Receiver-Driven Bandwidth Sharing for TCP and its Application to Video Streaming Puneet Mehra, Christophe De Vleeschouwer, and Avideh Zakhor IEEE Transactions on Multimedia, August 2005

Introduction Last-hop connections are often the bottleneck on the Internet Many applications run together to compete for the bandwidth resource Propose Receiver-Driven Bandwidth Sharing System (BWSS) Apply on last-hop link Allocate bandwidth according to user preferences

System overview Objectives: Achieve full utilization of receiver ’ s access link Satisfy user preferences (how the bottleneck bandwidth should be shared) Essential idea: constrain the throughput of certain low priority flows to provide additional bandwidth to high priority flows

Block diagram of bandwidth sharing system (BWSS)

TCP flow control system (FCS) Achieve a particular bit-rate for a given TCP flow Input: desired bit rate Output: advertised window (an integer number of packets, must be greater than zero) Goal: R: actual rate, T: target rate T ω

FCS algorithm

FCS analysis ( ) T: target rate  set ω to Proceed in an iterative bandwidth estimation to adjust advertised window T ω R

FCS analysis

Measuring flow RTT and bandwidth Calculate RTT: use TCP Timestamp option Calculate bandwidth Estimate at the end of each period ψ, ψ is set to in all experiments, εis set to 0.3 in all experiments

Frequency to adjust the advertisement window Frequency φ is bounded based on: Round trip time (RTT) Bandwidth estimation period (ψ) φ should be greater than RTT+ψ We set φ>RTT+3 ψ Allow enough time for the window adjustment to affect on throughput

Bandwidth sharing system (BWSS) Separate “ priority ” and “ weight ” Some aps require minimal bandwidth, but the more is not necessarily the better, ex: streaming Some aps don ’ t require minimal bandwidth, but the more is the better, ex: ftp Minimal rate should be provided to each connection in decreasing order of priority The remaining bandwidth should be shared proportionally to the weight

Target rate allocation & receiver preferences If system ’ s total bit rate Else =min(, max(0, ) )

Congestion Congestion in certain connection Threshold: γT  allocate bandwidth to other application or not

Experiment environment Buffer incoming packets to limit bandwidth Throughput: 960kbps Additional delay: 30ms

Experiment 1: the ideal case First 40 seconds: standard TCP Weights: 2, 1, 3, respectively No minimal rate

Experiment 2: Link bandwidth reduction Weight: 1, 2, respectively 40~80s: a 320 kbps UDP stream

Experiment 3: bandwidth redistribution Stream minimal rate: 496 kbps 40~100s: congestion, stream ↓ 160kbps

Experiment 4: RealVideo streaming (under standard TCP)

Experiment 4: RealVideo streaming (under UDP)

Experiment 4: RealVideo streaming (under BWSS)

Conclusion Investigated a bandwidth-sharing system (BWSS) for TCP connections Allow users specify preferences Don ’ t need to change network infrastructure Experiment results show that streaming with BWSS offers superior performance Drawback: BWSS may suffer starving condition