SIP REFER support in Asterisk

Asterisk Asterisk SIP
1

Would like to know if Asterisk supports SIP REFER over the SIP trunks?

Asterisk version:15.5
FreePBX version: 14

Asterisk is connected to Cisco CME via SIP Trunk.

Scenario:

  1. Cisco CME user-1 calls an Asterisk User
  2. Asterisk User does a call transfer back to Cisco CME User-2
  3. REFER is expected to be sent from Asterisk to Cisco CME however only RE-INVITE is sent from Asterisk to Cisco CME during the call transfer.

Need a confirmation if Asterisk can send SIP REFER to far end(Cisco CME) instead of Re-INVITE during call transfer?

2

What are SIP trunks. There is no such concept in SIP or Asterisk.

Asterisk supports REFER and REFER/Replaces when acting as a UAS, whether the peer is a phone or another PABX.

It also supports REFER, but not REFER/Replaces, as a UAC. Again it doesn’t care whether the peer is a phone or another PABX.

This is for chan_sip, but I assume that the same is true for PJSIP.

Asterisk doesn’t automatically de-trombone calls. If it receives REFER when acting as a UAS, it will not forward REFER upstream, but will rather just brdige the call internally. You have to use the Transfer application, rather than DIal, to send a REFER.

3

Thanks for the input.

SIP Trunk is nothing but the TRUNK that is configured as a part of “Connectivity->Trunks” using the FreePBX GUI to connect two PABX.

We are currently using PJSIP. When Asterisk “user/Endpoint/IP-Phone” receives a call from Cisco CME user-1 via the SIP trunk and then transfers the call back to Cisco CME USer-2, Asterisk “user/Endpoint/IP-Phone” sends a REFER message to Asterisk server.

Asterisk consumes the REFER and sends a Re-INVITE to Cisco CME to complete the transfer process.

We are trying to find out if Asterisk can send the received REFER to Cisco CME instead of Re-INVITE to complete the transfer process?

4

Neither chan_sip or chan_pjsip really support forwarding the REFER or doing anything in that regard.

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5

Thanks for the confirmation that REFER cannot be forwarded in Asterisk to a different PABX.

6

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