The clearing of the switched connection shall be effected by using the D-channel signalling procedures for call clearing as specified in 5.3. For access to PSPDN services, no exceptions apply. For the ISDN virtual circuit service, the messages of 3.2 are used, and the following exceptions apply:
- The terms defined in 5.3.1 (Terminology) apply by replacing "circuit-switched ISDN connection" with"demand packet mode access connection".
- The exception condition f) specified in 5.3.2 does not apply.
- The procedures for clearing with tones and announcements provided in 5.3.4.1 do not apply.
The B-channel may be cleared at any time by the user though, in general, it will be cleared following the clearing of the last virtual call over that B-channel. In the ISDN virtual circuit service, if the user clears the B-channel access connection using a Q.931 clearing message while X.25 virtual calls still exist on the B-channel, the network shall clear the X.25 virtual call(s) with cause No. 17, remote procedure error, and diagnostic No. 64, call set-up, call clearing, or registration problem.
In Case B, if a Q.931 RESTART message is received by the PH during the X.25 data transfer phase, the X.25 virtual calls shall be treated as follows:
- For switched virtual circuits, an X.25 clear indication packet shall be sent with cause No. 9, out of order and diagnostic No. 0, no additional information.
- For any virtual calls which are established on a semi-permanent connection to the packet handler, no action shall be taken.
At the expiration of timer T320, the network may disconnect the X.25 link layer and the access connection. B-channel clearing is as described in 5.3 with the exceptions above, with cause No.102, recovery on timer expiry.