SIP protocol always seems to be complicated than I thought/expected.
one example : Sip header Privacy
This header is like this:
Privacy: value
the value could be:
header, session, user, none, and critical ( defined in RFC 3323)
id ( defined in RFC 3325 )
history ( defined RFC 4244 )
The basic idea seems to be simple, based on those value, we should obscured some target information ( header or SDP) while processing sip messages.
Here are some explanations:
Privacy Type Description Reference ------------- ---------------------------------- ---------- user Request that privacy services [RFC3323] provide a user-level privacy function header Request that privacy services modify [RFC3323] headers that cannot be set arbitrarily by the user (Contact/Via). session Request that privacy services provide [RFC3323] privacy for session media none Privacy services must not perform any [RFC3323] privacy function critical Privacy service must perform the [RFC3323] specified services or fail the request id Privacy requested for Third-Party [RFC3325] Asserted Identity
history Privacy requested for [RFC4244] History-Info header(s)
for id: RFC 3325 defines the P-Asserted-Identity header and a priv-value "id", which is used to request privacy for only the P-Asserted-Identity header, but it does not specify how other priv- values may impact the privacy handling of the P-Asserted-Identity header.
If you want to really understand what those means, you should take a look at: https://tools.ietf.org/html/rfc5379
In asterisk, you can get this header using SIP_HEADER ( only from invite method )
exten => _X.,n,Set(Privacy=${SIP_HEADER(Privacy)})
