Integrated Services Differentiated Services

1. 1 Chapter 17 Integrated Services & Differentiated Services

2. Chapter 17: Integrated and 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

3. Chapter 17: Integrated and Differentiated Services 3 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 Internet Traffic

4. 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

5. 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

6. Chapter 17: Integrated and Differentiated Services 6 IntServ Architecture (ISA) - requirements at each router

7. 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

8. Chapter 17: Integrated and Differentiated Services 8 Leaky Bucket Scheme

9. 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

10. Chapter 17: Integrated and Differentiated Services 10 Queuing Disciplines (Scheduling)

11. Chapter 17: Integrated and Differentiated Services 11 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

12. 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 Si and Fi as 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

13. Chapter 17: Integrated and Differentiated Services 13 PS vs. BRFQ Example

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

15. Chapter 17: Integrated and Differentiated Services 15 Queuing Discipline Examples

16. Chapter 17: Integrated and Differentiated Services 16 Queuing Discipline � Priority Queuing

17. Chapter 17: Integrated and Differentiated Services 17 Queuing Discipline � Weighted Fair Queuing

18. Chapter 17: Integrated and Differentiated Services 18 Weighted Fair Queue (WFQ)

19. 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)

20. 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

21. Chapter 17: Integrated and Differentiated Services 21 RED Buffer Management

22. Chapter 17: Integrated and Differentiated Services 22 Generalized RED Algorithm calculate the average queue size, avg if avg < THmin queue the packet else if THmin ? 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

23. Chapter 17: Integrated and Differentiated Services 23 RED Algorithm avg lags 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

24. Chapter 17: Integrated and Differentiated Services 24 RED Probability Function(Increasing F)

25. Chapter 17: Integrated and Differentiated Services 25 RED Probability Function(Constant F)

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

27. 27 Chapter 17 continued Differentiated Services

28. Chapter 17: Integrated and 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

29. 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

30. Chapter 17: Integrated and Differentiated Services 30 DiffServ Terminology

31. 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.

32. Chapter 17: Integrated and Differentiated Services 32 DS and IPv4 TOS Fields

33. Chapter 17: Integrated and Differentiated Services 33 DS Domains/Regions

34. Chapter 17: Integrated and Differentiated Services 34 DS Traffic Classifier/Conditioner

35. 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)

36. 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

37. Chapter 17: Integrated and Differentiated Services 37 Differentiated ServicesAssured Forwarding PHB

38. Chapter 17: Integrated and Differentiated Services 38 Differentiated ServicesAssured Forwarding PHB

39. Chapter 17: Integrated and Differentiated Services 39 Real-Time Traffic Flow

40. Chapter 17: Integrated and Differentiated Services 40 Real-Time Packet Transmission