T1: A Survival Guide

Configuring Frame Relay

After ordering a frame relay connection, the carrier provides configuration information for the connection. Part of this information is the parameters for the T1 access circuit (encoding, T1 framing type, and so on). The rest of the information is specific to the frame relay link. Here are some things you’ll need to know:

LMI type

Frame relay carriers use LMI to monitor the access link and any PVCs associated with it. If there is an LMI type mismatch, the frame relay switch will not activate PVCs associated with the access link and no traffic will pass. When the LMI type is mismatched, the physical line will be up, but the logical link layer will be down.

Some equipment can perform LMI-type autodetection. Some automatic LMI selection procedures require that the LMI DLCI to be known in advance. It is typically DLCI 0, because the Gang of Four LMI is not widely used any more.

Encapsulation

Unless there is an agreement to pass only a certain network protocol, multiprotocol encapsulation must be configured. With rare exceptions, the scheme is RFC 1490. Some vendors may require explicit selection of RFC 1490 encapsulation, while for others, it may be the only mode of operation.

IP addressing

PVCs used for Internet access or private IP networks will have IP addresses. In the former case, the ISP provides IP address information; in the latter, consult the internal address administrators. Because frame relay PVCs are often used as cheaper leased-line replacements, ...