Annex A

Table A.1/Q.764 – Timers in the ISDN User Part

Symbol

Time-out
value

Cause for initiation

Normal termination

At expiry

Reference

T1

15-60 seconds

When release message is sent

At the receipt of Release complete message

Retransmit release message and start timer T1

2.9.6
2.2, 2.3

T2

3 minutes

When controlling exchange receives suspend (user) message

At receipt of resume (user) message at controlling exchange

Initiate release procedure

Rec. Q.733.4 [26]

T3

2 minutes

At receipt of overload message

On expiry

Initiate release procedure

2.9.9

T4

5-15 minutes

At receipt of MTP-STATUS primitive with the cause "inaccessible remote user "

On expiry, or at receipt of user part available message (or any other)

Send user part test message. Start T4

2.13.2

T5

5-15 minutes

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, stop T1, start T17. Procedure continues until maintenance intervention occurs

2.9.6

T6

Covered in Rec. Q.118 [10]

When controlling exchange receives suspend (network)

At receipt of resume (network) message or release message

Initiate release procedure

2.4.1
2.4.2
2.4.3

T7

20-30 seconds

When the latest address message is sent

When the condition for normal release of address and routeing information is met (receipt of ACM, CON messages)

Release all equipment and connection (send release message)

2.1.1
2.1.2
2.1.4
2.9.8.3

T8

10-15 seconds

When an exchange receives Initial address message requiring continuity check on this circuit or indicates that continuity check has been performed on a previous circuit

At receipt of continuity message

Release all equipment and connection into the network (send release message)

2.9.8.3

T9

Interval specified in Rec. Q.118 [10]

When national controlling or outgoing international exchange receives ACM

At the receipt of answer

Release connection send back release message

2.1.4
2.1.7
2.9.8.3

T10

4-6 seconds

When last digit is received in interworking situations

At the receipt of fresh information

Send address complete message

2.1.2.1
2.1.4.9

T11

15-20 seconds

When latest address message is received in interworking situations

When ACM is sent

Send address complete message

2.1.4.9

T12

15-60 seconds

When blocking message is sent

At receipt of blocking acknowledgement

Retransmit blocking message and start T12

2.9.4

T13

5-15 minutes

When initial blocking message is sent

At receipt of blocking acknowledgement

Transmit blocking message and alert maintenance personnel, start T13, stop T12. Procedure continues until maintenance intervention occurs

2.9.4

T14

15-60 seconds

When unblocking message is sent

At receipt of unblocking acknowledgement

Retransmit unblocking message and start T14

2.9.4

T15

5-15 minutes

When initial unblocking message is sent

At receipt of unblocking acknowledgement

Retransmit unblocking message alert maintenance personnel, start T15 and stop T14. Procedure continues until maintenance intervention occurs

2.9.4

T16

15-60 seconds

When reset circuit message is sent not due to expiry of T5

At the receipt of the acknowledgement (RLC message)

Retransmit reset circuit message and start T16

2.9.3.1

T17

5-15 minutes

When initial reset circuit message is sent

At the receipt of the acknowledgement

Alert maintenance personnel, retransmit reset circuit message, start T17, stop T16. Procedure continues until maintenance intervention occurs

2.9.3.1

T18

15-60 seconds

When group blocking message is sent

At receipt of group blocking acknowledgement

Retransmit group blocking message and start T18

2.9.4

T19

5-15 minutes

When initial group blocking message is sent

At receipt of group blocking acknowledgement

Retransmit group blocking message, alert maintenance personnel, start T19, stop T18. Procedure continues until maintenance intervention occurs

2.9.4

T20

15-60 seconds

When group unblocking message is sent

At receipt of group unblocking acknowledgement

Retransmit group unblocking message and start T20

2.9.4

T21

5-15 minutes

When initial group unblocking message is sent

At receipt of group unblocking acknowledgement

Retransmit group unblocking message, alert maintenance personnel, start T21, stop T20. Procedure continues until maintenance intervention occurs

2.9.4

T22

15-60 seconds

When circuit group reset message is sent

At receipt of the acknowledgement

Retransmit circuit group reset message and start T22

2.9.3.2

T23

5-15 minutes

When initial circuit group reset message is sent

At the receipt of the acknowledgement

Alert maintenance personnel and start T23, retransmit circuit group reset message, stop T22. Procedure continues until maintenance intervention occurs

2.9.3.2

T24

< 2 seconds

When check tone is sent

At the receipt of the backward check tone

Send continuity message with failure indication and:

a)   start T25 if continuity check was asked in IAM and make automatic repeat attempt, or

b)   start T24 if continuity check was asked in CCR

Rec. Q.724 [15]

T25

1-10 seconds

When initial continuity check failure is detected

Send CCR message and repeat continuity check

Rec. Q.724 [15]

T26

1-3 minutes

When second or subsequent continuity check failure is detected

Send CCR message and repeat continuity check

Rec. Q.724 [15]

T27

4 minutes

When continuity check failure is received

At receipt of continuity check request message

Send reset circuit message, start T16 and T17

2.1.8

T28

10 seconds

When send CQM

At receipt of CQR

Alert maintenance

2.9.3.2

T29

300-600 ms

Congestion indication received when T29 not running

New congestion indication will be taken into account

2.10.2

T30

5-10 seconds

Congestion indication received when T29 not running

Restore traffic by one step if not yet at full load and start T30

2.10.2

T31

> 6 minutes

Release of ISDN User part signalling connection based on CO SCCP

On expiry

Call reference reusable

Rec. Q.730 [16]

T32

3-5 seconds

When response to request of end-to-end connection establishment is sent

At receipt of first end-to-end message from the remote end

End-to-end message allowed to be sent

Rec. Q.730 [16]

T33

12-15 seconds

When send INR

On receipt of INF

Release call, alert maintenance personnel

2.1.6.2
2.9.7
Rec. Q.730 [16]

T34

2-4 seconds

When indication of a segmented message is received on an IAM, ACM, CPG, ANM or CON message

At receipt of a segmentation message

Proceed with call

2.1.12

T35

15-20 seconds

At receipt of the latest digit (< >ST) and before the minimum or fixed number of digits have been received

At receipt of ST or when the minimum or fixed number of digits have been received

Send release message (cause 28)

2.2.5
2.9.8.3

T36

10-15 seconds

When transit or incoming international exchange receives continuity check request message

At receipt of continuity or release message

Release all equipment , send reset circuit message, start T16 and T17

2.1.8

T37

– reserved for ISUP'92

2-4 seconds

T38

Interval specified in Rec. Q.118 [10]

When the incoming international exchange sends to the preceding exchange a suspend (network) message

At receipt of resume (network) or release message

Send release message (cause 102)

2.4.1
2.4.2
2.4.3

T39

Interval specified in Rec. Q.730 [16]

When a MCID request is sent

At receipt of a MCID response

Call continues

Rec. Q.731.7 [27]