Nortel Networks CG030601 - Manual

Configuration Guide
Contivity Secure IP Services Gateway
Frame Relay on Contivity Secure IP Services Gateway
CG030601 2.00 July 2003 Page: 1 of 14
Introduction to Frame Relay
Frame relay is a high-speed, packet-switching WAN protocol that connects
geographically dispersed LANs. A public network provider usually offers frame relay.
However, private organizations can acquire and manage their own frame relay networks
as well.
Frame relay is a connection-oriented protocol. This means it relies on end-to-end paths
between devices connected across the network. It implements these connections using
permanent virtual circuits (PVCs).
Frame relay assumes that networks use transmission lines with low error rates, such as
digital transmission media. Therefore, frame relay provides only basic error detection
with no error recovery. This minimizes the processing required for each packet, allowing
frame relay networks to operate at high speeds with few network delays.
Because frame relay performs only basic error checking, end stations running upper-layer
protocols such as the Internet Protocol (IP) are responsible for resending packets that did
not transmit correctly the first time.
Permanent virtual circuits
A permanent virtual circuit (PVC) is a dedicated logical path that connects two devices
over a network. When configured, a PVC is always available to the connected devices; a
PVC does not require setup before data can travel across the network, nor does it need to
be disconnected after data has passed. Because many PVCs can coexist for one physical
line, devices can share the bandwidth of the transmission line.
Frame Relay packets
The structure of a frame relay packet is shown in the following figure .
Figure 1 Frame Relay packet
The packet’s header field includes the following components:
Data link connection identifier (DLCI)
The DLCI is the virtual circuit identification number. The frame relay network uses the
DLCI to direct basic data flow. You configure the DLCI for PVCs.