A single session
may require a dialog with multiple entities, in which case the Call-ID is used by each
of these entities as a reference.
This is not the same as a dialog. Each of the endpoints within a session will have its
own dialog (identified by a dialog ID, which is explained in Chapter 5). The Call-ID is
different than the dialog ID and is used much differently. Think of the Call-ID as the
Session Initiation Protocol (SIP) 71
identifier for an overall session, while the dialog ID is used by each endpoint to keep
track of communications with another endpoint.
CALL ID: f81d4fae-15apr-11d0-a765-00a0c91e6bf6@raleigh.com
Call-Info This is a way for SIP to provide additional information about either the called
party or the calling party. For example, the calling party may send an ICON as a representation
of themselves (as shown in the example that follows), along with a ???business
card??? (using vcard, for example) to the called party. The header field can be sent either
in a request (in which case information about the calling party is sent) or in a response
to a request (in which case information about the called party is included).
There is potential risk in using this header field. Malicious use of this header field
could result in questionable content being sent to a calling or called party. The standards
recommend use of this header field only if the source can be authenticated and
is a trusted source.
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