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<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<table summary="layout" width="66%" border="0" cellpadding="0" cellspacing="0"><tr><td><table summary="layout" width="100%" border="0" cellpadding="2" cellspacing="1">
<tr><td class="header">iptel</td><td class="header">B. Rosen</td></tr>
<tr><td class="header">Internet-Draft</td><td class="header">NeuStar</td></tr>
<tr><td class="header">Expires: December 27, 2006</td><td class="header">June 25, 2006</td></tr>
</table></td></tr></table>
<div align="right"><span class="title"><br />Dialstring parameter for the Session
Initiation Protocol Uniform Resource Identifier</span></div>
<div align="right"><span class="title"><br />draft-rosen-iptel-dialstring-04.txt</span></div>
<h3>Status of this Memo</h3>
<p>
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.</p>
<p>
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.</p>
<p>
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.”</p>
<p>
The list of current Internet-Drafts can be accessed at
<a href='http://www.ietf.org/ietf/1id-abstracts.txt'>http://www.ietf.org/ietf/1id-abstracts.txt</a>.</p>
<p>
The list of Internet-Draft Shadow Directories can be accessed at
<a href='http://www.ietf.org/shadow.html'>http://www.ietf.org/shadow.html</a>.</p>
<p>
This Internet-Draft will expire on December 27, 2006.</p>
<h3>Copyright Notice</h3>
<p>
Copyright © The Internet Society (2006).</p>
<h3>Abstract</h3>
<p>RFC3966 explicitly states that 'tel' URIs may not represent a dial
string. That leaves no way specify a dial string 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 dial string as a 'sip:' or 'sips:' URI.
</p><a name="toc"></a><br /><hr />
<h3>Table of Contents</h3>
<p class="toc">
<a href="#anchor1">1.</a>
Introduction<br />
<a href="#anchor2">2.</a>
Terminology<br />
<a href="#anchor3">3.</a>
Requirements<br />
<a href="#anchor4">4.</a>
Solution<br />
<a href="#anchor5">5.</a>
IANA Considerations<br />
<a href="#security">6.</a>
Security Considerations<br />
<a href="#rfc.references1">7.</a>
Normative References<br />
<a href="#rfc.authors">§</a>
Author's Address<br />
<a href="#rfc.copyright">§</a>
Intellectual Property and Copyright Statements<br />
</p>
<br clear="all" />
<a name="anchor1"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<a name="rfc.section.1"></a><h3>1. Introduction</h3>
<p>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). The user enters a series of digits that invoke some kind of
function. The entered sequence, called a "dial string", may be
translated to a telephone number, or it may invoke a special service. In
many newer designs, the mapping between a dial string 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 dial string in a 'sip:' or 'sips:' URI <a class="info" href="#RFC3261">[RFC3261]<span> (</span><span class="info">Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.</span><span>)</span></a> to an intermediary that can transform the
dial string to a phone number or a service invocation. The intermediary
is able to perform this transform provided that it knows the context
(i.e., dialing plan) within which the number was dialed.
</p>
<p>There is a problem here. The intermediary can apply its transformation
only if it recognizes that the user part of the SIP URI is a dial string.
However, there is currently no way to distinguish an user part consisting
of a dial string from an user part that happens to be composed of characters
that would appear in a dial string.
</p>
<p>Use of DTMF detectors after the initial number has been dialed is not uncommon. A common function
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 a series of DTMF digits 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. This is another case where the ability to indicate that a dialstring is
being presented would be useful.
</p>
<a name="anchor2"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<a name="rfc.section.2"></a><h3>2. Terminology</h3>
<p>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 <a class="info" href="#RFC2119">[RFC2119]<span> (</span><span class="info">Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.</span><span>)</span></a>.
</p>
<p>It is assumed that the reader is familiar with the terminology and acronyms defined in <a class="info" href="#RFC3261">[RFC3261]<span> (</span><span class="info">Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.</span><span>)</span></a>
</p>
<a name="anchor3"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<a name="rfc.section.3"></a><h3>3. Requirements</h3>
<p>A mechanism to express a dial string in a 'sip:' or 'sips:' URI is required.
A dial string consists of a sequence of </p>
<blockquote class="text"><dl>
<dt></dt>
<dd>* The digits 0-9
</dd>
<dt></dt>
<dd>* The special characters # and *
</dd>
<dt></dt>
<dd>* The DTMF digits A-D
</dd>
<dt></dt>
<dd>* characters representing a short Pause, and a "Wait for call
completion" in a dial string
</dd>
<dt></dt>
<dd> 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
dial string.
</dd>
</dl></blockquote>
<p>A dial string always exists within a context. The context MUST be
specified when expressing a dial string.
</p>
<p>It MUST be possible to distinguish between a dial string and an user
part that happens to consist of the same characters.
</p>
<a name="anchor4"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<a name="rfc.section.4"></a><h3>4. Solution</h3>
<p>A new value for the "user" parameter of the 'sip:' or 'sips:' URI schemes is
defined, "dialstring". This value may be used in a 'sip:' or 'sips:' URI when
the user part is a dial string. The user part is a sequence of the
characters 0-9, A-F, P and X. E represents *, F represents #, P is a
pause (short wait, like a comma in a modem string) and X represents "wait for call completion".
</p>
<p>When the "user=dialstring" is used, a context parameter as defined in
<a class="info" href="#RFC3966">[RFC3966]<span> (</span><span class="info">Schulzrinne, H., “The tel URI for Telephone Numbers,” December 2004.</span><span>)</span></a> MUST be specified. The context parameter would normally be a domain name.
The domain name does not have to resolve to any actual host but MUST
be under the administrative control of the entity managing the local
phone context. The context parameter value is normally configured in the user agent.
