidth is guaranteed. Assuming that an application transmits streaming video data over a Diffserv network, we have performed simulation experiments to evaluate performance of real-time transmission using standard internet protocols, UDP and TCP as a transport layer protocol. The application is designed to buffer a portion of the data on the receiver before starting the playback and to operate in a streaming mode. Consequently, when packets are lost over Diffserv networks, TCP shows better performance than UDP. Simulation results show that employment of SACK option for TCP can recover lost packets efficiently and improve performance of real-time transmission. Currently, a growing number of real-time media applications over Internet are being implemented using UDP, because reliable delivery mechanism of TCP can obstruct real-time data transmission that is timing critical. However, in our experimental environment, retransmission and congestion control mechanism of TCP make use of bandwidth guaranteed by Diffserv, and help to provide more reliable delivery of real-time data than UDP without serious impacts on time-sensitive delivery. Therefore, despite of the general belief that TCP is not suitable for times-sensitive delivery, in our experiment, we show that TCP is a transport layer protocol suitable for real-time data transmission over Diffserv networks.