Re: [cuss] "isdn-uui" versus "isdn-network"

[Andrew Allen <[e-mail]>]

Vijay

I don't think we are talking about applying this to the nth degree I think we are simply recognizing that in this case there are deployed systems out there that we ought to attempt to interoperate with if that can relatively easily be achieved..

I am not sure it complicates the parser greatly to have two possible tokens (A or B) as the value of a parameter and then in the call processing logic have an if A or B statement.

Andrew

-----Original Message-----
From: Vijay K. Gurbani [mailto:[e-mail]] 
Sent: Thursday, November 21, 2013 12:25 PM
To: Andrew Allen; [e-mail]; [e-mail]
Subject: Re: [cuss] "isdn-uui" versus "isdn-network"

[As individual, of course.]

On 11/21/2013 09:31 AM, Andrew Allen wrote:
>
> I have some sympathy for Bruno's position. He is merely asking to 
> align with the principle of "Be strict in what you send, but generous 
> in what you receive".

I must say that I disagree.  I suspect that Postel's Law was not designed to allow multiple tokens to represent the same semantic.
Plus, implementing Postel's Law to the n-th degree leads to brittle parsers and easy to attack systems.

There is a school of thought that parsers for large and complex grammars like SIP should be designed using a language-theoretic approach since these grammars produce essentially a complex language.  Such complex grammars are PSPACE-complete, making it daunting to come up with a bullet-proof parser if we keep on adding multiple ways to represent similar concepts.

But regardless, I don't mean to hammer on this.  If folks feel that we need to grandfather "isdn-network", that is fine with me.

Thanks,

- vijay
--
Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane, Rm. 9C-533, Naperville, Illinois 60563 (USA)
Email: vkg@{bell-labs.com,acm.org} / [e-mail]
Web: http://ect.bell-labs.com/who/vkg/  | Calendar: http://goo.gl/x3Ogq
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