530 Chapter 8: WAN Protocols and Design
Frame Relay Features and Terminology
Frame Relay is a multiaccess network, which actually means that more than two devices can
attach to the medium. Multiaccess is the first and most obvious difference between Frame Relay
and leased lines. However, leased lines are used as the access link component of Frame Relay
networks. Consider Figure 8-4, which is a valuable resource for reviewing Frame Relay
concepts.
Figure 8-4
Frame Relay Components
The access link between the router and the Frame Relay switch is a leased line. Both sites
represented in Figure 8-4 are connected to some nearby switch via a leased line. The service
provider interconnects their switches to provide connectivity.
Table 8-9 lists the components in Figure 8-4 and some associated terms.
Table 8-9
Frame Relay Terms and Concepts
Virtual circuit (VC)
A VC is a logical concept that represents the path that frames travel
between DTEs. VCs are particularly useful when comparing Frame
Relay to leased physical circuits.
Permanent virtual circuit (PVC)
A PVC is a VC that is predefined. A PVC can be equated to a
leased line in concept.
Switched virtual circuit (SVC)
An SVC is a VC that is set up dynamically. An SVC can be equated
to a dial connection in concept.
DCE
Frame
Relay
LMI
Messages
Access
Link
Access
Link
LMI
Messages
Frame Relay
Header
Layer 3
Packet
DCE
ch08.fm Page 530 Monday, March 20, 2000 5:17 PM