CHABOT COLLEGE CISCO NETWORKING ACADEMY Chabot College Frame Relay Part 1

CHABOT COLLEGE CISCO NETWORKING ACADEMYCHABOT COLLEGE CISCO NETWORKING ACADEMY

Chabot CollegeChabot College

Frame RelayFrame RelayPart 1Part 1


Frame Relay OverviewFrame Relay Overview


Frame Relay OperationFrame Relay Operation

Many other WAN technologies (PPP, ATM) can be used inside the FR cloud.


Frame Relay Uses PVCsFrame Relay Uses PVCs

PVCs have ID numbers called DLCIs.

DLCI - Data Link Control Identifier


DLCIs Identify ConnectionsDLCIs Identify Connections

Frame Relay provides a means for statistically multiplexing many logical data conversations (referred to as virtual circuits) by assigning each pair of DTEs connection identifiers.


DLCIDLCIA number that identifies the logical circuit between the source and destination device. The FR switch maps the DLCIs between each pair of routers to create a PVC.


DLCIsDLCIs

• Can have “local only” significance.


Local Access RateLocal Access RateThe clock speed (port speed) of the connection (local loop) to the Frame Relay cloud. It is the rate at which data travels into or out of the network.


Local Management InterfaceLocal Management InterfaceA signaling standard between the CPE device and the FR switch that is responsible for managing the connection and maintaining status between the devices.


Possible LMI FunctionsPossible LMI Functions

• keepalive mechanism, which verifies that data is flowing

• a multicast mechanism which can provide the network server with its local DLCI

• multicast addressing

• the ability to give DLCIs global (whole Frame Relay network) significance

• a status mechanism


Flavors of LMIFlavors of LMI

Different flavors have different features. Currently, ansi is the most common:

ciscocisco—LMI type defined jointly by Cisco, StrataCom, Northern Telecom, and DEC

ansi—Annex D defined by ANSI standard T1.617

q933a—ITU-T Q.933 Annex A


LMI ConfigurationLMI Configuration

Remember to configure your router’s interface to use the same LMI type that the FR provider’s equipment is using.

(config-if)#frame-relay lmi-type cisco

(config-if)#frame-relay lmi-type ansi

(config-if)#frame-relay lmi-type q933a


CIR - Committed Info RateCIR - Committed Info Rate

The rate, in bits per second, that the Frame Relay switch agrees to transfer data.

Excess Burst—The maximum number of uncommitted bits that the Frame Relay switch will attempt to transfer beyond the CIR.


DE - Discard EligibilityDE - Discard Eligibility

When the router detects network congestion, the FR switch will drop packets with the DEDE bit set first. The DE bit is set on the oversubscribed traffic; that is, the traffic that was received after the CIR was met.


FECN and BECNFECN and BECN

Forward explicit congestion notification:Forward explicit congestion notification:

When a Frame Relay switch recognizes congestion in the network, it sends an FECN packet to the destination device indicating that congestion has occurred.



Backward explicit congestion notification:Backward explicit congestion notification:

When a Frame Relay switch recognizes congestion in the network, it sends a BECNBECN packet to the source router instructing the router to reduce the rate at which it is sending packets.




DLCIsDLCIs

• Can be a number between 16-1007.

illegal


LMI - TypesLMI - Types


Frame Relay EncapsulationFrame Relay Encapsulation

• The router must be configured to choose which Frame Relay encapsulation will be used.

IETF Encapsulation Type(Most common)

Cisco Encapsulation Type


IETF Frame Relay FrameIETF Frame Relay Frame

variable


Inverse ARPInverse ARP


Inverse ARPInverse ARP

The Inverse ARPInverse ARP mechanism allows the router to automatically build the Frame Relay map. The router learns the DLCIs that are in use from the switch during the initial LMI exchange. The router then sends an Inverse ARP request to each DLCI for each protocol configured on the interface if the protocol is supported.


The Frame Relay MapThe Frame Relay Map






B.S. - Before SubinterfacesB.S. - Before Subinterfaces

Network 8888

Network 7777


SubinterfacesSubinterfaces


SubinterfacesSubinterfaces


Multipoint SubinterfacesMultipoint Subinterfaces


Point-to-Point SubinterfacesPoint-to-Point Subinterfaces


11.2 + Autodetects LMI type11.2 + Autodetects LMI type


FR VerificationFR Verification

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CHABOT COLLEGE CISCO NETWORKING ACADEMY Chabot College Frame Relay Part 1