1. Chapter 17 Integrated and Differentiated Services 1 Integrated and Differentiated Services COMP5416 Chapter 17

2. Chapter 17 Integrated and Differentiated Services 2 Review Demands on IP-based internets are rising IP-based internets were designed for elastic applications that tolerate variations in throughput and loss Now, they are used to support high volumes and various traffic mix including real-time and non real-time applications –These are sensitive to delay and throughput variations and requires high quality of service (QoS) Thus, they now need to provide service differentiations for different applications like ATM network!

3. Chapter 17 Integrated and Differentiated Services 3 Introduction New additions to Internet increasing traffic –High volume client/server application –Web –Real time voice and video Need to manage traffic and control congestion Two complementary IETF standards: –Integrated services (IntServ) Provides collective service to set of traffic demands placed in a domain –Limit demand per capacity & reserve resources to meet QoS –Differentiated services (DiffServ) Classify traffic in groups Different group traffic handled differently

4. Chapter 17 Integrated and Differentiated Services 4 Internet Traffic Elastic –Can adjust to changes in delay and throughput –E.g. common TCP and UDP application like email, FTP, web Inelastic –Does not easily adapt to changes in delay and throughput –real time traffic such as web streaming, voice over IP (VoIP) –Requires minimum throughput, bounded delay and jitter (i.e. variation of delay)

5. Chapter 17 Integrated and Differentiated Services 5 IntServ Architecture IPv4 header fields for precedence/priority and type of service usually ignored ATM is only network designed to support TCP, UDP and real-time traffic from inception –However, need new installation & costly Need to support Quality of Service (QoS) within TCP/IP architecture –Requires adding functionality to routers –Means of requesting QoS

6. Chapter 17 Integrated and Differentiated Services 6 IntServ Approach Enable provision of QoS over IP (RFC2211,2212) Enables sharing available capacity when congested Currently, routers have these mechanisms: –Dynamic Routing Algorithms Select to minimise delay to balance load –Active Queue Management (AQM) Causes TCP sender to back off and reduce load These are not sufficient, and are enhanced by IntServ

7. Chapter 17 Integrated and Differentiated Services 7 IntServ Functions Admission control –For specific QoS, reservation required for new flow –Resource reSerVation Protocol (RSVP) used Routing algorithm –Base decision on QoS parameters, not shortest path only Queuing discipline –Take account of different flow requirements –Meet QoS AQM policy –Manage congestion

8. Chapter 17 Integrated and Differentiated Services 8 IntServ Implementation in Router Background Functions Forwarding functions

9. Chapter 17 Integrated and Differentiated Services 9 IntServ Components – Background Functions Reservation Protocol –Reserve resources for new flows Admission control –Determines whether current resources enough to support new request Management agent –Can use agent to modify traffic control database and direct admission control Routing protocol –Directs next hop for each address and flow

10. Chapter 17 Integrated and Differentiated Services 10 IntServ Components – Forwarding Classifier and route selection –Incoming packets mapped to classes Single flow or set of flows with same QoS –E.g. all video flows Based on IP header fields –Determines next hop Packet scheduler –Manages one or more queues for each output –Order in which queued packets sent Based on class, traffic control database, current and past activity on outgoing port –Policing Determine whether flow exceed its requested capacity

11. Chapter 17 Integrated and Differentiated Services 11 IntServ Services Service defined on two levels –General categories of service: Guaranteed (~ CBR) Controlled load (~ VBR) Best effort (default) (~ UBR) –Particular flow within category Service for a flow is specified by certain parameters known as traffic specification (TSpec) TSpec is part of the traffic contract

12. Chapter 17 Integrated and Differentiated Services 12 IntServ Services – Guaranteed Service Most demanding service Provides assured data rate Has specific upper bound on queuing delay through network –Must be added to propagation delay to get total delay –May be wise to set high to accommodate rare long queue delays Has no queuing losses –i.e. no buffer overflow

