[Serusers] SER, ATA-186 & Cisco AS5300

[Linus Surguy]

Thanks all (especially Alex), I know now why, and it does seem that the
'NAT' device - in this case a Draytek Vigor ADSL router is rewriteing the
SIP packet incorrectly. However, if I wanted to be tolerant of this, is
there a way to instruct SER to re-evaluate the 'content-length' and rewrite
it correctly?

(ngrep dumps below)

Internal to NAT:

U 10.0.0.212:5060 -> 213.166.5.135:5060
  INVITE sip:448000664901 at gk.magrathea.net;user=phone SIP/2.0..Via: SIP/
  2.0/UDP 10.0.0.212:5060..From: sip:linus at gk.magrathea.net;tag=30449371
  62..To: <sip:448000664901 at gk.magrathea.net;user=phone>..Call-ID: 10341
  00418 at 10.0.0.212..CSeq: 1 INVITE..Contact: <sip:linus at 213.162.109.118:
  5060;transport=udp>..User-Agent: Cisco ATA 186  v2.16.1 ata18x (030709
  a)..Expires: 300..Content-Length: 249..Content-Type: application/sdp..
  ..v=0..o=linus 14148 14148 IN IP4 10.0.0.212..s=ATA186 Call..c=IN IP4
  213.162.109.118..t=0 0..m=audio 16384 RTP/AVP 4 8 0 101..a=rtpmap:4 G7
  23/8000/1..a=rtpmap:8 PCMA/8000/1..a=rtpmap:0 PCMU/8000/1..a=rtpmap:10
  1 telephone-event/8000..a=fmtp:101 0-15..

But what actually arrives is:

U 213.162.109.118:5060 -> 213.166.5.135:5060
  INVITE sip:448000664901 at gk.magrathea.net;user=phone SIP/2.0..Via:
SIP/2.0/UDP
  213.162.109.118:5060..From: sip:linus at gk.magrathea.net;tag=3044937162..To:
<si
  p:448000664901 at gk.magrathea.net;user=phone>..Call-ID:
1034100418 at 213.162.109.1
  18..CSeq: 1 INVITE..Contact:
<sip:linus at 213.162.109.118:5060;transport=udp>..U
  ser-Agent: Cisco ATA 186  v2.16.1 ata18x (030709a)..Expires:
300..Content-Leng
  th: 259..Content-Type: application/sdp....v=0..o=linus 14148 14148 IN IP4
213.
  162.109.118..s=ATA186 Call..c=IN IP4 213.162.109.118..t=0 0..m=audio 16384
RTP
  /AVP 4 8 0 101..a=rtpmap:4 G723/8000/1..a=rtpmap:8 PCMA/8000/1..a=rtpmap:0
PCM
  U/8000/1..a=rtpmap:101 telephone-event/8000..a=fmtp:101 0-15..