root@beat:/etc/asterisk# ngrep -W byline -d lo
interface: lo (127.0.0.0/255.0.0.0)

#
U 192.168.50.101:5060 -> 192.168.50.101:5060
INVITE sip:enum-test@sip.nemox.net:0 SIP/2.0.
Via: SIP/2.0/UDP 192.168.50.101:5060;branch=z9hG4bK60211d77;rport.
Max-Forwards: 70.
From: "User" <sip:2000@192.168.50.101:0>;tag=as5c568e81.
To: <sip:enum-test@sip.nemox.net:0>.
Contact: <sip:2000@192.168.50.101:0>.
Call-ID: 65a558df359bdf2f6f39cd4439f780a6@192.168.50.101.
CSeq: 102 INVITE.
User-Agent: Asterisk PBX 1.6.0.3-rc1.
Date: Thu, 11 Dec 2008 12:45:15 GMT.
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY.
Supported: replaces, timer.
Content-Type: application/sdp.
Content-Length: 316.
.
v=0.
o=root 528546667 528546667 IN IP4 192.168.50.101.
s=Asterisk PBX 1.6.0.3-rc1.
c=IN IP4 192.168.50.101.
t=0 0.
m=audio 15904 RTP/AVP 0 3 8 101.
a=rtpmap:0 PCMU/8000.
a=rtpmap:3 GSM/8000.
a=rtpmap:8 PCMA/8000.
a=rtpmap:101 telephone-event/8000.
a=fmtp:101 0-16.
a=silenceSupp:off - - - -.
a=ptime:20.
a=sendrecv.

#
U 192.168.50.101:5060 -> 192.168.50.101:5060
SIP/2.0 482 Loop Detected.
Via: SIP/2.0/UDP 192.168.50.101:5060;branch=z9hG4bK60211d77;received=192.168.50.101;rport=5060.
From: "User" <sip:2000@192.168.50.101:0>;tag=as5c568e81.
To: <sip:enum-test@sip.nemox.net:0>;tag=as5c568e81.
Call-ID: 65a558df359bdf2f6f39cd4439f780a6@192.168.50.101.
CSeq: 102 INVITE.
User-Agent: Asterisk PBX 1.6.0.3-rc1.
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY.
Supported: replaces, timer.
Content-Length: 0.
X-Asterisk-HangupCause: User busy.
X-Asterisk-HangupCauseCode: 17.
.

#
U 192.168.50.101:5060 -> 192.168.50.101:5060
ACK sip:enum-test@sip.nemox.net:0 SIP/2.0.
Via: SIP/2.0/UDP 192.168.50.101:5060;branch=z9hG4bK60211d77;rport.
Max-Forwards: 70.
From: "User" <sip:2000@192.168.50.101:0>;tag=as5c568e81.
To: <sip:enum-test@sip.nemox.net:0>;tag=as5c568e81.
Contact: <sip:2000@192.168.50.101:0>.
Call-ID: 65a558df359bdf2f6f39cd4439f780a6@192.168.50.101.
CSeq: 102 ACK.
User-Agent: Asterisk PBX 1.6.0.3-rc1.
Content-Length: 0.
.