13. Chapter 17 Integrated and Differentiated Services 13 IntServ Services – Controlled Load Tightly approximates to best efforts under unloaded conditions No upper bound on queuing delay –High percentage of packets do not experience delay over minimum transit delay Propagation delay plus router processing with no queuing delay Very high percentage delivered –Almost no queuing loss Useful for adaptive (or soft) real time applications To provide these service categories, routers adopt suitable queuing discipline

14. Chapter 17 Integrated and Differentiated Services 14 Queuing Discipline Traditionally FIFO or FCFS at each router port No special treatment to high priority packets (flows) Small packets held up by large packets ahead of them in queue –Larger average delay for smaller packets –Flows of larger packets get better service Greedy TCP connection can crowd out altruistic (i.e. unselfish) connections –If one connection does not back off, others may back off more

15. Chapter 17 Integrated and Differentiated Services 15 Fair Queuing (FQ) Multiple queues for each port –One for each source or flow Queues serviced in round robin –Each busy queue gets exactly one packet per cycle Achieves load balancing among flows –No advantage to being greedy Your queue gets longer, increasing your delay Drawback: Short packets penalized as each queue sends one packet per cycle

16. Chapter 17 Integrated and Differentiated Services 16 FIFO and FQ

17. Chapter 17 Integrated and Differentiated Services 17 Processor Sharing (PS) Not practical but same principle adopted in another scheme Multiple queues as in FQ Send one bit from each queue per round –Longer packets no longer get an advantage Work out virtual start and finish time for a given packet (of queue  ) However, we wish to send packets, not bits in reality

18. Chapter 17 Integrated and Differentiated Services 18 Bit-Round Fair Queuing (BRFQ) Based on PS Each flow gets  1/nth of bandwidth (n flows) Compute virtual start and finish time as in PS When a packet finished, the next packet sent is the one with the earliest virtual finish time Good approximation to performance of PS –Throughput and delay of queues converge as time increases

19. Chapter 17 Integrated and Differentiated Services 19 Comparison of FIFO, FQ and BRFQ

20. Chapter 17 Integrated and Differentiated Services 20 Generalised Processor Sharing (GPS) BRFQ can ’ t provide different capacities to different flows Enhancement called weighted fair queuing (WFQ), based on generalised PS From PS, allocate weighting to each flow that determines how many bits are sent during each round –If weighted 5, then 5 bits are sent per round Gives means of responding to different service levels => The concept of service differentiation! Can provide guarantees that delays do not exceed certain bounds

21. Chapter 17 Integrated and Differentiated Services 21 Weighted Fair Queuing Emulates GPS Same strategy as BRFQ Enables a router to assign weight to each flow and guarantee bound on delay Max buffer size needed proportional to defined max delay

22. Chapter 17 Integrated and Differentiated Services 22 Example: BFRQ vs WFQ Received these packets all at about the same time and same output link  Service with BRFQ: PacketSizeFlow 11001 2 1 3602 41202 5602 –pkt tx sequence: 3,1,4,2,5 Service with WFQ –Assume flow 2 gets 1.5 of flow 1 –So, weight ratio  2 : 3 PacketSizeFlowFiFi 11001 2 1200 3602 41202180 5602240 PacketSizeFlowFiFi 1100150 21001 360220 4120260 5 280 –Sequence: 3,1,4,5,2

23. Chapter 17 Integrated and Differentiated Services 23 Active Queue Management (AQM) A congestion control function! In face of congestion, informed discard policy is needed Congestion management by proactive packet discard is used: –Before buffer becomes full –Used on single FIFO queue or multiple queues –E.g. Random Early Detection (RED)

24. Chapter 17 Integrated and Differentiated Services 24 RED Motivation Surges may fill buffers and cause discards On TCP this is a signal to enter slow start phase, reducing load –Lost packets need to be resent Adds to load and delay –And may entail Global Synchronisation in drop-tail policy Traffic burst fills queues so packets lost Many TCP connections enter slow start Traffic drops so network becomes under utilized Connections leave slow start at same time causing burst Just bigger buffers do not help Try to anticipate onset of congestion and tell one connection to slow down

