(Internetwork operation (chapter 16
اسلاید 1: William Stallings Data and Computer CommunicationsChapter 16Internetwork Operation
اسلاید 2: Routing ProtocolsRouting InformationAbout topology and delays in the internetRouting AlgorithmUsed to make routing decisions based on information
اسلاید 3: Autonomous Systems (AS)Group of routersExchange informationCommon routing protocolSet of routers and networks managed by signle organizationA connected networkThere is at least one route between any pair of nodes
اسلاید 4: Interior Router Protocol (IRP)Passes routing information between routers within ASMay be more than one AS in internetRouting algorithms and tables may differ between different ASRouters need some info about networks outside their ASUsed exterior router protocol (ERP)IRP needs detailed modelERP supports summary information on reachability
اسلاید 5: Application of IRP and ERP
اسلاید 6: Border Gateway Protocol (BGP)For use with TCP/IP internetsPreferred EGP of the InternetMessages sent over TCP connectionsOpenUpdateKeep aliveNotificationProceduresNeighbor acquisitionNeighbor reachabilityNetwork reachability
اسلاید 7: BGP Messages
اسلاید 8: BGP ProcedureOpen TCP connectionSend Open messageIncludes proposed hold timeReceiver selects minimum of its hold time and that sentMax time between Keep alive and/or update messages
اسلاید 9: Message TypesKeep AliveTo tell other routers that this router is still hereUpdateInfo about single routes through internetList of routes being withdrawnIncludes path infoOrigin (IGP or EGP)AS_Path (list of AS traversed)Next_hop (IP address of boarder router)Multi_Exit_Disc (Info about routers internal to AS)Local_pref (Inform other routers within AS)Atomic_Aggregate, Aggregator (Uses address tree structure to reduce amount of info needed)
اسلاید 10: Uses of AS_Path and Next_HopAS_PathEnables routing policyAvoid a particular ASSecurityPerformanceQualityNumber of AS crossedNext_HopOnly a few routers implement BGPResponsible for informing outside routers of routes to other networks in AS
اسلاید 11: Notification MessageMessage header errorAuthentication and syntaxOpen message errorSyntax and option not recognizedUnacceptable hold timeUpdate message errorSyntax and validity errorsHold time expiredConnection is closedFinite state machine errorCeaseUsed to close a connection when there is no error
اسلاید 12: BGP Routing Information ExchangeWithin AS, router builds topology picture using IGPRouter issues Update message to other routers outside AS using BGPThese routers exchange info with other routers in other ASRouters must then decide best routes
اسلاید 13: Open Shortest Path First (1)OSPFIGP of InternetReplaced Routing Information Protocol (RIP)Uses Link State Routing AlgorithmEach router keeps list of state of local links to networkTransmits update state infoLittle traffic as messages are small and not sent oftenRFC 2328Route computed on least cost based on user cost metric
اسلاید 14: Open Shortest Path First (2)Topology stored as directed graphVertices or nodesRouterNetworkTransitStubEdgesGraph edgeConnect two routerConnect router to network
اسلاید 15: Sample AS
اسلاید 16: Directed Graph of AS
اسلاید 17: OperationDijkstra’s algorithm (Appendix 10A) used to find least cost path to all other networksNext hop used in routing packets
اسلاید 18: Integrates Services ArchitectureChanges in traffic demands require variety of quality of service Internet phone, multimedia, multicastNew functionality required in routersNew means of requesting QoSISARFC 1633
اسلاید 19: Internet TrafficElasticCan cope with wide changes in delay and/or throughputFTP sensitive to throughputE-Mail insensitive to delayNetwork Management sensitive to delay in times of heavy congestionWeb sensitive to delayInelasticDoes not easily adapt to variationse.g. real time traffic
اسلاید 20: Requirements for Inelastic TrafficThroughputDelayJitterDelay variationPacket lossRequire preferential treatment for certain types of trafficRequire elastic traffic to be supported as well
اسلاید 21: ISA ApproachCongestion controlled byRouting algorithmsPacket discardAssociate each packet with a flowUnidirectionalCan be multicastAdmission ControlRouting AlgorithmQueuing disciplineDiscard policy
اسلاید 22: ISA Components
اسلاید 23: Token Bucket Traffic SpecificationToken replenishment rate RContinually sustainable data rateBucket size BAmount that data rate can exceed R for short periodDuring time period T amount of data sent can not exceed RT + B
اسلاید 24: Token Bucket Scheme
