Streaming Video over a Wireless Network.ppt
- 1. Streaming Video over a Wireless Network So what is the problem!! WPI CS Research Rugby Bob Kinicki November 30, 2004
- 2. CC-Wireless Rugby Team prop hooker Feng Li Mingzhe Li wireless measurement wireless bandwidth estimation flanker flanker Jae Chung Yubing Wang congestion control retransmissions scrumhalf Robert Kinicki protocols flyhalf Huahui Wu weak side wing FEC Emmanuel Agu low-level wireless fullback Mark Claypool multimedia
- 3. Outline Motivation – the Future Streaming Video over Wireless What Problems? Background Layered network architecture Networking ‘religious’ tenets Measurement and Tools Streaming multimedia primer Introduction to wireless networks Focus: Wireless Bandwidth Estimation Discussion ??
- 4. Streaming Video Video Frames
- 5. Streaming Video over Wireless Video Frames Wired network AP
- 6. Networking Protocol Layers Application Layer: Real Player,Windows Media Player, MPEG Transport Layer: TCP, UDP Network Layer: IP Data Link Layer (MAC): 802.3, 802.11b, 802.11g
- 8. Wireless Streaming Multimedia Lab Topology Slide courtesy of Mingzhe’s PEDS presentation Monday October 25,2005
- 10. Preliminary Wireless Measurements Application Layer Network Layer Data Link Layer
- 11. Video Streaming Choices Media Player or Real Player TCP or UDP Single layer encoding or multilayer encoding
- 12. MediaPlayer ™ vs. RealPlayer ™ A Comparison of Network Turbulence
- 13. Real vs WMP Playout Rate RealPlayer buffers at a higher rate
- 14. Video Compression Standard MPEG Popular compression standard Intra-compression and inter-compression Three types of frames: I, P and B Group Of Pictures (GOP)
- 15. 340 Kbps Clip - Bottleneck Capacity 725 Kbps < 0.001 packet loss After 15 seconds TCP Friendly?
- 16. 548 Kbps Clip - Bottleneck Capacity 725 Kbps ~ 0.003 packet loss for WSM ~ 0.006 packet loss for TCP after 15 seconds Not TCP- Friendly!
- 17. 1128 Kbps Clip - Bottleneck Capacity 725 Kbps Responsive to Capacity?
- 19. Wireless Issues Higher error rates - Bursty? Hidden terminal problem Variable bandwidth Mobile versus stationary MAC layer saturation
- 20. Hidden Terminal Problem 802.11 Solution to the Hidden Terminal Problem Use a four-way handshake: RTS-CTS-DATA-ACK where the RTS and CTS packets are significantly smaller than the average data packet. The maximum number of RTS retransmissions is set to 7. However, the 802.11 protocol will still have problems if the MAC layer becomes saturated!! 1 2 3
- 21. Rate Constrained TFRC A seven-hop chain network was simulated. The TFRC sending rate is manually constrained. The MAC layer saturates at 300Kbps.
- 23. Performance Definitions The capacity , C i , of hop i is the maximum possible IP layer transfer at that hop. Namely, the bit rate for transferring MTU-sized IP packets. The available bandwidth , A i , of a link relates to the unused capacity of a link during a time period. The Bulk-Transfer-Capacity (BTC) is the maximum throughput obtainable by a single TCP connection.
- 24. Bandwidth Estimation Techniques Variable Packet Size (VPS) probing : used to measure minimum RTT’s to all hops on path. pathchar, pchar, ... Packet pair probing : each packet pair consists of two packets of the same size sent back-to-back. The goal is to measure the dispersion of a packet pair. Packet train probing : extends packet-pair probing by using multiple back-to-back packets. Self-Loading Periodic Streams (SLoPS) : send a train of packets (k=100) equal-sized packets at a rate R. Sender continues to vary R to get it close to A. Trains of Packet Pairs (TOPP) : send many packet pairs at gradually increasing rates from source to sink.
- 26. Bandwidth Estimation Techniques pathchirp : uses an exponentially spaced chirp probing train and launches m packet chirps where each chirp is made up of N UDP probe packets each of size P bytes. pathchirp discards all chirps with dropped packets!
- 27. Bandwidth Estimation and Video Currently, bandwidth estimation used in Windows Media Player Capacity estimation before streaming starts Uses packet pair Mingzhe’s Research : new approach to bandwidth estimation to improve performance of video over wireless networks.
- 28. Discussion ?
Editor's Notes
- #18: 04/29/10 Need to precisely quantify performance during the buffering period Synching up application and network level measurements is a challenge (even on one host) We came up with a way to parse RTSP packets and application level data to do so. Point out: 1) buffering (loss 2) Not TCP-friendly 3) Responsive to capacity --- NOT FIREHOSE CBR 4) Depends on the encoding rate vs. the capacity (lots of burden on content provider)