Subject: More Digit Map Fixes

From: Tom-PT Taylor <[email-masked]>
Date: Thu, 3 Feb 2000 21:04:44 -0500

I took a closer look at digit maps (section 7.1.14) as a result of a private
discussion and found an ambiguity in our current rules.  I also learned a
bit more about the intent behind the "L", "S", and DOT symbols.  This leads
to the following proposed additions to the errata list:

A. Timer Rules (section 7.1.14)
---------------------------------------------

Current rules regarding timer use:

1.      The start timer (T) is used prior to any digits having been dialed.
2.      If the Media Gateway can determine that at least one more digit is
needed for a digit string to match any of the allowed patterns in the digit
map, then the interdigit timer value should be set to a long (L) duration
(e.g.-16 seconds).
3.      If the DigitMap specifies that a variable number of additional
digits may be needed then the short timer (S) is used.
The problem is with that third rule -- it is indistinguishable from the
second one as it currently reads.  Here is a proposed alternative phrasing
of the rule:

"3.   If the digit string has matched one of the patterns in the digit map,
but it is possible that more digits could be received which would cause a
match with a different pattern, then instead of reporting the match
immediately, the MG must apply the short timer (S) and wait for more
digits."

B. Digit Map Completion Event (currently in section E.6.2)
----------------------------------------------------------------------------
-------

We need a way to report a long duration tone match as part of a pattern.
The simplest thing is to report the portion of the digit map which was
matched, as a string of digit map symbols rather than tone IDs.  We can use
tone IDs to report any extra digits collected.

It is also useful for the MGC to know whether the report came from a match,
a short timeout (match of an ambiguous pattern), or another timeout
(permanent signal/partial dial).

I therefore propose that the event be defined as follows:

DigitMap Completion Event
EventID: ce, 0x0001
Raised when pattern match or timeout is detected on a digit map.
EventsDescriptor parameters: none
ObservedEventsDescriptor parameters:
        DigitString
                ParameterID: ds (0x0001)
                Type: string of digit map symbols (possibly empty)
                Possible values: any sequence of the characters "0" through
"9", "A" through "F", and the long duration modifier "L".
                Description: the actual sequence of observed events,
represented by their corresponding digit map symbols, which matched part or
all of a digit map string.
        Extras
                ParameterID: ex (0x0002)
                Type:  list of toneIDs
                Possible values: any of the DTMF toneIDs defined in the
table in section E.5.3
                Description: the sequence of tone events detected in the
interval subsequent to completion of the (sub)string reported in DigitString
and before initial, long, or short timer expiry as applicable.
        Completion
                ParameterID: cm (0x0002)
                Type: enumeration
                Possible values: "M" (unambiguous match), "S" (short timer
expiry), or "T" (initial or long timer expiry)

C. Use Of DOT
----------------------
Our ABNF mentions DOT as a possible digit map symbol.  I've learned that DOT
was intended to stand for an arbitrary number of repetitions of the
preceding symbol.  Thus the string "x.F" stands for an arbitrary number of
digits between 0 and 9, terminated by the "#" sign (if DTMF is being used).
Long timing would be used throughout after the first digit.  The string "x."
would achieve the same purpose with short timing used after the first digit
(rule 3 above), and a terminating "#" sign reported as an extra in the DTMF
completion event described above.

Disposition: add text to describe the use of DOT in the description of digit
map symbols in 7.1.14.

Tom Taylor
Advisor -- Emerging Carrier IP Standards
E-mail: [email-masked] (internally, Tom-PT Taylor)
Phone and FAX: +1 613 736 0961

---

From: Paul Hollis <[email-masked]>
Date: Fri, 4 Feb 2000 15:36:52 +0100

Hi Tom,

I'm still a bit confused about how all these timers work! We define the timers,
but have we defined what happens at timeout?

Regards Paul.

--

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  Paul Hollis
  Ericsson Eurolab Deutschland GmbH
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  Germany
  Phone: +49 2407 575 8092
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