The Effect of TCP Variants on the Coexistence of MMORPG and Best-Effort Traffic

Massive Multiplayer Online Role Playing Games (MMORPGs) have been reported as real-time applications using TCP. This surprising fact makes it interesting to study their behavior when sharing a link with other TCP flows. In this paper the coexistence of an MMORPG flow and an FTP background application is studied. A network scenario which fits an access network is simulated with NS2, using synthetic traffic of a game, generated according to a statistical model. The FTP background application uses different TCP variants. The results show that TCP Vegas is able to maintain a constant rate while competing with the traffic of the game, since it prevents packet loss and high queuing delays by avoiding the increase of the sending window size. In contrast, TCP SACK and TCP New Reno tend to indefinitely increase their window size, thus causing packet loss and adding undesired delays to the game traffic. Finally, small buffers have been proved to be more convenient when dealing with real-time applications, since big ones add higher delays.