| Description | This table contains a list of the SIP option tags (SIP
extensions) that are either required, supported, or
unsupported by the SIP entity. These option tags are
used in the Require, Proxy-Require, Supported, and
Unsupported header fields.
Example: If a user agent client supports, and requires the
server to support, reliability of provisional responses
(RFC 3262), this table contains a row with the option tag string
'100rel' in sipCommonOptionTag and the OCTET STRING value of
'1010 0000' or '0xA0' in sipCommonOptionTagHeaderField.
If a server does not support the required feature (indicated in
a Require header to a UAS, or in a Proxy-Require to a Proxy
Server), the server returns a 420 Bad Extension listing the
feature in an Unsupported header.
Normally, the list of such features supported by an entity is
static (i.e., will not change over time). |