Subject: [SIP] Comparison of Media Authorization drafts

From: Burcak Beser <[email-masked]>
Date: Mon, 18 Dec 2000 18:17:12 -0800

As an author of SIP Extensions for Media Authorization”  I tried to
compare the draft with the draft “Session setup with media
authorization”.

All comments/suggestions/questions are welcome.

Burcak Beser
Pacific Broadband Communications

-------------

Draft “SIP Extensions for Media Authorization” defines the
Media-Authorization-Token as a hex blob. The draft does not force any
meaning to the hex blob; the examples in the draft give two known uses
for this field.

As described in the draft “Session setup with media authorization”, if
there are to be many fields:

* All of these fields have to be send to the Edge Router.

* The End Host (UAS) does not necessarily know what is the meaning of
any of the proposed fields.

As a result, we can say that there is no need for SIP defined
sub-encoding(s) for the Media-Authorization-Token field. The token can
be formatted and populated as PDP and PEP agrees.

Since it is impossible to predict from today what kind of information
has to exchange will occur between PDP and PEP (for example one possible
way is that the information will contain the Credit Card number to be
billed) the best way is to threat the information as a byte blob.

The draft  “SIP Extensions for Media Authorization” does not state in
any place (as incorrectly stated in draft “Session setup with media
authorization”):

* The end-host is connected to a known point in the network.

*  Same policy server makes decisions related to both service
authorization and resource utilization.

* Session managers and policy servers know each other’s existence and
have a pre-defined trust relationship.

 The draft “SIP Extensions for Media Authorization” is written such that
only the SIP protocol use is focused; the draft clearly defines how each
SIP end will behave and how the information will be passed between them
using SIP protocol. But it does not impose any other restrictions on any
other entities or protocols. It is possible to device many other methods
and elements that the creative authorization methods will take place and
the draft only covers for all these protocols the question how to
deliver the Media-Authorization information to the UAS in a generic way.

 As a summary it can be said that the draft “SIP Extensions for Media
Authorization” includes all the features that draft “Session setup with
media authorization” proposes and enables more features/modes.

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