Wide-Area Networks - CCIE Routing and Switching Exam Certification Guide - page 202

Frame Relay Service Figure 5-5

Router (DTE) Router

PVCs

Switch (DCE)

Frame Relay Network

Router

Frame Relay switch

Router

PVCs

Frame Relay Encapsulation
There are two choices on Cisco routers for the encapsulation of network protocols over Frame
Relay. Both support encapsulation of multiple protocols. One method is Cisco proprietary and
is the default encapsulation. The other method is defined in RFC 2427, “Multiprotocol Inter-
connect over Frame Relay”. RFC 2427 covers aspects of both bridging and routing and describes
the procedure for fragmenting large frames over a Frame Relay network with a smaller MTU.

The encapsulation type must be the same on the two end systems (ESs) that are communicating
over the Frame Relay network. If connecting to another vendor's router, unless that vendor
supports Cisco encapsulation, you need to configure the ietf standard encapsulation. To configure
ietf encapsulation, use the ietf keyword in the encapsulation command as follows:

interface serial 0
encapsulation frame-relay ietf

Committed Information Rate (CIR)
Frame Relay is usually leased by carriers with a contract that bandwidth is guaranteed up to a
maximum limit. Although the CIR guarantees the rate, the user traffic can burst to higher rates,
if the provider's frame relay network is underutilized. The CIR is defined in two ways, and its
use depends on the Frame Relay provider's implementation. The CIR is either the maximum
speed that the Frame Relay provider transfers information for each PVC, or it is the average rate