| The Call-ID header field uniquely identifies a particular invitation or all
registrations of a particular client. A single multimedia conference can give rise to
several calls with different Call-IDs, for example, if a user invites a
single individual several times to the same (long-running) conference.
Call-IDs are case-sensitive and are simply compared byte-by-byte.
Call-ID is generated by the combination of a random string and the
softphone's host name or IP address. The combination of the To tag,
From tag, and Call-ID completely defines a peer-to-peer SIP relationship
between two users and is referred to as a dialog. It MUST be the same for
all requests and responses sent by either User Agent in a dialog. It SHOULD be the
same in each registration from a User Agent.
All SIP User Agents must have a means to guarantee that the Call-ID header fields
they produce will not be inadvertently generated by any other User Agent. Note
that when requests are retried after certain failure responses that solicit
an amendment to a request (for example, a challenge for authentication),
these retried requests are not considered new requests, and therefore do
not need new Call-ID header fields.
Use of cryptographically random identifiers in the generation of Call-IDs is
RECOMMENDED. Implementations MAY use the form "localid@host".
For Example:
Call-ID: f81d4fae-7dec-11d0-a765-00a0c91e6bf6@jcp.org
author:
BEA Systems, NIST
version:
1.2 |