1. 1 School of Computing Science Simon Fraser University CMPT 820: Multimedia Systems Introduction Instructor: Dr. Mohamed Hefeeda

2. 2 Course Objectives r Understand fundamentals of networked multimedia systems r Know current research issues in multimedia r Develop research skills

3. 3 Course Info r Course web page http://nsl.cs.sfu.ca/teaching/09/820/ r References m [Burg09] Burg, The Science of Digital Media, Prentice Hall, 2009 m [KR08] Kurose and Rose, Computer Networking: A top- down Approach Featuring the Internet, 4th edition, Addison Wesley, 2008 m [SN04] Steinmetz and Nahrstedt, Multimedia Systems, Springer, Springer, 2004 m [LD04] Li and Drew, Fundamentals of Multimedia, Prentice Hall, 2004 m Complemented by research papers

4. 4 Course Info: Grading r Class participation: 40% m Read all Mandatory Reading m Present one chapter and 1—2 papers r Final Project: 60% m New Research Idea (publishable  A+) m Implementation and evaluation of an already-published algorithm/technique/system m Quantitative and/or qualitative comparisons between two already-published algorithm/techniques/systems. m A survey of a multimedia topic m … m Check wiki page for suggestions

5. 5 Course Info: Topics (Tentative) r QoS Requirements for Multimedia Systems r Review of Video and Audio Coding r OS Support for Multimedia r Multimedia Serve Design r Synchronization of Multimedia Streams r Models for Scalable Coding of Multimedia Streams (layered, FGS, MDC,...) r Adaptive Multimedia Streaming r Streaming to Wireless and Mobile Devices r Content-aware Streaming and Storage of Multimedia Streams r Security of Scalable Multimedia Streams r Implementation of Multimedia Systems (protocols, packetization, client buffering, server design,...)

6. 6 Introduction r Motivations r Definitions r QoS Specifications & Requirements r Reading: Ch. 7 in [KR08] and Ch. 2 in [SN04]

7. 7 Definitions and Motivations r “Multimedia” is an overused term m Means different things to different people m Because it touches many disciplines/industries Computer Science/Engineering Telecommunications Industry TV and Radio Broadcasting Industry Consumer Electronics Industry …. r For users m Multimedia = multiple forms/representation of information (text, audio, video, …)

8. 8 Definitions and Motivations r Why should we study/research multimedia topics? r Huge interest and opportunities m High speed Networks m Powerful (cheap) computers (desktops … cell phones) m Abundance of multimedia capturing devices (cameras, speakers, …) m Tremendous demand from users (mm content makes life easier, more productive, and more fun) m Here are some statistics …

9. 9 Definitions and Motivations r YouTube: fastest growing Internet server in history m Serves about 300—400 million downloads per day m Has 40 million videos, most of them (87%) less than 5 min m Adds 120,000 new videos (uploads) per day r CBS streamed the NCAA March Madness basketball games in 2007 online m Had more than 200,000 concurrent clients m And at peak time there were 150,000 Waiting r AOL streamed 8 live concerts online in 2006 m There were 180,000 clients at peak time r Plus … m Pretty much all major web sites have multimedia clips/demos/news/broadcasts/…

10. 10 Definitions and Motivations r Given all of this, are users satisfied? r Not Really! m We still get tiny windows for video m Low quality m Glitches, rebuffering m Limited scalability (same video clip on PDA and desktop) m Server/network outages (capacity limitations) r Users want high-quality multimedia, anywhere, anytime, on any device! r We (researchers) still strive to achieve this vision in the future!

