[SIPForum-discussion] clarification on contact header

[Andrew Yu]

Hi Abhishek,

Excellent explanation that has brought me to enlightenment on SIP 
contact header! Thank you!

----
Cheers,

Asiatel Singapore Pte Ltd
Andrew Yu

19 Jalan Kilang Barat
#06-01, Acetech Centre
Singapore 159361

Tel: +65 6271 8233
Fax: +65 6274 4266


Abhishek Mishra wrote:
> Hi Andrew, Halit
>  
> I think, the Contact header works in a different was from your perseption.
>  
> From RFC 3261: Contact contains a SIP or SIPS URI that represents a 
> direct route to
>    contact Alice, usually composed of a username at a fully qualified
>    domain name (FQDN)
>  
> Contact header contains a routable address of the party sending 
> contact header. It is used for sending future request. The basic 
> difference between Contact and From header is that URI in the From 
> header is the 'address-of-record' which is registered to the proxy. 
> For example, you have a e-mail account on gmail then you would be 
> allocated an ID of the form yourname at gmail.com 
> <mailto:yourname at gmail.com>. Similarly, the AOR in the From header 
> contains the domain of the Proxy where user is registering.
>  
> Contact header denotes the actual address where other endpoint can 
> directly send the request. So, in case of INVITE, Contact header would 
> contact the IP/FQDN of the originating endpont (not AOR) and its in 
> 200OK, Contact header would contain IP/FQDN of the terminating 
> endpoint. Since 200 OK contains the Contact header therefore ACK is 
> usually sent directly to the terminating endpoing (unless Record-Route 
> is used).
>  
> Contact header is mandatory in INVITE request so that ACK and future 
> request could be sent directly and does not required re-routing.
>  
> Contact header is optional in REGISTER method. When used, registrar 
> uses its value to maintain mapping between user's AOR and actual 
> IP/FQDN where user could be used. If contact header is not sent in the 
> REIGSTER request, registrar would simply return the present bindings.
>  
> Please tell if this does not answers your query.
>  
> Kind Regards,
> -Abhishek
>
> ------------------------------------------------------------------------
> *From:* discussion-bounces at sipforum.org on behalf of Halit Sakca
> *Sent:* Sun 7/29/2007 4:44 PM
> *To:* andrew at asiatel.com.sg; discussion at sipforum.org
> *Subject:* Re: [SIPForum-discussion] clarification on contact header
>
> Hi Andrew,
>  
> As far as I know about the Contact header is, when SBC sends a request 
> to Redirect server it founds the related proxy and turns back to SBC 
> with contact header (f.e in 302) that contains the IP address of this 
> Element.
> It is clear that with contact header info, related element directly 
> send respond to this element (could be element or UA)
>  
> hope its helpful,
> Halit
>
>
>
>
> ------------------------------------------------------------------------
>
> > Date: Sat, 28 Jul 2007 01:43:20 +0800
> > From: andrew at asiatel.com.sg
> > To: discussion at sipforum.org
> > Subject: [SIPForum-discussion] clarification on contact header
> >
> > Dear members,
> >
> > I'm some difficulties on understanding the purpose of the contact
> > header. Please advice what role does it play and how it is different
> > when compared with the FROM header? and why is that contact header is
> > not mandatory in all SIP requests as described in 8.1.1 RFC3261. 
> Thank you.
> >
> > --
> > Cheers,
> >
> > Asiatel Singapore Pte Ltd
> > Andrew Yu
> >
> > 19 Jalan Kilang Barat
> > #06-01, Acetech Centre
> > Singapore 159361
> >
> > Tel: +65 6271 8233
> > Fax: +65 6274 4266
> >
> > _______________________________________________
> > This is the SIP Forum discussion mailing list
> > TO UNSUBSCRIBE, or edit your delivery options, please visit 
> http://sipforum.org/mailman/listinfo/discussion
> > Post to the list at discussion at sipforum.org
>
>
> ------------------------------------------------------------------------
> Live.com'u deneyin - hýzlý ve kiþiselleþtirilmiþ giriþ sayfanýzla 
> istediðiniz her þey tek bir yerde. Live.com'u deneyin: çevrimiçi 
> dünyanýzý bir araya getirin; haberler, spor, hava durumu ve çok daha 
> fazlasý. <http://www.live.com/getstarted>
>
>
> __________ NOD32 2428 (20070730) Information __________
>
> This message was checked by NOD32 antivirus system.
> http://www.eset.com