Prestige 153X Supplement
User's Guide Supplement
6
1.3 How To Configure Frame Relay for Internet Access
1.3.1 Encapsulation
Be sure to use the encapsulation method required by your ISP. The Prestige supports the following methods.
RFC 1973 (PPP over FR)
RFC 1973 describes the use of Frame Relay for framing PPP encapsulated packets. Please refer to RFC 1973
for more information.
RFC 1490
RFC 1490 describes Multiprotocol over Frame Relay encapsulation which is an encapsulation method for
carrying network interconnect traffic (both bridging and routing) over a frame relay backbone. It also
describes a simple fragmentation procedure for carrying large frames over a frame relay network with a
smaller MTU (Maximum Transmission Unit).
1.3.2 DLCI
The carrier gives you a specific DLCI (data link connection identifier) for each PVC which is a path number
of a portion of the PVC (the DLCI changes for each hop through the network), not the address of the
destination. It is a logical identifier with local significance. Identifiers can range from 1 to 991 with
restrictions as shown in the following table. The default DLCI for the Prestige is 16 for the first PVC.
Table 3
Data Link Connection Identifiers
DLCI
Usage
0
Channel Signaling
1-15
Reserved
16 – 991
Frame Relay
1.3.3 CIR (Committed Information Rate)
The carrier programs virtual circuits into the network between your sites and charges you for a specific level
of service called the committed information rate (CIR). The CIR is a negotiated rate and is basically a
guarantee that the carrier will always have that bandwidth available. The CIR limit for the Prestige is
256Kbps. The sum of CIRs from all channels in a line cannot exceed 256Kbps due to the processing limit of
the P153X CPU. In field tests, the P153X was found to have a maximum throughput (with Frame Relay) of
roughly 180Kbps.