11. 11 Multimedia:The Big Picture [SN04]

12. QoS in Networked Multimedia Systems r Quality of Service = “well-defined and controllable behavior of a system according to quantitatively measurable parameters” r There are multiple entities in a networked multimedia system m User m Network m Local system (memory, processor, file system, …) 12

13. QoS in Networked Multimedia Systems r Different parameters belong to different entities  QoS Layers 13

14. 14 QoS Layers User Application System Local Devices Network Perceptual (e.g., window size, security) Media Quality (e.g., frame rate, adaptation rules) Traffic (e.g., bit rate, loss, delay, jitter) Processing (e.g., CPU scheduling, memory, hard drive)

15. QoS Layers r QoS Specification Languages m Mostly application specific m XML based m See: Jin & Nahrstedt, QoS Specification Languages for Distributed Multimedia Applications: A Survey and Taxonomy, IEEE MultiMedia, 11(3), July 2004 r QoS mapping between layers m Map user requirements to Network and Device requirements m Some (but not all) aspects can be automated m For others, use profiles and rule-of-thumb experience m Several frameworks have been proposed in the literature m See: Nahrstedt et al., Distributed QoS Compilation and Runtime Instantiation, IWQoS 2000 15

16. QoS Layers r QoS enforcement methods m The most important/challenging aspect m How do we make the network and local devices implement the QoS requirements of MM applications? r We will study (briefly) m Enforcing QoS in the Network (models/protocols) m Enforcing QoS in the Processor (CPU scheduling for MM) m When we combine them, we get end-to-end QoS r Notice: m This is enforcing application requirements, if the resources are available m If not enough resources, we have to adapt (or scale) the MM content (e.g., use smaller resolution, frame rate, drop a layer, etc) 16

17. 17 QoS in IP Networks: Two Models r Guaranteed QoS m Need to reserve resources r Statistical (or Differential) QoS m Multiple traffic classes with different priorities r In both models, network devices (routers) should be able to perform certain functions (in addition to forwarding data packets)

18. 18 Principles for QoS Guarantees r Let us explore these functions using a simple example m 1Mbps IP phone, FTP share 1.5 Mbps link. m bursts of FTP can congest router, cause audio loss m want to give priority to audio over FTP packet marking needed for router to distinguish between different classes; and new router policy to treat packets accordingly Principle 1

19. 19 Principles for QoS Guarantees (more) r what if applications misbehave (audio sends higher than declared rate) m policing: force source adherence to bandwidth allocations r marking and policing at network edge: provide protection (isolation) for one class from others Principle 2

20. 20 Principles for QoS Guarantees (more) r Allocating fixed (non-sharable) bandwidth to flow: inefficient use of bandwidth if flows doesn’t use its allocation While providing isolation, it is desirable to use resources as efficiently as possible Principle 3

21. 21 Principles for QoS Guarantees (more) r Basic fact of life: can not support traffic demands beyond link capacity Call Admission: flow declares its needs, network may block call (e.g., busy signal) if it cannot meet needs Principle 4

22. 22 Summary of QoS Principles Let’s next look at mechanisms for achieving this ….

23. 23 Scheduling And Policing Mechanisms r scheduling: choose next packet to send on link r FIFO (first in first out) scheduling: send in order of arrival to queue m discard policy: if packet arrives to full queue: who to discard? Tail drop: drop arriving packet priority: drop/remove on priority basis random: drop/remove randomly

24. 24 Scheduling Policies: more Priority scheduling: transmit highest-priority queued packet r multiple classes, with different priorities m class may depend on marking or other header info, e.g. IP source/dest, port numbers, etc..

25. 25 Scheduling Policies: still more Weighted Fair Queuing: r generalized Round Robin r each class gets weighted amount of service in each cycle

26. 26 Policing Mechanisms Goal: limit traffic to not exceed declared parameters Three common-used criteria: r (Long term) Average Rate: how many pkts can be sent per unit time (in the long run) m crucial question: what is the interval length: 100 packets per sec and 6000 packets per min (ppm) have same average! r Peak Rate: e.g., m Avg rate: 6000 ppm m Peak rate: 1500 ppm r (Max.) Burst Size: max. number of pkts sent consecutively (with no intervening idle)

27. 27 Policing Mechanisms Leaky Bucket: limit input to specified Burst Size and Average Rate. r bucket can hold b tokens r tokens generated at rate r token/sec unless bucket full r over interval of length t: number of packets admitted less than or equal to (r t + b).

