1 / 17

X.25 and Frame Relay

X.25 and Frame Relay. Compiled By: Ashish Kr. Jha. X.25. Designed to provide a low cost alternative for data communication over public network ▫ Pay only for bandwidth Standard provides error detection and correction for reliable data transfer.

barnett
Download Presentation

X.25 and Frame Relay

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. X.25 and FrameRelay Compiled By: Ashish Kr. Jha

  2. X.25 • Designed to provide a low cost alternative for data communication over publicnetwork • ▫ Pay only for bandwidth • Standard provides error detection and correction for reliable data transfer. • Can support speed of 9.6kbps to2Mbps • LAPB(Link Access Procedure, Balanced : version of HDLC) is X.25 DLLprotocol • LAPB manages communication and packet framing between DTE andDCE. • Makes sure frames are delivered in sequence anderror-free Compiled By: Ashish Kr. Jha

  3. X.25Layers • An interface between DTE and DCE for terminal operation at the packet mode on public datanetwork. Compiled By: Ashish Kr. Jha

  4. X.25 • LAPB frameTypes • ▫ I-Frames (InformationFrames) • Carry data as well as Next Send (NS) and Next Receive(NR) • counts • ▫ S-Frames (SupervisoryFrames) • Controls flow of data with Receiver Ready (RR), ReceiverNot • Ready (RNR), and Reject (REJ)frames • ▫ U-Frames (UnnumberedFrames) • Establish and maintain communications with, Unnumbered Acknowledgment (UA), Disconnect (DISC), Disconnect Mode (DM) and Frame Reject(FRMR) Compiled By: Ashish Kr. Jha

  5. X.25 LAPB FrameFormat Flag : 8 bits indicates start and end offrame Address : (8 bit) Data : (sizevaries) Control : (8bit) FCS : (16 bit) Frame CheckSequence • Packet Layer Protocol (PLP) is X.25 network layerprotocol • PLP manages calls between a pair DTE devices using Permanent Virtual Circuit(PVC) or Switched VirtualCircuit(SVC) • PLPhandlessegmentation,reassembly,bitpaddinganderrorand • flowcontrol. Compiled By: Ashish Kr. Jha

  6. PLP Operates in FiveModes • CallSetup • ▫ Used to setup virtual circuit forSVC • Data Transfer • ▫ Used for transferring data with both SVC andPVC • Idle • ▫ Used when SVC call has been established but no datais • currently beingtransferred • CallClearing • ▫ Used to end communication between DTEs for aSVC • Restarting • ▫ Used to synchronize DTE and DCE for all virtual circuits that exist betweenthem Compiled By: Ashish Kr. Jha

  7. X.25Devices • Data Terminal Equipment(DTE) • ▫ Terminals, personal computers, and networkhosts • ▫ Located on premises ofsubscriber • Data Circuit-terminating Equipment(DCE) • ▫ Modems and packetswitches • ▫ Usually located at carrierfacility • Packet Switching Exchange(PSE) • ▫ Switches that make up the carriernetwork Compiled By: Ashish Kr. Jha

  8. Sample X.25Network X.25 WAN PSE PSE Modem DCE Personal Computer DTE Terminal DTE Modem DCE Modem DCE PSE PSE Server DTE Compiled By: Ashish Kr. Jha

  9. Packet Assembler/Disassembler(PAD) • Acts as intermediary device between DTE andDCE • Performs threefunctions • Buffering to store data until a device is ready to processit • PacketAssembly • PacketDisassembly PSE X.25Packet Data PAD Terminal DTE Modem DCE PSE Data Assembly/ Disassembly Buffer Compiled By: Ashish Kr. Jha

  10. FrameRelay • Frame Relay (FR) is a high-performance WAN protocol that operates at the physical and data link layers of the OSI referencemodel. • FR originally was designed for use across Integrated Service Digital Network (ISDN)interfaces. • Today, it is used over a variety of other network interfaces aswell. • FR is an example of a packet-switchedtechnology. • Packet-switched networks enable end stations to dynamically share the network medium and the available bandwidth. • Usually considered a replacement for X.25 using more advanced digital and fiber opticconnections Compiled By: Ashish Kr. Jha

  11. FrameRelay • FR is strictly a Layer 2 protocol suite, whereas X.25 provides • services at Layer 3 (the network layer) aswell. • This enables FR to offer higher performance and greatertransmission efficiency than X.25, and makes FR suitable for current WAN applications, such as LANinterconnection. • DevicesattachedtoaFrameRelayWANfallintothe following two generalcategories: • ▫ Data terminal equipment(DTE) • DTEs generally are considered to be terminating equipment for a specific network and typically are located on the premises of a customer. • ExampleofDTEdevicesareterminals,personalcomputers, routers, andbridges. • ▫ Data circuit-terminating equipment(DCE) • DCEs are carrier-owned internetworkingdevices. • The purpose of DCE equipments is to provide clocking and • switching services ina network, whicharethe devicesthat actually transmit data through theWAN. Compiled By: Ashish Kr. Jha

  12. Sample Frame RelayNetwork PacketSwitch DCE PacketSwitch DCE PersonalComputer DTE Terminal DTE FrameRelay WAN PacketSwitch DCE PacketSwitch DCE NetworkHost DTE Compiled By: Ashish Kr. Jha

  13. FrameRelay • Assembler/Disassembler(FRAD) • A FRAD can either be a separate device or part of a router/switch X.25 ATM PPP X.25 ATM PPP FrameRelay FRAD FRAD Compiled By: Ashish Kr. Jha

  14. FrameRelay • Link Access Protocol for Frame Modes Services (LAPF) is the protocol defined for Frame Relay Layer 2services • LAPF is a version ofHDLC • ▫ Does not provide flow or errorcontrol Compiled By: Ashish Kr. Jha

  15. Frame Relay OperatingStates • Original Frame Relay standard only coveredPVC • SVC support was added but does not havewidespread • implementation • PVCStates • ▫ Data Transfer – data is being transmitted between DTEdevices • ▫ Idle – connection is still active but no data is beingtransferred • SVC required the addition of two additionalstates • ▫ Call Setup – virtual circuit between DTE devices isestablished • ▫ Call Termination – virtual circuit between DTE devices isterminated Compiled By: Ashish Kr. Jha

  16. LAPF FrameFormat • DLCI:(10 bits) Data Link Connection Identifier is used to identify the Virtual Circuit number • C/R:(1 bit) Provided for up layers to determine commands andresponses • EA:(1 bit) Determines if this byte is last byte of address (0=more,1=last) • FECN:(1 bit) Forward Explicit Congestion Notification indicates congestion in the direction the frame istraveling • BECN:(1 bit) Backward Explicit Congestion Notification indicates congestion inthe • opposite direction the frame istraveling • DE:(1 bit) Discard Eligibility indicates that a frame is low priority whenset Compiled By: Ashish Kr. Jha

  17. Comparison of X.25 and FrameRelay Compiled By: Ashish Kr. Jha

More Related