[SIPForum-discussion] Allow Header usage

vijay baskar vijaybaskar.sm at gmail.com
Mon Aug 22 03:02:15 UTC 2011


Is the Allow header is mandatory in INVITE and 200 OK, after reading the RFC
it looks like it is mandatory.
But there are some UA still accepting the INVITE/200 OK without Allow

Please clarify.

>From RFC 3261:

 13.2.1 Creating the Initial INVITE
*Since the initial INVITE represents a request outside of a dialog, its
construction follows the procedures of **Section 8.1.1. Additional
processing is required for the specific case of INVITE. An Allow header
field (Section **20.5) SHOULD be present in the INVITE. It indicates what
methods can be invoked within a dialog, on the UA **sending the INVITE, for
the duration of the dialog. For example, a UA capable of receiving INFO
requests within **a dialog [34] SHOULD include an Allow header field listing
the INFO method. ** *
* * The INVITE is Accepted
 *The UAS core generates a 2xx response. This response establishes a dialog,
and therefore follows the **procedures of Section 12.1.1 in addition to
those of Section 8.2.6. A 2xx response to an INVITE SHOULD **contain the
Allow header field and the Supported header field, and MAY contain the
Accept header field. ** *

Thanks in advance.

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