Subject: [Sip] 181 Call is being forwarded

From: Suganya <[email-masked]>
Date: Tue, 11 Oct 2005 10:52:42 +0530

Hi all,

I need to know if a UA can send 181 response. In RFC 3261, it is given
that this response will be sent by a server and no mention about UAs.

Regards,
B.Suganya

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From: "Bourne Li" <[email-masked]>
Date: Tue, 11 Oct 2005 16:17:35 +0800

Suganya,

RFC 3261 section 6 defines the server, UA and UAS:

Server: A server is a network element that receives requests in
         order to service them and sends back responses to those
         requests.  Examples of servers are proxies, *user agent servers*,
         redirect servers, and registrars.

User Agent (UA): A logical entity that can act as both a user
         agent client and *user agent server*.

User Agent Server (UAS): A user agent server is a logical entity
         that generates a response to a SIP request.  The response
         accepts, rejects, or redirects the request.  This role lasts
         only for the duration of that transaction.  In other words, if
         a piece of software responds to a request, it acts as a UAS for
         the duration of that transaction.  If it generates a request
         later, it assumes the role of a user agent client for the
         processing of that transaction.

So, if UA can provide the call forwarding like service, which can 
generate the 181 response. Then, this UA is taking the UAS role and is 
one type of server.

Regards,
Bourne