Prestige 681 SDSL Router
4-8
Internet Access
4.6 Encapsulation
Note: The P681 must reboot when the Encapsulation method is changed in Menu 4 or
Menu 11.1
4.6.1 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).
4.6.2 PPP
RFC 1662 defines PPP over HDLC
(High-level Data Link Control). HDLC is a bit-oriented, (meaning that
the data is monitored bit by bit) link layer protocol for the transmission of data over synchronous networks.
Transmissions consist of binary data without any special control codes. Information in the frame contains
control and response commands, however. HDLC supports full-duplex transmission in which data is
transmitted in two directions at the same time, resulting in higher throughput. HDLC is suitable for point-
to-point and multipoint (multidrop or one-to-many) connections.
4.7 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 only. Identifiers can range from 1 to 1023
with restrictions shown in the following table. The default DLCI for the P681 is 16 when you choose RFC
1490 encapsulation and N/A (not applicable) for PPP encapsulation.
Table 4-3
Data Link Connection Identifiers
DLCI
Usage
0
Channel signaling
1-15
Reserved
16 – 1007
Frame Relay
1008 – 1022
Reserved
1023
LMI
