Goals of Today s Lecture Traffic characterization EE 122 Quality of Service QoS models Ion Stoica TAs Junda Liu DK Moon David Zats Token bucket Integrated Services End to end network reservations Differentiated Services First Class vs Coach http inst eecs berkeley edu ee122 fa09 Materials with thanks to Vern Paxson Jennifer Rexford and colleagues at UC Berkeley 1 Reserving Resources End to End Source sends a reservation message How to Specify Bursty Traffic E g this flow needs 5 Mbps Each router along the path Keeps track of the reserved resources Checks if enough resources remain Creates state for flow and reserves resources E g the link has 6 Mbps left E g 6 Mbps 5 Mbps so circuit can be accepted E g now only 1 Mbps is available Option 1 Specify the maximum bit rate Problems Maximum bit rate may be much higher average Reserving for the worst case is wasteful Option 2 Specify the average bit rate Problems Average bit rate is not sufficient Network will not be able to carry all of the packets Reserving for average case leads to bad performance Option 3 Specify the burstiness of the traffic Specify both the average rate and the burst size Allows the sender to transmit bursty traffic and the network to reserve the necessary resources 1 Characterizing Burstiness Token Bucket Traffic Enforcement Example Parameters r average rate i e rate at which tokens fill the bucket b bucket depth limits size of burst R maximum link capacity or peak rate r bps 2 2Kb T 2ms packet transmitted b 3Kb 1Kb 2ms 100Kbps 2 2Kb T 0 1Kb packet arrives Maximum of bits sent bits a 3Kb A bit can be transmitted only when a token is available r 100 Kbps b 3 Kb R 500 Kbps b c slope r b R R r d 3Kb 2 4Kb b bits e 0 6Kb slope R T 4ms 3Kb packet arrives R bps b R r regulator Source Traffic Characterization Arrival Curve T 16ms packet transmitted Arrival Curve Example Arrival curve maximum amount of bits transmitted during any interval of time t Use token bucket to bound arrival curve Arrival curve maximum amount of bits transmitted during any interval of time t Use token bucket to bound arrival curve bps T 10ms packet needs to wait until enough tokens are in the bucket time bits bits R 2 b 1 r 1 Arrival curve 2 5 4 Arrival curve bps 3 time 2 2 1 1 t 0 1 2 3 4 5 time 1 3 4 t 2 QoS Guarantees Per hop Reservation End host specify arrival rate characterized by token bucket with parameters b r R the maximum tolerable delay D no losses Ensuring the Source Behaves Router allocate bandwidth ra buffer space Ba such that no packet is dropped no packet experiences a delay larger than D slope ra slope r bits Arrival curve D Integrated Services Required Elements Reservation Protocol How network decides if it can accept flow Packet scheduling algorithms Mark all data in excess of the traffic specification and give these packets lower priority in the network Control Plane vs Data Plane Control plane How information gets to routers Data plane What routers do with that information when processing data packets How routers deliver service Architecture for solution IntServ How service request gets from host to network Admission control algorithm Delay the data until it obeys the traffic specification Solution 3 marking Ba Drop all data in excess of the traffic specification Solution 2 shaping R Extra traffic might overload one or more links Leading to congestion and resulting delay and loss Solution need to enforce the traffic specification Solution 1 policing b R R r Guarantees depend on the source behaving Provides service guarantees at a per flow granularity Control Data 3 Control Plane Resource Reservation Sender Receiver Control Plane Resource Reservation Path established or perhaps admission control denies path Sender Receiver Control Plane Resource Reservation Sender sends specification Sender of traffic profile Receiver Control Plane Resource Reservation Sender Receiver The receiver accepts reservation request 4 Control Plane Admission Control Per flow state soft state Sender Receiver Data Plane Control Plane Admission Control Sender Per flow state on all routers in path Receiver Data Plane Receiver Sender Per flow classification on each router Receiver Sender Per flow classification on each router 5 Data Plane Per flow scheduling on each router Sender Admission Control Receiver Parameter based worst case analysis Measurement based measure current traffic Guaranteed service Lower utilization Controlled load service Higher utilization Remember that best effort service co exists No need for IntServ traffic to achieve high utilization Problems with IntServ Scalability per flow state classification Aggregation encapsulation techniques can help Can overprovision big links per flow ok on small links Scalability can be fixed but no second chance Economic arrangements Need sophisticated settlements between ISPs Contemporary settlements are primitive 5 Minute Break Questions Before We Proceed Unidirectional or barter User charging mechanisms need QoS pricing On a fine grained basis 6 Differentiated Services DiffServ Give some traffic better treatment than other Core routers Fewer drops Lower delay Lower delay variation jitter DS 2 DS 1 Ingress Provides weaker services But much more scalable Egress Can t give all traffic better service Edge router Ingress Egress Must limit the amount of traffic that gets better service Core router Expedited Forwarding EF Give packet minimal delay and loss service E g put EF packets in high priority queue To make this a true absolute service Implement Per Hop Behavior PHB for each DSCP Process packets based on DSCP Bits in packet header Traffic Limitations Police or shape traffic Set Differentiated Service Code Point DSCP in IP header Deals with traffic in aggregate Ingress routers entrance to a DiffServ domain How to know which packets get better service What kind of better service could you give Application requirements interactive vs bulk transfer Economic arrangements first class versus coach Diffserv Architecture All SLAs must sum to less than the link speed Service Level Agreements SLA Source agrees to limit amount of traffic in given class Network agrees to give that traffic better service Economics play an important fatal role in QoS For a price 7 Is Delay the Problem Packets are dropped when queue starts to grow Assured Forwarding AS Packets are all serviced in order Thus delays are mostly speed of light latency Service quality is mostly expressed by drop rate Want to give traffic different
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