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Versions: 00 01 02 03 04 05 RFC 4967

iptel                                                           B. Rosen
Internet-Draft                                                   NeuStar
Expires: September 4, 2006                                March 03, 2006


      Dialstring parameter for the Session Initiation Protocol URI
                  draft-rosen-iptel-dialstring-03.txt

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   RFC3966 explicitly states that TEL URIs may not represent a dial
   string.  That leaves no way specify a dialstring in a standardized
   way.  Great confusion exists with the SIP URI parameter "user=phone",
   and specifically, if it can represent a dial string.  This memo
   creates a new value for the user parameter "dialstring", so that one
   may specify "user=dialstring" to encode a dialstring as a SIP or SIPS
   URI.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8








































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1.  Introduction

   A user at a phone often has a limited User Interface, and in some
   cases, is limited to a 10 key pad (and sometimes a "flash" function
   with the switchhook).  One enters a series of digits that invoke some
   kind of function.  The entered sequence, called a "dialstring" might
   be translated to a telephone number, or it may invoke a special
   service.  In many newer designs, the mapping between a dialstring and
   a phone number or service URI is contained within the phone
   (digitmap).  However, there are many phones and terminal adapters
   that do not have internal translation mechanisms.  Without a
   translation mechanism in the phone, the phone must send the
   dialstring in a SIP or SIPS URI [RFC3261]to an intermediary that can
   transform the dialstring to a phone number or a service invocation.

   At some point, a dialstring is translated to a phone number.  After
   that point, it is no longer a dialstring.  However, there is no
   current way for any entity to determine if translation has already
   been accomplished.  The "user=phone" parameter in a SIP or SIPS URI
   could denote a telephone number, but would need another value to
   denote a dialstring.

   Use of DTMF detectors post dial is not uncommon.  A common functions
   some systems have is to express a string that incorporates fixed time
   delays, or in some cases, actual "wait for call completion" after
   which additional DTMF signals are emitted.  For example, many
   voicemail systems use a common phone number, after which the system
   expects the desired mailbox number as DTMF to deposit a message for.
   Many gateways have the ability to interpret such strings, but there
   is no standardized way to express them, leading to interoperability
   problems between endpoints.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


3.  Requirements

   A mechanism to express a dialstring in a SIP or SIPS uri is required.
   A dialstring consists of a sequence of







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      * The digits 0-9
      * The special characters # and *
      * The MF digits A-D

   Note: DTMF = Dual Tone MultiFrequency.  Each "tone:" is actually two
   frequencies superimposed.  DTMF is a 4 x 4 matrix with four row
   frequencies (697, 770, 852, 941 Hz) and four column frequencies
   (1209, 1336, 1477, 1633).  Most telephones only implement 3 of the 4
   columns, which are used just like the telephone dial pad implies they
   are.  Thus, the digit 2 is the first row, second column, and consists
   of 770Hz and 1209Hz frequencies mixed together.  The fourth column is
   not used in the PSTN.  The "digits" for the fourth column are usually
   expressed using the letters A through D. Thus, "C" is 852/1633Hz.
   Some equipment does use these digits, so we include them in the
   definition of the dialstring.

   A dialstring always exists within a context.  The context MUST be
   specified when expressing a dialstring.

   It MUST be possible to distinguish between a dialstring and a phone
   number.

   It MUST be possible to express a short Pause, and a "Wait for call
   completion" in a dialstring.


4.  Solution

   A new value for the "user" parameter of the SIP/SIPS URI schemes is
   defined, "dialstring".  This value may be used in a SIP or SIPS URI
   when the userpart is a dialstring.  The userpart is a sequence of the
   characters 0-9, A-F, P and X. E is represent *, F represents #, P is
   a pause (short wait, like a comma in a modem string) and X represents
   call completion.

   When the "user=dialstring" is used, a context parameter as defined in
   [RFC3966] MUST be specified.

   A proxy server or B2BUA which is authoritative for the context may
   translate the dialstring to a telephone number or service invocation
   URI.  If such a translation is performed, the proxy server MUST
   change the URI to specify user=phone.









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   (Examples of dialstring use include)
   ; what a SIP Phone might emit when a user dials extension 123
   sip:123@sippbx.example.com;user=dialstring;
      phone-context='AtlantaDialPlan'

   ;existing voicemail systems have a local access extension,
   ;then expect to see the extension number as DTMF for the mailbox
   sips:4500P4123@sip.example.com;user=dialstring;
      phone-context='BiloxiDialPlan'
   ()


5.  IANA Considerations

   [RFC3969] defines a SIP/SIPS URI Parameter sub registry.  The "user"
   parameter is specified as having predefined values.

   This RFC defines a new value for the "user" parameter, "dialstring".
   This RFC would be added to the references listed for the "user"
   parameter.

   This RFC defines a new parameter in the sub-registry, "phone-
   context", whose meaning and syntax are derived from the same
   parameter in [RFC3969]


6.  Security Considerations

   Dialstrings exposed to the Internet may reveal information about
   internal network details or service invocations that could allow
   attackers to use the PSTN or the Internet to attack such internal
   systems.  Dialstrings normally should not be sent over the open
   Internet without some kind of protection against eavesdropping.

7.  References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3261]  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.

   [RFC3966]  Schulzrinne, H., "The tel URI for Telephone Numbers",
              RFC 3966, December 2004.

   [RFC3969]  Schulzrinne, H., "The tel URI for Telephone Numbers",



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              RFC 3966, December 2004.


















































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Author's Address

   Brian Rosen
   NeuStar
   470 Conrad Dr
   Mars, PA  16046
   US

   Phone: +1 724 382 1051
   Email: br@brianrosen.net









































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   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
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Acknowledgment

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




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