Fast RetransmitFast RetransmitFast Retransmit and Fast RecoveryReview: TCP Congestion ControlReview: TCP Congestion ControlDatagram RoutingInter-Domain Routing ReviewTraffic Engineering?Quality of Service ?Quality of Service?High Speed IP Router?Asynchronous Transfer Mode: ATMFour IdeasVirtual Circuit ConceptVirtual Circuit ConceptsVirtual Circuit Switching: Label SwappingSignaling ProtocolATM architectureATM Layer: Virtual CircuitsCell Size: 32 bytes or 64 bytes?ATM Cell FormatQuestionsProtocol vs. ServiceUser Network Interface (UNI)vs. Network Network Interface (NNI)ATM Layer ServiceIssues of IP over ATMATM Adaptation Layer (AAL) 5ATM: network or link layer?Where is ATM Today?MPLSMPLS HeaderMPLS HeaderMPLS VocabularyMPLS VocabularyMPLS VocabularyMPLS VocabularyMPLS VocabularyForwarding Equivalence ClassesLABEL SWITCHED PATH (vanilla)EXPLICITLY ROUTED LSP ER-LSPMPLS just another ATM?A label by any other name …...Protocol Comparison115-441 Computer NetworksATM and MPLSProfessor Hui [email protected] RetransmitTimeSequence NoXPacketsAcks33333Fast RetransmitTimeSequence NoDuplicate AcksRetransmissionXPacketsAcks44444Fast Retransmit and Fast RecoverycwndSlow StartCongestionAvoidanceTime Retransmit after 3 duplicated acks prevent expensive timeouts No need to slow start again At steady state, cwnd oscillates around the optimal window size.55555Review: TCP Congestion ControlTimeCongestionWindow66666Review: TCP Congestion ControlTimeCongestionWindowInitialSlowstartFast Retransmitand RecoverySlowstartto pacepacketsTimeoutsmay stilloccur77777Datagram Routing128.2/16E-BGP128.2/16I-BGP88888Inter-Domain Routing Review Each border router receives multiple E-BGP and I-BGP feeds, it needs to select, among many choices, one AS path for each prefix Consistency requirement: no AS level loop Each internal router receives multiple I-BGP feeds, it needs to select, among many choices, one egress border router for each prefix Consistency requirement: different internal nodes need to pick consistent egress nodes for each prefix99999Traffic Engineering?1010101010Quality of Service ? Guaranteed 40Mbps throughput for blue traffic? Minimum latency?1111111111Quality of Service? Guaranteed 40Mbps throughput for blue traffic? Minimum latency? Denver DCKCNJ.2.1.2.110.0.41/30AtlantaLA192.168.0.1192.168.1.1192.168.4.1192.168.3.1192.168.2.1 192.168.5.1192.168.6.1SF.2.110.0.13/3010.0.0/3010.0.24/30.1.210.0.1/30.2.110.0.8/30.1.210.0.2/30.2.110.0.16/30.2.110.0.15/30.1.2NYHickNetBoston1212121212High Speed IP Router?Nodeincoming links outgoing linksMemory Dest IP address lookup for every packet Switching and buffer management for variable size packet1313131313Asynchronous Transfer Mode: ATM ITU standard for high-speed (155Mbps to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture Most of the work done in 90’s Goal: integrated, end-end transport of carry voice, video, data meeting timing/QoS requirements of voice, video (versus Internet best-effort model) “next generation” telephony: technical roots in telephone world1414141414Four Ideas Flexible and efficient Î packet switching Support voice, video, data Æ needs end-to-end Quality of Service Æ connection-oriented network Æ virtual circuit network Scale to high performance switch Æ fixed size packet Support low jitter voice Æ small size packet1515151515Virtual Circuit Concept Logical Connection Connection is first established using signaling protocol Route from the source to the destination is chosen The same route is used for all packets of the connection No routing decision for every cell1616161616Virtual Circuit Concepts No dedicated capacity Packet switching to enable statistical multiplexing Each packet contains enough information for node (switch) to forward it towards the destination1717171717Virtual Circuit Switching: Label Swapping AABBDDCCEEFFVC7VC4VC3VC3VC3VC5VC3VC5VC2VC2Table at Node AINLINKIN VC OUTLINKOUTVCCA7 AB 4CA2 AB 5DA 3 AB 31818181818Signaling Protocol Signaling protocol establishes/tears down virtual circuit Signaling message are routed Signaling protocol fills the forwarding table Parameters used for establishing Virtual Circuits Source and destination Addresses Traffic Characteristics QoS Parameters Others? Parameters can be stored in forwarding table to help forwarding decision1919191919ATM architecture Adaptation layer: only at edge of ATM network data segmentation/reassembly roughly analagous to Internet transport layer ATM layer: “network” layer cell switching, routing Physical layer2020202020ATM Layer: Virtual Circuits VC transport: cells carried on VC from source to dest call setup, teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain “state” for each passing connection link,switch resources (bandwidth, buffers) may be allocated to VC: to get circuit-like performance Permanent VCs (PVCs) long lasting connections Switched VCs (SVC): dynamically set up on per-call basis2121212121Cell Size: 32 bytes or 64 bytes? Cell size of 32 and 64 bytes: 64 bytes cells have better transmission efficiency 32 bytes cells have small delay both sizes are integer power of 2 Europe wanted 32 bytes size, US and Japan wanted 64 bytes size Compromise: 48 bytes2222222222ATM Cell FormatHeader :5 bytes Payload (Information) 48 bytesGFC VPI VCI PT HECVPI VCI PT HEC12 16 3 1 8 bitsCLPCLP4 8 16 3 1 8 bitsatUNIatNNIGFC : Generic Flow Control VPI : Virtual Path IdentifierVCI : Virtual Circuit Identifier PT : Payload TypeCLP : Cell Loss Priority HEC : Header error CheckUNI : User Network Interface NNI : Network-Network Interface2323232323Questions How many Virtual Circuits can one ATM switch support? What is the purpose of Virtual Path?2424242424Protocol vs. Service Service – says what a layer does Ethernet: unreliable subnet unicast/multicast/broadcast datagram service IP: unreliable end-to-end unicast datagram service TCP: reliable end-to-end bi-directional byte stream service Guaranteed bandwidth/latency unicast service Protocol – says how is the service implemented a set of rules and
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