The timers specified in Table 9-2 are maintained in the user side of the interface. Timers T305, T308 and T313 are mandatory for all user side implementations.
Timers in the network side
Timer number |
Default time-out value |
State of call |
Cause for start |
Normal stop |
At the first expiry |
At the second expiry |
Cross-reference |
T301 |
Minimum 3 min |
Call received |
ALERT received |
CONNECT received |
Clear call |
Timer is not restarted |
(Note 2) |
T302 |
10-15 s |
Overlap sending |
SETUP ACK sent Receipt of INFO, restarts T302 |
With sending complete indication, or network alert, or connect request received |
Clear if call information determined to be definitely incomplete; else send CALL PROC |
Timer is not restarted |
Mandatory |
T303 |
4 s |
Call present |
SETUP sent |
ALERT, CONNECT CALL PROC or SETUP ACK received, REL COMPLETE received if SETUP sent on point-point data link |
Retransmit SETUP; restart T303. If REL COMPLETE has been received, clear the call |
Clear network connection. Enter call abort state |
Mandatory |
T304 |
20 s |
Overlap receiving |
SETUP ACK received. Sending of INFO restarts T304 |
Send INFO; receive CALL PROC, ALERT or CONNECT |
Clear the call |
Timer is not restarted |
Mandatory only if 5.2.4 implemented |
T305 |
30 s |
Disconnect indication |
DISC without progress indicator No. 8 sent |
REL or DISC received |
Network sends REL |
Timer is not restarted |
Mandatory |
T306 |
30 s |
Disconnect indication |
DISC with progress indicator No. 8 sent |
REL or DISC received |
Stop the tone/announcement. Send REL |
Timer is not restarted |
Mandatory when in band tones/announcements are provided; see 5.4, 5.3.4.1, and Rec. I.300-Series |
T307 |
3 min |
Null |
SUSPEND ACK sent |
RES ACK sent |
Clear the network connection. Release call identity |
Timer is not restarted |
Mandatory |
T308 |
4 s |
Release request |
REL sent |
REL COMPLETE or REL received |
Retransmit REL and restart T308 |
Place B-channel in maintenance condition Release call reference (Note 9) |
Mandatory |
T309 |
90 s |
Any sTable state |
Data link disconnection. Calls in sTable states are not lost |
Data link reconnected |
Clear network connection. Release B-channel and call reference |
Timer is not restarted |
Mandatory |
T310 |
10 s |
Incoming Call Proceeding |
CALL PROC received |
ALERT, CONNECT or DISC received. If DISC, retain cause and continue timing |
Clear call in accordance with 5.2.5.3 |
Timer is not restarted |
Mandatory |
T312 |
T303 + 2 s |
Call Present, Call Abort, etc. |
SETUP sent or resent on broadcast data link |
Timeout |
(Note 4) |
Timer is not restarted |
Mandatory |
T314 |
4 s |
Receiving segmented message |
Message segment received |
Last message segment received |
Discard message |
Timer is not restarted |
Mandatory see Annex H |
T316 |
2 min |
Restart request |
RESTART sent |
RESTART ACK received |
RESTART may be retransmitted several times |
RESTART may be retransmitted several times |
Mandatory when 5.5 is implemented |
T317 |
(Note 3) |
Restart |
RESTART received |
Internal clearing of call references |
Maintenance notification |
Timer is not restarted |
Mandatory when 5.5 is implemented |
T320 |
30 s |
a) For B-channel access: active b) For D-channel access: null |
a) For B-channel access: connection b) For D-channel access: c) Last logical channel, cleared received |
Call request packet received; or incoming call packet delivered; or DISC received; or for D-channel access DL-RELEASE indication received |
a) For B-channel access: disconnect link layer and initiate clearing b) For D-channel access: send DL-RELEASE request |
Timer is not restarted |
Optional. See 6.3 |
T321 |
30 s |
Any call state |
D-channel failure |
Response to layer 3 message received |
Send DL-ESTABLISHMENT request on both D-channels |
Timer is not restarted |
Mandatory when Annex is implemented |
T322 |
4 s |
Any all state |
STATUS ENQ sent |
STATUS DISC REL or REL COMPLETE received |
STATUS ENQ may be retransmitted several times |
STATUS ENQ may be retransmitted several times |
Mandatory when 5.8.10 is implemented |
NOTES 1. This default value assumes the use of default values at layer 2 (i.e. N200 + 1] times T200). Whether these values should be modified when layer 2 default values are modified by an automatic negotiation procedure is for further study. 2. The network may already have applied an internal alerting supervision timing function; e.g. incorporated within call control. If such a function is known to be operating on the call, then timer T301 is not used. 3. The value of this timer is implementation dependent but should be less than the value of T316. 4. If in the call abort state, the call reference is released. Otherwise, no action is taken on expiry of timer T312. 5. The value of timer T302 may vary beyond these limits, e.g. as a result of called party number analysis. 6. The value of timer T306 may depend on the length of the announcement. 7. The value of timer T310 may be different in order to take into account the characteristics of a private network. 8. This value may vary by network-user agreement. 9. The restart procedures contained in 5.5 may be used on B-channels in the maintenance condition. 10. The value of this timer is network dependent. |
