Frame Relay (FR) support for linux is built into a two tiered system of device
drivers. The upper layer implements RFC1490 FR specification, and uses the
Data Link Connection Identifier (DLCI) as its hardware address. Usually these
are assigned by your network supplier, they give you the number/numbers of
the Virtual Connections (VC) assigned to you.
You can find the rest of the document in
/usr/src/linux/Documentation/networking/framerelay.txt
