Message Transfer Part 3 Timers

Tables G-2 and G-3 define the Message Transfer Part 3 (MTP3) timer values for ITU and ANSI networks, respectively. Timers T1 through T17 are defined the same for both ITU and ANSI. However, the subsequent timer values are defined differently.

Table G-2. MTP3 Timers for ITU Networks

Timer	Use	Range
T1	Delay to avoid missequencing on changeover	500 (800)–1200 ms
T2	Waiting for changeover acknowledgment	700 (1400)–2000 ms
T3	Time-controlled diversion delay—avoid missequencing on changeback	500 (800)–1200 ms
T4	Waiting for changeback acknowledgment (first attempt)	500 (800)–1200 ms
T5	Waiting for changeback acknowledgment (second attempt)	500 (800)–1200 ms
T6	Delay to avoid message missequencing on controlled rerouting	500 (800)–1200 ms
T7	Waiting for signaling data link connection acknowledgment	1–2 s
T8	Transfer prohibited inhibition timer	800–1200 ms
T9	Not used	Not used
T10	Waiting to repeat signaling route-set test message	30–60 s
T11	Transfer restricted timer	30–90 s
T12	Waiting for uninhibit acknowledgment	800–1500 ms
T13	Waiting for force uninhibit	800–1500 ms
T14	Waiting for inhibition acknowledgment	2–3 s
T15	Waiting to start signaling route-set congestion test	2–3 s
T16	Waiting for route-set congestion status update	1.4–2 s
T17	Delay to avoid oscillation of initial alignment failure and link restart	800–1500 ms
T18	Within an SP with MTP restart for supervision of links, link set activation and routing data updating	The value is implementation- and network-dependent (ITU-T); criteria to choose T18 can be found in § 9.2 of Q.704
T19	Supervision timer during MTP restart to avoid possible ping-pong of TFP, TFR, and TRA messages	67–69 s
T20	Overall MTP restart timer at the SP whose MTP is restarting	59–61 s 90–120 s
T21	Overall MTP restart timer at an SP adjacent—one whose MTP is restarting	63–65 s
T22	Local inhibit test timer	3–6 minutes (provisional value)
T23	Remote inhibit test timer	3–6 minutes (provisional value)
T24	Stabilization timer after removal of local processor outage (national option)	500 ms (provisional value)

Table G-3. MTP3 Timers for ANSI Networks

Timer	Use	Range
T1	Delay to avoid missequencing on changeover	500 (800)–1200 ms
T2	Waiting for changeover acknowledgment	700 (1400)–2000 ms
T3	Time-controlled diversion delay—avoid missequencing on changeback	500 (800)–1200 ms
T4	Waiting for changeback acknowledgment (first attempt)	500 (800)–1200 ms
T5	Waiting for changeback acknowledgment (second attempt)	500 (800)–1200 ms
T6	Delay to avoid message missequencing on controlled rerouting	500 (800)–1200 ms
T7	Waiting for signaling data link connection acknowledgment	1–2 s
T8	Transfer prohibited inhibition timer	800–1200 ms
T9	Not used	Not used
T10	Waiting to repeat signaling route; set test message	30–60 s
T11	Transfer restricted timer	30–90 s
T12	Waiting for uninhibit acknowledgment	800–1500 ms
T13	Waiting for force uninhibit	800–1500 ms
T14	Waiting for inhibition acknowledgment	2–3 s
T15	Waiting to start signaling route-set congestion test	2–3 s
T16	Waiting for route-set congestion status update	1.4–2 s
T17	Delay to avoid oscillation of initial alignment failure and link restart	800–1500 ms
T18	Repeat TFR once by response method	2–20 s
T19	Failed link craft referral timer	480–600 s
T20	Waiting—repeat local inhibit test	90–120 s
T21	Waiting—repeat remote inhibit test; repeat local inhibit test	90–120 s
T22	Timer used at a restarting SP; waiting for signaling links to become available	Network-dependent
T23	Timer used at a restarting SP; waiting to receive all traffic restart allowed message after starting T22	Network-dependent
T24	Timer used at a restarting STP; waiting to broadcast all traffic restart allowed messages after starting T23	Network-dependent
T25	Timer at adjacent SP to restarting SP; waiting for traffic restart message	30–35 s
T26	Timer at restarting SP; waiting to repeat traffic restart waiting message	12–15 s
T27	Minimum duration of unavailability for full restart	2(3)–5 s
T28	Timer at adjacent SP to restarting SP; waiting for traffic restart waiting message	3–35 s
T29	Timer started when TRA is sent in response to unexpected TRA or TRW	60–65 s
T30	Timer to limit sending of TFPs and TFRs in response to unexpected TRA or TRW	30–35 s

The values in parentheses are applicable where routes with long propagation delays—such as routes including satellite sections—are used.

ITU timer values are defined in ITU-T Q.704 [53]. ANSI T1.111-2001 [1] and Telcordia GR-246-Core (formerly Bellcore TR-NWT-000246) [114] specify timers that are applicable to the U.S. network.

Whereas 56 kbps and 64 kbps links are assumed for ANSI, 64 kbps links are assumed for ITU-T.