Managing Inter-domain Traffic in the Presence of BitTorrent File-Sharing Srinivasan Seetharaman and Mostafa Ammar School of Computer Science Objective: i) Analyze impact of BitTorrent file-sharing on the load balance across inter-domain access links, ii) Investigate existing Traffic management schemes, and iii) Propose strategies for better coexistence Typically in BitTorrent swarms… Main characteristics Centralized tracker regulating neighborhood, with no knowledge of peer location or piece distribution Dynamically swap peers by choke/unchoke protocol, every 30 seconds! Tit-for-tat incentive for uploading decisions Leecher: Unchoke the fastest uploaders Seed: Unchoke the fastest downloaders Popular strategy to improve performance Optimistic unchoke: Periodically look for faster peers Objective: Minimize (Download finish time) Similarity to Overlay Routing Selfish protocol, with no concern for native layer preferences Peer and piece selection is similar to picking multi-hop overlay path Simulating BitTorrent swarms Pick 100 ASes with 60% being non-stub ASes. Generate 1-50 peers per AS. Each associates with 1-3 torrents Torrent birth time is uniformly distributed between [-6 hrs, 18 hrs] L1 Data2 Each torrent has between [100, 10000] pieces with each piece being 256KB Data1 D B F F Arrival rate decreases exponentially: (t) = 0 e-t/ 0 = initial arrival rate  = attentuation factor 0 is uniformly distributed between 1-10 and  is set at 5000 for all torrents B1 B2 C A3 A2 A A1 E L2 BY 50 peers randomly assigned by tracker AX Observations We tried the following changes to the BitTorrent protocol, neither of reduced impact satisfactorily Make peer selection random Make piece selection random Reduce duration of optimistic unchoking Freeze list of unchoked peers after 10 mins Tune the unchoking timers Native layer Traffic Management  Inter-domain Traffic Engg  Rate Throttling at the border  Locality-based traffic management strategies Summary: They are effective. But, incur drop in user experience or infrastructure costs Friendly BitTorrent Strategies …to resolve cross-layer conflict Observation 1: Several peers simultaneously unchoke same peer, causing large # of parallel downloads Strategy 1: Limit number of parallel downloads Observation 2: Often, two peers in the same AS contact the same peer outside the AS Strategy 2: Stop this synchronization by avoiding common neighbors (Requires bilateral exchange of neighbor info.) Summary: Reduces maximum utilization effecitvely, without incurring inflation of client finish times Aggressive and performance-aware causing high max. util Applying TE does not make much difference Disproportionate load on inter-domain access links