SIPPING                                                        E. Burger
Internet-Draft                                  SnowShore Networks, Inc.
Expires: March 1, 2004                                 September 1, 2003

                    Keypad Stimulus Protocol (KPML)

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.


   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",
   "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

   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

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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

   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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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

      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">
             <regex value="ZF"
                     href=" \
                        session=19fsjcalksd&keypress=long-pound" />

   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">
             <regex value="0"
             <regex value="00"
             <regex value="7xxx"
             <regex value="9xxxxxxx"
             <regex value="9xxxxxxxxxx"
             <regex value="91xxxxxxxxxx"
             <regex value="011x."

   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">
           <pattern barge=off>

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             <regex value="5"
      href="$9awj08asd7?keep" />
             <regex value="7"
      href="$9awj08asd7?replay" />
             <regex value="3"
      href="$9awj08asd7?delete" />

   Figure 5 - IVR KPML Example Code

   The target of the http post, "sess$9aej08asd7", identifies the SIP

      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">
             <regex value="ZF"
                     href="sip:" />

   Figure 6 - Long Octothorpe Example

   The response body is identical to the response that Figure 1 would

9. Report Body

   The body of the response from the user device is a KPML response

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   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"/>

   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=""
     <xs:element name="kpml">
         <xs:documentation>IETF Keypad Markup Language
           <xs:element name="request">
                 <xs:element name="pattern">
                       <xs:element name="regex"

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                           <xs:attribute name="value"
                            type="xs:string" use="required"/>
                           <xs:attribute name="href"
                            type="xs:anyURI" use="required"/>
                     <xs:attribute name="barge"
                       use="optional" default="true"/>
                     <xs:attribute name="interdigittimer"
                       use="optional" default="100"/>
           <xs:element name="response">
               <xs:attribute name="code" type="xs:string"
               <xs:attribute name="text" type="xs:string"
               <xs:attribute name="suppressed"
                type="xs:boolean" use="optional"/>
               <xs:attribute name="digits" type="xs:string"

   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

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]

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,

   [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


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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   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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