Log from FreeSWITCH server:
~~~~~~~~~~~~~~~~~~~~~~~~~~~
2011-07-27 13:23:18.329809 [NOTICE] switch_core_session.c:1310 Close Channel sofia/internal/203@domain.tld [CS_DESTROY]
send 1202 bytes to udp/[CLN.IP.ADD.RES]:42512 at 20:23:24.909861:
   ------------------------------------------------------------------------
   INVITE sip:201@CLN.IP.ADD.RES:42512;ob SIP/2.0
   Via: SIP/2.0/UDP SRV.IP.ADD.RES;rport;branch=z9hG4bK1ZU7rHKHr042e
   Max-Forwards: 69
   From: "FS-203 PL" <sip:FS - 203@domain.tld>;tag=7FpepvmD7B4pK
   To: <sip:201@CLN.IP.ADD.RES:42512;ob>
   Call-ID: 0c8b411e-3331-122f-7dbe-298c3e6a8b40
   CSeq: 15563022 INVITE
   Contact: <sip:mod_sofia@SRV.IP.ADD.RES:5060>
   User-Agent: FreeSWITCH-mod_sofia/1.0.head-git-
   Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, UPDATE, INFO, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
   Supported: timer, precondition, path, replaces
   Allow-Events: talk, hold, presence, dialog, line-seize, call-info, sla, include-session-description, presence.winfo, message-summary, refer
   Privacy: none
   Content-Type: application/sdp
   Content-Disposition: session
   Content-Length: 317
   X-FS-Support: update_display
   P-Asserted-Identity: "FS-203 PL" <sip:FS - 203@domain.tld>

   v=0
   o=FreeSWITCH 1311774005 1311774006 IN IP4 SRV.IP.ADD.RES
   s=FreeSWITCH
   c=IN IP4 SRV.IP.ADD.RES
   t=0 0
   m=audio 24168 RTP/AVP 8 98 99 9 0 3 101 13
   a=rtpmap:98 G7221/32000
   a=fmtp:98 bitrate=48000
   a=rtpmap:99 G7221/16000
   a=fmtp:99 bitrate=32000
   a=rtpmap:101 telephone-event/8000
   a=fmtp:101 0-16
   a=ptime:20
   ------------------------------------------------------------------------
Log from CSS:
~~~~~~~~~~~~~
E/libpjsip( 7230):  13:23:08.058 sip_transport.  Error processing 1202 bytes packet from UDP SRV.IP.ADD.RES:5060 : PJSIP syntax error exception when parsing '' header on line 4 col 29:
E/libpjsip( 7230): INVITE sip:201@CLN.IP.ADD.RES:42512;ob SIP/2.0
E/libpjsip( 7230): Via: SIP/2.0/UDP SRV.IP.ADD.RES;rport;branch=z9hG4bK1ZU7rHKHr042e
E/libpjsip( 7230): Max-Forwards: 69
E/libpjsip( 7230): From: "FS-203 PL" <sip:FS - 203@domain.tld>;tag=7FpepvmD7B4pK
E/libpjsip( 7230): To: <sip:201@CLN.IP.ADD.RES:42512;ob>
E/libpjsip( 7230): Call-ID: 0c8b411e-3331-122f-7dbe-298c3e6a8b40
E/libpjsip( 7230): CSeq: 15563022 INVITE
E/libpjsip( 7230): Contact: <sip:mod_sofia@SRV.IP.ADD.RES:5060>
E/libpjsip( 7230): User-Agent: FreeSWITCH-mod_sofia/1.0.head-git-
E/libpjsip( 7230): Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, UPDATE, INFO, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
E/libpjsip( 7230): Supported: timer, precondition, path, replaces
E/libpjsip( 7230): Allow-Events: talk, hold, presence, dialog, line-seize, call-info, sla, include-session-description, presence.winfo, message-summary, refer
E/libpjsip( 7230): Privacy: none
E/libpjsip( 7230): Content-Type: application/sdp
E/libpjsip( 7230): Content-Disposition: session
E/libpjsip( 7230): Content-Length: 317
E/libpjsip( 7230): X-FS-Support: update_display
E/libpjsip( 7230): P-Asserted-Identity: "FS-203 PL"