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Reza RejaieCIS Dept. @ UO 1
Prof. Reza RejaieComputer & Information Science
University of Oregonhttp://www.cs.uoregon.edu/~reza
Fall 2002
Multimedia Networking Seminar
Reza RejaieCIS Dept. @ UO 2
Class Information
Pre-requisites: CIS532 Class structure• Read assigned papers and submit a review• A designated student presents assigned papers• Participate in class discussions
Goals of the seminar:• To become familiar with research issues,
proposed interesting ideas, design and evaluation methodologies in Multimedia Networking
• To evaluate previous work and identify interesting open research problems in this area
Reza RejaieCIS Dept. @ UO 3
Class Information (cont’d)
Grading P/NP Office hours: W 9-10 Send me an email an specify your presentation topic by Oct 7th. Class schedule!
Reza RejaieCIS Dept. @ UO 4
Format of Presentation/Reviews
What is the problem? Why is it important? What are the assumptions? What is the proposed solution? Which part of the solution is new/interesting? What is the evaluation methodology? What are the interesting & new findings? What are the main contributions and key “take away” points? Leave unimportant details out.
Reza RejaieCIS Dept. @ UO 5
Prof. Reza RejaieComputer & Information Science
University of Oregonhttp://www.cs.uoregon.edu/~reza
Fall 2002
An Overview of Research Problems on Internet Multimedia Networking
Reza RejaieCIS Dept. @ UO 6
Motivation
Rapid growth of multimedia streaming • Popularity of the Web and the Internet• High-bandwidth access (Cable, DSL, LAN)
Poor and inconsistent quality of streams• Small picture size• Low frame rate• Fluctuation in quality
High overhead imposed on the Internet• Long, high-bandwidth streams• Unfriendly to traditional TCP traffic
Reza RejaieCIS Dept. @ UO 7
Internet: An Overview
Heterogeneous network in any way• Protocols, routing, links, network technologies,
end-hosts, bandwidth, delay, etc
Best effort service• Available BW is unknown and variable• Loss rate and loss pattern are unknown and
variable
Resources are shared• Data sources should be well-behaved, i.e. adjust
their transmission with network load Internet applications should be congestion
controlled for network stability and inter-protocol fairness.
Reza RejaieCIS Dept. @ UO 8
Streaming Applications
Encoding mechanisms (e.g. MPEG) are used to compress audio/video signalsAverage BWenc depends on:• Encoding algorithm• Desired quality
Tradeoff between compression efficiency and loss resiliencyAverage BWenc is rather constant but BWenc could be burstyRealtime constraint
Encoder
Decoder
A/V Source
Display
IPB
BWenc
quality
Reza RejaieCIS Dept. @ UO 9
Supporting Streaming Applications
Mismatch between streaming applications’ requirements and best-effort service Alternative solutions:• Add new services to the network
• Integrated Services (IntServ)• Differentiated Services (DiffServ)
• Enable applications to cope with best-effort service
• Adaptive streaming applications
Encoder
Decoder
Display
BWenc
quality
BWave
Reza RejaieCIS Dept. @ UO 10
Adaptive Streaming Applications
CC should be integrated Important losses should be repaired/recoveredQuality adaptation matches stream BW with avg. available BW• To avoid buffer
over/underflow
Can we use TCP?
Cong. Ctrl
Buffer
Decoder
Server
Display
Encoder
Source
TCPTCPInternet
QualityAdapt
Reza RejaieCIS Dept. @ UO 11
Role of Quality Adaptation
BW(t)
Time
Mismatch between ave. BW and stream BW• Buffering absorbs
short-term mismatch• Long-term mismatch
triggers quality adaptation
Frequent variations in quality is disturbing
Ave. BW
Stream BW
Reza RejaieCIS Dept. @ UO 12
Delay sensitivity of Streaming App.
