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Versions: 00 01 02 03 04 05 rfc4967                                     
sipping                                                         B. Rosen
Internet-Draft
Marconi
Expires: November 16, 2004                                  May 18, 2004


                  Dialstring parameter for the sip URI
                  draft-rosen-iptel-dialstring-00.txt

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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   This Internet-Draft will expire on November 16, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   RFC2806bis explicitly disclaims 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 URI.








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Table of Contents

   1.   Requirements notation  . . . . . . . . . . . . . . . . . . . . 3
   2.   Problem  . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.   Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.   Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.   Security Considerations  . . . . . . . . . . . . . . . . . . . 4
   6.   References . . . . . . . . . . . . . . . . . . . . . . . . . . 4
        Author's Address . . . . . . . . . . . . . . . . . . . . . . . 5
        Intellectual Property and Copyright Statements . . . . . . . . 6









































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1.  Requirements notation

   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].

2.  Problem

   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 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.

   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.

3.  Requirements

   A mechanism to express a dialstring is required.  A dialstring
   consists of a sequence of
      * The digits 0-9
      * The special characters # and *
      * The MF digits A-D

   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



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   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 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
   RFC2806bis MUST be specified.

   A proxy server or B2BUA which is authoratative 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.

5.  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.

6  References

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

   [RFC2806]  Vaha-Sipila, A., "URLs for Telephone Calls", RFC 2806,
              April 2000.

   [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.











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Author's Address

   Brian Rosen
   Marconi
   2000 Marconi Drive
   Warrendale, PA  15086
   US

   Phone: +1 724 742 6826
   EMail: brian.rosen@marconi.com









































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Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
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   The IETF invites any interested party to bring to its attention any
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Full Copyright Statement

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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgment

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











































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