SIPPING E. Burger
Internet-Draft SnowShore Networks, Inc.
Expires: March 1, 2004 September 1, 2003
Keypad Stimulus Protocol (KPML)
draft-ietf-sipping-kpml-00
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The Keypress Stimulus Protocol uses the Keypad Markup Language (KPML)
to provide instructions to SIP User Agents for the reporting of user
key presses.
Conventions used in this document
RFC2119 [1] provides the interpretations for the key words "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" found in this document.
In the narrative discussion, the "user device" is a User Agent that
will report stimulus. it could be, for example, a SIP phone or media
gateway. An "application" is a User Agent requesting the user device
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to report stimulus. The "user" is an entity that stimulates the user
device. In English, the user device is a phone, the application is
an application server or proxy server, and the user presses keys to
generate stimulus.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Keypress Stimulus Protocol . . . . . . . . . . . . . . . . . 4
2.1 Operation . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Message Format - KPML . . . . . . . . . . . . . . . . . . . 4
4. Digit Suppression . . . . . . . . . . . . . . . . . . . . . 6
5. One-Shot and Persistant Triggers . . . . . . . . . . . . . . 7
6. Multiple, Simultaneous Markup . . . . . . . . . . . . . . . 7
7. Reports . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1 Monitoring for Octorhorpe . . . . . . . . . . . . . . . . . 8
8.2 Dial String Collection . . . . . . . . . . . . . . . . . . . 8
8.3 Interactive Digit Collection . . . . . . . . . . . . . . . . 9
8.4 SIP Request . . . . . . . . . . . . . . . . . . . . . . . . 10
9. Report Body . . . . . . . . . . . . . . . . . . . . . . . . 10
10. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 11
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . 12
11.1 IANA Registration of MIME media type application/kpml+xml . 12
11.2 Schema Registration . . . . . . . . . . . . . . . . . . . . 13
12. Security Considerations . . . . . . . . . . . . . . . . . . 13
Normative References . . . . . . . . . . . . . . . . . . . . 13
Informative References . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . 15
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15
B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . 17
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1. Introduction
This document describes the Keypress Stimulus Protocol. The Keypress
Stimulus Protocol exchanges messages over SIP with message bodies
formed from the Keypad Markup Language, KPML. KPML is a markup [9]
that enables "dumb phones" to report user key-press events.
Colloquially, this mechanism provides for "digit reporting" or "DTMF
reporting" in the signaling path.
We strongly discourage the use of non-validating XML parsers, as one
can expect problems with future versions of KPML. That said, one
could envision user devices that only accept SIP reporting and have a
fixed parser, rather than a full XML parser. This means that a goal
of KPML is to fit in an extremely small memory and processing
footprint. Note KPML has a corresponding lack of functionality. For
those applications that require more functionality, please refer to
VoiceXML [10] and MSCML [11].
The name of the markup, KPML, reflects its legacy support role. The
public switched telephony network (PSTN) accomplished end-to-end
signaling by transporting Dual-Tone, Multi-Frequency (DTMF) tones in
the bearer channel. This is in-band signaling.
From the point of view of an application being signaled, what is
important is the fact the stimulus occurred, not the tones used to
transport the stimulus. For example, an application may ask the
caller to press the "1" key. What the application cares about is the
key press, not that there were two cosine waves of 697 Hz and 1209 Hz
transmitted.
A SIP-signaled [2] network transports end-to-end signaling with
RFC2833 [12] packets. In RFC2833, the signaling application inserts
RFC2833 named signal packets as well as or instead of generating
tones in the media path. The receiving application gets the signal
information, which is what it wanted in the first place.
RFC2833 is the only method that can correlate the time the end user
pressed a digit with the user's media. However, out-of-band
signaling methods, as are appropriate for user device to application
signaling, do not need millisecond accuracy. On the other hand, they
do need reliability, which RFC2833 does not provide.
An interested application could request notifications of every key
press. However, many of the use cases for such signaling has the
application interested in only one or a few keystrokes. Thus we need
a mechanism for specifying to the user device what stimulus the
application would like notification of.
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2. Keypress Stimulus Protocol
2.1 Operation
The keypress stimulus protocol uses explicit subscription requests
and notification requests.
NOTE: The exact mechanism is coming in a later draft. The
mechanism may or may not use the framework described by the
applications interaction framework [13]. The protocol uses the
mechanism described by the app-info [3] header.
