Signaling System No. 7 (SS7/C7): Protocol, Architecture, and Services

Signaling System No. 7

By Lee Dryburgh and Jeff Hewett

Appendix H. ISUP Timers for ANSI/ETSI/ITU-T Applications

This appendix lists all ISUP timers. The timer values are specified in ITU-T Q.764 [78]. ETSI ISUP timers [18] are identical to ITU-T timers.

Timers applicable to the US network are specified in ANSI T1.113-2000 [3].

Table H-1. ISUP Timers Specified in ANSI, ETSI and ITU-T

Timer

Duration Before Time-Out

Starts

Normal Termination

Action at Time-Out

T1

15–60 sec (ITU)

4–15 sec (ANSI)

When Release Message is sent

Upon receipt of Release Complete Message

Retransmit Release Message and start timer T1

T2

(ITU-T ONLY)

3 min

When controlling exchange receives Suspend (User) Message

Upon receipt of Resume (User) Message, at controlling exchange

Initiate release procedure

T3

(ITU-T ONLY)

2 min

Upon receipt of Overload Message

Upon expiry

Initiate release procedure

T4

(ITU-T ONLY)

5–15 min

Upon receipt of MTP-STATUS primitive with the cause "inaccessible remote user" or at receipt of MTP-RESUME primitive [1]

Upon expiry, or at receipt of User Part Available Message (or any other)

Send User Part Test Message and start T4

T5

5–15 min (ITU)

1 min

(ANSI)

When initial Release Message is sent

Upon receipt of Release Complete Message

Send Reset Circuit Message, alert maintenance personnel, and remove the Circuit from service, stop T1, and start T17

T6

10–32 sec, with preference for 30 sec

(specified in Rec. Q.118 [113])

When controlling exchange receives suspend (network)

Upon receipt of Resume (Network) Message or Release Message

Initiate release procedure

T7

20–30 sec

When the latest Address Message is sent

When the condition for normal release of address and routing information is met (receipt of ACM and CON Messages)

Release all equipment and connection (send Release Message)

T8

10–15 sec

Upon receipt of Initial Address Message requiring continuity check on this circuit, or indicating that continuity check has been performed on a previous circuit

Upon receipt of Continuity Message

Release all equipment and connection into the network (send Release Message)

T9

1.5–3 min (Specified in Q.118 [113])

When national controlling (ITU ONLY) or outgoing international exchange receives ACM (ANSI and ITU)

Upon receipt of Answer Message

Release connection and send Release Message

T10

(ITU-T ONLY)

4–6 sec

Upon receipt of last digit in interworking situations

Upon receipt of fresh information

Send Address Complete Message

T11

15–20 sec

Upon receipt of the latest address message (i.e., IAM) in interworking situations

When Address Complete Message is sent

Send Address Complete Message

T12

15–60 sec (ITU)

4–15 sec

(ANSI)

When Blocking Message is sent

Upon receipt of Blocking Acknowledgement Message

Retransmit Blocking Message and restart T12

T13

5–15 min (ITU)

1 min (ANSI)

When initial Blocking Message is sent

Upon receipt of Blocking Acknowledgment

Retransmit Blocking Message and alert maintenance personnel, start T13, and stop T12

T14

15–60 sec (ITU)

4-15 sec

(ANSI)

When Unblocking Message is sent

Upon receipt of Unblocking Acknowledgment

Retransmit Unblocking Message and start T14

T15

5–15 min (ITU)

1 min

(ANSI)

When initial Unblocking Message is sent

Upon receipt of Unblocking Acknowledgment Message

Retransmit Unblocking Message, alert maintenance personnel, start T15, and stop T14

T16

15–60 sec

(ITU)

4-15 sec

(ANSI)

When Reset Circuit Message is sent not due to expiry of T5

Upon receipt of the Acknowledgment (RLC Message)

Retransmit Reset Circuit Message and start T16

T17

5–15 min

(ITU)

1 min

(ANSI)

When initial Reset Circuit Message is sent

At the receipt of the Acknowledgment

(RLC Message)

Alert maintenance personnel, retransmit Reset Circuit Message, start T17, and stop T16

T18

15–60 sec

(ITU)

4–15 sec (ANSI)

When Circuit Group Blocking Message is sent

At receipt of Circuit Group Blocking Acknowledgment

Retransmit Circuit Group Blocking Message and start T18

T19

5–15 min (ITU)

1 min (ANSI)

When initial Circuit Group Blocking Message is sent

Upon receipt of Circuit Group Blocking Acknowledgment

Retransmit Circuit Group Blocking Message, alert maintenance personnel, start T19, and stop T18

T20

15–60 sec (ITU)

4–15 sec

(ANSI)

When Circuit Group Unblocking Message is sent

Upon receipt of Circuit Group Unblocking Acknowledgment

Retransmit Circuit Group Unblocking Message and start T20

T21

5–15 min (ITU)

1 min (ANSI)

When initial Circuit Group Unblocking Message is sent

Upon receipt of Circuit Group Unblocking Acknowledgment

Retransmit Circuit Group Unblocking Message, alert maintenance personnel, start T21, and stop T20

T22

15–60 sec (ITU)

4–15 (ANSI)

When Circuit group Reset Message is sent

Upon receipt of the Acknowledgment

Retransmit Circuit Group Reset Message and start T22

T23

5–15 min

(ITU)

1 min

(ANSI)

