Difference between revisions of "RFC4967"
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Session Initiation Protocol Uniform Resource Identifier | Session Initiation Protocol Uniform Resource Identifier | ||
− | Status of This Memo | + | '''Status of This Memo''' |
This document specifies an Internet standards track protocol for the | This document specifies an Internet standards track protocol for the | ||
Internet community, and requests discussion and suggestions for | Internet community, and requests discussion and suggestions for | ||
improvements. Please refer to the current edition of the "Internet | improvements. Please refer to the current edition of the "Internet | ||
− | Official Protocol Standards" (STD 1) for the standardization state | + | Official Protocol Standards" ([[STD1|STD 1]]) for the standardization state |
and status of this protocol. Distribution of this memo is unlimited. | and status of this protocol. Distribution of this memo is unlimited. | ||
− | Copyright Notice | + | '''Copyright Notice''' |
Copyright (C) The IETF Trust (2007). | Copyright (C) The IETF Trust (2007). | ||
− | Abstract | + | '''Abstract''' |
− | RFC 3966 explicitly states that 'tel' URIs may not represent a dial | + | [[RFC3966|RFC 3966]] explicitly states that 'tel' URIs may not represent a dial |
string. That leaves no way specify a dial string in a standardized | string. That leaves no way specify a dial string in a standardized | ||
way. Great confusion exists with the SIP URI parameter "user=phone", | way. Great confusion exists with the SIP URI parameter "user=phone", | ||
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may specify "user=dialstring" to encode a dial string as a 'sip:' or | may specify "user=dialstring" to encode a dial string as a 'sip:' or | ||
'sips:' URI. | 'sips:' URI. | ||
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− | |||
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== Introduction == | == Introduction == | ||
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that do not have internal translation mechanisms. Without a | that do not have internal translation mechanisms. Without a | ||
translation mechanism in the phone, the phone must send the dial | translation mechanism in the phone, the phone must send the dial | ||
− | string in a 'sip:' or 'sips:' URI [RFC3261] to an intermediary that | + | string in a 'sip:' or 'sips:' URI [[RFC3261]] to an intermediary that |
can transform the dial string to a phone number or a service | can transform the dial string to a phone number or a service | ||
invocation. The intermediary is able to perform this transform | invocation. The intermediary is able to perform this transform | ||
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", | The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", | ||
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this | "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this | ||
− | document are to be interpreted as described in [RFC2119]. | + | document are to be interpreted as described in [[RFC2119]]. |
It is assumed that the reader is familiar with the terminology and | It is assumed that the reader is familiar with the terminology and | ||
− | acronyms defined in [RFC3261]. | + | acronyms defined in [[RFC3261]]. |
== Requirements == | == Requirements == | ||
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When the "user=dialstring" is used, a context parameter, as defined | When the "user=dialstring" is used, a context parameter, as defined | ||
− | in [RFC3966], MUST be specified. The context parameter would | + | in [[RFC3966]], MUST be specified. The context parameter would |
normally be a domain name. The domain name does not have to resolve | 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 | to any actual host but MUST be under the administrative control of | ||
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The syntax of the context parameter follows the same conventions as | The syntax of the context parameter follows the same conventions as | ||
− | the same parameter in [RFC3966], that is, it appears between the | + | the same parameter in [[RFC3966]], that is, it appears between the |
− | digits and the "@" in the userinfo [RFC3261] of the URI: | + | digits and the "@" in the userinfo [[RFC3261]] of the URI: |
− | dialstring = dialstring-digits context; context from RFC 3966 | + | dialstring = dialstring-digits context; context from [[RFC3966|RFC 3966]] |
dialstring-digits = *dialstring-element dialstring-digit | dialstring-digits = *dialstring-element dialstring-digit | ||
*dialstring-element | *dialstring-element | ||
− | dialstring-digit = HEXDIG / "*" / "#"; HEXDIG from RFC 3966 | + | dialstring-digit = HEXDIG / "*" / "#"; HEXDIG from [[RFC3966|RFC 3966]] |
dialstring-element = dialstring-digit / "P" / "X" / | dialstring-element = dialstring-digit / "P" / "X" / | ||
− | visual-separator; visual-separator from RFC 3966 | + | visual-separator; visual-separator from [[RFC3966|RFC 3966]] |
A dial string SHOULD NOT be used for an AoR (Address of Record) in a | A dial string SHOULD NOT be used for an AoR (Address of Record) in a | ||
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equivalent, which is probably not desirable. | equivalent, which is probably not desirable. | ||
− | A proxy server or Back to Back User Agent (B2BUA) [RFC3261], which is | + | A proxy server or Back to Back User Agent (B2BUA) [[RFC3261]], which is |
authoritative for the context, may translate the dial string to a | authoritative for the context, may translate the dial string to a | ||
telephone number or service invocation URI. The telephone number MAY | telephone number or service invocation URI. The telephone number MAY | ||
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== IANA Considerations == | == IANA Considerations == | ||
− | [RFC3969] defines a 'sip:' or 'sips:' URI Parameter sub registry. | + | [[RFC3969]] defines a 'sip:' or 'sips:' URI Parameter sub registry. |
The "user" parameter is specified as having predefined values. | The "user" parameter is specified as having predefined values. | ||
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of the UAC (User Agent Client). If they are sent across the | of the UAC (User Agent Client). If they are sent across the | ||
Internet, they SHOULD be protected against eavesdropping with TLS | Internet, they SHOULD be protected against eavesdropping with TLS | ||
