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
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 4, 2006.
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.
Rosen Expires September 4, 2006 [Page 1]
Internet-Draft Dialstring Parameter March 2006
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
Rosen Expires September 4, 2006 [Page 2]
Internet-Draft Dialstring Parameter March 2006
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
Rosen Expires September 4, 2006 [Page 3]
Internet-Draft Dialstring Parameter March 2006
* 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.
Rosen Expires September 4, 2006 [Page 4]
Internet-Draft Dialstring Parameter March 2006
(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",
Rosen Expires September 4, 2006 [Page 5]
Internet-Draft Dialstring Parameter March 2006
RFC 3966, December 2004.
Rosen Expires September 4, 2006 [Page 6]
Internet-Draft Dialstring Parameter March 2006
Author's Address
Brian Rosen
NeuStar
470 Conrad Dr
Mars, PA 16046
US
Phone: +1 724 382 1051
Email: br@brianrosen.net
Rosen Expires September 4, 2006 [Page 7]
Internet-Draft Dialstring Parameter March 2006
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Rosen Expires September 4, 2006 [Page 8]