Subject: RE: [P2Prg] SIP

From: "Ayyasamy, Senthilkumar \(UMKC-Student\)" <[email-masked]>
Date: Mon, 8 Dec 2003 10:59:38 -0600

> SIP extensions are usually pretty harmeless ( they dont change the 
> protocol operation - they just add new messages types and headers and 
> proxy servers can tell end points if they do support the extensions).  
> I dont see the a-priori hestitation needing to add extensions if we 
> find that is necessary. There are many stacks around for SIP which are 
> able to handle extensions (for example consider JAIN-SIP if you will 
> excuse the shameless self promotion).  I dont see SIP extensions as a 
> show stopper. Extensions are a part of the protocol itself so in some 
> sense "Extension" is an oxymoron of sorts. SIP extensions for all sorts 
> of things exist at this point. 
 
extensions exists and is useful; but, your observations that extenions are 
harmless is not true. From a implementor perspective, extensions are mere 
addition of a block of code to the existing system. But, extensions has 
price in terms of network management. It makes the task of parameter
tweaking/setting difficult. This makes network administrator task complex 
(given, a large percentage of enterprise/network system failures are 
attributed to manual misconfiguration errors.) Also, I think there is a 
protocol design requirement in maintaining modularity.

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From: "M. Ranganathan" <[email-masked]>
Date: Mon, 08 Dec 2003 13:01:58 -0500

Ayyasamy, Senthilkumar (UMKC-Student) wrote:

>harmless is not true. 

Well, I guess I should clarify -- extensions do not require basic 
protcol changes they only require  message and header types that can be 
understood by implementors of the extension . That is what I had meant 
by harmless. I should perhaps have said "unobtrusive".  If a sip element 
(proxy or UA) does not implement an extension,  it can indicate that the 
extension is not supported. All of this is nicely architected. That is 
all that I had  meant to imply.

>From a implementor perspective, extensions are mere 
>price in terms of network management. 
>

That would depend upon the extension.  I should like to understand a few 
things before proceeding:

1. What are the requirements of a P2P system, ( Or to be even more 
direct, I dont understand fully what we are talking about when we say 
P2P here and I should like to nail that down. Perhaps I could read a 
document if  this has already been defined somewhere.  )

2. A thought experiment based on the above to tease out how SIP can be 
used to implement 1 (with or without extensions). 

>It makes the task of parameter

-- 
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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