When initial Circuit Group Reset Message is sent

Upon receipt of the Acknowledgment

Alert maintenance personnel and start T23; retransmit Circuit Group Reset Message, and stop T22

T24

< 2 sec

When check tone is sent

Upon receipt of the backward check tone

Send Continuity Message indicating failure, and

(ITU-T ONLY)

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

(ANSI ONLY)

c) Start T25 and make automatic repeat attempt (if applicable)

T25

1–10 sec

When initial continuity check failure is detected

Upon expiry

Send Continuity Check Request Message and repeat continuity check

T26

1–3 min

When second or subsequent continuity check failure is detected

When continuity is detected

Send Continuity Check Request Message and repeat continuity check (starting T26)

T27

4 min

(ITU-T)

>3 min

(ANSI)

Upon receipt of continuity check failure

Upon receipt of Continuity Check Request Message

Send Reset Circuit Message, start T16 and T17

T28

10 sec

When a Circuit Query Message is sent

Upon receipt of Circuit Query Response Message

Alert maintenance

T29 (ITU-T ONLY)

300–600 ms

Congestion indication received when T29 not running

New congestion indication will be taken into account

T30 (ITU-T ONLY)

5–10 sec

Congestion indication received when T29 not running

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

T31

> 6 min

Release of ISDN user part end-to-end signaling connection, based on connection oriented SCCP

Upon expiry

Call reference reusable

T32

3–5 sec

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

Upon receipt of first End-to-end Message from the remote end

End-to-end Message allowed to be sent

T33

12–15 sec

When Information Request Message is sent

Upon receipt of an Information Message

Release call and alert maintenance personnel

T34 (ITU-T)

2–4 sec

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

T34 (ANSI)

10–15 sec

When Loop-Back Acknowledgment Message is sent in response to receipt of Continuity Check Request Message

Upon receipt of Continuity or Release Message

Release all equipment, send Reset Circuit Message, and start T16 and T17

T35 (ITU-T)

15–20 sec

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

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

Send Release Message (cause 28)

T36 (ITU-T)

10–15 sec

When transit or incoming international exchange receives Continuity Check Request Message

Upon receipt of Continuity or Release Message

Release all equipment, send Reset Circuit Message, start T16 and T17

T36 (ANSI)

2–4 sec

When a message is received indicating that another segment follows

Upon receipt of a Segmentation Message

Proceed with call processing

T37 (ITU-T)

—reserved for ISUP '92

2–4 sec

     

T37 (ANSI)

30 sec

When ISUP availability test is started

Upon receipt of a message from the affected ISUP

Proceed with call processing

T38 (ITU-T)

Interval Specified in Rec. Q.118 [113]

When the incoming international exchange sends a Suspend (network) Message to the preceding exchange

Upon receipt of Resume (Network) or Release Message

Send Release Message (cause 102)

T39 (ITU-T ONLY)

4–15 sec interval specified in Rec. Q. 731-7 §7.9

When a MCID request is sent

Upon receipt of a MCID response

Call continues

TACC,r (ANSI ONLY)

5 sec

Upon receipt of ACC indicator

Upon expiry

Remove ACC controls in the exchange

TCCR (ANSI ONLY)

2 sec

When Continuity Check Request Message is sent

Upon receipt of Loop-Back Acknowledgment Message

Disconnect transceiver, send Reset Circuit Message, and start T16 and T17

TCCR,r (ANSI ONLY)

20 sec

Upon receipt of initial Continuity Message, indicating failure

Upon receipt of Continuity Check Request Message

Send Reset Circuit Message and start T16 and T17

TCGB (ANSI ONLY)

5 sec

Upon receipt of Circuit Group Blocking Message

Upon receipt of Circuit Group Blocking or Circuit Group Unblocking Message

Accept subsequent Circuit Group Blocking Message as a new message

TCRA (ANSI ONLY)

20 sec

When Circuit Reservation Acknowledgment Message is sent

Upon receipt of Initial Address Message or Release Message

Initiate release procedure

TCRM (ANSI ONLY)

3–4 sec

When Circuit Reservation Message is sent

Upon receipt of Circuit Reservation Acknowledgment Message

Initiate release procedure

TCVT (ANSI ONLY)

10 sec

When Circuit Validation Test Message is sent

Upon receipt of Circuit Validation Response Message

Retransmit Circuit Validation Test Message and restart TCVT; alert maintenance personnel at second expiry

TEXM,d (ANSI ONLY)

Network Dependent

When Initial Address Message is sent to succeeding network

Upon expiry

Send Exit Message to proceeding exchange

TGRS (ANSI ONLY)

5 sec

Upon receipt of Circuit Group Reset Message

Upon receipt of Circuit Group Reset Message

Accept subsequent Circuit Group Reset Message as new message

THGA (ANSI ONLY)

0–5 min

Carrier loss

Carrier restoral

Alert maintenance personnel

TSCGA (ANSI ONLY)

0–2 min

Upon failure of initial Demand Continuity Check in SCGA group

Upon success of initial Demand Continuity Check in SCGA group

Alert maintenance personnel

TSCGA,d (ANSI ONLY)

5–120 sec

Upon failure of initial Demand Continuity Check in SCGA group

Upon expiry

Initiate Demand Continuity Check on another circuit in failed group

min = minute(s)

sec = seconds(s)

ms = millisecond(s)

+ Share This