NETS3303 Networked Systems

1. 1 NETS3303 Networked Systems

2. 2 Section 2 IP QoS

3. 3 Outcomes • Understanding components of IP QOS • What they do • Why they are used or proposed • Have knowledge of some case study technologies • Understanding the relevance to MM delivery

4. 4 IP QoS • Today’s Outline • What is QoS? • Types of traffic • IntServ • Signalling • Queuing and Scheduling • DiffServ

5. 5 QoS ? • Many definitions in literature • My definition is: • “A perceived level of quality of a service or function in relation to the wanted or expected level of quality” • In this course, application behaviour depending on network performance

6. 6 IP QoS • IP provides only Best Effort service: • No guarantees full stop • No guaranteed packet delivery • No guaranteed time • No guaranteed order • IP is ignorant of packet content • No “Flows” in IP • Compare telephony network

7. 7 QoS Get lost Lost speech: “ing”, “is easy here honey” Internet Getting lost is easy here honey. • Network parameters • Packet loss • Delay • Jitter

8. 8 Where did he go? QoS Delay 1000 ms Silence Internet Getting lost is easy here honey. • Network parameters • Packet loss • Delay • Jitter

9. 9 What the QoS G ettinglos tis easyhere h on ey Delay 1000 ms Internet Getting lost is easy here honey. • Network parameters • Packet loss • Delay • Jitter

10. 10 Types of Traffic • Different applications generate different types of traffic e.g. • Web pages (delay sensitive) • FTP (BW sensitive) • Streamed Media (BW sensitive) • Conversational Multimedia (delay and BW)

11. 11 Edge Router Edge Router Building blocks Routers Routers Network Region Network Region End host End host • End – to – end signalling • Routers: Queuing and Scheduling • Edge Routers: Add admission control • A defined set of rules or classes to request

12. 12 IntServ • Provides a set of service classes per flow • Guaranteed Service • Hard guarantees (Conversational MM) • Controlled Load • Same behaviour as lightly loaded BE network (adaptive MM etc.) • Best Effort • All other types of traffic

13. 13 Is there a problem with the per-flow specification?

14. 14 RSVP • Create notion of flow: • E2E Signalling • IETF proposal • Resource Reservation Protocol, RSVP • Allows Applications to make reservations

15. 15 Router Router Router RSVP • App fills in Traffic specification (T-Spec) • Each router: admission control • If requirements met: make reservations OK Flow End Host End Host Can I get? Can I get? Can I get? Can I get?

16. 16 Why is signalling receiver-based?

17. 17 Admission Control • Token Bucket (rate r, size b) • Start with full bucket • If enough tokens in bucket accept packets and remove tokens • Tokens keep filling with rate r

18. 18 Queuing • Traditional queuing: FIFO, one input one output • Need to separate traffic into classes • Need to give different priority to different classes • Need to manage the different queues

19. 19 QoS Router • Standard QoS Router Components • Routing Policy (rules for classification) • Routing table (Where to send packets) • Input Lines (where packets com in, no queue) • Output queues (where packets wait to be sent) • Classifier (puts packets into queues acc. to policy) • Scheduler (decides which queue to empty)

20. 20 Scheduling • The scheduler assigns resources to tasks • In a computer: divide CPU runtime to processes • In a router: divide available BW (output queues) to packets • Operates based on router policy

21. 21 FCFS • Work Conserving (if packet waiting, serve) • Klienrock Conservation Law ρ = link utilisation q = mean scheduler delay C = a constant If delay for one flow is lowered, the delay for one or more other flows must increase

22. 22 Non Work Conserving • Scheduler can be idle even if packets waiting • Switches packets to • The right destination • At the right time • Reduces jitter • Makes traffic predictable

23. 23 Scheduling Requirements • Easy to implement • Simple makes fast • Few states allows HW implementation • High speed routing • Fairness • Local means global • Protect from other misbehaving flows • Performance bounds • Per flow bounds • Deterministic guaranteed) • Statistical • Data rate, jitter, delay, loss • Admission Control • Easy to implement • efficient

24. Priority levels How many Serve higher priority queues first? (can cause starvation) Work conserving? Delay/jitter control required? Extra cost acceptable? Flow Aggregation Granularity? Per flow Per application Per terminal Per queue policy FCFS? Look inside each packet and decide? Performance/overhead 24 Scheduling choices

25. 25 Priority Queuing • K queues • 1 ≤ k ≤ K • Queue k+1 higher prio. than queue k • Higher prio. served first • Simple implementation • Low processing overhead • No fairness, low prio. queues can be starved

26. 26 WFQ • Round robin scheme • Estimate time to send packet (finish number) • Tag packet with finish number • Serve packet with smallest finish number • Regardless of queue • Weights can be assigned to enable prioritisation • Implemented by manufacturers

27. 27 CBQ Root 100 % Y • Assigns fractions of BW to class nodes • Values minimum • Nodes can borrow unused BW • Priority to flows within a class X 40 % 60 % RT NRT 40 % 20 %

28. 28 Question:Can we do QoS management without Queuing / Scheduling?

29. 29 DiffServ • IntServ per-flow scalability problem • Solution: aggregate flows • Treat classes not individual flows • Thus, tables kept small • IP TOS field becomes DSCP • 6 bit identifier of class

30. 30 Ingress Router Egress Router Core Router Core Router DiffServ domain PHB PHB PHB Dimensioned to meet Ingress router admission control

31. 31 DiffServ PHB • Expedited Forwarding, EF • Highest priority • WFQ suitable • Assured Forwarding, AF • Three drop probability classes • Graceful behaviour

32. 32 What if two DiffServ domains have different definitions of what a DSCP translates to?

33. 33 The QoS stair QoS Level Domain A B C D

34. 34 DiffServ:Scales wellStatistical guarantee only

35. 35 Summary • IP, no flows, no traffic separation • Different types of traffic, different needs • QoS management: • Classification • Signalling • Admission control • Queuing/scheduling • IntServ, DiffServ, RSVP

36. 36 Reading • Deeper understanding: • RFCs 2205-2216, 2474-2475

37. 37 Other areas • MPLS • VLANS • Working Intserv and Diffserv together • QoS in 3G, bearer services, signalling etc. • Service Level Agreements • Billing and business models • Fibre, channel allocations DWDM etc.