Raj JainThe Ohio State University1Frame RelayFrame RelayRaj JainProfessor of Computer and Information SciencesThe Ohio State UniversityColumbus, OH 43210 http://www.cis.ohio-state.edu/~jain/Raj JainThe Ohio State University2OverviewOverviewq What is Frame Relay?q Why not leased lines or X.25?q Frame formats and protocolsq SignalingRaj JainThe Ohio State University3Problems withProblems withLeased LinesLeased 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 more IXC circuitsRouter RouterRouterRouterIXCLECRaj JainThe Ohio State University4Solution: 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 more IXC circuitsq Share leased lines ⇒ Virtual Private NetworksRouter RouterRouterRouterIXCLECRaj JainThe Ohio State University5Data Link ControlData Link ControlIdentifiers (DLCI)Identifiers (DLCI)RouterRouterRouterRouterFRFRFR12 2111312Raj JainThe Ohio State University6Data Link ControlData Link ControlIdentifierIdentifierq Only local significanceq Allows multiple logical connectionsover one circuitq Some ranges preassignedq DLCI = 0 is used for signalingRaj JainThe Ohio State University7X.25X.25q In-band signaling. VC setup and clearingmessages in the same 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 ExchangeSource Destination12345678129 101113141516Raj JainThe Ohio State University9Frame Relay ExchangeFrame Relay ExchangeSource Destination18273645Raj JainThe Ohio State University10Frame Relay:Frame Relay:Key FeaturesKey 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 Switchingq Switching = Relaying + Ack +Flow control + Error recovery +loss recoveryq Switching = X.25q Relay = Unreliable multiplexing serviceRaj JainThe Ohio State University12Q.931/Q.933LAPDQ.921I.430/I.431LAPF Q.922 CoreControl UserPhysicalDatalinkNetworkNetworkUser SelectableFrame RelayFrame RelayUNI ArchitectureUNI Architectureq UNI = User-network Interfaceq LAPF = Link Access Procedure - Frame Relayq LAPD = Link Access Procedure for D ChannelRaj JainThe Ohio State University13Control PlaneControl Planeq Signaling over D channelq Data transfer over B, D, or Hq LAPD used for reliable signalingq ISDN Signaling Q.933 + Q.931 used for signalingmessagesq SAPI = 0 in LAPD⇒ Q.933 + Q.931 Frame relay messageRaj JainThe Ohio State University14User PlaneUser Planeq Link Access Procedure for Frame-Mode bearerservices (LAPF)q Q.922 = Enhanced LAPD (Q.921)= LAPD + Congestionq LAPF defined in Q.922q Core functions defined in Q.922 appendix:m Frame delimiting, alignment, and flag transparencym Virtual circuit multiplexing and demultiplexingm Octet alignment ⇒ Integer number of octets beforezero-bit insertionm Checking min and max frame sizesRaj JainThe Ohio State University15User Plane (Cont)User Plane (Cont)m Error detection, Sequence andnon-duplicationm Congestion controlq LAPF control may be used for end-to-end signalingNetworkLayerLAPFControlI.430/I.431LAPF CoreNetworkLayerLAPFControlI.430/I.431LAPF CoreI.430/I.431LAPF CoreI.430/I.431LAPF CoreRaj JainThe Ohio State University16SignalingSignalingq Permanent Virtual Circuit (PVC)q Switched Virtual Circuit (SVC)q Q.933 used for FR connections over PVC or SVC⇒ Q.933 is a subset of Q.931q Message Types: Alerting, call proceeding, connect,connect ack, 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 University17Connection Control Connection Control MsgsMsgsq Call establishment1. Alerting2. Call proceeding3. Connect4. Connect Acknowledge5. Progress6. Setupq Call clearing7. Disconnect8. Release9. Release CompleteRaj JainThe Ohio State University18q Miscellaneous10. Status11. Status EnquiryRaj JainThe Ohio State University19Signaling 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 University20ReleaseCompleteSignaling Example (Signaling Example (contcont))NT ISDN Frame Relay NTDisconnectDisconnectReleaseReleaseCompleteD-ChannelQ.931 exchangeto releaseB-ChannelCircuit switchedConnectionDisconnectDisconnectB-Channel Q.933exchange to release B-Channel frame-mode connectionReleaseReleaseReleaseCompleteReleaseReleaseCompleteRaj JainThe Ohio State University21Physical Layer OptionsPhysical Layer Optionsq Both ANSI and ITU-T define frame relay on ISDNq Frame relay forum's implementation agreements:m Metallic interface at DS1 1.544 Mbps(ANSI T1.403)m Leased lines at 56 kbps (V.35)m Metallic interface at E1 2.048 Mbps (G.703)m Synchronous interface at E1 2.048 Mbps (G.704)m X.21 interface for synchronous transmissionq MCI offers frame relay at 56 kbps, 64 kbps, fractionalT1, N × 56 or N × 64 kbps.Raj JainThe Ohio State University22SummarySummaryq X.25 designed for unintelligent devicesover error-prone networks ⇒ Slowq Frame relay = simplified X.25q Higher data rates than X.25q Developed for ISDN but runs in non-ISDNenvironmentsq Two layer protocol architectureRaj JainThe Ohio State University23HomeworkHomeworkq Read Chapter 11 of Stallings’ ISDN bookRaj JainThe Ohio State University24Frame Relay StandardsFrame Relay StandardsITU:q I.122, Framework for Frame Mode BearerServices, 1993.q I.223, Frame Mode Bearer Services, 1992.q I.370, Congestion management for the ISDN FrameRelaying Bearer Service, 1991.q I.372, Frame Relay Bearer Service Network-to-network Interface Requirements, 1993.q I.555, Frame Mode Bearer Services Interworking,1992.Raj JainThe Ohio State University25Standards (Cont)Standards (Cont)q Q.922, ISDN Data