Chapter 17

1. Chapter 17 Integrated Services & Differentiated Services

2. Introduction • Modern Internet applications demand services not provided by a best-effort service model • Two complementary, yet fundamentally different, traffic management frameworks have evolved: • Integrated Services (IS, ISA, IntServ): reserve resources per session and limit total demand to the capacity that can be handled by the network • Differentiated Services (DS, DiffServ): classify traffic into a number of traffic groups and handle traffic based on its group • Traffic control mechanisms: queuing discipline, packet discard policy • Services are specified within a given domain Chapter 17: Integrated and Differentiated Services

3. elastic traffic must still be supported Internet Traffic • Elastic Traffic • traffic that can adapt, over a wide range, to delay and throughput changes • typically TCP/UDP • QoS perceived based on application • Inelastic Traffic • traffic does not adapt well • requires guarantees on: throughput, delay, jitter, packet loss • e.g. traffic generated by real-time applications Chapter 17: Integrated and Differentiated Services

4. IntServ Approach • Two key features form core of architecture • Resource reservation – routers must maintain state of available resource reserved for each “session” • Call/session setup – each router on the session’s path must verify availability of required resources for a session and admit sessions only if requirements can be met • Call Admission process (more later) • Traffic characterization (Tspec) • Desired QoS caharterizatio (Rspec) • Reservation signaling (RSVP, RFC 2210) • Per-element call admission per Tspec and Rspec Chapter 17: Integrated and Differentiated Services

5. IntServ Implementation • Associate each packet with a “flow” • a distinguishable stream of related IP packets that result from a single user activity and demand the same QoS(per RFC 1633) • unidirectional, can have multiple recipients • typically identified by: source & destination IP addresses, port numbers and protocol type • Provide for enhanced router functions to manage flows: • Admission control based on requested QoS and availability of required network resources • Routing protocol based on QoS (like OSPF/MOSPF) • Queuing/scheduling disciplines based on QoS • Packet discard policy based on QoS Chapter 17: Integrated and Differentiated Services

6. IntServ Architecture (ISA) - requirements at each router RSVP Background Functions Primary Forwarding Functions Chapter 17: Integrated and Differentiated Services

7. ISA: 3 Categories of Service • Guaranteed Service • assured capacity (data rate) • specified upper bound on queuing delay through the network • no queuing loss (i.e., no buffer overflow) • Controlled Load • roughly equivalent to best-effort under no-load conditions (dprop + dtrans) • no specified upper bound on queuing delay, but will approximate minimum expected transit delay • almost no queuing loss • Best Effort Chapter 17: Integrated and Differentiated Services

8. Leaky Bucket Scheme • Used to: • Characterize traffic in a flow. • Describe the load imposed by a flow. • Traffic policing. Note that, during any time period T, the amount of data sent cannot exceed RT+B, and Maximum queuing delay by a packet is B/R. Chapter 17: Integrated and Differentiated Services

9. Queuing Disciplines • Single FIFO queues have numerous drawbacks relative to QoS demands • no special treatment based on priority • larger packets get better service • connections can get an unfair share of resources • IntServ allows for multiple queues • one per flow • separate discipline per flow • fair queuing policy Chapter 17: Integrated and Differentiated Services

10. Round Robin (Fair Queuing) FIFO (First-Come-First-Served) Queuing Disciplines (Scheduling) Drawbacks? Drawbacks? • Flows with busy (greedy) sources crowd out others • Flows with shorter packets are penalized • Flows with shorter packets are penalized Chapter 17: Integrated and Differentiated Services

11. EXAMPLE QUEUE  QUEUE  QUEUE  Packet 1 Packet 2 Packet 1 Packet 2 Packet 1 Real arrival time,i 0 2 1 2 3 Transmission time, Pi 3 1 1 4 2 Virtual start time, Si 0 3 1 2 3 Virtual finish time, Fi 3 4 2 6 5 Processor Sharing Approach • Processor Sharing (PS) • ideal, but not a practical policy • transmit only one bit per round per queue • with N queues, each queue receives exactly 1/N of the available capacity • consider each queue independently to calculate “virtual” start and finish times for each transmission Chapter 17: Integrated and Differentiated Services

