Reza Rejaie CIS UO1 Prof. Reza Rejaie Computer & Information Science University of Oregon Fall 2002 Multimedia Networking Seminar

Reza Rejaie CIS UO2 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 Rejaie CIS UO3 Class Information (cont’d) Grading P/NP Office hours: W 9-10 Send me an an specify your presentation topic by Oct 7 th. Class schedule!

Reza Rejaie CIS UO4 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 Rejaie CIS UO5 Prof. Reza Rejaie Computer & Information Science University of Oregon Fall 2002 An Overview of Research Problems on Internet Multimedia Networking

Reza Rejaie CIS UO6 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 Rejaie CIS UO7 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 Rejaie CIS UO8 Streaming Applications Encoding mechanisms (e.g. MPEG) are used to compress audio/video signals Average BWenc depends on: Encoding algorithm Desired quality Tradeoff between compression efficiency and loss resiliency Average BWenc is rather constant but BWenc could be bursty Realtime constraint Encoder Decoder A/V Source Display I P B BW enc quality

Reza Rejaie CIS UO9 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 BW enc quality BW ave

Reza Rejaie CIS UO10 Adaptive Streaming Applications CC should be integrated Important losses should be repaired/recovered Quality 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 TCP Internet QualityAdapt

Reza Rejaie CIS UO11 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 Rejaie CIS UO12 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 Interactive

Reza Rejaie CIS UO13 Issues with Client-Server Streaming Congestion control (CC) Loss repair (LR) Quality adaptation (QA)

Reza Rejaie CIS UO14 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 detected Conflicting 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 Rejaie CIS UO15 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 Rejaie CIS UO16 Quality Adaptation Adaptive encoding Switching between multiple encoding Trans-coding or Selective Frame Dropping Layered encoding Multiple Description encoding  Effect of quality adaptation on perceived quality is encoding-specific

Reza Rejaie CIS UO17 Protocols & Other Design Issues Protocols: RTP/RTCP RTSP Packetization Application Level Framing (ALF)

Reza Rejaie CIS UO18 Limitations of Client-Server Arch. Limited scalability Limited & unstable quality Asynchronous access could be inefficient RTT 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 Client Internet Server server Client Internet

Reza Rejaie CIS UO19 New Distribution Architectures Extending client-server architecture Proxy Caching Content Distribution Networks (CDN) Replacing client-server architecture Peer-to-Peer Networks

Reza Rejaie CIS UO20 Proxy Caching for Streaming Media Client Server1 Internet Server2 Client Proxy ISP Campus

Reza Rejaie CIS UO21 CDN for Streaming Media Client Server1 Internet Server2 Client Server1 ISP Campus

Reza Rejaie CIS UO22 Proxy Caching & CDN: Design Issues Idea: Bring popular contents close to clients Goals: 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 Rejaie CIS UO23 Peer-to-peer Networks for Streaming Client Server1 Internet Client ISP Server2

Reza Rejaie CIS UO24 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 Rejaie CIS UO25 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 Rejaie CIS UO26 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 Rejaie CIS UO27 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 to select a topic for your presentation by Oct 7 th.