[Bug]: Linphone not sending ACK to correct port

[brianomchugh]

Context

I am using linphone SDK in an iOS app. I am trying to make an outgoing call with TLS and SRTP using an outbound proxy.

• If the outbound proxy is set to 5060, the call fails because linphone sends ACK packets to port 5061 (for some unknown reason)
  -If I change outbound proxy to 5080, everything works as expected and ACK packets are sent to 5080-- and the call completes.

Here is an example of a "BAD" call, where linphone tries to send the ACK to port 5061 (when port is 5060): "Trying to connect to [TLS://::ffff:1.2.3.144:5061]"
port_5060_bad.txt

Here is a "GOOD" call, where the port is set to 5080 and the ACK to sent just fine.
port_5080_good.txt

Is 5061 just hardcoded in when the port is set to 5060?

General information

• Device: iPhone 13 mini
• OS: iOS 18.1.1
• Version of the SDK: 5.3.96

Expected behaviour

When the outbound proxy is listening on port 5060, I expect linphone/softphone to sent ACK to port 5060. Instead it is trying to send to 5061.
If I change the outbound proxy to port 5080, linphone sends the ACK to 5080 as expected. The weird behavior above only happens when 5060 is specified.

To Reproduce

1. Register to SIP server with TLS, and an outbound proxy with port 5060
2. Make an outbound call with SRTP enabled.
3. Call eventually fails because ACK is sent from linphone to outbound proxy at port 5061 instead of 5060:
   2024-11-27 15:09:23:037 belle-sip-message- Trying to connect to [TLS://::ffff:1.2.3.4:5061]

Additional context

No response

SDK logs URL

No response