It is only there
for display on end devices.
82 Chapter 3
This information is also easily spoofed and therefore should never be trusted. The information
can be populated by the originating requestor, or it can be modified by proxies
along the call path. This header is analogous with the TO header in an e-mail.
The first part of this header contains the display name to appear in the receiving
device??™s display. The portion contained within ???<>??? is the actual address of the recipient.
The ???tag??? is used as part of the dialog ID and is used by the receiving device to correlate
this request with other requests/responses.
TO: Travis Russell
;tag=1df789jkf
Unsupported Similar to the SUPPORTED header, this header is used to identify extensions
that are not supported by an entity.
UNSUPPORTED: 100 rel
User-Agent This header is like the SERVER header, providing the software version
of the SIP user agent processing a request. The two headers can be used together to
identify the software versions on both devices. This information can then be used by
operators for profiling and other applications.
For example, in today??™s networks cell phones send an International Mobile Equipment
Identifier (IMEI) identifying the make and model of the device, and configuration information
about the device. Operators that collect this information can then use the data
to track the activities of the subscriber by reference to their phone make and model.
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