If the user device receives a subscription for the same user
instance, the user device MUST terminate the existing KPML request
(if any) and replace it with the new request.
If the user device supports multiple, simultaneous KPML requests, the
application must register the separate request at a different user
instance at the user device. It is the responsibility of the
application to ensure it uses unique user instance names.
If the user device does not support multiple, simultaneous KPML
requests, it MUST reject the request with a 488 NOT ACCEPTABLE HERE.
[Assuming SIP for requests.]
A KPML request can be persistent or one-shot. Persistent requests
are active until either the dialog terminates, the client replaces
them, or the client deletes them by sending a null document on the
user instance.
Response messages are KPML documents (messages). If the user device
matched a digit map, the response indicates the digits detected and
whether the user device suppressed digits. If the user device had an
error, such as a timeout, it will indicate that, instead.
3. Message Format - KPML
The Keypress Stimulus Protocol exchanges KPML messages. A KPML
document (message) contains a <pattern> tag with a series of <regex>
tags. The <regex> tag has a value attribute that is a H.248.1 [4]
digit map.
NOTE: We use RFC3525 digit maps instead of MGCP [14] digit maps
because the former is an IETF standard and the latter is not.
NOTE: We do not use SRGS [15] DTMF grammars because it is unlikely
one would use KPML for independent digit collection in a browser
context.
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Interface attributes, such as the interdigit timeout and what
constitutes a long key press, are implementation matters beyond the
scope of this document.
For many applications, the user device needs to quarantine (buffer)
digits. Some applications use modal interfaces where the first few
key presses determine what the following digits mean. For a novice
user, the application may play a prompt describing what mode the
application is in. However, "power users" often barge through the
prompt.
The protocol provides a barge attribute to the <pattern> tag. The
default is "barge=yes". Enabling barge means that the user device
buffers digits and applies them immediately when the next KPML
message arrives. Disabling barge by specifying "barge=no" means the
user device flushes any collected digits before collecting more
digits and comparing them against the <pattern> tags.
NOTE: Quarantine and barge are separate actions. However, the
barge action directly determines the quarantine action. Thus the
protocol only specifies the barge action request.
If the user presses a key not matched by the <regex> tags, the user
device discards the key press from consideration against the current
or future KPML messages. However, as described above, once there is
a match, the user device quarantines any keys the user enters
subsequent to the match.
KPML messages are independent. Thus it is not possible for the
current document to know if a following document will enable barging
or want the digits flushed. Therefore, the user device MUST
quarantine all digits detected between the time of the report and the
interpretation of the next script, if any. If the next script has
"barge=no", then the interpreter MUST flush all collected digits. If
the next script has "barge=yes", then the interpreter MUST apply the
collected digits against the digit maps presented by the script's
<regex> tags. If there is a match, the interpreter MUST quarantine
the remaining digits. If there is no match, the interpreter MUST
flush all of the collected digits.
Unless there is a suppress indicator in the digit map, it is not
possible to know if the signaled digits are for local KPML processing
or for other recipients of the media stream. Thus, in the absence of
a digit suppression indicator, the user device transmits the digits
to the far end in real time, using either RFC2833, generating the
appropriate tones, or both.
The following section details the operation of the suppress
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indicator.
4. Digit Suppression
Under basic operation, a KPML endpoint will transmit in-band tones
(RFC2833 [12] or actual tone) in parallel with digit reporting.
NOTE: If KPML did not have this behavior, then a user device
executing KPML could easily break called applications. For
example, take a personal assistant that uses "*9" for attention.
If the user presses the "*" key, KPML will hold the digit, looking
for the "9". What if the user just enters a "*" key, possibly
because they accessed an IVR system that looks for "*"? In this
case, the "*" would get held by the user device, because it is
looking for the "*9" pattern. The user would probably press the
"*" key again, hoping that the called IVR system just did not hear
the key press. At that point, the user device would send both "*"
entries, as "**" does not match "*9". However, that would not
have the effect the user intended when they pressed "*".
On the other hand, there are situations where passing through tones
in-band is not desirable. Such situations include call centers that
use in-band tone spills to effect a transfer.
For those situations, KPML adds a digit suppression token to H.248.1
[4] digit maps. The digit suppression token is a "Q". There MUST
NOT be more than one Q in any given <regex>.
If there is only a single <pattern> and a single <regex>, the
suppression processing is straightforward. The end-point passes
digits until the stream matches the regular expression up to the
suppression token, Q. At that point, the endpoint will continue
collecting digits, but will suppress the generation or pass-through
of any in-band digits.
