How to add transport=UDP to Contact/From/To headers


I need to add “trasport=UDP” to the Contact , From and To headers.
I am using chan_sip driver. How can I configure this ?


You should fix the peer instead. transport=UDP is the default and is not needed.

so, I should make the remote side accept the headers without “transport=UDP” ?
but it is an SBC of the ISP; I can’t change the behaviour there.

There is no configuration for this. You’d have to modify the code if you really need it.