ANNEX A
(to Recommendation Q.764)

Timers used in Recommendation Q.764 (Sheet 1 of 6)
 Symbol	 Time–out value	 Significance	 Cause for initiation	 Normal termination	 At the first expiry	 At the following expiry	
 T1	 4–15 s	 Local	 When release message is sent	 At the receipt of release complete message	 Retransmit release message and reinitialize timer T1	 Same as the first expiry	
 T2	 3 min	 Dual	 When controlling exchange receives suspend (user) message	 At the receipt of resume (user) message at controlling exchange	 Initiate release procedure	 –	
 T3	 3 min	 Dual	 When local exchange sends delayed release message	 When hold condition is removed	 Initiate release procedure	 –	
 T4	 4–15 s	 Dual	 When local exchange sends call modification request message	 At the reception call modification complete message		–	
 T5	 1 min	 Local	 When initial release message is sent	 At receipt of release complete message	 Send reset circuit message, alert maintenance personnel, and remove the circuit from service	 The sending of the de reset circuit message should continue at 1–min intervals until maintenance intervention occurs	
 T6	 Covered in Q.118	 Dual	 When controlling exchange receives suspend (network)	 At the receipt of resume (network) message	 Initiate release procedure	 –	

Timers used in Recommendation Q.764 (Sheet 2 of 6)
 Symbol	 Time–out value	 Significance	 Cause for initiation	 Normal termination	 At the first expiry	 At the following expiry	
 T7	 20–30 s	 Dual	 When the latest address message is sent	 When the condition for normal release of address and routing informations is met (receipt of ACM, CON, messages)	 Release all equipment and connection (Send release message)	 –	
 T8	 10–15 s	 Local	 When transit of incoming international exchange receives initial adress message	 At receipt of continuity message	 Release all equipment and connection into national network (Send release message)	 –	
 T9	 Interval specified in Q.118	 Dual	 When national controlling or outgoing international exchange sends latest address message after the receipt of ACM	 At the receipt of answer	 Release connection send back release message	 –	
 T10	 4–6 s	 Dual	 When last digit is received in interworking situations	 At the receipt of fresh information	 Send address complete message	 –	
 T11	 15–20 s	 Dual	 When latest address message is received in interworking situations	 Send ACM	 Send address complete message	 –	

Timers used in Recommendation Q.764 (Sheet 3 of 6)
 Symbol	 Time–out value	 Significance	 Cause for initiation	 Normal termination	 At the first expiry	 At the following expiry	
 T12	 4–15 s	 Local	 When blocking message is sent	 At receipt of blocking acknowledgement	 Retransmit blocking message and initiate T12	 Same as the left until T13 expires	
 T13	 1 min	 Local	 When initial blocking message is sent	 At receipt of blocking acknowledgement	 Retransmit blocking message and alert maintenance personnel and start T13. Stop T12	 The reception of message should be continued until maintenance intervention occurs and circuit taken out of service as appropriate	
 T14	 4–15 s	 Local	 When unblocking message is sent	 At receipt of unblocking acknowledgement	 Retransmit unblocking message and initiate T14 timer	 Same as the left until T15 expires	
 T15	 1 min	 Local	 When initial unblocking message is sent	 At receipt of unblocking acknowledgement	 Retransmit unblocking message alert maintenance personnel, start T15 timer and stop T14	 The repetition of message should be continued until maintenance intervention occurs and circuit taken out of service as appropriate	
 T16	 4–15 s	 Local	 When reset circuit message is sent	 At the receipt of the acknowledgement (RLC message)	 Retransmit reset circuit message and restart T16	 Same as the left until T17 expires	
 T17	 1 min	 Local	 When initial reset circuit message is sent	 At receipt of the acknowledgement	 Alert maintenance personnel retransmit reset circuit message, restart T17 and stop T16	 The repetition of message should be continued until maintenance intervention occurs	

Timers used in Recommendation Q.764 (Sheet 4 of 6)
 Symbol	 Time–out value	 Significance	 Cause for initiation	 Normal termination	 At the first expiry	 At the following expiry	
 T18	 4–15 s	 Local	 When group blocking message is sent	 At receipt of group blocking acknowledgement	 Retransmit group blocking message and initiate T18	 Same as the left until T18 expires	
 T19	 1 min	 Local	 When initial group blocking message is sent	 At receipt of group blocking acknowledgement	 Retransmit group blocking message, alert maintenance personnel, initiate T19 and stop T18	 The repetition of message should be continued until maintenance intervention occurs and circuits taken out of service as appropriate	
 T20	 4–15 s	 Local	 When group unblocking message is sent	 At receipt of group unblocking acknowledgement	 Retransmit group unblocking message and initiate T20	 Same as the left until T20 expires	
 T21	 1 min	 Local	 When initial group unblocking message is sent	 At receipt of group unblocking acknowledgement	 Retransmit group unblocking message, alert maintenance personnel, initiate T21 and stop T20	 The repetition of message should be continued until maintenance intervention occurs and circuits taken out of service as appropriate	
 T22	 4–15 s	 Local	 When circuit group reset message is sent	 At the receipt of the acknowledgement	 Retransmit circuit group reset message and restart T22	 Same as the first expiry until T23 expires	

Timers used in Recommendation Q.764 (Sheet 5 of 6)
 Symbol	 Time–out value	 Significance	 Cause for initiation	 Normal termination	 At the first expiry	 At the following expiry	
 T23	 1 min	 Local	 When initial circuit group reset message is sent	 At the receipt of the acknowledgement	 Alert maintenance personnel and restart Timer T23. Retransmit circuit group reset message. Stop timer T22	 The reception of message should be continued until maintenance intervention occurs	
 T24	 < 2 s	 Local	 When check tone is sent	 At the receipt of backward check tone	 Report failure	 –	
 T25	 1–10 s	 Local	 When continuity check failure is detected (on receipt of continuity recheck request)	 –	 Send CCR message	 –	
 T26	 1–3 min	 Local	 When second continuity check failure is detected	 –	 Send CCR message	 –	
 T27	 4 min	 Local	 When continuity recheck request is requested	 At receipt of continuity check request message	 Return to idle	 –	
 T28	 10 s	 Local	 When send CQM	 At receipt of CQR	 Alert maintenance	 –	

Timers used in Recommendation Q.764 (Sheet 6 of 6)
 Symbol	 Time–out value	 Significance	 Cause for initiation	 Normal termination	 At the first expiry	 At the following expiry	
 T29	 300–600 ms	 Local	 First congestion/first congestion indication after T30 expires	 –	 –	 –	
 T30	 5–10 s	 Local	 First congestion indication	 –	 –	 –	
 T31	 > 6 min	 Local	 Release of ISDN User part signalling connection based on CO SCCP	 On expiry	 –	 Call reference reusable	
 T32	 3–5 s	 Local	 On receipt of end–to–end message	 On expiry	 –	 End–to–end message to be sent	
 T33	 12–15 s	 Local	 When send INR	 On receipt of INF	 Release call	 –	
 T34	 12–15 s	 Local	 When send circuits group query	 On receipt of circuits group query response	 Maintenance action	 –