[Enum] Overlap dialing user experience (Re: I-D Action: New draft - draft-bellis-enum-send-n-00)

[Otmar Lendl <lendl at nic.at>]

On 2008/04/04 19:04, Brian Rosen <br at brianrosen.net> wrote:
> One thing I don't think we have to do is give the black phone or black phone
> connected to TA a BETTER experience than they have now.
> 
> Those of you in countries that allow this kind of "enterprise can define how
> long the number is", what is the user experience?  You can route as soon as
> the prefix is entered.  What is the user experience after that?  What if
> there was a short or a long pause between the prefix and one of the
> internally consumed digits?  After all, the originating switch doesn't know
> how many digits the enterprise uses.

The simple answer is: The user does not notice that the PBX on the
terminating side is not integrated into the operator's switch. It's all
completely transparent and realtime. Overlap dialing is an end-to-end
feature: individual digits are passed from originating PBX, via
originating carrier, via destiation carrier to the receiving PBX.

Here are some D-channel traces to explain this (using Asterisk 
connected to a Colt ISDN PRI, calling is via Telekom Austria.)

Lines starting with < are receiving, the ones with > are sent to the
operator.

I'm calling extension 300 on +43 1 25397. 

1) Direct dialing (incl. extension)

< Message type: SETUP (5)
< Called Number (len= 6) [ Ext: 1  TON: Unknown Number Type (0)  NPI:
ISDN/Telephony Numbering Plan (E.164/E.163) (1)  '300' ]

New call coming in, indicting extension 300. Actually, it is a config
option on an ISDN line whether these "Called Number" messages contains
just the extension or the national number + extension.

> Message type: SETUP ACKNOWLEDGE (13)
> Message type: CONNECT (7)

"300" is known, thus Asterisk accpects the call.

< Message type: CONNECT ACKNOWLEDGE (15)

2) overlap dialing.

On the sending side, all digits are passed one by one to the operator,
the second I hit the '7' key, I see on the receiving side:

< Message type: SETUP (5)
There is no "called number" information element in the setup message

> Message type: SETUP ACKNOWLEDGE (13)

I continue dialing and see

< Message type: INFORMATION (123)
< Called Number (len= 4) [ Ext: 1  TON: Unknown Number Type (0)  NPI:
ISDN/Telephony Numbering Plan (E.164/E.163) (1)  '3' ]

then:

< Message type: INFORMATION (123)
< Called Number (len= 4) [ Ext: 1  TON: Unknown Number Type (0)  NPI:
ISDN/Telephony Numbering Plan (E.164/E.163) (1)  '0' ]

< Message type: INFORMATION (123)
< Called Number (len= 4) [ Ext: 1  TON: Unknown Number Type (0)  NPI:
ISDN/Telephony Numbering Plan (E.164/E.163) (1)  '0' ]

At this point, the Asterisk knows that the extension is complete
and thus sends:

> Message type: CONNECT (7)

3) Timeout (receiving side):

Here is the case where the receiving side implements a timeout:

Overlap-dialing till the 7, then waiting:

< Message type: SETUP (5)   (no called party IE)
> Message type: SETUP ACKNOWLEDGE (13)

(some seconds later)

> Message type: CONNECT (7)

4) Timeout (sending side)

I can't reproduce this right now, but I rememeber that when calling
from a POTS phone, the network will issue a "SENDING COMPLETE" IE
to the receiving ISDN line after a suitable delay.

------------

I hope this helps a bit.

/ol
-- 
// Otmar Lendl <lendl at nic.at>, T: +43 1 5056416 - 33, F: - 933
// nic.at Internet Verwaltungs- und Betriebsgesellschaft m.b.H
// http://www.nic.at/  LG Salzburg, FN 172568b, Sitz: Salzburg
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