EECS 122 Introduction to Computer Networks Resource Management and QoS Computer Science Division Department of Electrical Engineering and Computer Sciences University of California Berkeley Berkeley CA 94720 1776 Katz Stoica F04 Mid Term Will be returned in discussion section Grading appeals must be submitted within one week of getting your test back no exceptions regrades will be over entire test not over single question score could go up or down Overall you did very well mode 85 median 85 mean 80 01 15 19 Katz Stoica F04 2 Mid Semester Resolutions Timestamps on slides starting next week Scott will try to slow down more interactive two hands up means stop Clearer delineation between required material and optional material More focused reading assignments Revising future topics more security 01 15 19 Katz Stoica F04 3 Today s Lecture 14 2 17 18 19 6 10 11 Application Transport 14 15 16 7 8 9 21 22 23 25 Network IP Link Physical 01 15 19 Katz Stoica F04 4 Quality of Service QoS The Internet s most contentious subject The Internet s most embarrassing failure almost nothing was accomplished the research community was dishonest and ineffective my worst experience as a researcher The textbook s worst chapter a rosy description of bad work 01 15 19 Katz Stoica F04 5 Today s Lecture Will be about what could be not what is today s Internet does not have nor will soon have a reasonable QoS solution Focus will be on what one could accomplish with simple and not so simple mechanisms you will only be expected to know basic concepts I will not discuss current deployed mechanisms an ugly hodge podge of hacks 01 15 19 Katz Stoica F04 6 What s the Problem Internet gives all flows the same best effort service no promises about when or whether packets will be delivered Not all traffic is created equal different owners different application requirements some applications require service assurances How can we give traffic different quality of service Thus begins the problem of QoS 01 15 19 Katz Stoica F04 7 Three Basic Problems Want to control how a link is shared Link sharing Want to give some traffic better service Differentiated service Want to gives some flows assured service Integrated service and perhaps differentiated service 01 15 19 Katz Stoica F04 8 A Different Taxonomy Giving better service can differ along three dimensions relative versus absolute dropping versus delay flows versus aggregates Each of these choices requires different set of mechanisms router scheduling and dropping decisions signaling protocols 01 15 19 Katz Stoica F04 9 Three Basic Questions How does a router service this packet scheduling various forms of priority and RR dropping fancy versions of RED How did the router know what to do with this packet bits in packet header or explicit signaling How can one control the level of traffic service level agreements SLAs or admission control 01 15 19 Katz Stoica F04 10 Back to Thee Basic Problems Link sharing one slide Differentiated Services long Integrated Services even longer 01 15 19 Katz Stoica F04 11 Link Sharing Two organizations share an access link and want to share it equally One approach partition the link Second approach use FQ with one queue for each organization s packets Which is better 01 15 19 Katz Stoica F04 12 Differentiated Services Some traffic should get better treatment application requirements interactive vs bulk transfer economic arrangements first class versus coach What kind of better service could you give measured by drops or delay and drops How do you know which packets to give better service to bits in packet header 01 15 19 Katz Stoica F04 13 Traffic Limitations Can t give all traffic better service Must limit the amount of traffic that gets better service Service Level Agreements SLA source agrees to limit amount of traffic in given class network agrees to give that traffic better service for a price economics play an important fatal role in QoS 01 15 19 Katz Stoica F04 14 DiffServ Code Points Use six of the ToS bits in IP packet header Define various code points Each code point defines a desired per hop behavior a description of the service the packet should get not a description of the router implementation of that service 01 15 19 Katz Stoica F04 15 Expedited Forwarding Give packet minimal delay and loss service e g put EF packets in high priority queue To make this a true absolute service all SLAs must sum to less than the link speed unlikely More likely a way to assure relatively low delay 01 15 19 Katz Stoica F04 16 Is Delay the Problem With RED most queues are small Packets are dropped when queue starts to grow Thus delays are mostly speed of light latency Service quality is mostly expressed by drop rate Want to give traffic different levels of dropping 01 15 19 Katz Stoica F04 17 Assured Forwarding Packets are all serviced in order makes TCP implementations perform well But some packets can be marked as low drop and others as high drop think of it as priority levels for dropping Can be implemented using variations of RED different drop probabilities for different classes 01 15 19 Katz Stoica F04 18 Example 10 premium traffic 90 ordinary traffic Overall drop rate is 5 Can give premium traffic 0 drops and ordinary traffic a 5 55 drop rate Can get a large improvement in service for the small class of traffic without imposing much of a penalty on the other traffic count on SLAs to control premium traffic 01 15 19 Katz Stoica F04 19 Advantages of DiffServ Very simple to implement Can be applied to different granularities flows institutions traffic types Marking can be done at edges or by hosts Allows easy peering bilateral SLAs 01 15 19 Katz Stoica F04 20 DiffServ Peering Ingress routers Police shape traffic Set Differentiated Service Code Point DSCP in DiffServ DS field Core routers Implement Per Hop Behavior PHB for each DSCP Process packets based on DSCP DS 2 DS 1 Ingress Egress Egress Edge router Ingress Egress Egress Core router 01 15 19 Katz Stoica F04 21 Disadvantages of DiffServ Service is still best effort just a better class of best effort except for EF which has terrible efficiency all traffic accepted within SLAs Some applications need better than this certainly some apps need better service than today s Internet delivers but perhaps if DiffServ were widely deployed premium traffic would get great service recall example nonetheless let s plunge ahead 01 15 19 Katz Stoica F04 22 Integrated Services An attempt to integrate
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