Hi, I found an error in the SER proxy behavior. I use SER v_2_0_0 from CVS. When SER forks requests because there is a number of registered users for particular AOR, and then receives first final response, it in the standard way cancels all other transaction. Problems is that it is not compliant with RFC3261 because it doesn't add Max-Forwards header to the CANCEL requests. RFC3261 says that Max-Forwards must be present in any SIP method. CANCEL sip:16@212.180.179.42:9360 SIP/2.0 Via: SIP/2.0/UDP 212.180.179.42:7060;branch=z9hG4bKb721.ceeb7aa5.1 From: <sip:pgr@sip.rd.touk.pl &lt;sip%3Apgr(a)sip.rd.touk.pl&gt;&gt;;tag=374595 Call-ID: 0da793c0ff2e7f2fc81b23e4166bbab3(a)212.180.179.42 To: <sip:tzl@sip.rd.touk.pl &lt;sip%3Atzl(a)sip.rd.touk.pl&gt;&gt; CSeq: 479638 CANCEL Route: <sip:sip.rd.touk.pl:7060;lr> User-Agent: Sip EXpress router(2.0.0 (x86_64/linux)) Content-Length: 0 Kind regards, Tomasz Zieleniewski