Hello, I used the below settings to test the keep-alive function within a dialog: modparam("dialog", "default_timeout", 60) modparam("dialog", "ka_timer", 10) modparam("dialog", "ka_interval", 30) and use dlg_set_property("ka-src") or dlg_set_property("ka-dst") to send OPTIONS to caller or callee. A few questions to ask: (1) What's the difference between ka_timer and ka_interval? I read the http://www.kamailio.org/docs/modules/4.2.x/modules/dialog.html , but still can not understand very clearly. I know the ka_interval means OPTIONS will be sent after 30 seconds when dialog started or last keep-alive has been done. but I don't know how ka_timer works. (2) From the packets captured I can see server sent OPTIONS and the client (caller or callee) sent back 200 OK. According to the document, "The dialog timeout is reset each time a sequential request is processed" However, the dialog was still timeout, it seems that the timeout value was not reset. And I make the clients send the OPTIONS and frequently , the dialog never expires now. So the refresh only works on the keep-alive sent by clients not the server here? Thanks :)