Communication Protocol; Hdlc-Based Q.921 Ccitt Lapd Protocol - Nortel DMS-100 Series Maintenance Manual

established at provisioning time. Messages over the embedded operations
channel (EOC) control the assignment of the D-channel.

Communication protocol

The host XPM and Star Hub communicate with the SuperNode switch over
DS-1 links that terminate on the host XPM. The high level data link control
(HDLC) protocol communicates between the host XPM and the Star Hub.

HDLC-based Q.921 CCITT LAPD protocol

HDLC protocol is message protocol used to communicate between the
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In the host XPM, the NTMX76AB messaging card uses the HDLC protocol.
The following figure shows the HDLC message structure.
Figure 3-4 HDLC message format
Bit
8 7
Octet
1
2
3
4
5
6
7
The Q.921 LAPD protocol
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host XPM and the Star Hub
Star Hub and the Star Module
6 5 4
Flag
Address
Control
Information
Frame check sequence
Flag
establishes data link communications between the
— host XPM and the Star Hub
— Star Hub and the Star Module
transmits information sent from a higher layer protocol
receives information for delivery to a higher layer protocol
DMS-100 Family NA100 Star Remote System XPM15 and up
Signaling for the Star Remote System 3-7
Flags at the beginning and end
3 2 1
of the message identify the
start and end of the message.
Frame check sequence is used
to detect transmission errors.