How to send instant message via SIP

Question

I have a windows desktop application, made by my mobile network provider, that does all kind of things with SIP: call, send message, etc. Screenshot of how does this app successfully send MESSAGE (the last 4 lines):

MESSAGE request, from desktop application, is sent as (4th line from behind) :

MESSAGE sip:FROM@DOMAIN SIP/2.0
Via: SIP/2.0/UDP LOCALIP:2112;branch=z9hG4bK-d8754z-905183245f478c76-1---d8754z-;rport
Max-Forwards: 70
To: "TO"<sip:TO@DOMAIN>
From: "FROM"<sip:USERNAME@DOMAIN>;tag=63088d09
Call-ID: NGVhMDJhYzQwNmExOTQyNThmNjc5OGNmOTViNDUyYWM.
CSeq: 2 MESSAGE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE, SUBSCRIBE, INFO
Content-Type: text/plain
Content-Length: 4

test

and successfull response for that is:

SIP/2.0 407 Proxy Authentication Required
Via: SIP/2.0/UDP LOCALIP:2112;received=EXTERNALIP;branch=z9hG4bK-d8754z-905183245f478c76-1---d8754z-;rport=2112
To: "TO"<sip:TO@DOMAIN>;tag=c005f0e30133ec730add76fc91f4bea
From: "FROM"<sip:USERNAME@DOMAIN>;tag=63088d09
Call-ID: NGVhMDJhYzQwNmExOTQyNThmNjc5OGNmOTViNDUyYWM.
CSeq: 2 MESSAGE
Content-Length: 0
Proxy-Authenticate: Digest nonce="3F178051B97E1F52000123000A3C53D4B",realm="DOMAIN",algorithm=MD5,qop="auth"

Then I try to send identical (and n-variations) request from PHP, but I always receive SIP/2.0 403 Forbidden instead of SIP/2.0 407 Proxy Authentication Required:

SIP/2.0 403 Forbidden
Via: SIP/2.0/UDP LOCALIP;received=EXTERNALIP
To: "TO"<sip:TO@DOMAIN>;tag=aprqngfrt-f7ccjj0000020
From: "FROM"<sip:USERNAME@DOMAIN>;tag=8f7be81d
Call-ID: 526576901edcc@localhost
CSeq: 1 MESSAGE
Reason: Q.850;cause=55;text="Call Terminated"
Content-Length: 0

The funny part is, that if I send REGISTER request it works, and I successfully receive SIP/2.0 401 Unauthorized header with WWW-Authenticate. I recalculate authorization, and resend it. Then I receive SIP/2.0 200 OK. Which is how it should work with MESSAGE.

What could be wrong? What did I miss? Does MESSAGE request need some other request before that (I have already tried REGISTER before)?
I have read RFC 3428 up and down, tried all the examples possible, but without success.

Answer 1

As I've told you in comments, I'm no SIP expert but a friend of mine is. I've asked him about your case and this is what he told me:

SIP protocol is a dialogue protocol meaning that each communication is a dialogue with a unique dialogue ID (something like session ID in HTTP). The difference between SIP and HTTP is that session ID is used among different TPC/IP connections (HTTP requests) while dialogue ID is used within the same TPC/IP connection but among different messages.

It seems to me that what you are trying to do here is somewhat like session hijacking in HTTP. While it is possible to hijack a session ID in HTTP and sent it from another client, the same is not for SIP. According to my friend SIP servers have an internal memory of which dialogue ID belongs to which connection and you can not slip your messages into someone else's dialogue just by knowing their dialogue ID.

Your question does not say if this is what actually you are trying to do, but in case it is, then I must say you can't. The fact that you can send the REGISTER command shows that your communication to SIP server is made. All you need to do is to initiate your own dialogue and take it from there.

Answer 2

If you look into received 403 response, you'll notice a Reason header. The Q.850 string at the beginning indicates that this would be a cause code defined by ITU-T Recomendation.

Specifically, provided cause code 55 is related to ISDN and literary means "Incoming calls barred within Closed User Group" (you can check it in RFC 3398) and, usually, means that, within a group of members, call reception is restricted.

On the other hand, cause 55 also denotes a problem within the request, specially in relation to a user (sender or receiver). Following diagram shows a normal MESSAGE exchange between SIP users:

      A             Server             B
      |    REGISTER    |               |
      |--------------->|               |
      |     200 OK     |               |
      |<---------------|               |
      |                |    REGISTER   |
      |                |<--------------|          
      |                |     200 OK    |
      |                |-------------->|
      |    MESSAGE     |               |
      |--------------->|    MESSAGE    |
      |                |-------------->|
      |                |     200 OK    |
      |                |<--------------|
      |     200 OK     |               |
      |<---------------|               |

Actually, been strict, REGISTER from user A is not needed but most systems (like IMS) uses it as an authentication mechanism. Then, in REGISTER request, special headers are:

Contact: <sip:USER_NAME@LOCAL_IP:LOCAL_PORT>
Expires: REGISTRATION_DURATION

Keep in mind that, 200 OK answers to a REGISTER, can contain an Expires: header or an expires parameter inside Contact: header that indicates accepted expiration time. For example:

SIP/2.0 200 OK
...
Contact: <sip:USER_NAME@LOCAL_IP:LOCAL_PORT>; expires=60 
...

In this situation, you should re-REGISTER before this expiration time (60 seconds in the example).

Keeping in mind that you're trying to send an SMS to a mobile phone, reception point is directly managed by your network provider's MGCF, so this leaves sender's registration or MESSAGE request.

About your original MESSAGE proposal, request URI (message's first line), should be:

 MESSAGE sip:TO@DOMAIN SIP/2.0

Because it refers to MESSAGE reception entity.

Hope this helps.