Re: Comments on RFC2806bis

At 10:02 am -0400 23/5/02, Michael Hammer wrote:
>So what happens if someone dials this "international" number from a 
>location outside of Austria and it gets routed through SIP to a GW 
>within Austria, is that considered originated inside Austria and 
>therefore allowed, or is it considered dialed outside Austria and 
>therefore blocked?
>
>Mike
>
To which I reply:
Good morning Mike, folks,
   The essential question is whether or not there is a route to the 
destination from your origination point.
The destination address may be unique (as in an E.164 number), 
without a route through to it from your place.

Answering your question as asked - it's allowed, IMHO.
However, whether the call is delivered depends on whether or not the 
Destination network Gateway Exchange through which your "far end" SIP 
MGW connects allows routing to the number it has received or not. It 
probably does.

This is a specific case; we should really generalise. However, for 
your entertainment...

Austria (as does Germany) uses a flexible numbering plan.
The current ITU recommendation on maximum NSN length means that, if 
someone tries to dial (using the old code) a Vienna number that is 
connected via a PBX from another Country (or an interconnect that 
uses a DN within the ISUP message that is in International Format), 
the number could exceed the maximum size allowed for a DN (15 digits, 
I seem to remember).
Remember that Austria has a 2 digit country code, the old code for 
Vienna was 222 (another 3 digits), so that leaves a maximum of 10 
digits for the complete local number, including any extension.

To avoid this truncation risk, the choice was to change the area code 
for Vienna to 1.
However, everyone in Austria is used to dialling 0222 to get Vienna, 
thus the two codes run in parallel.
The only problem is that, if the International Gateway exchange gets 
a number with area code 222, that number may have been truncated. To 
avoid trying to place the call using an incomplete number, it's 
blocked.
The 15 digit limit is not a problem within Austria (as International 
Register length is not an issue), so it passes.

Thus, your question should be - can the destination number I've 
dialled be delivered to the far end gateway without truncation, and 
if so, is that far end MGW connected so that it can avoid using 
(International) ISUP messages when placing the call onwards to the 
destination end point.

This may also address your subsequent question - the reason to have 
this as an E.164 number is that it won't change in the future as 
maximum register size increases; the only thing that will change is 
whether or not a call origination has gone via an ISUP interconnect 
that might have truncated it.

all the best,
   Lawrence

-- 
[email protected]: +44 1794 833666::<my opinions>: