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INTERNET QOS: A BIG PICTURE XIPENG XIAO AND LIONEL M. NI, MICHIGAN STATE UNIVERSITY Jinyoung You CS540, Network Architect
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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 2
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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 3
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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 4
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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? 5
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Outline 1. IntServ/RSVP 2. DiffServ 3. MPLS 4. Traffic Engineering/CBR 5. Comparison of ATM Networks 6. Conclusion 7. Q&A 6
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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-ef fort service 7
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IntServ/RSVP 8
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Components Signaling protocol Admission control routine Classifier Packet scheduler 9
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IntServ/RSVP Limitations Scalability State information is proportional to amount of flow Overhead on routers Should have all components; RSVP, admission control, MF c lassification, packet scheduling Ubiquitous deployment is required 10
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DiffServ Motivation The difficulty in implementing and deploying IntServ and R SVP 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 11
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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 in gress routers Domain DF field is remarked by SLA between the domains 12
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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 DiffServ and IntServ State information is proportional to the number of classes Process complexity is only at the edge router 13
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DiffServ Assured Service Provide reliable services even in times of network con gestion 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 14
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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 15
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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 16
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DiffServ 17
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DiffServ 18
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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
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MPLS MPLS: Multi Protocol Label Switching Incoming packets are assigned a “label” by edge router Packets are routed according to the label By a label switch router(LSR) The path a packet traverses is called label switched path(LSP) Network protocol independent
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MPLS
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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
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Traffic Engineering/CBR Motivation IntServ/RSVP and DiffServ 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
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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
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Traffic Engineering/CBR Shortest Path Problem
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Traffic Engineering/CBR Constrained Based Routing Compute QoS route May select longest lightly-loaded path rather than heavily shortest path Improve network resource utilization
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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
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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
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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
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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 or MPLS Provide QoS on the router network Reduce ATM cell header overhead
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Conclusion QoS is hotly debated issue Fibers and WDM will make bandwidth so abundant and cheap QoS will 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 QoS problem There is little hope for success But, Way to go
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Q&A
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