12. Bit-Round Fair Queuing • Bit-Round Fair Queuing (BRFQ) • emulates PS round-robin approach for packets and multiple synchronous queues • uses packet length and flow identification (queue) to schedule packets • calculate Siand Fias though PS were running • when a packet finishes transmission, send next packet based on smallest value of Fi over all queues • algorithm is fair on the basis of amount of data transmitted instead of number of packets Chapter 17: Integrated and Differentiated Services

13. PS vs. BRFQ Example Drawback? No precedence or priority weighting of flows. Chapter 17: Integrated and Differentiated Services

14. Load equals capacity Queuing Discipline Examples Chapter 17: Integrated and Differentiated Services

15. Load exceeds capacity Queuing Discipline Examples Drawbacks? Chapter 17: Integrated and Differentiated Services

16. Data Communications and Networking, Forouzan, 2004 Queuing Discipline – Priority Queuing Chapter 17: Integrated and Differentiated Services

17. Queuing Discipline – Weighted Fair Queuing Data Communications and Networking, Forouzan, 2004 Chapter 17: Integrated and Differentiated Services

18. Guaranteed Rate (weight) = .5 Pi  Fi = Si + Guaranteed Rate = .05 ,  = weight Bi (Ki-1)LiKi Lmax Ri Ri m=1 Cm Di    Weighted Fair Queue (WFQ) Maximum delay for flow i Di = max. delay for flow i Bi = token bucket size for flow i Ri = token rate for flow i Ki = number of nodes in flow i path Li = max. packet size for flow i Lmax = max. packet length for all flows through all nodes on flow i path Cm = outgoing link capacity at node m Chapter 17: Integrated and Differentiated Services

19. Scheduling vs. Queue Management (see RFC 2309) • Closely related, but different performance issues… • Scheduling: managing allocation of bandwidth between flows by determining which packet to send next (queuing discipline) • Queue Management: managing the length of packet queues by proactively dropping packets when necessary (packet discard policy) Chapter 17: Integrated and Differentiated Services

20. Random Early Detection (RED) • Queuing discipline with proactive packet discard • anticipate congestion and take early avoidance action • improved performance for elastic traffic by not penalizing bursty traffic • avoids “global synchronization” phenomenon at congestion onset • control average queue length (buffer size) within deterministic bounds… therefore, control average queuing delay Chapter 17: Integrated and Differentiated Services

21. RED Buffer Management • Discard probability is calculated for each packet arrival • at the output queue based on: • the current weighted average queue size, and • the number of packets sent since the previous packet discard Chapter 17: Integrated and Differentiated Services

22. Generalized RED Algorithm calculate the average queue size, avg ifavg < THmin queue the packet else ifTHminavg < THmax calculate probability Pa with probability Pa discard the packet else with probability 1 – Pa queue the packet else if avgTHmax discard the packet See Figure 17.8, page 489 Chapter 17: Integrated and Differentiated Services

23. RED Algorithm • avglags considerably behind changes in actual queue size (weight, wq, is small… typ. 0.002) • avg  (1 – wq)avg + wqq • prevents reaction to short bursts • count, number of packets passed without discard, increases incrementally while Thmin < avg < Thmax • probability of discard, Pa, increases as count increases • helps ensure fairness across multiple flows Chapter 17: Integrated and Differentiated Services

24. 1 Pa = 1/(F x Pmax) - count avg - THmin F = THmax - THmin RED Probability Function(Increasing F) Chapter 17: Integrated and Differentiated Services

25. RED Probability Function(Constant F) avg - THmin Fconst = THmax - THmin Pb = F x Pmax 1 Pa = 1/Pb - count Chapter 17: Integrated and Differentiated Services

