Internet QOS: A Big Picture Xipeng Xiao and Lionel M. Ni, Michigan State University

1. Internet QOS: A Big PictureXipeng Xiao and Lionel M. Ni, Michigan State University Jinyoung You CS540, Network Architect

2. Motivation • Today’s Internet • Best-effort service • No guarantee as to timeliness or actual delivery • No guarantee of low-delay and low-jitter services • No service classes • No abundant and cheap bandwidth

3. Motivation • What’s the QoS? • Guarantee a certain level of performance • e.g.) Packet dropping probability , Delay, Jitter, Out-of-order delivery, Error, Congestion • Why QoS? • The network capacity is insufficient • Real-time streaming multimedia applications • e.g.) VoIP, IPTV • Requires fixed bit rate and are delay sensitive

4. Motivation • Misunderstanding of QoS • Cannot provide nonexistent bandwidth • Cannot make the network faster • Cannot cure poorly performing network • Contribution of QoS • Provide relative prioritization of traffic

5. Motivation • Service Models and Mechanisms of IETF • Integrated Services/Resource Reservation Protocol (RSVP) Model • Differentiated Services (DS) model • Multi Protocol Label Switching (MPLS) • Traffic engineering • Constrained Based Protocol • How they differ from and relate to each other? • Which system they fit?

6. Outline • IntServ/RSVP • DiffServ • MPLS • Traffic Engineering/CBR • Comparison of ATM Networks • Conclusion • Q&A

7. IntServ/RSVP • Resource reservation • For real-time service, before data are transmitted, • Apps must first set up paths and reserve resources • Service classes • Guaranteed service: fixed delay bound • Controlled-load service: reliable and enhanced best-effort service

8. IntServ/RSVP

9. IntServ/RSVP • Components • Signaling protocol • Admission control routine • Classifier • Packet scheduler

10. IntServ/RSVP • Limitations • Scalability • State information is proportional to amount of flow • Overhead on routers • Should have all components; RSVP, admission control, MF classification, packet scheduling • Ubiquitous deployment is required

11. DiffServ • Motivation • The difficulty in implementing and deploying IntServ and RSVP • DS is essentially a relative-priority scheme • Using DS fields of packet header to indicate service classes • Process complexity • core network → edge network • More scalable

12. DiffServ • Customer • Have a Service Level Agreement (SLA) with its ISP • Which service class to provide? • Mark the DS field according to the service class • Router • Classification, policing, shaping, scheduling occur at only ingress routers • Domain • DF field is remarked by SLA between the domains

13. DiffServ • Possible services of DiffServ • Premium service • For low-delay and low-jitter service • Assured service • For better reliability than best-effort service • Olympic service • gold, silver, and bronze, with decreasing quality • Differences between DiffServandIntServ • State information is proportional to the number of classes • Process complexity is only at the edge router

14. DiffServ • Assured Service • Provide reliable services even in times of network congestion • Be implemented as follows: • Classification and policing are done at the ingress routers • All packets, in and out, are put into an AQ • The queue is managed by a RED or RIO

15. DiffServ • Premium Service • SLA specifies a peak bit-rate • Provide low delay and low jitter • e.g.) Internet Telephony, Video Conferencing, VPN • More expensive, But more prior than Assured Service • Be implemented as follows: • Use P-bit on DS field • If P-bit is on, the packet goes to Premium Queue • Uneven distribution of traffic may cause a problem

16. DiffServ • Service Allocation in Customer Domains • How to decide services; Assured or Premium Service • Each host makes its own decision • Bandwidth Broker(BB) makes decision • Resource Allocations in ISP Domains • How boundary routers handle incoming traffic • Static SLAs, Manually configured. • Dynamic SLA, RSVP

17. DiffServ

18. DiffServ

19. DiffServ • Requirements on Routers • Edge router: MF classifications, marking, and shaping • ISP ingress router: policing, re-marking • ISP egress routers: re-shaping • BA classification, Assured Queue, Premium Queue • For dynamic SLA, BB at the customer domain

20. MPLS • MPLS: Multi Protocol Label Switching • Incoming packets are assigned a “label” by edge router • Packets are routed according to the label • Bya label switch router(LSR) • The path a packet traverses is called label switched path(LSP) • Network protocol independent

21. MPLS

22. MPLS • MPLS is strategically significant • Provides faster packet classification and forwarding • Provides an efficient tunneling mechanism • without encryption • Moves processing to edge routers • Core did forwarding only, Scalable

23. Traffic Engineering/CBR • Motivation • IntServ/RSVPandDiffServ has degradation of performance when traffic load is heavy. • Major goal • Provide efficient and reliable network operation • Optimize network resource utilization • To efficiently manage bandwidth resources • Optimize traffic performance • To enhance QoS of traffic stream

24. Traffic Engineering/CBR • The factor of Congestion • Lack of network resource • Upgrade infrastructure • Uneven distribution • Because of Shortest Path problem • Constraint Based Routing • Automatically Traffic Engineering

25. Traffic Engineering/CBR • Shortest Path Problem

26. Traffic Engineering/CBR • Constrained Based Routing • Compute QoSroute • May select longest lightly-loaded path rather than heavily shortest path • Improve network resource utilization

27. Traffic Engineering/CBR • Distribution of Link State Information • Needs of link available bandwidth, buffer space information • Link state advertisement of OSPF, IS-IS • Route Computation • Various algorithm for distinct metrics; cost, hop-count, bandwidth, reliability, delay, jitter • Let d(i, j) be a metric for link (i, j). For any path P = (i, j, k, …,l, m), metric d is: • Additive if d(P) = d(i, j) + d(j, k) + … + d(l, m) • e.g.) delay, jitter, cost and hop-count • Multiplicative if d(P) = d(i, j) * d(j, k) * … * d(l, m) • e.g.) reliability (1-loss rate) • Concave if d(P) = min{d(i, j), d(j, k), …, d(l, m)} • e.g.) bandwidth

28. Traffic Engineering/CBR • Pros • Meeting the needs for QoS requirement of flows • Improved network utilization • Cons • Increased communication and computation overhead • Increased routing table size • Longer path may consume more resources • Potential routing instability

29. Traffic Engineering/CBR • The Position of CBR • DiffServ: Not for replacing, but helping DiffServ • RSVP: Independent with RSVP • CBR just determines the path of RSVP messages • MPLS • MPLS: forwarding scheme, CBR: routing scheme • Work together for traffic engineering

30. Comparison of ATM Networks • ATM Network • Use Virtual Circuit Switching • Pros • Fast • Provide QoS • Cons • ATM cell header overhead • Switch can not work at the boundary of network • ATM Network with DiffServ orMPLS • Provide QoS on the router network • Reduce ATM cell header overhead

31. Conclusion • QoS is hotly debated issue • Fibers and WDM will make bandwidth so abundant and cheap • QoSwill be automatically delivered • However, New application will be invented to consume it • Thus, Mechanism will be needed to provide QoS • Many mechanisms are provided but they not solve QoSproblem • There is little hope for success • But, Way to go

32. Q&A