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Streaming Video over a Wireless Network So what is the problem!! WPI CS Research Rugby Bob Kinicki November 30, 2004 CC-Wireless Rugby Team prop Feng Li wireless measurement hooker Mingzhe Li wireless bandwidth estimation flanker Jae Chung congestion control flanker Yubing Wang retransmissions scrumhalf Robert Kinicki protocols flyhalf Huahui Wu FEC weak side wing Emmanuel Agu low-level wireless fullback Mark Claypool multimedia Research Rugby November 30, 2004 2 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 ?? Research Rugby November 30, 2004 3 Streaming Video Video Frames Network Cloud Server Research Rugby November 30, 2004 Client 4 Streaming Video over Wireless Video Frames Wired network AP Client Server Research Rugby November 30, 2004 5 Networking Protocol Layers Application Layer: Real Player,Windows Media Player, MPEG Transport Layer: Network Layer: TCP, UDP IP Data Link Layer (MAC): 802.3, 802.11b, 802.11g Research Rugby November 30, 2004 6 Measurement and Tools Wireless Streaming Multimedia Lab Topology WM Tracker Real Tracker Ethereal Ethereal Monitor Mode Wireless sniffer (seine) Hub 7x 8x 9x 1x 2x 3x 10x 11x 12x 7x 8x 9x 4x 5x 6x 1x 2x 3x 10x 11x 12x 4x 5x 6x 7x 8x 9x 1x 2x 3x 10x 11x 12x 7x 8x 9x 4x 5x 6x 1x 2x 3x 10x 11x 12x 4x 5x 6x C 7 8 9 101112 A Ethernet Access point Ethernet Mobile station (yangtze) 12 34 56 A B Switch NFS Server (york) WPI Campus Network C 7 8 9 101112 A 12 34 56 A B Video Camera Video capture Emulated Internet VCR IDC WM Tracker Real Tracker Ethereal Media Client (???) Packet Sniffer (merlot) NAT Router (streamit) DVD DVD Player Windows media server Real streaming Server Quick time Darwin Windows IIS server Ethereal Windows 2003 server (saco) Slide courtesy of Mingzhe’s PEDS presentation Monday October 25,2005 Research Rugby November 30, 2004 8 Wireless Measurement Study Research Rugby November 30, 2004 9 Preliminary Wireless Measurements Application Layer Network Layer Data Link Layer Research Rugby November 30, 2004 10 Video Streaming Choices Media Player or Real Player TCP or UDP Single layer encoding or multilayer encoding Research Rugby November 30, 2004 11 MediaPlayer vs. ™ RealPlayer A Comparison ™ of Network Turbulence Real vs WMP Playout Rate RealPlayer buffers at a higher rate Bandwidth (Kbits/sec.) 700 Real Player (284K) 600 Real Player (36K) 500 Windows Media Player (323K) 400 Windows Media Player (49K) 300 200 100 0 0 50 100 150 200 250 Time (seconds) Research Rugby November 30, 2004 13 Video Compression Standard I0 B00 B01 P1 B10 P2 I0 MPEG – Popular compression standard – Intra-compression and inter-compression – Three types of frames: I, P and B – Group Of Pictures (GOP) Research Rugby November 30, 2004 14 340 Kbps Clip - Bottleneck Capacity 725 Kbps TCP Friendly? Research Rugby November 30, 2004 < 0.001 packet loss After 15 seconds 15 548 Kbps Clip - Bottleneck Capacity 725 Kbps Not TCP- Friendly! Research Rugby November 30, 2004 ~ 0.003 packet loss for WSM ~ 0.006 packet loss for TCP after 15 seconds 16 1128 Kbps Clip - Bottleneck Capacity 725 Kbps Responsive to Capacity? Research Rugby November 30, 2004 17 Wireless Networks Wireless Issues Higher error rates - Bursty? Hidden terminal problem Variable bandwidth Mobile versus stationary MAC layer saturation Research Rugby November 30, 2004 19 Hidden Terminal Problem 1 2 3 802.11 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!! Research Rugby November 30, 2004 20 Rate Constrained TFRC A seven-hop chain network was simulated. The TFRC sending rate is manually constrained. The MAC layer saturates at 300Kbps. Research Rugby November 30, 2004 21 Wireless Bandwidth Estimation Performance Definitions The capacity, Ci , 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, Ai , 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. Research Rugby November 30, 2004 23 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. Research Rugby November 30, 2004 24 Packet Dispersion Research Rugby November 30, 2004 25 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! Research Rugby November 30, 2004 26 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. Research Rugby November 30, 2004 27 Discussion ? Research Rugby November 30, 2004 28