1. K. Salah 1 Beyond Best Effort Technologies Our primarily objective here is to understand more on QoS mechanisms so that you can make informed decision on opting for network devices and gadgets that support it. Chapter 6 of Kurose & Ross

2. K. Salah 2 Multimedia, Quality of Service: What is it? Multimedia applications: network audio and video (“continuous media”) network provides application with level of performance needed for application to function. QoS

3. K. Salah 3 Goals Principles r Classify multimedia applications r Identify the network services the apps need r Making the best of best effort service r Mechanisms for providing QoS Protocols and Architectures r Specific protocols for best-effort r Architectures for QoS

4. K. Salah 4 outline r Multimedia Networking Applications r Beyond Best Effort r Scheduling and Policing Mechanisms r Integrated Services r RSVP (covered earlier) r Differentiated Services

5. K. Salah 5 MM Networking Applications Fundamental characteristics: r Typically delay sensitive m end-to-end delay m delay jitter r But loss tolerant: infrequent losses cause minor glitches r Antithesis of data, which are loss intolerant but delay tolerant. Classes of MM applications: 1) Streaming stored audio and video 2) Streaming live audio and video 3) Real-time interactive audio and video Jitter is the variability of packet delays within the same packet stream

6. K. Salah 6 Real-time interactive applications r PC-2-PC phone m instant messaging services are providing this r PC-2-phone m Dialpad m Net2phone r videoconference with Webcams Going to now look at a PC-2-PC Internet phone example in detail

7. K. Salah 7 Interactive Multimedia: Internet Phone Introduce Internet Phone by way of an example r speaker’s audio: alternating talk spurts, silent periods. m 64 kbps during talk spurt r pkts generated only during talk spurts m 20 msec chunks at 8 Kbytes/sec: 160 bytes data r application-layer header added to each chunk. r Chunk+header encapsulated into UDP segment. r application sends UDP segment into socket every 20 msec during talkspurt.

8. K. Salah 8 Internet Phone: Packet Loss and Delay r network loss: IP datagram lost due to network congestion (router buffer overflow) r delay loss: IP datagram arrives too late for playout at receiver m delays: processing, queueing in network; end-system (sender, receiver) delays m typical maximum tolerable delay: 400 ms r loss tolerance: depending on voice encoding, losses concealed, packet loss rates between 1% and 10% can be tolerated.

9. K. Salah 9 constant bit rate transmission Cumulative data time variable network delay (jitter) client reception constant bit rate playout at client client playout delay buffered data Delay Jitter r Consider the end-to-end delays of two consecutive packets: difference can be more or less than 20 msec

10. K. Salah 10 outline r Multimedia Networking Applications r Beyond Best Effort r Scheduling and Policing Mechanisms r Integrated Services r RSVP r Differentiated Services

11. K. Salah 11 Improving QOS in IP Networks Thus far: “making the best of best effort” Future: next generation Internet with QoS guarantees m RSVP: signaling for resource reservations m Differentiated Services: differential guarantees m Integrated Services: firm guarantees r simple model for sharing and congestion studies:

12. K. Salah 12 Principles for QOS Guarantees r Example: 1MbpsI P 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

13. K. Salah 13 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: m similar to ATM UNI (User Network Interface) provide protection (isolation) for one class from others Principle 2

14. K. Salah 14 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

15. K. Salah 15 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

16. K. Salah 16 Summary of QoS Principles Let’s next look at mechanisms for achieving this ….

17. K. Salah 17 outline r Multimedia Networking Applications r Beyond Best Effort r Scheduling and Policing Mechanisms r Integrated Services r RSVP r Differentiated Services

18. K. Salah 18 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 real-world example? 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

19. K. Salah 19 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.. m Real world example?

20. K. Salah 20 Scheduling Policies: still more round robin scheduling: r multiple classes r cyclically scan class queues, serving one from each class (if available) r real world example?

21. K. Salah 21 Scheduling Policies: still more Weighted Fair Queuing: r generalized Round Robin r each class gets weighted amount of service in each cycle r real-world example?

22. K. Salah 22 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 or 6000 packets per min have same average! r Peak Rate: e.g., 6000 pkts per min. (ppm) avg.; 1500 ppm peak rate r (Max.) Burst Size: max. number of pkts sent consecutively (with no intervening idle)

23. K. Salah 23 Policing Mechanisms Token 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).

24. K. Salah 24 Policing Mechanisms (more) r token bucket, WFQ combine to provide guaranteed upper bound on delay, i.e., QoS guarantee! WFQ token rate, r bucket size, b per-flow rate, R D = b/R max arriving traffic

25. K. Salah 25 outline r Multimedia Networking Applications r Beyond Best Effort r Scheduling and Policing Mechanisms r Integrated Services r RSVP r Differentiated Services

26. K. Salah 26 IETF Integrated Services r architecture for providing QOS guarantees in IP networks for individual application sessions r resource reservation: routers maintain state info (a la VC) of allocated resources, QoS req’s r admit/deny new call setup requests: Question: can newly arriving flow be admitted with performance guarantees while not violating QoS guarantees made to already admitted flows?

27. K. Salah 27 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

28. K. Salah 28 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

29. K. Salah 29 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 1992, Cruz 1988] Controlled load service: r "a quality of service closely approximating the QoS that same flow would receive from an unloaded network element.“ r Simple and no calculation r Works well under lightly loaded network, but degrades in performance under high load. WFQ token rate, r bucket size, b per-flow rate, R D = b/R max arriving traffic

30. K. Salah 30 outline r Multimedia Networking Applications r Beyond Best Effort r Scheduling and Policing Mechanisms r Integrated Services r RSVP r Differentiated Services

31. K. Salah 31 IETF Differentiated Services Concerns with Intserv: r Scalability: signaling, maintaining per-flow router state difficult with large number of flows r Flexible Service Models: Intserv has only very few classes. Also want “qualitative” service classes m “behaves like a wire” 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

32. K. Salah 32 Diffserv Architecture Edge router: - per-flow traffic management - marks packets as 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 - Assured Forwarding scheduling... r b marking

33. K. Salah 33 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

34. K. Salah 34 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 PHB (per-hop behavior) that the packet will receive r (CU) bits are currently unused

35. K. Salah 35 Classification and Conditioning may be desirable to limit traffic injection rate of some class: r user declares traffic profile (eg, rate, burst size) r traffic metered, shaped if non-conforming

36. K. Salah 36 Forwarding (PHB) r PHB results 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

37. K. Salah 37 Forwarding (PHB) PHBs being developed: r Expedited Forwarding: pkt departure rate of a class equals or exceeds specified rate m logical link with a minimum guaranteed rate m Provides isolation among traffic classes r Assured Forwarding: 4 classes of traffic m each guaranteed minimum amount of bandwidth m each with three drop preference partitions