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Table 9-2/Q.931
Timers in the user side
T301 |
Minimum 3 min. |
Call Delivered |
ALERT received |
CONNECT received |
Clear call |
Timer is not restarted |
Mandatory when Annex D is implemented (Note 3) |
T302 |
15 s |
Overlap receiving |
SETUP ACK sent Restart when INFO received |
INFO received with sending complete indication; or internal alerting; or internal connection; or a determination that sufficient information has been received |
Clear if call information determined to be incomplete; else send CALL PROC |
Timer is not restarted |
Mandatory only if 5.2.4 is implemented |
T303 |
4 s |
Call Initiated |
SETUP sent |
ALERT (Annex D), CONNECT (Annex D), SETUP ACK, CALL PROC or REL COMPLETE received |
Retransmit SETUP; restart T303. If REL COMPLETE was received, clear the call (Annex D) |
Clear internal connection. Send REL COMPLETE. Enter Null state |
Mandatory when Annex D is implemented; otherwise optional |
T304 |
30 s |
Overlap Sending |
INFO sent Restarted when INFO sent again |
CALL PROC, ALERT, CONNECT or DISC received |
DISC sent |
Timer is not restarted |
Optional |
T305 |
30 s |
Disconnect Request |
DISC sent |
REL or DISC received |
REL sent |
Timer is not restarted |
Mandatory |
T308 |
4 s |
Release request |
REL sent |
REL COMPLETE or REL received |
Retransmit REL; and restart T308. |
B-channel is placed in maintenance condition. Call reference released (Note 5) |
Mandatory |
T309 |
90 s |
Any sTable state |
Data link disconnection. Calls in sTable states are not lost |
Data link reconnected |
Clear internal connection. Release B-channel and call reference |
Timer is not restarted |
Optional |
T310 |
30-120 s |
Outgoing Call Proceeding |
CALL PROC received |
ALERT, CONNECT, DISC, or PROGRESS received |
Send DISC |
Timer is not restarted |
Mandatory when Annex D is implemented |
T313 |
4 s |
Connect request |
CONNECT sent |
CONNECT ACK received |
Send DISC |
Timer is not restarted |
Mandatory |
T314 |
4 s |
Receiving Segmented Message |
Message segment received |
Last message segment received |
Discard message |
Timer is not restarted |
Not initially required |
T316 |
2 min |
Restart Request |
RESTART sent |
RESTART ACK received |
RESTART may be retransmitted several times |
RESTART may be retransmitted several times |
Mandatory when 5.5 is implemented |
T317 |
(Note 2) |
Restart |
RESTART received |
Internal clearing of call reference |
Maintenance notification |
Timer is not restarted |
Mandatory when 5.5 is implemented |
T318 |
4 s |
Resume Request |
RES sent |
RES ACK or RES REJ received |
Send RELEASE message with cause No. 102 |
Timer is not restarted |
Mandatory when 5.6 is implemented |
T319 |
4 s |
Suspend Request |
SUSPEND sent |
SUSPEND ACK or SUSP REJ received |
Enter Active state. Notify user application |
Timer is not restarted |
Mandatory when 5.6 is implemented |
T321 |
30 s |
Any call state |
D-channel failure |
Response to layer 3 message received |
Send DL-ESTABLISHMENT request on both D-channels |
Timer is not restarted |
Mandatory when Annex F is implemented |
T322 |
4 s |
Any call state |
STATUS ENQ sent |
STATUS, DISC, REL, REL COMPLETE received |
STATUS ENQ may be retransmitted several times |
STATUS ENQ may be retransmitted several times |
Mandatory when 5.8.10 is implemented |
NOTES 1. This default value assumes the use of default values at layer 2, i.e. [N200 + 1] times T200. Whether these values should be modified when layer 2 default values are modified by an automatic negotiation procedure is for further study. 2. The value of this timer is implementation dependent, but should be less than the value of T316. 3. The user may already have applied an internal alerting supervision timing function, e.g. incorporated within call control. If such a function is known to be operating on the call, then timer T301 is not used. 4. T310 is not started if progress indicator 1 or 2 has been delivered in the CALL PROCEEDING message or in a previous PROGRESS message. 5. The restart procedures contained in 5.5 may be used on B-channels in the maintenance conditions. 6. The value of this timer is implementation dependent. |
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