اسلاید 25: ISA ServicesGuaranteedAssured data rateUpper bound on queuing delayNo queuing lossReal time playbackControlled loadApproximates behavior to best efforts on unloaded networkNo specific upper bound on queuing delayVery high delivery successBest Effort
اسلاید 26: Queuing DisciplineTraditionally FIFONo special treatment for high priority flow packetsLarge packet can hold up smaller packetsGreedy connection can crowd out less greedy connectionFair queuingQueue maintained at each output portPacket placed in queue for its flowRound robin servicingSkip empty queuesCan have weighted fair queuing
اسلاید 27: FIFO and Fair Queue
اسلاید 28: Resource Reservation: RSVPUnicast applications can reserve resources in routers to meet QoSIf router can not meet request, application informedMulticast is more demandingMay be reducedSome members of group may not require delivery from particular source over given timee.g. selection of one from a number of “channels”Some group members may only be able to handle a portion of the transmission
اسلاید 29: Soft StateSet of state info in router that expires unless refreshedApplications must periodically renew requests during transmissionResource ReSerVation Protocol (RSVP)RFC 2205
اسلاید 30: RSVP GoalsAbility for receivers to make reservationsDeal gracefully with changes in multicast group membershipSpecify resource requirements such that aggregate resources reflect requirementsEnable receivers to select one sourceDeal gracefully with changes in routesControl protocol overheadIndependent of routing protocol
اسلاید 31: RSVP CharacteristicsUnicast and MulticastSimplexReceiver initiated reservationMaintain soft state in the internetProvide different reservation stylesTransparent operation through non-RSVP routersSupport for IPv4 and IPv6
اسلاید 32: Data Flow ConceptsSessionData flow identified by its destinationFlow descriptor Reservation request issued by destinationMade up of flowspec and filterspecFlowspec gives required QoSFilterspec defines set of packets for which reservation is required
اسلاید 33: Treatment of Packets
اسلاید 34: RSVP Operation
اسلاید 35: RSVP Message TypesResvOriginate at multicast receiversPropagate upstream through distribution treeCreate soft states within routersReach sending host enabling it to set up traffic control for first hopPathProvide upstream routing information
اسلاید 36: Operation From Host PerspectiveReceiver joins multicast group (IGMP)Potential sender issues Path messageReceiver gets message identifying senderReceiver has reverse path info and may start sending Resv messagesResv messages propagate through internet and is delivered to senderSender starts transmitting data packetsReceiver starts receiving data packets
اسلاید 37: Differentiated ServicesProvide simple, easy to implement, low overhead tool to support range of network services differentiated on basis of performanceIP Packets labeled for differing QoS using existing IPv4 Type of Service or IPv6 Traffic calssService level agreement established between provider and customer prior to use of DSBuilt in aggregationGood scaling to larger networks and loadsImplemented by queuing and forwarding based on DS octetNo state info on packet flows stored
اسلاید 38: DS ServicesDefined within DS domainContiguous portion of internet over which consistent set of DS policies are administeredTypically under control of one organizationDefined by service level agreements (SLA)
اسلاید 39: SLA ParametersDetailed service performanceExpected throughputDrop probabilityLatencyConstraints on ingress and egress pointsTraffic profilese.g. token bucket parametersDisposition of traffic in excess of profile
اسلاید 40: Example ServicesLevel A - low latencyLevel B - low lossLevel C - 90% of traffic < 50ms latencyLevel D - 95% in profile traffic deliveredLevel E - allotted twice bandwidth of level F trafficTraffic with drop precedence X higher probability of delivery than that of Y
اسلاید 41: DS Octet - Code PoolsLeftmost 6 bits used3 pools of code pointsxxxxx0assignment as standardsxxxx11experimental or local usexxxx01experimental or local but may be allocated for standards in future
اسلاید 42: DS Octet - Precedence FiedlRouting selectionNetwork serviceQueuing discipline
اسلاید 43: DS Domains
اسلاید 44: DS Configuration and OperationWithin domain, interpretation of DS code points is uniformRouters in domain are boundary nodes or interior nodesTraffic conditioning functionsClassifierMeterMarkerShaperDropper
اسلاید 45: DS Traffic Conditioner
اسلاید 46: Required ReadingStallings chapter 16RFCs identified in textComer, Internetworking with TCP/IP volume 1
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