Nortel Networks CG030601 - Manual (Page 2)

Configuration Guide
Contivity Secure IP Services Gateway
Frame Relay on Contivity Secure IP Services Gateway
CG030601 2.00 July 2003 Page: 2 of 14
Command/response bit (C/R)
ITU-T (formerly CCITT) standards do not use this bit.
Forward explicit congestion notification (FECN) and backward explicit congestion
notification (BECN)
The FECN and BECN indicate congestion on the network. For information about how the
frame relay software uses these bits, see “Congestion Control”.
Discard eligibility (DE)
The DE bit allows the router to mark specific frames as low priority (discard eligible)
before transmitting them to the frame relay network.
Extended address bit (EA)
The EA bit signals whether the next byte is part of the address. This bit indicates the last
byte of the DLCI.
Management protocols
Frame relay is an access protocol that runs between a CES or data terminal equipment
(DTE) and a switch or data communications equipment (DCE). The CES and the switch
use the Data Link Control Management Interface (DLCMI) to exchange information
about the interface and the status of each virtual circuit.
DLCMI supports three standard data link management specifications: LMI, ANSI T1.617
Annex D, and CCITT (now ITU-T) Q.933 Annex A.
• The networking industry first developed the local management interface (LMI)
specification. The LMI approach is asymmetric; the router sends a status-inquiry
message to the network, signaling that the router’s connection to the network is
functioning. The network replies with a status response.
• ANSI modified the LMI specification and incorporated it as Annex D to ANSI
standard T1.617. The ANSI method is generally similar to the LMI approach.
• The CCITT (now ITU-T) modified the ANSI standard and adopted it as Annex A
to Q.933. The CCITT Annex A specification is similar to Annex D, but it uses an
international numbering scheme.
Be sure to configure the frame relay interface on the CES to use the same management
protocol as the switched network to which it is connected.