The higher the level of interactions, the higher the sensitivity to delay, the lower the amount of buffered data
• Internet telephony, Video conferencing• Video games• Live but non-interactive (i.e. lecture-mode)• On-demand playback of stored video
Less
Inte
ract
ive
Reza RejaieCIS Dept. @ UO 13
Issues with Client-Server Streaming
Congestion control (CC) Loss repair (LR) Quality adaptation (QA)
Reza RejaieCIS Dept. @ UO 14
CC for Streaming
Goal: to achieve a fair share of network BW among co-existing flows• TCP-friendly CC is desired
CC should probe for excess BW and reduce tx rate when congestion is detectedConflicting requirements:• Smooth adjustments in BW are desired• Responsive to changes in network load
Sender-driven vs Receiver-driven CC Rate-based vs Window-based
Reza RejaieCIS Dept. @ UO 15
Loss Repair (Error Control)
Primary approaches:• Retransmission (Retx)• Forward Error Correction (FEC)
Retx has higher BW efficiency but results in longer recovery delay => More buf.• Appropriate for non-interactive app
FEC has shorter recovery delay but lower BW efficiency => Less buf.• Media-dependent vs media-independent
Effect of pkt loss on perceived quality is encoding-specific
Reza RejaieCIS Dept. @ UO 16
Quality Adaptation
Adaptive encodingSwitching between multiple encodingTrans-coding or Selective Frame DroppingLayered encodingMultiple Description encoding
Effect of quality adaptation on perceived quality is encoding-specific
Reza RejaieCIS Dept. @ UO 17
Protocols & Other Design Issues
Protocols:• RTP/RTCP• RTSP
Packetization• Application Level Framing (ALF)
Reza RejaieCIS Dept. @ UO 18
Limitations of Client-Server Arch.
Limited scalabilityLimited & unstable qualityAsynchronous access could be inefficientRTT could be high• High delay VCR-functions• Large startup delay
Increasing network capacity doesn’t solve these problems?
Content should be close to interested clients
Server
ClientClientClient
Internet
Server
server
Client Client Client
Internet
Reza RejaieCIS Dept. @ UO 19
New Distribution Architectures
Extending client-server architecture• Proxy Caching• Content Distribution Networks (CDN)
Replacing client-server architecture• Peer-to-Peer Networks
Reza RejaieCIS Dept. @ UO 20
Proxy Caching for Streaming Media
Client
Client
Client
Client
Client
Server1Internet
Server2
Client
Client
Proxy
Proxy
ISP
Campus
Reza RejaieCIS Dept. @ UO 21
CDN for Streaming Media
Client
Client
Client
Client
Client
Server1Internet
Server2
Client
Client
Server1
Server1
ISP
Campus
Reza RejaieCIS Dept. @ UO 22
Proxy Caching & CDN: Design Issues
Idea: Bring popular contents close to clientsGoals: Minimizing network load, Maximizing delivered quality Main design issue: content-management
1) Push or Pull a popular streaming object?2) Which stream to push/pull & When?
• How to determine popularity/value of an object?
3) Which replacement algorithm?• Granularity of replacement, e.g. replacing part of an
unpopular stream or the entire stream?
4) Which quality of a stream to cache/load?
Reza RejaieCIS Dept. @ UO 23
Peer-to-peer Networks for Streaming
Client
Client
Client
Client
Client
Server1Internet
Client
Client
ISP
Server2
Reza RejaieCIS Dept. @ UO 24
P2P streaming: Design Issues
Idea: No central server, each active peer who has an object could act as a server for that object. Goals: localize traffic, and balance load among active peers Main design issues:• How to locate an object?• Which object to cache/replace at a peer?
No server => new way of thinking• e.g. streaming a MD. encoded stream from
multiple peers
Reza RejaieCIS Dept. @ UO 25
Measurement & Characterization
Measurement is a useful method to gain more insight about certain behavior/phenomenon• e.g. Behavior of aggregate traffic at a server,
user access pattern to a server• Measurement often leads to characterization
of the behavior/phenomenon under investigation
• Characterization of a behavior allows us to improve design/performance of a related network component (e.g. protocols/server)
Main issues: Data collection & Data analysis (and both are challenging)
Reza RejaieCIS Dept. @ UO 26
Measurement for Streaming Media
Sample measurement issues:1) What is the characterization of user
access pattern to mm objects at a server, a proxy, or a peer (in a p2p network)?
2) What is the characterization of mm objects on the Web (e.g. length, bw, etc)?
3) What kind of CC, QA or LR mechanisms (if any) existing streaming applications implement?
Reza RejaieCIS Dept. @ UO 27
Summary of Topics
Congestion control (2 sessions) Quality adaptation (1/2 session) Loss repair (1 session) Multimedia proxy caching (1 session) CDN for streaming (1/2 session) MM traffic measurement (2 sessions)
You should send me an email to select a topic for your presentation by Oct 7th .
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