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Frame Relay

Frame Relay. CCNA 4 Module 5. Overview. Frame Relay is a ______-switched, connection-_______ technology. Because it was designed to operate on high-quality digital lines, Frame Relay provides no error recovery mechanism.

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Frame Relay

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  1. Frame Relay CCNA 4 Module 5

  2. Overview • Frame Relay is a ______-switched, connection-_______ technology. • Because it was designed to operate on high-quality digital lines, Frame Relay provides no error recovery mechanism. • If there is an error in a frame, as detected by any node, it is _________ without__________. packet oriented discarded notification

  3. Frame Relay Concepts • Access Link – leased line • DTE =_______ • Frame-Relay switches = _____ • LMI (Local Management Interface) – keep alive messages between routers and Frame-Relay switches • DLCI – Data Link Connection Identifier Router DCEs

  4. Non-Data DLCIs

  5. Virtual Circuits • VC – virtual circuit – path that a frame travels between DTEs • ____– a VC in which the service provider has preconfigured the details of the path • ____– a VC that is set up dynamically when needed. Frame-Relay switches learn the route on demand. • PVCs for sites that communicate directly, SVCs for sites that don’t often communicate. They must go through the main site. PVC SVC

  6. More Concepts • Multi-access network – a network in which more than two devices are connected. • Non-broadcast multi-access – a network in which broadcasts are not supported, but more than two devices can be connected

  7. Advantages of Frame Relay • More cost-effective than leased lines. • Leased lines provide a fixed amount of bandwidth all of the time. • Frame-Relay guarantees an amount of bandwidth, but saving are accrued because the service provider sells more bandwidth than the pipe holds, knowing that not all customers will be using their full bandwidth at the same time. • CIR –______________________ – guaranteed minimum amount of bandwidth you receive from the service provider committed information rate

  8. LMIs • Messages used between the DTE (router) and DCE (F-R switch) • Signaling messages for SVCs, PVC status messages, and keepalives • F-R switch and router care about the LMI being used. • Examples of LMI types - Cisco (cisco), ANSI (ansi), ITU (q933a) • Frame-relay lmi-type command used on older IOS’s where LMI autosencing isn’t available. • Through LMIs and Inverse ARPs, a DTE learns how to map VCs DLCIs to network layer addresses

  9. LMI and Encapsulation • LMI and encapsulation types are often confused. • LMI type must be agreed upon between the DCE and DTE. • Encapsulation must be the same for both DTEs • Frame Relay switches don’t care about encapsulation only LMI. • Encapsulation defines headers used by a DTE to communicate with another DTE at the end of a VC.

  10. Configuring Encapsulation • In Serial Interface config mode, command is encapsulation frame-relay … • _____ (default) version of HDLC for FR • ____ is used to connect to a non-Cisco router Cisco ietf

  11. DLCI • ________ Control Identifier – is number noting a specific VC. • It is locally significant. (It’s probably not the same number on each end. The Frame Relay switches take care of getting it from one end to the other.) • The DLCI is added to the address field of every frame transmitted. Data Link

  12. Rates and Times • Speed of line = access speed or port speed • CIR (committed information rate) is the dedicated bandwidth availability. • The sum of the CIRs for all VCs is often more than the port speed due to the “bursty” nature of data flow. • EIR (excess info rate) – difference between CIR and port speed. • Committed Time (TC) – time interval over which rates are calculated

  13. Rates and Times • Committed Burst (BC) – number of bits in (TC) • Excess Burst (BE) - extra bits above committed burst (up to maximum access link speed.) • Although the FR switch accepts frames in excess of the CIR, each excess frame is marked as discard eligible (DE) • Frames with DE bit set are dropped from the queue first if the switch gets backed up. • There are also ECN bits in add. Field. • The FECN bit is set on every frame the switch gets from a congested link. • The BECN bit is set on every frame the switch puts on a congested link.

  14. Explicit Congestion Notification • The FECN bit is set to let the destination router know the frame traveled along a congested link. • The BECN bit is set on packets back to the source to let the router know it helped create the congestion.

  15. Multiple VCs • Frame Relay is most cost-effective when multiple sites are interconnected. • Because split-horizon tries to avoid routing loops by not allowing info in from one interface to go out that interface, the issue must be addressed for FR with multiple VCs on the same interface. • _____________are the answer to this problem. Sub-interfaces

  16. Static Maps • If remote router doesn’t support inverse ____ a static frame-relay map must be configured. • Command in int config mode to create static map is frame-relay map ip ipadd dlci# [broadcast] • Broadcast is optional and allows dynamic routing protocol to broadcast over VC ARP

  17. Various Show Outputs

  18. Debug Frame-Relay lmi

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