Subject: RE: [Sipping] Re: AW: Optional optimisation for SIP overlap to IS UP en-bloc (Overla p WG LC)

From: David Oliver <[email-masked]>
Date: Thu, 13 Jun 2002 17:02:05 -0500

Mike and Denis,
 
Comments inline.
 
Regards,

David C. Oliver
Principal Engineer
SecureLogix Corp
Email:  <mailto:[email-masked]> [email-masked]
Tel:    210.402.9669
Fax:   210.402.6996 

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Thursday, June 13, 2002 4:17 PM
To: [email-masked]
Cc: [email-masked]; [email-masked]
Subject: [Sipping] Re: AW: Optional optimisation for SIP overlap to ISUP
en-bloc (Overla p WG LC)

In a message dated 6/13/02 4:20:10 AM Eastern Daylight Time,
[email-masked] writes: 

<...>

2. If the egress gateway determines that the number contained in the INVITE
is not a complete number and the PSTN it is connected to does not support
overlap, the egress gateway SHOULD respond with a 484, Address Incomplete.
If it receives a subsequent INVITE, it treats it as if it were the first
one.   

[DA] I think it will be good to recommend the Ingress GW to keep the same
Call-ID and From-tag for the new INVITEs even if they are belonging to the
different SIP call setups in this case. It will be useful for accounting,
provisioning and so on. 

[MAP] Absolutely, keeping the same Call-ID and From-tag (and whatever else
associates the new INVITE with the previous) is an important part of the
solution. I'm not sure what you mean by "even if they are belonging to the
different SIP call setups". Could there be a case in which the ingress GW
sends an INVITE with some of the digits, and then, when it gets more digits,
it decides to release the first call attempt and start a new one? If so,
this would be a "different SIP call setup". But I see this as not being
needed, since the ingress GW should always wait for the minimum number of
digits before sending the first INVITE, meaning that the destination has
already been determined. 

[David Oliver] Unfortunately, it is not always realistic to know when all
digits have been dialed. In the North American (+1) area, all valid numbers
are of the form [1] [ABC] DEF GHIJ, where neither A nor D are a '1', and ABC
and DEF (essentially) do not overlap (apparent exceptions such as (210)
210-3456 have unique representations inside (210-3456) or outside
(210.210-3456) the 210 area code).

Other national  codes have varying length area codes, and various length
local numbers, sometimes even within the same area code. Maintaining an
accurate, up-to-date record of all international dialing plans is
impractical and error prone: many US-based online white pages were confused
when Rome changed its international area code from +39(0)6 to +39-06 (!). It
is, therefore, common for PBXs and Gateways to accumulate a "reasonable"
number of digits, based on the best information available, waiting for a
pause in dialing and attempt to place a call with the digits accumulated,
handling additional dialed digits specially depending on whether the call
has completed.

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