− | (Transport Layer Security) per the procedures in [RFC3261]. | + | (Transport Layer Security) per the procedures in [[RFC3261]]. |
== Normative References == | == Normative References == | ||
− | [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate | + | [[RFC2119]] Bradner, S., "Key words for use in RFCs to Indicate |
− | Requirement Levels", BCP 14, RFC 2119, March 1997. | + | Requirement Levels", [[BCP14|BCP 14]], [[RFC2119|RFC 2119]], March 1997. |
− | [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, | + | [[RFC3261]] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, |
A., Peterson, J., Sparks, R., Handley, M., and E. | A., Peterson, J., Sparks, R., Handley, M., and E. | ||
− | Schooler, "SIP: Session Initiation Protocol", RFC 3261, | + | Schooler, "SIP: Session Initiation Protocol", [[RFC3261|RFC 3261]], |
June 2002. | June 2002. | ||
− | [RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", | + | [[RFC3966]] Schulzrinne, H., "The tel URI for Telephone Numbers", |
− | RFC 3966, December 2004. | + | [[RFC3966|RFC 3966]], December 2004. |
− | [RFC3969] Camarillo, G., "The Internet Assigned Number Authority | + | [[RFC3969]] Camarillo, G., "The Internet Assigned Number Authority |
(IANA) Uniform Resource Identifier (URI) Parameter | (IANA) Uniform Resource Identifier (URI) Parameter | ||
Registry for the Session Initiation Protocol (SIP)", | Registry for the Session Initiation Protocol (SIP)", | ||
− | BCP 99, RFC 3969, December 2004. | + | [[BCP99|BCP 99]], [[RFC3969|RFC 3969]], December 2004. |
Author's Address | Author's Address | ||
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This document is subject to the rights, licenses and restrictions | This document is subject to the rights, licenses and restrictions | ||
− | contained in BCP 78, and except as set forth therein, the authors | + | contained in [[BCP78|BCP 78]], and except as set forth therein, the authors |
retain all their rights. | retain all their rights. | ||
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made any independent effort to identify any such rights. Information | made any independent effort to identify any such rights. Information | ||
on the procedures with respect to rights in RFC documents can be | on the procedures with respect to rights in RFC documents can be | ||
− | found in BCP 78 and BCP 79. | + | found in [[BCP78|BCP 78]] and [[BCP79|BCP 79]]. |
Copies of IPR disclosures made to the IETF Secretariat and any | Copies of IPR disclosures made to the IETF Secretariat and any | ||
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Funding for the RFC Editor function is currently provided by the | Funding for the RFC Editor function is currently provided by the | ||
Internet Society. | Internet Society. | ||
+ | |||
+ | [[Category:Standards Track]] |
Latest revision as of 20:12, 5 October 2020
Network Working Group B. Rosen Request for Comments: 4967 NeuStar Category: Standards Track July 2007
Dial String Parameter for the Session Initiation Protocol Uniform Resource Identifier
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
RFC 3966 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.
Contents
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 a user part consisting of a dial string from a user part that happens to be composed of characters that would appear in a dial string.
Use of DTMF (dual tone multi-frequency) 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, an 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 dial string is being presented would be useful.
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.
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 multi-frequency. 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 as the telephone dial pad implies. 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 (Public Switched Telephone Network). The "digits" for the fourth column are usually expressed using the letters A through D. Thus, "C" is 852/1633Hz. Some systems do 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 a user part that happens to consist of the same characters.
Solution
A new alternative value for the "userinfo" 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 dial string is a sequence of the characters 0-9, A-F, P, X, '*' and '#'. 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.
The syntax of the context parameter follows the same conventions as the same parameter in RFC3966, that is, it appears between the digits and the "@" in the userinfo RFC3261 of the URI:
dialstring = dialstring-digits context; context from RFC 3966 dialstring-digits = *dialstring-element dialstring-digit *dialstring-element dialstring-digit = HEXDIG / "*" / "#"; HEXDIG from RFC 3966 dialstring-element = dialstring-digit / "P" / "X" / visual-separator; visual-separator from RFC 3966
A dial string SHOULD NOT be used for an AoR (Address of Record) in a REGISTER. Parameters are ignored in registration. Thus, two registrations with different phone-contexts would be considered equivalent, which is probably not desirable.
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. The telephone number MAY be expressed as a global or local tel: URI, or it MAY be left as a sip: or sips: URI with the URI parameter value changed from "user= " to "user=phone".
Examples of dial string use include:
- what a SIP Phone might emit when a user dials extension 123
sip:123;[email protected];user=dialstring
- existing voicemail systems have a local access extension,
- then expect to see the extension number as DTMF for the mailbox
sip:450X123;[email protected];user=dialstring
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 has been added to the references listed for the "user" parameter.
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. Dial strings normally SHOULD NOT be sent beyond the domain of the UAC (User Agent Client). If they are sent across the Internet, they SHOULD be protected against eavesdropping with TLS (Transport Layer Security) per the procedures in RFC3261.
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, 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.
Author's Address
Brian Rosen NeuStar 470 Conrad Dr Mars, PA 16046 USA
Phone: +1 724 382 1051 EMail: [email protected]
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
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.
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Acknowledgement
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