If the endpoint suppresses digits, it MUST indicate this by including
the attribute "suppressed" with a value of "yes" in the digit report.
A KPML endpoint MAY perform digit suppression. If it is not capable
of digit suppression, it ignores the digit suppression token and will
never send a suppressed indication in the digit report.
At some point in time, the endpoint will collect enough digits to the
point it hits a suppression marker. The interdigittimer attribute
indicates how long to wait once the user enters digits before
reporting a time-out error. If the interdigittimer expires, the
endpoint MUST issue a time-out report and transmit the suppressed
digits on the media stream.
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After digit suppression begins, it may become clear that a match will
not occur. For example, take the regular expression
"*8Qxxx[2-9]xxxxxx". At the point the endpoint receives "*8", it
will stop forwarding digits. Let us say that the next three digits
are "408". If the next digit is a zero or one, the pattern will not
match.
NOTE: It is critically important for the endpoint to have a
sensible inter-digit timer. This is because an errant dot (".")
may suppress digit sending forever.
Applications should be very careful to indicate suppression only when
they are fairly sure the user will enter a digit string that will
match the regular expression. In addition, applications should deal
with situations such as no-match or time-out. This is because the
endpoint will hold digits, which will have obvious user interface
issues in the case of a failure.
5. One-Shot and Persistant Triggers
NOTE: This section will be heavily dependent on the transport
mechanism chosen, as the nature of the request could be determined by
transport parameters rather than KPML parameters. KPML is probably a
better route.
6. Multiple, Simultaneous Markup
NOTE: This section will be heavily dependent on the transport
mechanism chosen. Most of the candidates will be able to a priori
correlate KPML documents to results. Most of the protocol machinery
will be around rules for simultaneous markup.
7. Reports
When the user enters keypress(es) that match a <regex> tag, the user
device will issue a report.
NOTE: Details coming soon.
After reporting, the interpreter terminates the KPML session unless
the KPML document has a persistence indicator. Otherwise, to collect
more digits, the requestor must issue a new request.
NOTE: This highlights the "one shot" nature of KPML, reflecting
the balance of features and ease of implementing an interpreter.
If your goal is to build an IVR session, we strongly suggest you
investigate more appropriate technologies such as VoiceXML [10] or
MSCML [11].
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8. Examples
NOTE: This section will DEFINATELY change and be expanded.
8.1 Monitoring for Octorhorpe
A common need for pre-paid and personal assistant applications is to
monitor a conversation for a signal indicating a change in user focus
from the party they called through the application to the application
itself. For example, if you call a party using a pre-paid calling
card and the party you call redirects you to voice mail, digits you
press are for the voice mail system. However, many applications have
a special key sequence, such as the octothorpe (#, or pound sign) or
*9 that terminate the called party leg and shift the user's focus to
the application.
The following figure shows the KPML for long octothorpe. Note that
the href is really on one line, but divided for clarity.
<?xml version="1.0">
<kpml version="1.0">
<request>
<pattern>
<regex value="ZF"
href="http://app.example.net/cgi-bin/prepaid? \
session=19fsjcalksd&keypress=long-pound" />
</pattern>
</request>
</kpml>
Figure 1 - Long Octothorpe Example
In this example, the parameter "session=19fsjcalksd" associates the
http POST with the SIP call session. One can use other methods to
associate the POST with a SIP call. The following examples will show
these various methods.
The regex value Z indicates the following digit needs to be a
long-duration key press. F, from the H.248.1 DTMF package, is the
octothorpe key. In fact, KPML supports all digits, 1-9, *, #, A-D
from the H.248 DTMF.1 package.
8.2 Dial String Collection
In this example, the user device collects a dial string. The
application uses KPML to quickly determine when the user enters a
target number. In addition, KPML indicates what type of number the
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user entered.
<?xml version="1.0">
<kpml version="1.0">
<request>
<pattern>
<regex value="0"
href="http://app.carrier.net/pp/12?local-operator/>
<regex value="00"
href="http://app.carrier.net/pp/12?ld-operator/>
<regex value="7xxx"
href="http://app.carrier.net/pp/12?vpn/>
<regex value="9xxxxxxx"
href="http://app.carrier.net/pp/12?local-number7/>
<regex value="9xxxxxxxxxx"
href="http://app.carrier.net/pp/12?local-number10/>
<regex value="91xxxxxxxxxx"
href="http://app.carrier.net/pp/12?ddd/>
<regex value="011x."
href="http://app.carrier.net/pp/12?iddd/>
</pattern>
</request>
</kpml>
Figure 4 - Dial String KPML Example Code
As before, the targets of the href's are opaque to KPML. Here the
href's indicate the type of dial string, such as direct dial (ddd) or
international direct dial (iddd).
