Subject: Re: [Ieprep] updated requirements documents (telephony)

From: Ken Carlberg <[email-masked]>
Date: Sat, 14 Dec 2002 14:40:19 +0000

> > [MAP] The above sentence about "alternate path routing at the 
> > application
> > layer" was copied verbatim from the draft (which has your name on it). 
> > I was
> > simply putting it under a heading that said "Call application layer". 
> > What
> > did it mean in the original draft?
>
> Out of context, it wasn't clear to me what was meant.  Those particular
> words (like most of them in either draft) were Ken's, so I'll let Ken
> explain (lest I botch the job and muddy the waters more thoroughly than
> usual :-).

I'm sorry, but its hard to dig out what the actual question is.  if
there is still an open question, could it be rephrased?  otherwise, I'll
assume that the thread is closed and stick to my previous comments.

regards,

-ken

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From: [email-masked]
Date: Tue, 17 Dec 2002 09:28:44 EST

In a message dated 12/14/2002 9:42:08 AM Eastern Standard Time, 
[email-masked] writes:

[KC] I'm sorry, but its hard to dig out what the actual question is.  if
there is still an open question, could it be rephrased?  otherwise, I'll
assume that the thread is closed and stick to my previous comments

[MAP] The original comment was mostly an editorial one as follows:

---------------------------------------------------------
I suggest this section on Alternate Paths be split into two separate 
sub-parts to address the two "layers" within IP and relate each to what the 
PSTN did (or couldn't do) as follows: 

1) Alternate paths 

Experience with GETS over the PSTN has shown the utility of alternate paths 
to a destination to help facilitate emergency-related communications. This is 
done at the application layer, independent of any lower layer rerouting 
(SONET rings, etc) that naturally applies to all traffic using the link, 
whether emergency or normal. Application of emergency telephony services to 
the Internet (and IP in general) means that there are two separate issues to 
be addressed. 

a) IP Packet Transport layer: Unlike the PSTN, which creates a fixed path 
(circuit) during call setup phase, the Internet uses dynamic routing for IP 
packets. This dynamic routing capability automatically causes IP packets to 
travel the best current path, which may change during the life of the "call" 
due to failures of infrastructure components. However, at the time of "call" 
set up (at the application layer), the route choice for the packet transport 
layer has a single choice (the best current one). An issue to be addressed is 
the utility and possibility of providing additional routes (even if less 
efficient) for packet flows for higher priority "calls". 

b) Call application layer:  The Internet infrastructure itself does not have 
the concept of a "call" or the concept of "call setup", although IP telephony 
applications using it would have application-layer awareness of calls or the 
call setup concept. Alternate path routing at the application layer may be 
useful in choosing one of possibly several egress points to the PSTN from the 
Internet. 

--------------------------------------------
This was mostly to help avoid the problems caused by the confusion between 
the two layers when each person focuses on a different part when reading it. 
Essentially, the only idea I added was the statement about "An issue to be 
addressed is the utility and possibility of providing additional routes" (for 
the IP transport layer), an idea already hinted at by the statement in the 
draft that is "may be difficult to achieve".

Mike Pierce
Artel