[Freeswitch-users] Responding to INVITE with 180 vs 183

[Ben Hood]

Hi all,

I'm wondering what influences Freeswitch's signalling response when it
responds to an INVITE.

In some instances it appears to follow this sequence:

Peer -> INVITE (SDP) -> FS
Peer <- 100 <- FS
Peer <- 183 (SDP) <- FS
Peer <- 200 (SDP) <- FS
Peer -> ACK -> FS

Which leads to a successful bridge between two legs.

But in other instances it appears to follow the sequence:

Peer -> INVITE (SDP) -> FS
Peer <- 100 <- FS
Peer <- 180 (SDP) <- FS
Peer <- 200 (SDP) <- FS (1st attempt)
Peer <- 200 (SDP) <- FS (2nd attempt)
....
Peer <- 200 (SDP) <- FS (nth attempt)
....timeout

I'm not 100% sure whether the remote peer (itself a SIP trunk) doesn't
like the 100/180/200 sequence (as opposed to 100/183/200), so I need
to find that out for myself.

But I am wondering what factors influence Freeswitch's decision of
what sequence signals to send in response to an INVITE.

Any pointers appreciated,

Ben