Active Analysis of BT with a Modified Azureus Client

Peer-to-peer (P2P) systems have become increasingly popular for a variety of applications in Internet for their several advantages over traditional client/server architecture. And they also generate most traffic in all regions around the world. Thus, the ISPs and all network administrators have a mutual interest in limiting P2P traffic. Before doing these, understanding and analyzing their traffic is necessary. In this paper, we inside analyze BitTorrent (BT) traffic with a special modified Vuze client in a stub network. Preliminary results indicate that among all BT clients we have detected, the most popular two outside China are μTorrent and Azureus. They have over 50%-86% market share. But in China, the Xunlei client is almost the No. 1, but is can not support the Message Stream Encryption (MSE) protocol. And there are also lots of proprietary or unknown BT clients can not support the MSE protocol, and some users looks like to be unwilling to use it. The proportion in China is bigger. And some BT clients may upgrade or downgrade the encryption level independently, disobeying the user configuration of MSE. All BT clients relied excessively on trackers, especially in China. Moreover, Distributed Hash Table (DHT) does not play the proper role as we expected. Although BT systems can use both TCP and UDP protocols for transportation, the TCP protocol is the dominant one by 99%. Finally, we investigate the port used by all peers. Unexpectedly, the most popular used port is 6881 outside China and 80 in China. And in China, small port numbers are often used.