[SIPForum-discussion] Difference

Samir Patni samir_patni at persistent.co.in
Sat May 23 12:05:23 UTC 2009

HI John,

Please find below what I can put together for OPTIONS and INVITE.

Functionality difference:

OPTIONS generally used for
1) query another UA or a proxy server as to its capabilities
2) ping support
3) used as a traceroute functionality to check for capabilities of
individual nodes.
4) used to determine basic state of a UAS, which can be an indication of
   whether the UAS will accept an INVITE request.

INVITE generally used for.
1) Initiate a session

2) Modify session parameters (ex changing addresses or ports,
   adding a media stream, deleting a media stream, and so on)

Processing difference.

1)    State machine for INVITE transaction is governed by invite client transaction and those of Options request is done by non-INVITE client transaction.

2)    Offer and answers can appear in INVITE requests , responses, and ACK. This can not be done for OPTIONS method.

3)    OPTIONS request received within a dialog generates a 200(OK) response that is identical to one constructed outside a dialog and does not have any impact on the dialog state.

4)    Allow, Accept, Accept-Encoding, Accept-Language, and Supported header fields SHOULD be present in a 200 (OK) response to an OPTIONS

Request, this is not needed for 200  (OK) response to an INVITE request.

5)    For Options Contact header fields MAY be present in a 200 (OK) response and have the same semantics as in a 3xx response.  That is, they may list a set of alternative names and methods of reaching the user.

However Contact header field present in the 200 (OK) response for an invite request contains a URI at which called party can be directly reached at his SIP phone.

6)    While a forked INVITE can  result in multiple 200 (OK) responses being returned, a forked OPTIONS will only result in a single 200 (OK) response, since it is treated by proxies using the non-INVITE handling.

7)    200 ok for an OPTIONS request is not acknowledged however 200 ok for an INVITE transaction is acknowledged.

Thanks and Regards,
Samir Patni

From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of sipsipsip sip
Sent: Thursday, May 21, 2009 11:20 AM
To: discussion at sipforum.org
Subject: [SIPForum-discussion] Difference

Hi all,

What is the difference between Option exchange and Invite


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