It can also be sent as
part of a response to indicate the same for the recipient of an INVITE. For example, a
response of 405 Method Not Allowed would contain the ALLOW header to indicate what
methods are supported by the responding endpoint.
ALLOW: INVITE, CANCEL, BYE, ACK, OPTIONS
Authorization When a device sends a request such as an INVITE or REGISTER, it can
include the AUTHORIZATION header containing its credentials as part of the authorization
process. The credentials are typically stored within the device on a Universal
Integrated Circuit Card (UICC).
If the AUTHORIZATION header is not present, then the receiving endpoint within
the IMS will send a 401 Not Authorized response. This is called the ???challenge???
and is sent by registrars and endpoints alike. The response will contain the WWWAUTHENTICATE
header describing the authentication scheme that is expected from
the device. Registration is explained in detail in Chapter 5.
Authorization: Digest username="travis",
realm="raleigh.com",
nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093",
uri="sip:travis@raleigh.com",
qop=auth,
nc=00000001,
cnonce="0a4f113b",
response="6629fae49393a05397450978507c4ef1",
opaque="5ccc069c403ebaf9f0171e9517f40e41"
Call-ID The Call-ID provides a unique identifier for all sessions, so proxies (such as
Call Session Control Functions) can correlate requests with responses.
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