28. 28 Policing Mechanisms (more) r Leaky bucket + WFQ  provide guaranteed upper bound on delay, i.e., QoS guarantee! How? m WFQ: guaranteed share of bandwidth m Leaky bucket: limit max number of packets in queue (burst)

29. 29 IETF Integrated Services (IntServ) r architecture for providing QoS guarantees in IP networks for individual application sessions r resource reservation: routers maintain state info of allocated resources, QoS req’s r admit/deny new call setup requests:

30. 30 IntServ: QoS guarantee scenario r Resource reservation m call setup, signaling (RSVP) m traffic, QoS declaration m per-element admission control m QoS-sensitive scheduling (e.g., WFQ) request/ reply

31. 31 Call Admission Arriving session must: r declare its QoS requirement m R-spec: defines the QoS being requested r characterize traffic it will send into network m T-spec: defines traffic characteristics r signaling protocol: needed to carry R-spec and T- spec to routers (where reservation is required) m RSVP

32. 32 IntServ QoS: Service models [rfc2211, rfc 2212] Guaranteed service: r worst case traffic arrival: leaky-bucket-policed source r simple (mathematically provable) bound on delay [Parekh 1993, Cruz 1988] WFQ token rate, r bucket size, b per-flow rate, R D = b/R max arriving traffic

33. 33 IETF Differentiated Services Concerns with IntServ: r Scalability: signaling, maintaining per-flow router state difficult with large number of flows m Example: OC-48 (2.5 Gbps) link serving 64 Kbps audio streams  39,000 flows! Each require state maintenance. r Flexible Service Models: Intserv has only two classes. Also want “qualitative” service classes m relative service distinction: Platinum, Gold, Silver DiffServ approach: r simple functions in network core, relatively complex functions at edge routers (or hosts) r Don’t define service classes, provide functional components to build service classes

34. 34 Edge router:  per-flow traffic management  Classifies (marks) pkts  different classes  within a class: in-profile and out-profile Core router:  per class traffic management  buffering and scheduling based on marking at edge  preference given to in-profile packets DiffServ Architecture scheduling... r b marking

35. 35 Edge-router Packet Marking r class-based marking: packets of different classes marked differently r intra-class marking: conforming portion of flow marked differently than non-conforming one r profile: pre-negotiated rate A, bucket size B r packet marking at edge based on per-flow profile Possible usage of marking: User packets Rate A B

36. 36 Edge-router: Classification and Conditioning r Packet is marked in the Type of Service (TOS) in IPv4, and Traffic Class in IPv6 r 6 bits used for Differentiated Service Code Point (DSCP) and determine Per-Hop Behavior (PHB) that the packet will receive r 2 bits are currently unused

37. 37 Edge-router: Classification and Conditioning may be desirable to limit traffic injection rate of some class: r user declares traffic profile (e.g., rate, burst size) r traffic metered, shaped if non-conforming

38. 38 Core-router: Forwarding (PHB) r PHB result in a different observable (measurable) forwarding performance behavior r PHB does not specify what mechanisms to use to ensure required PHB performance behavior r Examples: m Class A gets x% of outgoing link bandwidth over time intervals of a specified length m Class A packets leave first before packets from class B

39. 39 Core-router: Forwarding (PHB) PHBs being developed: r Expedited Forwarding (EF): pkt departure rate of a class equals or exceeds specified rate m logical link with a minimum guaranteed rate m May require edge routers to limit EF traffic rate m Could be implemented using strict priority scheduling or WFQ with higher weight for EF traffic r Assured Forwarding: multiple traffic classes, treated differently m amount of bandwidth allocated, or drop priorities m Can be implemented using WFQ + leaky bucket or RED (Random Early Detection) with different threshold values. See Sections 6.4.2 and 6.5.3 in [Peterson and Davie 07]