What is frame relay in the network

Preparation CCNP: Frame Relay Summary

To prepare for certification as a CCNP, it may help you to prepare your own knowledge in writing. As a suggestion for such summaries, I'll start with the subject of "Frame Relay".

Frame Relay works on Layer 2 and is a NBMA (Non Broadcast Multiple Access) technology.

DTE and DCE

Router is DTE, DCE is the FR switch at the provider.

Local management interface LMI

  • runs between DTE and DCE

  • Allocation of the DLCI to DTE possible

  • Keepalives

  • LMI types: Cisco, ANSI, Q933a

  • Autosensing from IOS 11.2

Topologies

  • Hub and spoke

  • Full mesh [requires n (n-1) / 2 links]

  • Partial mesh

With “hub and spoke” and “partial mesh”, “split horizon” strikes. Solution: subinterfaces.

Terms

CIR

Committed information rate

MinCIR

minimum transfer rate

Tc

CIR measurement interval, usually 125 ms

Bc

Committed Burts Size,

Number of bits that are normally transmitted in Tc

Be

Excess burst size,

Amount of data that can be transmitted in addition to Bc in time Tc, DE is set

DE

Discard Eligibility,

Identification for loading data, can also be set specifically for individual protocols

 

Basic configuration

Encapsulation: Cisco or IETF

(config) #intint
(config-if) #encapsulation frame relay
(config-if) #interface subintpoint-to-point
(config-subif) #ip address ip addr mask
(config-subif) #frame-relay interface-dlcidlci

or

(config) #intint
(config-if) #encapsulation frame relay
(config-if) #interfacesubintmultipoint
(config-subif) #ip addressipaddr mask
(config-subif) #frame-relay map ipipaddr dlci

With the "frame-relay map" the local DLCI and the remote IP are given.

Router #show frame-relay pvc

Status PVC and statistics.

Router #show frame-relay lmi
Router #debug frame relay lmi

LMI info

Router #show frame-relay map

Traffic shaping

German: traffic control

Possibility of FR-DTE to react to overload reports from the network.

ECN vs. ICN

Frame Relay implements an explicit overload notification (ECN) with the bits FECN and BECN. The overload is signaled before frames are discarded.

With the implicit overload message (ICN, e.g. TCP), the overload is only noticed when frames have been discarded (no ACK).

Configuration

No reaction to BECN (only information about the CIR)

(config) #map-class frame relaySurname

(config-map-class) #frame-relay traffic-rateaverage [peak]

In response to BECN

The router reduces the transmission rate for each BECN by 25 percent until the MinCIR is reached.

(config) #map-class frame relaySurname

(config-map-class) #frame-relay adaptive-shaping becn

(config-map-class) #frame relay cir [in | out]bits

(config-map-class) #frame relay bc [in | out]bits

(config-map-class) #frame relay be [in | out]bits

(config-map-class) #frame relay mincir [in | out]bits

and then on the interface:

(config) #intint

(config-if) #encapsulation frame relay

(config-if) #frame relay traffic shaping

(config-if) #int subint point-to-point

(config-subif) #frame-relay interface-dlci dlci

(config-fr-dlci) #classSurname

or

(config) #intint

(config-if) #encapsulation frame relay

(config-if) #frame relay traffic shaping

(config-if) #frame-relay class Surname

Control again with

Router #show frame-relay pvc

Left

MPLS and Frame Relay Alliance