iptel B. Rosen Internet-Draft NeuStar Expires: December 27, 2006 June 25, 2006 Dialstring parameter for the Session Initiation Protocol Uniform Resource Identifier draft-rosen-iptel-dialstring-04.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 December 27, 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 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. Rosen Expires December 27, 2006 [Page 1] Internet-Draft Dialstring Parameter June 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 7. Normative References . . . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . . 8 Rosen Expires December 27, 2006 [Page 2] Internet-Draft Dialstring Parameter June 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). 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 [RFC3261] 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. 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. 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. 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]. It is assumed that the reader is familiar with the terminology and acronyms defined in [RFC3261] Rosen Expires December 27, 2006 [Page 3] Internet-Draft Dialstring Parameter June 2006 3. Requirements A mechanism to express a dial string in a 'sip:' or 'sips:' URI is required. A dial string consists of a sequence of * The digits 0-9 * The special characters # and * * The DTMF digits A-D * characters representing a short Pause, and a "Wait for call completion" in a dial string 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. A dial string always exists within a context. The context MUST be specified when expressing a dial string. It MUST be possible to distinguish between a dial string and an user part that happens to consist of the same characters. 4. Solution 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". When the "user=dialstring" is used, a context parameter as defined in [RFC3966] 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. A proxy server or Back to Back User Agent (B2BUA) [RFC3261] which is authoritative for the context may translate the dial string to a telephone number or service invocation URI. If such a translation is Rosen Expires December 27, 2006 [Page 4] Internet-Draft Dialstring Parameter June 2006 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. Examples of dial string use include: ; 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' 5. IANA Considerations [RFC3969] defines a 'sip:' or '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 must 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 [RFC3966]. This parameter does not have a set of predefined values. 6. Security Considerations 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 [RFC3261]. 7. Normative 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, Rosen Expires December 27, 2006 [Page 5] Internet-Draft Dialstring Parameter June 2006 June 2002. [RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966, December 2004. [RFC3969] Camarillo, G., "The Internet Assigned Number Authority (IANA) Uniform Resource Identifier (URI) Parameter Registry for the Session Initiation Protocol (SIP)", BCP 99, RFC 3969, December 2004. Rosen Expires December 27, 2006 [Page 6] Internet-Draft Dialstring Parameter June 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 December 27, 2006 [Page 7] Internet-Draft Dialstring Parameter June 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 December 27, 2006 [Page 8]