Title: Streaming Video over a Wireless Network So what is the problem
1Streaming Video over aWireless NetworkSo 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
-
3Outline
- 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 ??
4Streaming Video
Video Frames
5Streaming Video over Wireless
Video Frames
Wired network
AP
6Networking 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
7Measurement and Tools
8Wireless Streaming Multimedia Lab Topology
Slide courtesy of Mingzhes PEDS
presentation Monday October 25,2005
9Wireless Measurement Study
10Preliminary Wireless Measurements
Application Layer
Network Layer
Data Link Layer
11Video Streaming Choices
- Media Player or Real Player
- TCP or UDP
- Single layer encoding or multilayer encoding
12MediaPlayer vs. RealPlayer A Comparison of
Network Turbulence
13Real vs WMP Playout Rate
RealPlayer buffers at a higher rate
14Video Compression Standard
- MPEG
- Popular compression standard
- Intra-compression and inter-compression
- Three types of frames I, P and B
- Group Of Pictures (GOP)
15340 Kbps Clip - Bottleneck Capacity 725 Kbps
lt 0.001 packet loss After 15 seconds
TCP Friendly?
16548 Kbps Clip - Bottleneck Capacity 725 Kbps
Not TCP- Friendly!
0.003 packet loss for WSM 0.006 packet loss
for TCP after 15 seconds
171128 Kbps Clip - Bottleneck Capacity 725 Kbps
Responsive to Capacity?
18Wireless Networks
19Wireless Issues
- Higher error rates - Bursty?
- Hidden terminal problem
- Variable bandwidth
- Mobile versus stationary
- MAC layer saturation
20Hidden 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!!
21Rate Constrained TFRC
- A seven-hop chain network was simulated.
- The TFRC sending rate is manually constrained.
- The MAC layer saturates at 300Kbps.
22Wireless Bandwidth Estimation
23Performance 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.
24Bandwidth Estimation Techniques
- Variable Packet Size (VPS) probing used to
measure minimum RTTs 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 (k100) 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.
25Packet Dispersion
26Bandwidth 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!
27Bandwidth Estimation and Video
- Currently, bandwidth estimation used in Windows
Media Player - Capacity estimation before streaming starts
- Uses packet pair
- Mingzhes Research new approach to bandwidth
estimation to improve performance of video over
wireless networks.
28Discussion ?