Proxy-based TCP-friendly streaming over mobile networks

Transcription

1 Proxy-based TCP-friendly streaming over mobile networks Frank Hartung Uwe Horn Markus Kampmann Presented by Rob Elkind Proxy-based TCP over mobile nets 1

2 Outline Introduction TCP Friendly Rate Control TCP Proxy Variable rate constraints and buffering delays Simulations Conclusion Proxy-based TCP over mobile nets 2

3 Introduction Streaming media becoming more important over wireless links Specialized requirements Timely delivery for playback Limited losses acceptable Receiver buffer used to compensate for data rate fluctuations Initial buffering delay needed to adjust for data rate changes Buffer Size Factors Encoding of content Available bandwidth during transmission Proxy-based TCP over mobile nets 3

4 RTP Overview Internet-standard protocol for the transport of real-time data, including audio and video Data part of RTP is a thin protocol providing support for applications with realtime properties including timing reconstruction, loss detection, security and content identification UDP/IP is its initial target Proxy-based TCP over mobile nets 4

5 WCMDA Overview (W-CDMA) Wideband Code-Division Multiple- Access implementation of third-generation (3G) cellular systems. Based on radio access technique proposed by ETSI Alpha group and the specifications was finalized W-CDMA link-level simulations are over 10 times more compute-intensive than current secondgeneration simulations. W-CDMA supports different users simultaneously transmitting at different data rates and data rates can even vary in time. Proxy-based TCP over mobile nets 5

6 Two Scenarios Proxy and End to End Proxy-based TCP over mobile nets 6

7 TCP - Friendly Rate Control Goal achieve fairness among TCP and non - TCP flows (improve utilization) Limit the drastic responses to congestion control for streaming Two major choices: Mimic AIMD Use throughput equation (less fluctuation) Proxy-based TCP over mobile nets 7

8 TCP throughput Eq TCP throughput = RTT 3 p MTU 27 p + T0 p( p ) Upper bound 1.22MTU RTT p Proxy-based TCP over mobile nets 8

9 TFRC t inter packet s x R0 = Throughput x M Equation-based congestion control Assigns network estimation to receiver Uses Weighting method to average p over number of loss intervals Uses EWMA (exponential weighted moving average) to calculate RTT Creates less fluctuation Proxy-based TCP over mobile nets 9

10 Weighted intervals Proxy-based TCP over mobile nets 10

11 TCP Proxy Needed because TCP has trouble fully utilizing mobile links Large RTT Non congestion packet loss Shields wireless link from Internet packet loss Proxy-based TCP over mobile nets 11

12 Traffic Smoothing Video streaming uses constant quality encoding results in variable rate streams To reduce fluctuations, server transmits frames into client playback buffer in advance of bursts Goal is to minimize required client buffer size and also don t over or under fill buffer Proxy-based TCP over mobile nets 12

13 Variable rate constraint Proxy-based TCP over mobile nets 13

14 Minimizing Initial Buffering Delay D...( ) { n k= N S late = max{ S late R, D }...( k < N) k k + 1 k k x w * * = = late max{ S k min{ w A k S late k w D k } Proxy-based TCP over mobile nets 14 0 }

15 Minimizing Initial Buffering Delay Proxy case 0...( k= 0) early { S = max{ S early + R, A } ( k > N k k 1 k k... ) Proxy-based TCP over mobile nets 15

16 Simulation Proxy-based TCP over mobile nets 16

17 TCP TFRC Transmission behavior Proxy-based TCP over mobile nets 17

18 Simulation Results Case R [kbps] W [sec] X [bytes] TCP, wired? TFRC, wired? TCP, wireless TFRC, wireless Proxy-based TCP over mobile nets 18

19 Proxy-based TCP over mobile nets 19

20 Simulation Results (Proxy) Case TCP TFRC TCP TFRC Without proxy R [kbps] W [sec] With Proxy X [bytes] n.a. n.a Proxy-based TCP over mobile nets 20

21 Conclusions Use of Proxy resulted in decrease of initial delay buffer and decreased client size buffer Also showed increased utilization and average throughput Many aspects still to consider in the future Proxy-based TCP over mobile nets 21

22 Questions? Proxy-based TCP over mobile nets 22