8.3 Interactive Digit Collection
This is an example where one would probably be better off using a
full scripting language such as VoiceXML [10] or MSCML [11] or a
device control language such as H.248.1 [4].
In this example, an application requests the user device to send the
user's signaling directly to the platform in HTTP, rather than
monitoring the entire RTP stream. Figure 5 shows a voice mail menu,
where presumably the application played a "Press K to keep the
message, R to replay the message, and D to delete the message"
prompt. In addition, the application does not want the user to be
able to barge the prompt.
<?xml version="1.0">
<kpml version="1.0">
<request>
<pattern barge=off>
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<regex value="5"
href="http://app.example.net/vm/sess$9awj08asd7?keep" />
<regex value="7"
href="http://app.example.net/vm/sess$9awj08asd7?replay" />
<regex value="3"
href="http://app.example.net/vm/sess$9awj08asd7?delete" />
</pattern>
</request>
</kpml>
Figure 5 - IVR KPML Example Code
The target of the http post, "sess$9aej08asd7", identifies the SIP
session.
NOTE: It is unclear if this usage of KPML is better than using a
device control protocol like H.248.1. From the application's
point of view, it has to do the low-level prompt-collect logic.
Granted, it is relatively easy to change the key mappings for a
given menu. However, often more of the call flow than a given
menu mapping gets changed. Thus there would be little value in
such a mapping to KPML. We STRONGLY suggest using a real
scripting language such as VoiceXML or MSCML for this purpose.
8.4 SIP Request
For example, the following figure is the example from Figure 1, but
with SIP NOTIFY reporting.
<?xml version="1.0">
<kpml version="1.0">
<request>
<pattern>
<regex value="ZF"
href="sip:" />
</pattern>
</request>
</kpml>
Figure 6 - Long Octothorpe Example
The response body is identical to the response that Figure 1 would
generate.
9. Report Body
The body of the response from the user device is a KPML response
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form.
The <response> tag has an attribute, "digits". The digits attribute
is the digit string. The digit string uses the conventional
characters '*' and '#' for star and octothorpe respectively.
Figure 7 shows a sample response body to the example in the Dial
String Collection (Section 8.2) section.
<?xml version="1.0">
<kpml version="1.0">
<response digits="0113224321234"/>
</kpml>
Figure 7 - Response Body
NOTE: KPML does not include a timestamp. There are a number of
reasons for this. First, what timestamp would in include? Would
it be the time of the first detected keypress? The time the
interpreter collected the entire string? A range? Second, if the
RTP timestamp is a datum of interest, why not simply get RTP in
the first place? That all said, if it is really compelling to
have the timestamp in the response, it could be an attribute to
the <response> tag.
10. Formal Syntax
The following syntax specification uses the XML Schema [5].
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xs:element name="kpml">
<xs:annotation>
<xs:documentation>IETF Keypad Markup Language
</xs:documentation>
</xs:annotation>
<xs:complexType>
<xs:choice>
<xs:element name="request">
<xs:complexType>
<xs:all>
<xs:element name="pattern">
<xs:complexType>
<xs:sequence>
<xs:element name="regex"
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maxOccurs="unbounded">
<xs:complexType>
<xs:attribute name="value"
type="xs:string" use="required"/>
<xs:attribute name="href"
type="xs:anyURI" use="required"/>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute name="barge"
type="xs:boolean"
use="optional" default="true"/>
<xs:attribute name="interdigittimer"
type="xs:integer"
use="optional" default="100"/>
</xs:complexType>
</xs:element>
</xs:all>
</xs:complexType>
</xs:element>
<xs:element name="response">
<xs:complexType>
<xs:attribute name="code" type="xs:string"
use="required"/>
<xs:attribute name="text" type="xs:string"
use="required"/>
<xs:attribute name="suppressed"
type="xs:boolean" use="optional"/>
<xs:attribute name="digits" type="xs:string"
use="optional"/>
</xs:complexType>
</xs:element>
</xs:choice>
</xs:complexType>
</xs:element>
</xs:schema>
Figure 9 - XML Schema for KPML
11. IANA Considerations
11.1 IANA Registration of MIME media type application/kpml+xml
MIME media type name: application
MIME subtype name: kpml+xml
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Required parameters: none
Optional parameters: charset
charset This parameter has identical semantics to the charset
parameter of the "application/xml" media type as specified in
XML Media Types [6].
