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T1, the transaction timeout, and Timer C

T1 seeds retransmissions, 64 times T1 ends the transaction, and Timer C is the proxy's longer INVITE arm.

Learn in 5 minutes

  1. State the defaults for T1, T2, and T4
  2. Compute Timer B as 64 times T1
  3. Keep Timer C separate from Timer B

Visual

Retransmit until 100, then wait · study drawing · cyphermonkeylabs.com UAPeer INVITE INVITE INVITE 100 200 ACK

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Change T1 and every timer that scales with it changes. Timer C does not use that formula.

Worked example

Count the gaps The second and third arrows are retransmissions. State the first Timer A value.

  1. Step the first three INVITEs.
  2. Note that the branch does not change.
  3. Name the timer that stops when 100 arrives.

Fault

A proxy cancels every INVITE at 32 seconds while the downstream phone is still ringing. The operator calls it Timer C.

Timer B is 64 times T1 on the transaction. The proxy's INVITE arm is Timer C.

Quiz

The default T1 is


Timer B is


Timer A


T2 and T4 default to


Timer C is


When Timer B fires the client


Ecosystem

Glossary, sister systems, and the integration seam for this room.

AI omni-channel agents A voice bot still needs a session. SIP creates, modifies, and ends sessions. Omni-channel, in the contact-center sense, means the same contact can also live on chat or another digital channel. Those channels do not replace the voice session. On Amazon Connect the platform owns the managed PSTN voice channel. Bridging an outside carrier into Connect with a Chime Voice Connector is not a supported pattern unless AWS reviews it. When an SBC forks the voice leg to a recorder, that fork is SIPREC, a different plane from the customer dialog.

AI agents A voice bot still needs a session. On Amazon Connect the platform owns the managed PSTN voice channel. Bridging an outside carrier into Connect with a Chime Voice Connector is not a supported pattern unless AWS reviews it. The FreeSWITCH manual page also describes SignalWire, founded by the FreeSWITCH team, as a hosted platform with AI agents behind REST APIs and SWML.

Glossary · Ecosystem map · Ports · Troubleshooting

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