</p>
<p>A proxy server or Back to Back User Agent (B2BUA) <a class="info" href="#RFC3261">[RFC3261]<span> (</span><span class="info">Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.</span><span>)</span></a> which is authoritative for the context may
translate the dial string to a telephone number or service invocation
URI. If such a translation is performed, the proxy server MUST change
the URI parameter value from "user=dialstring" to "user=phone". This translation MUST occur
prior to the call leaving the domain of the context.
</p>
<p>Examples of dial string use include:
</p><pre>; what a SIP Phone might emit when a user dials extension 123
sip:123@sippbx.example.com;user=dialstring;
phone-context=atlanta.example.com
;existing voicemail systems have a local access extension,
;then expect to see the extension number as DTMF for the mailbox
sips:4500X4123@sip.example.com;user=dialstring;
phone-context='biloxi.example.com'</pre>
<p>
</p>
<a name="anchor5"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<a name="rfc.section.5"></a><h3>5. IANA Considerations</h3>
<p><a class="info" href="#RFC3969">[RFC3969]<span> (</span><span class="info">Camarillo, G., “The Internet Assigned Number Authority (IANA) Uniform Resource Identifier (URI) Parameter Registry for the Session Initiation Protocol (SIP),” December 2004.</span><span>)</span></a> defines a 'sip:' or 'sips:' URI Parameter sub
registry. The "user" parameter is specified as having predefined
values.
</p>
<p>This RFC defines a new value for the "user" parameter, "dialstring".
This RFC must be added to the references listed for the "user"
parameter.
</p>
<p>This RFC defines a new parameter in the sub-registry,
"phone-context", whose meaning and syntax are derived from the same
parameter in <a class="info" href="#RFC3966">[RFC3966]<span> (</span><span class="info">Schulzrinne, H., “The tel URI for Telephone Numbers,” December 2004.</span><span>)</span></a>. This parameter does not have
a set of predefined values.
</p>
<a name="security"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<a name="rfc.section.6"></a><h3>6. Security Considerations</h3>
<p>dial strings 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 beyond the domain of the UAC.
If they are sent across the Internet, they SHOULD be protected against eavesdropping
with TLS per the procedures in <a class="info" href="#RFC3261">[RFC3261]<span> (</span><span class="info">Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.</span><span>)</span></a>.
</p>
<a name="rfc.references1"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<h3>7. Normative References</h3>
<table width="99%" border="0">
<tr><td class="author-text" valign="top"><a name="RFC2119">[RFC2119]</a></td>
<td class="author-text"><a href="mailto:sob@harvard.edu">Bradner, S.</a>, “<a href="ftp://ftp.isi.edu/in-notes/rfc2119.txt">Key words for use in RFCs to Indicate Requirement Levels</a>,” BCP 14, RFC 2119, March 1997 (<a href="ftp://ftp.isi.edu/in-notes/rfc2119.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2119.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2119.xml">XML</a>).</td></tr>
<tr><td class="author-text" valign="top"><a name="RFC3261">[RFC3261]</a></td>
<td class="author-text">Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “<a href="ftp://ftp.isi.edu/in-notes/rfc3261.txt">SIP: Session Initiation Protocol</a>,” RFC 3261, June 2002.</td></tr>
<tr><td class="author-text" valign="top"><a name="RFC3966">[RFC3966]</a></td>
<td class="author-text">Schulzrinne, H., “<a href="ftp://ftp.isi.edu/in-notes/rfc3966.txt">The tel URI for Telephone Numbers</a>,” RFC 3966, December 2004.</td></tr>
<tr><td class="author-text" valign="top"><a name="RFC3969">[RFC3969]</a></td>
<td class="author-text">Camarillo, G., “<a href="ftp://ftp.isi.edu/in-notes/rfc3969.txt">The Internet Assigned Number Authority (IANA) Uniform Resource Identifier (URI) Parameter Registry for the Session Initiation Protocol (SIP)</a>,” BCP 99, RFC 3969, December 2004.</td></tr>
</table>
<a name="rfc.authors"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<h3>Author's Address</h3>
<table width="99%" border="0" cellpadding="0" cellspacing="0">
<tr><td class="author-text"> </td>
<td class="author-text">Brian Rosen</td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">NeuStar</td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">470 Conrad Dr</td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">Mars, PA 16046</td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">US</td></tr>
<tr><td class="author" align="right">Phone: </td>
<td class="author-text">+1 724 382 1051</td></tr>
<tr><td class="author" align="right">Email: </td>
<td class="author-text"><a href="mailto:br@brianrosen.net">br@brianrosen.net</a></td></tr>
</table>
<a name="rfc.copyright"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="bug" align="right"><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></table>
<h3>Intellectual Property Statement</h3>
<p class='copyright'>
The IETF takes no position regarding the validity or scope of any
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to pertain to the implementation or use of the technology
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Information on the procedures with respect to
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<p class='copyright'>
Copies of IPR disclosures made to the IETF Secretariat and any
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users of this specification can be obtained from the IETF on-line IPR
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<p class='copyright'>
The IETF invites any interested party to bring to its attention
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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 <a href='mailto:ietf-ipr@ietf.org'>ietf-ipr@ietf.org</a>.</p>
<h3>Disclaimer of Validity</h3>
<p class='copyright'>
This document and the information contained herein are provided
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THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY),
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<h3>Copyright Statement</h3>
<p class='copyright'>
Copyright © The Internet Society (2006).
This document is subject to the rights,
licenses and restrictions contained in BCP 78,
and except as set forth therein,
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<h3>Acknowledgment</h3>
<p class='copyright'>
Funding for the RFC Editor function is currently provided by the
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