Frame RelayOverviewProblems with Leased LinesSolution: X.25/Frame RelayX.25X.25 ExchangeFrame Relay ExchangeFrame Relay: Key FeaturesRelay vs SwitchingDatalink Control IdentifiersData Link Control IdentifierISDN Reference ModelFrame Relay UNI ArchitectureControl PlaneUser PlaneUser Plane (Cont)LAPF-Core Frame FormatLAPF Address FieldSlide 19Local Management Interface (LMI)LMI OperationDLCI ExtensionsNetwork-to-Network Interface (NNI)Major NNI OperationsSummaryHomeworkAdditional ReferencesRaj JainThe Ohio State University1Frame Frame RelayRelayRaj Jain Professor of Computer and Information SciencesThe Ohio State UniversityColumbus, OH 43210These slides are available at http://www.cse.ohio-state.edu/~jain/cis777-99/Raj JainThe Ohio State University2OverviewOverviewWhat is Frame Relay?Why not leased lines or X.25?Frame formats and protocolsSignalingRaj JainThe Ohio State University3Router RouterRouterRouterIXCLECProblems with Leased LinesProblems with Leased LinesMultiple logical links  Multiple connectionsFour nodes  12 ports, 12 local exchange carrier (LEC) access lines, 6 inter-exchange carrier (IXC) connectionsOne more node  8 more ports, 8 more LEC lines, 4 more IXC circuitsRaj JainThe Ohio State University4Solution: X.25/Frame RelaySolution: X.25/Frame RelayFour nodes: 4 ports, 4 LEC access lines, 6 IXC circuitsOne more node: 1 more port, 1 more access line, 4 more IXC circuitsShare leased lines  Virtual Private Networks Router RouterRouterRouterIXCLECRaj JainThe Ohio State University5X.25X.25In-band signaling. VC setup and clearing messages in the same channel as data.Three layer protocol. Third layer for multiplexing.Flow controlError control 12 messages for one packet transfer Only 6 messages without flow control and error controlRaj JainThe Ohio State University6X.25 ExchangeX.25 ExchangeDCEDTEDestinationDCE5678129 101113DTESource1234141516Raj JainThe Ohio State University7Frame Relay ExchangeFrame Relay ExchangeSource Destination18273645Raj JainThe Ohio State University8Frame Relay: Key FeaturesFrame Relay: Key FeaturesX.25 simplifiedNo flow and error controlOut-of-band signalingTwo layersProtocol multiplexing in the second layerCongestion control added Higher speed possible.X.25 suitable to 200 kbps. Frame relay to 2.048 Mbps.Raj JainThe Ohio State University9Relay vs SwitchingRelay vs SwitchingSwitching = Relaying + Ack + Flow control + Error recovery + loss recoverySwitching = X.25Relay = Unreliable multiplexing serviceRaj JainThe Ohio State University10Datalink Control IdentifiersDatalink Control IdentifiersRouterRouterRouterRouterFRFRFR121132DLCI: Similar to Logical Channel Numbers in X.25Raj JainThe Ohio State University11Data Link Control IdentifierData Link Control IdentifierOnly local significanceAllows multiple logical connections over one circuitSome ranges preassignedDLCI = 0 is used for signalingRaj JainThe Ohio State University12ISDN Reference ModelISDN Reference Model7654321ControlUserManagementRaj JainThe Ohio State University13Q.931/Q.933LAPDQ.921/Q.922I.430/I.431LAPF Q.922 CoreControl UserPhysicalDatalinkNetworkNetworkUser SelectableFrame Relay UNI ArchitectureFrame Relay UNI ArchitectureUNI = User-network InterfaceLAPF = Link Access Protocol - Frame Mode ServicesLAPD = Link Access Protocol - D ChannelRaj JainThe Ohio State University14Control PlaneControl PlaneSignaling over D channel (D = Delta = Signaling)Data transfer over B, D, or H (B = Bearer)LAPD used for reliable signalingISDN Signaling Q.933 + Q.931 used for signaling messagesService Access Point Identifier (SAPI) in LAPD = 0 Q.933 + Q.931 Frame relay messageRaj JainThe Ohio State University15User PlaneUser PlaneLink Access Procedure for Frame-Mode bearer services (LAPF)Q.922 = Enhanced LAPD (Q.921) = LAPD + CongestionLAPF defined in Q.922Core functions defined in Q.922 appendix:Frame delimiting, alignment, and flag transparencyVirtual circuit multiplexing and demultiplexingOctet alignment  Integer number of octets before zero-bit insertionChecking min and max frame sizesRaj JainThe Ohio State University16User Plane (Cont)User Plane (Cont)Error detection, Sequence and non-duplicationCongestion control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 University17LAPF-Core Frame FormatLAPF-Core Frame FormatLAPF is similar to LAPD: Flag, bit stuffing, FCSNo control frames in LAPF-Core  No control fieldNo inband signalingNo flow control, no error control, no sequence numbersLogical Link Control (LLC) may be used on the top of LAPF coreFlag01111110Address Information FCSFlag011111101B 2-4B 2B 2BRaj JainThe Ohio State University18LAPF Address FieldLAPF Address Field 2 Octet: 3 Octet:Upper DLCI EA 0C/R8 7 6 5 4 3 2 1Lower DLCI EA 1DEFECNBECNUpper DLCI EA 0C/RDLCI EA 0DEFECNBECNLower DLCI or DL-Core control EA 1D/CUpper DLCI EA 0C/RDLCI EA 0DEFECNBECNDLCI EA 0Lower DLCI or DL-Core control EA 1D/C 4 Octet:Raj JainThe Ohio State University19LAPF Address FieldLAPF Address FieldAddress length = 2, 3, or 4 bytesData Link Control Identifier (DLCI) = 10, 16, 17, or 23 bitsAddress Extension (EA) bits: 0  More bytesD/C = Remaining bits for DLCI or for core control protocol (No use for core control has been defined)C/R = Command/response (not used)FECN = Forward Explicit Congestion IndicationBECN = Backward Explicit Congestion IndicationRaj JainThe Ohio State University20Local Management Local Management Interface (LMI)Interface (LMI)Extension designed by a group of vendorsTo overcome problems observed in early implementationsMay be standardized by both ANSI and ITU-TStatus Enquiry (SE) message from user to networkStatus (S) message from network to userUses HDLC UI frames (with sequence numbers)Uses protocol ID=00001001, DLCI=1023Raj JainThe Ohio State University21LMI OperationLMI OperationUserNetworkSE, S = 4, R = 3S, S = 4, R = 4SEFS (All PVCs)SES (New PVCs)Raj JainThe Ohio State University22DLCI ExtensionsDLCI ExtensionsGlobal DLCI  DLCI points to the same destination at all time and points (OK for small networks)MulticastingOne-way multicasting: 1 to NTwo-way multicasting: 1 to N and N to 1N-way