25. Chapter 17 Integrated and Differentiated Services 25 RED Design Goals Congestion avoidance Global synchronisation avoidance Avoidance of bias to bursty traffic –Discard only arriving packets will do this Bound on average queue length –Hence control on average delay –Average filters out transient congestion

26. Chapter 17 Integrated and Differentiated Services 26 RED Buffer

27. Chapter 17 Integrated and Differentiated Services 27 RED Algorithm Calculate average queue size avg if avg < TH min queue packet else if TH min  avg  Th max calculate probability P a with probability P a discard packet else with probability 1-P a queue packet else if avg  TH max discard packet

28. Chapter 17 Integrated and Differentiated Services 28 Differentiated Services (DiffServ) IntServ is complex to deploy! May not scale well for large volumes of traffic –Amount of control signals (  overhead) –Maintenance of state information at routers Intserv has only two classes DiffServ (RFC2475) designed to provide simple, easy to implement, low overhead tool –simple functions in network core, relatively complex functions at edge routers (or hosts) –Doesn ’ t define service classes, provide functional components to build service classes

29. Chapter 17 Integrated and Differentiated Services 29 Characteristics of DiffServ Use IPv4 header Type of Service or IPv6 Traffic Class field (called DS field) –So, no change to IP! Service level agreement (SLA) established between provider and customer prior to use of DiffServ All traffic with same DS field treated same –E.g. multiple voice connections

30. Chapter 17 Integrated and Differentiated Services 30 DiffServ Architecture Edge/Boundary router: - per-flow traffic management - marks packets as in-profile and out-profile Core/Interior router: - per class traffic management - buffering and scheduling based on marking at edge - preference given to in-profile packets scheduling... marking ©J.F Kurose and K.W. Ross

31. Chapter 17 Integrated and Differentiated Services 31 Edge-router Packet Marking profile: pre-negotiated rate packet marking at edge based on per-flow profile class-based marking: packets of different classes marked differently intra-class marking: conforming portion of flow marked differently than non-conforming one Possible usage of marking: ©J.F Kurose and K.W. Ross

32. Chapter 17 Integrated and Differentiated Services 32 Classification and Conditioning Packet is marked in the DS field 6 bits used for Differentiated Service Code Point (DSCP) and determine PHB that the packet will receive 2 bits are currently unused ©J.F Kurose and K.W. Ross

33. Chapter 17 Integrated and Differentiated Services 33 Classification and Conditioning Traffic conditioning to provide desired service Classifier –Separate packets into classes Meter/Police –Measure traffic for conformance to profile Marker –Policing by remarking codepoints if required Shaper Dropper

34. Chapter 17 Integrated and Differentiated Services 34 Classification and Conditioning may be desirable to limit traffic injection rate of some class: user declares traffic profile (e.g., rate, burst size) traffic metered, shaped or dropped if non-conforming ©J.F Kurose and K.W. Ross

35. Chapter 17 Integrated and Differentiated Services 35 Forwarding (PHB) I Per Hop Behaviour results in a different observable (measurable) forwarding performance behaviour PHB does not specify what mechanisms to use to ensure required behavior Examples: –Class A gets x% of outgoing link bandwidth over time intervals –Class A packets leave first before packets from class B ©J.F Kurose and K.W. Ross

36. Chapter 17 Integrated and Differentiated Services 36 Forwarding (PHB) II Defined PHBs: Expedited Forwarding: pkt departure rate of a class equals or exceeds specified rate –c.f. logical link with a minimum guaranteed rate Assured Forwarding: 4 classes of traffic –each guaranteed minimum amount of bandwidth –each class with three drop preference partitions ©J.F Kurose and K.W. Ross

37. Chapter 17 Integrated and Differentiated Services 37 Summary IntServ and DiffServ are QoS frameworks for IP internets IntServ requires additional signalling protocol to reserve resource and need to keep state per flow => not scalable DiffServ works based on aggregate classes and has minimal impact on the end-systems => scalable & a more popular alternative Next: Protocols for QoS Support