Subject: RE: TRIP

From: "Drage, Keith" <[email-masked]>
Date: Thu, 30 Dec 1999 11:31:11 +0000

I don't know which part of Q.767 you are looking at, but my understanding
says that the mode of operation used across the international interface is
subject to bilateral agreement, and therefore neither method of address
sending is preferred. See statements throughout the document of the form:

"Note - The use of en-bloc or overlap signalling is based on bi-lateral
agreements"

I would also note that while Q.767 is still extensively used, particularly
for international operation, I would expect network providers to be
specifying base Q.761 through Q.764 nowadays for international operation,
noting that these documents do specify the behaviour of international
gateway exchanges. Current ETSI specifications (ISUP version 3) for
international operation are based on the 1997 version of the ITU-T
Recommendations, and will shortly move to the recently approved 1999
versions. Again these documents do not mandate either en-bloc or overlap
sending.

I have no direct understanding of the amount of use overlap dialling gets
across the international interface. I know operators try to collect as many
digits as possible before presenting the call to the international network
in the first place, if only because as soon as you send the Initial Address
Message (IAM), you have a circuit allocated that could potentially be used
elsewhere in generating revenue. This is done using timeouts as well as
knowledge of the numbering plan. This however does not necessarily mean that
they eliminate overlap dialling across the international interface, even if
they prefer not to use it.

The main justification for keeping overlap dialling has always been for
those countries with open numbering plans (primarily Germany and Austria).
Here, private networks using DDI are allowed to specify their own length of
the DDI number (within the constraints of the maximum number of digits
specified by E.164), and therefore even the receiving public network does
not necessarily know the length of any number unless it is an end subscriber
on their own system. I see no signs of these two countries wanting to remove
this capability, and therefore it will remain fundamentally part of E.164
(in that is unlikely that there will be a rule fixing the length of
subscriber numbers within a particular NDC). This probably also partly
explains the different views of these two countries on the best way to
handle number portability within their networks.

In my opinion, extensive use of timeouts is particularly unfriendly to the
calling user. To be effective, the timeouts have to be short, and occur just
when the user is referring back to his list for the remaining digits of the
long number he is dialling. The only real solution to avoiding overlap
dialling is where all terminals on the calling network are forced to predial
their numbers before hitting the send key. So far only the mobile networks
seem to have managed this.

Note that this is not a defence of overlap, merely a statement that it is a
fact of life in telecommunication signalling.

Keith Drage

> ---------------------------------------------------------------
> Keith Drage ([email-masked])
> Siemens Communications Limited,
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-----Original Message-----
From: Vance Shipley [mailto:[email-masked]]
Sent: Tuesday, December 28, 1999 8:59 PM
To: James Yu; 'Jonathan Rosenberg'
Cc: John Mainwaring; Mark Foster; [email-masked];
[email-masked]
Subject: RE: TRIP

James Yu writes:
}
}  Overlap dialing probably happens often for international calls where the
}  switch in the originating country don't know much about the numbering
plan
}  of the destination country.  The criteria to begin processing the
received

Actually no.  The ITU recommendation Q.767 "Application of the ISDN user
part
of CCITT Signalling System No. 7 for international ISDN interconnections" is
used today on the International Plane between countries public telephone
networks.
This recommendation defines how ISUP signaling is to be applied toward the
application of international gateway interconnections to other countries
gateways.

Q.767 does not allow for overlap signaling.  If the local serving office
switch
for the originating subscriber uses overlap signaling to speed up call
routing
then an intermediate switch, or the gateway switch itself, will gather up
all
the digits and send the call forward enbloc.

Overlap signaling is not used in ANSI ISUP at all.  Overlap signaling was
used
in the days of in band signaling to speed up the delays caused by the
relatively
long duration of the tones used.  One area where it was almost always used
was
in fact international calls.  In the case of FGD signaling in North America
when
an international call was presented the country code was sent first using
<KP>CC<ST> so that the switch could begin route selection and grab an
outgoing
route while the rest of the digits where pulsed in.  This becomes
unnecessary
when ISUP signaling is used.

In my mind overlap signaling should never be generated but may have to be
supported
when received.  The receiving switch must buffer the received digits until
it
decides
that all have been received and then forward the call enbloc.  There are two
methods
the switch may use to recognize when all digits have been received.  The
best is
when
the switch has an accurate view of the dialing plan(s).  It would know that
country
code XX, city code YYY requires exactly 7 digits in the subscriber number
and
when it
received all 12 digits it would forward the call enbloc.  If it never
received
enough
digits it would eventually time out and release the call with a cause code
indicating
"address incomplete".  The second method simply applies an inter digit timer
and
maximum
number of digits.  Digits are buffered until either the maximum expected are
received,
the inter digit delay timer expires or an end-of-dial digit is recognized
(e.g.
<ST>
or '#').  These methods are generally both used where some dial plans are
recognized
(e.g. North American Plan) and the rest use the time out.

	-Vance

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