Quality of Service QoS DiffServ EE 122 Intro to Communication Networks Fall 2007 WF 4 5 30 in Cory 277 Vern Paxson TAs Lisa Fowler Daniel Killebrew Jorge Ortiz http inst eecs berkeley edu ee122 Materials with thanks to Jennifer Rexford Ion Stoica and colleagues at Princeton and UC Berkeley 1 Our Story So Far QoS attaining some sort of reliable performance from the network Max Min Fairness as concept for allocating capacity across a set of flows Weighted Fair Queuing as way to attain Max Min Fairness Token Bucket as way to describe bounds on burstiness of a flow s packet s arriving at a queue Integrated Services IntServ as means by which flows can Describe burstiness using Token Bucket descriptors Set up soft state reservations end to end Entails admission control decision o Answer could be no you don t get it 2 1 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 o Unidirectional or barter User charging mechanisms need QoS pricing On a fine grained basis 3 Differentiated Services DiffServ Give some traffic better treatment than other Application requirements interactive vs bulk transfer Economic arrangements first class versus coach What kind of better service could you give Fewer drops Lower delay Lower delay variation jitter How to know which packets get better service Bits in packet header Deals with traffic in aggregate Provides weaker services But much more scalable 4 2 Diffserv Architecture Ingress routers entrance to a DiffServ domain Police or shape traffic Set Differentiated Service Code Point DSCP in IP header Core routers Implement Per Hop Behavior PHB for each DSCP Process packets based on DSCP DS 2 DS 1 Ingress Ingress Egress Egress Edge router Core router 5 Differentiated Service DS Field 0 5 6 DS Field 0 4 8 Version HLen TOS Identification TTL 7 ECN 16 19 Flags 31 Length Fragment offset Protocol Header checksum Source address Destination address IP header Data DS field encodes Per Hop Behavior PHB E g Expedited Forwarding all packets receive minimal delay loss E g Assured Forwarding packets marked with low high drop probabilities 6 3 Comparison to Best Effort Intserv Service Best Effort Diffserv Intserv Connectivity Per aggregate isolation Per flow isolation No isolation Service scope No guarantees End to end Domain End to end Long term setup Per flow steup Complexity No setup Scalability Per flow guarantee Per aggregate guarantee Highly scalable Scalable nodes maintain edge routers only routing state maintain per aggregate state core routers per class state Not scalable each router maintains per flow state 7 Discussion Limited QoS Deployment End to end QoS across multiple providers domains is not available today Issue 1 complexity of payment Requires payment system among multiple parties o And agreement on what constitutes service Diffserv tries to structure this as series of bilateral agreements o but lessens likelihood of end to end service o Architecture includes notion of Bandwidth Broker for end toend provisioning Solid design has proved elusive Need infrastructure for metering billing end user 8 4 Limited QoS Deployment con t Issue 2 prevalence of overprovisioning Within a large ISP links tend to have plenty of headroom Inter ISP links are not over provisioned however Is overprovisioning enough If so is this only because access links are slow What about Korea Japan and other countries with fast access links Disconnect ISPs overprovision users get bad service Key difference intra ISP vs general end to end 9 Summary Basic mechanism for achieving better than best effort performance scheduling Multiple queues allow priority service Fair queuing provides isolation between flows But still need end to end mechanisms Reservations admission control Descriptions of bursty traffic token buckets IntServ provides per flow performance guarantees But lacks scalability DiffServ provides per aggregate tiers of relative perf Scalable but not as powerful Neither is generally available end to end today ISPs manipulating what services receive what performance 10 raises issues of network neutrality 5
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