Hello, The BYE, generated by Kamailio in case of dialog timeout, is malformed: BYE <sip:anonymous@192.168.225.2:50601> sip:anonymous@192.168.225.2:50601 SIP/2.0 Via: SIP/2.0/UDP 172.16.60.113;branch=z9hG4bK77b6.941684b6.0 Via: SIP/2.0/UDP 10.1.1.10;branch=z9hG4bKsr-JfymiMenCtp4urS5CXSnCHJnCXJZiHvRCHYJb6ggNPN9NVDL3 -TWhdW0UvOfN1KPTReRiHy1CHmcs6mZiHS* To: <sip:anonymous;cpc=ordinary@192.168.225.2;tag=01e3a8c0-c1c2-t-1> sip:anonymous;cpc=ordinary@192.168.225.2;tag=01e3a8c0-c1c2-t-1 From: <sip:1255010006@192.168.225.2:5060;user=phone;tag=813142547-1366730270587> sip:1255010006@192.168.225.2:5060;user=phone;tag=813142547-1366730270587 CSeq: 465332801 BYE Call-ID: <mailto:1aebb42c-01e3a8c0-000007c2@192.168.225.2> 1aebb42c-01e3a8c0-000007c2(a)192.168.225.2 Content-Length: 0 User-Agent: kamailio (3.3.2 (x86_64/linux)) Max-Forwards: 69 The bad syntax is located in the "To" header field. According to the RFC 3261 section 25.1, the grammar of the To header field is as follow: To = ( "To" / "t" ) HCOLON ( name-addr / addr-spec ) *( SEMI to-param ) name-addr = [ display-name ] LAQUOT addr-spec RAQUOT addr-spec = SIP-URI / SIPS-URI / absoluteURI to-param = tag-param / generic-param The RFC 3261 section 20.10 explains that: Even if the "display-name" is empty, the "name-addr" form MUST be used if the "addr-spec" contains a comma, semicolon, or question mark. There may or may not be LWS between the display-name and the "<". As the "addr-spec" <sip:anonymous;cpc=ordinary@192.168.225.2> sip:anonymous;cpc=ordinary@192.168.225.2 contains a semicolon, it means that the "name-addr" form must be used. The "To" header field should be encoded as follow: To: < <sip:anonymous;cpc=ordinary@192.168.225.2> sip:anonymous;cpc=ordinary@192.168.225.2>;tag=01e3a8c0-c1c2-t-1 BR, Julia