RPORT: in response, must have the port

<--- Received SIP request (1029 bytes) from UDP:132.177.252.173:51422 --->
REGISTER sip:digium-test-01.digium.sipit.net SIP/2.0
Via: SIP/2.0/UDP 132.177.252.173:51422;branch=z9hG4bK-524287-1---6fcb1703ddba8d61
Max-Forwards: 70
Route: <sip:digium-test-01.digium.sipit.net;transport=udp;lr>
Contact: <sip:1010@132.177.252.173>;expires=119;+sip.instance="<urn::uuid:0f973ccb0a80ec2c72af4b26fcef34254d823212>";reg-id=1
To: "1010"<sip:1010@digium-test-01.digium.sipit.net>
From: "1010"<sip:1010@digium-test-01.digium.sipit.net>;tag=b1d5a640
Call-ID: 0ZWM3NzgwZTcxNjMyYjExNTcxZThjZGQ4M2VjYjRiOTg
CSeq: 8 REGISTER
Expires: 120
Allow: OPTIONS, INVITE, ACK, CANCEL, BYE, REFER, INFO, NOTIFY, SUBSCRIBE, MESSAGE
Supported: outbound, path, gruu
User-Agent: CPCAPI2-based UA
Authorization: Digest username="1010",realm="asterisk",nonce="1412251551/1e96c89599b3e8247d0aa76aaef95902",uri="sip:digium-test-01.digium.sipit.net",response="6062ff44efc6454d98b2d4b8888ad665",cnonce="f4c8c5339dd7a5d7601b49578fe83eca",nc=00000001,qop=auth,algorithm=md5,opaque="76de0e1c09a2fe7d"
xxx: yyy
Content-Length: 0


<--- Transmitting SIP response (557 bytes) to UDP:132.177.252.173:51422 --->
SIP/2.0 200 OK
Via: SIP/2.0/UDP 132.177.252.173:51422;rport;received=132.177.252.173;branch=z9hG4bK-524287-1---6fcb1703ddba8d61
Call-ID: 0ZWM3NzgwZTcxNjMyYjExNTcxZThjZGQ4M2VjYjRiOTg
From: "1010" <sip:1010@digium-test-01.digium.sipit.net>;tag=b1d5a640
To: "1010" <sip:1010@digium-test-01.digium.sipit.net>;tag=z9hG4bK-524287-1---6fcb1703ddba8d61
CSeq: 8 REGISTER
Date: Thu, 02 Oct 2014 12:05:51 GMT
Contact: <sip:1010@132.177.252.173>;expires=118
Supported: path
Server: Asterisk PBX SVN-group-asterisk-13-sipit-URL:-r424293M
Content-Length:  0





   When a server compliant to this specification (which can be a proxy
   or UAS) receives a request, it examines the topmost Via header field
   value.  If this Via header field value contains an "rport" parameter
   with no value, it MUST set the value of the parameter to the source
   port of the request.  This is analogous to the way in which a server
   will insert the "received" parameter into the topmost Via header
   field value.  In fact, the server MUST insert a "received" parameter
   containing the source IP address that the request came from, even if
   it is identical to the value of the "sent-by" component.  Note that
   this processing takes place independent of the transport protocol.