26. RED Performance (vs. Drop Tail Queuing Policy) Pmax = 0.02 Chapter 17: Integrated and Differentiated Services

27. Chapter 17 continued Differentiated Services

28. Differentiated Services (DS) • ISA and RSVP deployment drawbacks • relatively complex • may not scale well for large traffic volumes • DiffServ solution (RFC2475, 3260) • designed as a simple, easily-implemented, low-overhead tool • offers a range of services in differentiated service categories… scalable and flexible service classification • Key characteristics • uses existing IPv4 TOS field or IPv6 Traffic Class field (for DS field) • SLA established in advance… no application changes required • built-in aggregation mechanism based on traffic category • routers queue and forward based on information carried in the DS Chapter 17: Integrated and Differentiated Services

29. DS Domains • Contiguous portion of the Internet over which a consistent set of DS policies are agreed and administered • Typically under control of a single management entity • Services in a domain defined by a Service Level Agreement (SLA) – a contract between service provider and user/another domain which specifies QoS parameters • detailed service parameters: throughput, drop probability, latency • ingress/egress constraints • service-based traffic profiles • disposition of excess (in violation of SLA) traffic • DS field carries a traffic class as specified by the SLA Chapter 17: Integrated and Differentiated Services

30. DiffServ Terminology Traffic conditioning functions Chapter 17: Integrated and Differentiated Services

31. DS Terminology • Service Level Agreement (per RFC 3260): • A Service Level Specification (SLS) is a set of parameters and their values which together define the service offered to a traffic stream by a DS domain. • A Traffic Conditioning Specification (TCS) is a set of parameters and their values which together specify a set of classifier rules and a traffic profile. A TCS is an integral element of an SLS. Chapter 17: Integrated and Differentiated Services

32. IP ECN Field, per RFC 3168 & RFC 3260 Replaces DS and IPv4 TOS Fields • 6-bit DS code point, in three pools • Pool 1: xxxxx0 - standards-based use (e.g. 000000, xxx000) • Pool 2: xxxx11 – experimental/local use • Pool 3: xxxx01 – experimental/local use, future standards Chapter 17: Integrated and Differentiated Services

33. DS Domains/Regions Border node: Per Hop Behavior (PHB) plus traffic conditioning mechanisms Interior node: typically only PHB mechanisms Chapter 17: Integrated and Differentiated Services

34. Conformance test per SLA (e.g peak rate, burstiness, …) Regulate traffic flow to achieve a specified traffic rate (e.g. with a token bucket) Separate traffic into classes based on fields as specified in the TCS (source IP, dest. IP, source port #, dest. port #, …) Mark with a DS codepoint, or re-mark as necessary (at domain ingress node, or at boundary between domains) Police traffic and drop packets if rate exceeds that specified in the SLA (per metering function) DS Traffic Classifier/Conditioner Chapter 17: Integrated and Differentiated Services

35. Per-Hop Behavior • RFC 2475 definition: • “a description of the externally observable forwarding behavior of a DiffServ node applied to a particular DiffServ behavior aggregate.” • Two standard PHBs defined: • Expedited Forwarding (RFC 2598) • Assured Forwarding (RFC 2597) • Expedited Forwarding • “Premium service” with low delay, low-loss, low jitter, and assured bandwidth • Domain boundary nodes control traffic aggregate to limit its characteristics (i.e. controlled rate and burstiness) • Interior nodes ensure that the aggregate’s maximum arrival rate is less than its minimum departure rate (i.e. limit the queuing effect) Chapter 17: Integrated and Differentiated Services

36. Per-Hop Behavior (cont.) • Assured Forwarding • designed to offer a service level that is superior to best-effort service • based on explicit allocation concept • choice of classes offered, each with different traffic profile • monitor traffic at boundary nodes, and mark as in or out based on conformance to profile • interior nodes handle packets based only on in or out mark • in congestion, drop outs before ins • implementation defines four AF classes and replaces in/out mark with a drop precedence codepoint • simple and easy to implement in nodes Chapter 17: Integrated and Differentiated Services

37. ECN RFC 2597 Designated AF1x, AF2x, AF3x, AF4x Differentiated ServicesAssured Forwarding PHB Chapter 17: Integrated and Differentiated Services

38. Differentiated ServicesAssured Forwarding PHB AF1 AF2 AF3 AF4 Low Medium High Chapter 17: Integrated and Differentiated Services