Encoding considerations: See RFC3023 [6].
Interoperability considerations: See RFC2023 [6] and this document.
Published specification: This document.
Applications which use this media type: Session-oriented applications
that have primitive user interfaces.
Intended usage: COMMON
11.2 Schema Registration
We really need a place to register the XML Schema. Where would that
be?
12. Security Considerations
Since a KPML document directs a device to send results to an
arbitrary URI, one could construct distributed denial of service
attacks. For example, an errant application might send out KPML to
numerous endpoints, all reporting to a single, unrelated href. Thus
the policies for accepting KPML, such as access control lists ("only
accept KPML from these hosts"), report limiting lists ("only send
KPML responses to these hosts"), and other protections must be well
thought out.
At the very least, the session startup protocol SHOULD be
non-reputable and secure.
KPML presents no further security issues beyond the startup issues
addressed in the companion documents to this document.
As an XML markup, all of the security considerations of RFC3023 [6]
apply.
Normative References
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[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[3] Jennings, C., "SIP Support for Application Initiation",
draft-jennings-sip-app-info-00 (work in progress), October 2002.
[4] Groves, C., Pantaleo, M., Anderson, T. and T. Taylor, "Gateway
Control Protocol Version 1", RFC 3525, June 2003.
[5] Thompson, H., Beech, D., Maloney, M. and N. Mendelsohn, "XML
Schema Part 1: Structures", W3C REC REC-xmlschema-1-20010502,
May 2001.
[6] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC
3023, January 2001.
[7] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[8] Burger, E., "The SIP APPINFO Method",
draft-burger-sip-appinfo-00 (work in progress), 2003.
Informative References
[9] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
REC REC-xml-20001006, October 2000.
[10] World Wide Web Consortium, "Voice Extensible Markup Language
(VoiceXML) Version 2.0", W3C Working Draft , April 2002,
<http://www.w3.org/TR/voicexml20/>.
[11] Burger, E., Van Dyke, J. and A. Spitzer, "SnowShore Media
Server Control Markup Language and Protocol",
draft-vandyke-mscml-00 (work in progress), November 2002.
[12] Schulzrinne, H. and S. Petrack, "RTP Payload for DTMF Digits,
Telephony Tones and Telephony Signals", RFC 2833, May 2000.
[13] Rosenberg, J., "A Framework and Requirements for Application
Interaction in SIP",
draft-rosenberg-sipping-app-interaction-framework-00 (work in
progress), November 2002.
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[14] Andreasen, F. and B. Foster, "Media Gateway Control Protocol
(MGCP) Version 1.0", RFC 3435, January 2003.
[15] Hunt, A. and S. McGlashan, "Speech Recognition Grammar
Specification Version 1.0", W3C CR CR-speech-grammar-20020626,
June 2002.
[16] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", RFC
1889, January 1996.
[17] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and
D. Gurle, "Session Initiation Protocol (SIP) Extension for
Instant Messaging", RFC 3428, December 2002.
[18] Van Dyke, J., Burger (Ed.), E. and A. Spitzer, "Basic Network
Media Services with SIP", January 2003.
Author's Address
Eric Burger
SnowShore Networks, Inc.
285 Billerica Rd.
Chelmsford, MA 01824-4120
USA
EMail: e.burger@ieee.org
Appendix A. Contributors
Robert Fairlie-Cuninghame, Cullen Jennings, Jonathan Rosenberg, and I
were the members of the Application Stimulus Signaling Design Team.
All members of the team contributed significantly to this work. In
addition, Jonathan Rosenberg postulated DML in his "A Framework for
Stimulus Signaling in SIP Using Markup" draft.
This version of KPML has significant influence from MSCML, the
SnowShore Media Server Control Markup Language. Jeff Van Dyke and
Andy Spitzer were the primary contributors to that effort.
That said, any errors, misinterpretation, or fouls in this document
are my own.
Appendix B. Acknowledgements
Hal Purdy and Eric Cheung of AT&T Laboratories helped immensely
through many conversations and challenges.
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Steve Fisher of AT&T Laboratories helped with the digit suppression
logic and syntax.
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