531 INVITE sip:<To> SIP/2.0
Via: SIP/2.0/UDP <From-Address>:<Local-Port>;branch=z9hG4bK00004351
From: 4351 <sip:<From>>;tag=4351
To: Receiver <sip:<To>>
Call-ID: <Call-ID>@<From-Address>
CSeq: <CSeq> INVITE
Contact: 4351 <sip:<From>>
Expires: 1200
Max-Forwards: 70
Content-Type: application/sdp
Content-Length: <Content-Length>

v=0
o=4351 4351 4351 IN IP4 <From-Address>
s=Session SDP
c=IN IP4 <From-IP>
t=0 0
m=audio 9876 RTP/AVP 0
a=rtpmap:0 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa/8000
252 <Teardown-Method> sip:<To> SIP/2.0
Via: SIP/2.0/UDP <From-Address>:<Local-Port>;branch=z9hG4bK00004351
From: 4351 <sip:<From>>;tag=4351
To: Receiver <sip:<To>>
Call-ID: <Call-ID>@<From-Address>
CSeq: <CSeq> <Teardown-Method>
Content-Length: 0