Raj JainThe Ohio State University1Raj JainRaj JainProfessor of Computer and Information SciencesProfessor of Computer and Information SciencesThe Ohio State UniversityThe Ohio State UniversityColumbus, OH 43210Columbus, OH [email protected]@ACM.Org http://www.cis.ohio-state.edu/~jain/ http://www.cis.ohio-state.edu/~jain/Frame RelayFrame RelayFrame RelayRaj JainThe Ohio State University2q What is Frame Relay?q Why not leased lines or X.25?q Frame formats and protocolsq SignalingOverviewRaj JainThe Ohio State University3Problems with Leased LinesProblems with Leased LinesProblems with Leased Linesq No user-to-user end-to-end signalingq Multiple logical links ⇒ Multiple connectionsq Four nodes ⇒ 12 ports, 12 local exchange carrier (LEC)access lines, 6 inter-exchange carrier (IXC) connectionsq One more node ⇒ 8 more ports, 8 more LEC lines, 4 moreIXC circuitsRouter RouterRouterRouterIXCLECRaj JainThe Ohio State University4Solution: Frame RelaySolution: Frame RelaySolution: Frame Relayq Four nodes: 4 ports, 4 LEC access lines, 6 IXC circuitsq One more node: 1 more port, 1 more access line, 4 moreIXC circuitsq Share leased lines ⇒ Virtual Private NetworksRouter RouterRouterRouterIXCLECRaj JainThe Ohio State University5Data Link Control IdentifiersData Link Control IdentifiersData Link Control Identifiers(DLCI)(DLCI)(DLCI)RouterRouterRouterRouterFRFRFR12 2111312Raj JainThe Ohio State University6Data Link Control IdentifierData Link Control IdentifierData Link Control Identifierq Only local significanceq Allows multiple logical connections over one circuitq Some ranges preassignedq DLCI = 0 is used for signalingRaj JainThe Ohio State University7X.25X.25X.25q In-band signaling. VC setup and clearing messages in thesame channel as data.q Three layer protocol. Third layer for multiplexing.q Flow controlq Error control⇒ 12 messages for one packet transferOnly 6 messages without flow control and error controlRaj JainThe Ohio State University8X.25 ExchangeX.25 ExchangeX.25 ExchangeSource Destination12345678129 101113141516Raj JainThe Ohio State University9Frame Relay ExchangeFrame Relay ExchangeFrame Relay ExchangeSource Destination18273645Raj JainThe Ohio State University10Frame Relay: Key FeaturesFrame Relay: Key FeaturesFrame Relay: Key Featuresq X.25 simplifiedq No flow and error controlq Out-of-band signalingq Two layersq Protocol multiplexing in the second layerq Congestion control added⇒ Higher speed possible.X.25 suitable to 200 kbps. Frame relay to 2.048 Mbps.Raj JainThe Ohio State University11Relay vs SwitchingRelay vs SwitchingRelay vs Switchingq Switching = Relaying + Ack + Flow control + Errorrecovery + loss recoveryq Switching = X.25q Relay = Unreliable multiplexing serviceRaj JainThe Ohio State University12Frame Relay UNI ArchitectureFrame Relay UNI ArchitectureFrame Relay UNI ArchitectureQ.931/Q.933LAPDQ.921I.430/I.431LAPF Q.922 CoreControl UserPhysicalDatalinkNetworkNetworkUser SelectableRaj JainThe Ohio State University13Control PlaneControl PlaneControl Planeq Signaling over D channelq Data transfer over B, D, or Hq LAPD used for reliable signalingq Q.933 + Q.931 used for signaling messagesq SAPI = 0 in LAPD ⇒ Q.933 + Q.931 Frame relay messageRaj JainThe Ohio State University14User PlaneUser PlaneUser Planeq Link Access Procedure for Frame-Mode bearer services(LAPF)q Q.922 = Enhanced LAPD (Q.921) = LAPD + Congestionq LAPF defined in Q.922q Core functions defined in Q.922 appendix:q Frame delimiting, alignment, and flag transparencyq Virtual circuit multiplexing and demultiplexingq Octet alignment ⇒ Integer number of octets before zero-bitinsertionq Checking minimum and maximum frame sizesq Error detection, Sequence and non-duplicationq Congestion controlRaj JainThe Ohio State University15q LAPF control functions may be used for end-to-endsignalingNetworkLayerLAPFControlI.430/I.431LAPF CoreI.430/I.431LAPF CoreI.430/I.431LAPF CoreNetworkLayerLAPFControlI.430/I.431LAPF CoreRaj JainThe Ohio State University16SignalingSignalingSignalingq Permanent Virtual Circuit (PVC)q Switched Virtual Circuit (SVC)q Q.933 used for logical FR connections over PVC or SVC⇒ Q.933 is a subset of Q.931q Message Types: Alerting, call proceeding, connect, connectack, progress, setup, disconnect, release, release complete,status, status inquiryq Frame relay forum has proposed to simplify Q.933 bydeleting progress, connect ack, and alerting.Also delete many information element.Add SVC.Raj JainThe Ohio State University17Digital Signaling System 1Digital Signaling System 1Digital Signaling System 1Message FormatMessage FormatMessage FormatProtocol DiscriminatorCall Reference lengthCall ReferenceMessage TypeOthers (information elements)080 0 0OctetsBits7 6 5 4 3 2 10Raj JainThe Ohio State University18Connection Control MessagesConnection Control MessagesConnection Control Messagesq Call establishment1. Alerting2. Call proceeding3. Connect4. Connect Acknowledge5. Progress6. Setupq Call clearing7. Disconnect8. Release9. Release Completeq Miscellaneous10. Status11. Status EnquiryRaj JainThe Ohio State University19Information ElementsInformation ElementsInformation ElementsInformation Element 1 2 3 4 5 6 7 8 9 10 11Protocol discriminator X X X X X X X X X X XCall reference X X X X X X X X X X XMessage type X X X X X X X X X X XCause X X X X XBearer capability XChannel identification X X X XData link connection ID X X X XProgress indicator X X X X XNetwork specific facilities XCall state XDisplay X X X X X X X X X X XEnd to end transit delay X XRaj JainThe Ohio State University20Information Elements (cont)Information Elements (cont)Information Elements (cont)Information Element 1 2 3 4 5 6 7 8 9 10 11Packet binary parameters X XLink core parameters X XLink protocol parameters X XCalling party number XCalled party number XCalled party subaddress XConnected number X X X XConnected subaddress X X X XTransit network selection XRepeat indicator XLow layer compatibility X XHigh layer compatibility XUser-User X X X X X XRaj JainThe Ohio State University21Signaling ExampleSignaling ExampleSignaling ExampleNT ISDN Frame Relay NTSetupSetupConnectConnect AckConnectConnect AckSetupSetupConnectConnect AckD-ChannelQ.931 exchangeto establishB-ChannelCircuit switchedConnectionB-Channel Q.933exchange to establish B-Channel frame-mode connectionRaj JainThe Ohio State University22Signaling Example (cont)Signaling Example (cont)Signaling Example (cont)NT ISDN Frame Relay