Quality of ServiceRealtime ApplicationsPlayback BufferExample Distribution of DelaysTaxonomyIntegrated ServicesFlowspecPer-Router MechanismsReservation ProtocolRSVP ExampleRSVP versus ATM (Q.2931)Differentiated ServicesDiffServ (cont)Spring 2003 CS 461 1Quality of ServiceOutlineRealtime ApplicationsIntegrated ServicesDifferentiated ServicesSpring 2003 CS 461 2Realtime Applications•Require “deliver on time” assurances–must come from inside the network•Example application (audio)–sample voice once every 125us–each sample has a playback time–packets experience variable delay in network–add constant factor to playback time: playback pointMicrophoneSpeakerSampler,A D converterBuffer,D ASpring 2003 CS 461 3Playback BufferSequence numberPacketgenerationNetworkdelayBufferPlaybackTimePacketarrivalSpring 2003 CS 461 4Example Distribution of Delays123Packets (%)90% 97% 98% 99%150 20010050Delay (milliseconds)Spring 2003 CS 461 5TaxonomyApplicationsReal timeTolerantAdaptive NonadaptiveDelay-adaptiveRate-adaptiveIntolerantRate-adaptive NonadaptiveInteractiveInteractivebulkAsynchronousElasticSpring 2003 CS 461 6Integrated Services•Service Classes–guaranteed–controlled-load•Mechanisms–signalling protocol–admission control–policing–packet schedulingSpring 2003 CS 461 7Flowspec•Rspec: describes service requested from network–controlled-load: none–guaranteed: delay target•Tspec: describes flow’s traffic characteristics–average bandwidth + burstiness: token bucket filter–token rate r–bucket depth B–must have a token to send a byte–must have n tokens to send n bytes–start with no tokens–accumulate tokens at rate of r per second–can accumulate no more than B tokensSpring 2003 CS 461 8Per-Router Mechanisms•Admission Control–decide if a new flow can be supported–answer depends on service class–not the same as policing•Packet Processing–classification: associate each packet with the appropriate reservation–scheduling: manage queues so each packet receives the requested serviceSpring 2003 CS 461 9Reservation Protocol•Called signaling in ATM•Proposed Internet standard: RSVP•Consistent with robustness of today’s connectionless model•Uses soft state (refresh periodically)•Designed to support multicast•Receiver-oriented•Two messages: PATH and RESV•Source transmits PATH messages every 30 seconds•Destination responds with RESV message•Merge requirements in case of multicast•Can specify number of speakersSpring 2003 CS 461 10RSVP ExampleRRRRRSender 1Sender 2PATHPATHRESV(merged)RESVRESVReceiver BReceiver ASpring 2003 CS 461 11RSVP versus ATM (Q.2931)•RSVP–receiver generates reservation–soft state (refresh/timeout)–separate from route establishment–QoS can change dynamically–receiver heterogeneity•ATM–sender generates connection request–hard state (explicit delete)–concurrent with route establishment–QoS is static for life of connection–uniform QoS to all receiversSpring 2003 CS 461 12Differentiated Services•Problem with IntServ: scalability•Idea: segregate packets into a small number of classes–e.g., premium vs best-effort•Packets marked according to class at edge of network•Core routers implement some per-hop-behavior (PHB)•Example: Expedited Forwarding (EF)–rate-limit EF packets at the edges–PHB implemented with class-based priority queues or WFQSpring 2003 CS 461 13DiffServ (cont)•Assured Forwarding (AF)–customers sign service agreements with ISPs–edge routers mark packets as being “in” or “out” of profile–core routers run RIO: RED with
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