Streaming Video over a Wireless Network So what is the problem!! WPI CS Research Rugby Bob Kinicki November 30, 2004

Research Rugby November 30, 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

Research Rugby November 30, 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, Streaming Video Video Frames

Research Rugby November 30, Streaming Video over Wireless Video Frames Wired network AP

Research Rugby November 30, Networking Protocol Layers Application Layer:Real Player,Windows Media Player, MPEG Transport Layer:TCP, UDP Network Layer: IP Data Link Layer (MAC):802.3, b, g

Measurement and Tools

Research Rugby November 30, Wireless Streaming Multimedia Lab Topology Slide courtesy of Mingzhe’s PEDS presentation Monday October 25,2005

Research Rugby November 30, Wireless Measurement Study

Research Rugby November 30, Preliminary Wireless Measurements Application Layer Network Layer Data Link Layer

Research Rugby November 30, Video Streaming Choices  Media Player or Real Player  TCP or UDP  Single layer encoding or multilayer encoding

MediaPlayer ™ vs. RealPlayer ™ A Comparison of Network Turbulence

Research Rugby November 30, Real vs WMP Playout Rate RealPlayer buffers at a higher rate

Research Rugby November 30, Video Compression Standard  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, Kbps Clip - Bottleneck Capacity 725 Kbps < packet loss After 15 seconds TCP Friendly?

Research Rugby November 30, Kbps Clip - Bottleneck Capacity 725 Kbps ~ packet loss for WSM ~ packet loss for TCP after 15 seconds Not TCP- Friendly!

Research Rugby November 30, Kbps Clip - Bottleneck Capacity 725 Kbps Responsive to Capacity?

Wireless Networks

Research Rugby November 30, Wireless Issues  Higher error rates - Bursty?  Hidden terminal problem  Variable bandwidth  Mobile versus stationary  MAC layer saturation

Research Rugby November 30, Hidden Terminal Problem  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 protocol will still have problems if the MAC layer becomes saturated!! 123

Research Rugby November 30, Rate Constrained TFRC  A seven-hop chain network was simulated.  The TFRC sending rate is manually constrained.  The MAC layer saturates at 300Kbps.

Wireless Bandwidth Estimation

Research Rugby November 30, 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.

Research Rugby November 30, 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, Packet Dispersion

Research Rugby November 30, 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, 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, Discussion ?