Subject: RE: [P2Prg] SIP

From: "Ayyasamy, Senthilkumar \(UMKC-Student\)" <[email-masked]>
Date: Sun, 7 Dec 2003 14:55:50 -0600

> Ah that is the question I should like to ponder! For 
>example perhaps one needs an extension for resource 
>discovery (?). 
 
The basic requirement for resource discovery is a
rendezvous mechanism (provided by SIP) and a proper 
attribute based naming system to describe the service
(provided by URI.) The search mechanism is facilitated
by globablly routable URI's of user agents. If you 
want to do a complex scenario ( e.g. finding a empty 
parking lot for your car through PDA -- which involves 
web cam input(parking lot), encoding etc...,) you have 
to use SIP API interface to write your application. 
I doubt a signaling protocol- SIP -requires an extension 
to cater your specific need. The bottomline is that the 
signaling protocol should be decoupled from the application
specific requirements.
 
On the other hand, to use SIP as a generic signaling protocol,
we should work on open problems which PF states in his NUTSS 
model ( traversal of TCP through NAT, applications, more 
mobility features etc..) 
 
But, if you want SIP to do content routing for supporting
resource discovery, it requires modifications. But, it
doesn't answer all our needs.

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From: "M. Ranganathan" <[email-masked]>
Date: Sun, 07 Dec 2003 18:30:04 -0500

I guess one needs to have a clear definition of what constitutes a Peer 
to Peer system in mind and which way one wishes to architect such a 
system. I am going to argue using jxta as an example :  I have long 
wondered if  it makes more sense to build SIP on top of a P2P system 
such as jxta for example or vice versa. After all SIP was intended to be 
a protocol to establish a peer to peer connection between to 
communicating endpoints and isnt that exactly what we want to do here. 
But then, I took a closer look at jxta and I discovered that there was 
more to the problem than that and what I see there is a lot of higher 
level mechanisms based on XML documents such as advertisements, peers 
and peer groups. These can be SIP message content.. SIP routes messages 
based on route headers present in requests. These route headers are put 
in place by a User Agent or Proxy Server discovering the route during 
session set up.  The question of how to discover the route usually 
involves looking up a location service, DNS service etc. This is loosely 
defined. If headers or messge content can be defined to describe a 
resource to which the session set up message (ie. INIVITE) can be 
directed then perhaps one can do relevant queries to discover how to 
route messages.  I argue that without too much of a stretch one can 
discover routes using yet to be defined mechanisms that are pertinent to 
P2P systems. Does this sound sufficiently vauge. OK I dont have the 
details worked out in my head - its just a thought experiment.

Ayyasamy, Senthilkumar (UMKC-Student) wrote:

>to cater your specific need. 
>
 I was just experimenting with the thought of architecting a higher 
level P2P protocol on top of SIP.

>The bottomline is that the 

I am not sure I can agree here. SIP may need some extensions (ie. new 
headers/message types) to be applicable to building a higher level P2P 
protocol.

>resource discovery, it requires modifications.
>

Not necessarily the protocol only the mechanism that is used to discover 
routes (which is actually outside the protocol).

> But, it

-- 
M. Ranganathan 

Advanced Networking Technologies Divsion,
National Institute of Standards and Technology (NIST),
100 Bureau Drive, Stop 8920, Gaithersburg, MD 20899. 

tel:301 975 3664 , fax:301 590 0932 , http://www.antd.nist.gov/~mranga

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