APPENDIX
Protocol Data Mode
2.10
•
19.01.2007
105
5.1.7.7 Establishment
A LAP link is established under the following conditions:
•
The LAP for the command channel is established immediately when the protocol data
mode is entered.
•
The LAP for a data channel is established when a call has been set-up using call control
procedures in the command channel (see section 5.1.9).
A newly created LAP protocol instance starts its operation in the Idle state. V(S), V(A) and
V(R) are set to 0, all conditions are cleared.
The host-side LAP starts establishment by sending an I-frame with P-bit set. This frame does
not carry any user data.
The module-side LAP answers by sending a RR-frame with F-bit set.
Now both peers are in Active state and may start exchanging I-frames as described in
sections 5.1.7.5 and 5.1.7.6.
The details of the link establishment are included in the SDL representation (see section
5.1.8).
5.1.7.8 Termination
The LAP operation for a data channel is terminated implicitly, when the associated call is
terminated using the call control procedures in the command channel.
The LAP operation for the command channel is terminated implicitly, when the protocol data
mode is quit.
5.1.7.9 Re-establishment
In error recovery situations any of the peer instance may invoke a link re-establishment by
sending a SABM-command with the P bit set and the NLF flag set.
It then sets V(S), V(A) and V(R) to 0 and clears all conditions.
Upon reception of the SABM-command the peer sets its V(S), V(A) and V(R) to 0 and clears
all conditions. It then responds with an UA-response with the F bit set and the NLF flag set.
If no UA response is received for a SABM command, the originator repeats the SABM
command. For details please refer to section 5.1.8.