Internet Draft N. Tsarmpopoulos October 19, 1999 UMEM, UMIST Expires: April 1999 SMS address format in Internet Mail Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [8]. 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. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. Abstract The Short Messaging System (SMS) is widely used by GSM mobile phones for the transmission of text messages. This memo specifies the general syntax for email addresses of terminal equipment with SMS capabilities. The purpose of the memo is to facilitate the transmission of SMS messages using a familiar e-mail client application. Minimal SMS address format in Internet Mail May 1999 1. Introduction Short Messages are two-way alphanumeric messages that can be sent and received by mobile phones or server equipment with Short Message Service (SMS) capabilities. The SMS service is provided by the Global System for Mobile Communications (GSM) [10], but other types of mobile or land-based networks also support similar services. Short Messages sent from mobile phones are called mobile originated, while messages received by mobile phones are called mobile terminated. Short messages are stored and forwarded by the Short Message Service Centres (SMSC). An SMSC is identified by a Global Switched Telephone Network (GSTN) number, which has to be known to the sender of a mobile originated message. The availability of the SMS service over different mobile networks depends on roaming agreements of the networks, as well as on a mechanism to deliver the messages. It is the network operator's responsibility to inform the user about the success or failure of the message delivery. This memo facilitates the integration of Internet Mail services with the Short Message Service, by defining the address element of an Internet Mail message sent to a terminal device or server equipment with SMS capabilities. This memo aims in achieving the following goals: - To provide an Internet Mail addressing format for GSTN-addressed terminals and server equipment with SMS capabilities. - To facilitate the development of gateways, which forward Internet Mail messages to the GSM network through the appropriate SMSC system. - To facilitate the use of Internet Mail as a transport mechanism for SMS messages. A general format for representing GSTN addresses with e-mail addresses is defined in [1] and [11]. This memo uses the extension mechanism introduced in [1] and the GSTN address element extensions of [2], to define a standard addressing format for terminals and server equipment with SMS capabilities. The format presented in this memo has been defined with respect to the requirements of the SMS service provided by GSM-based networks, but similar services can also be found on other types of mobile and land-based networks. Such services may use the format and syntax defined in this memo, by defining a new value of the "NET" service qualifier and the required network-specific service qualifiers. This memo covers only addressing issues. Message encoding and transport issues are not discussed. The addressing format presented here complies fully with the general syntax specified in [11], i.e. addresses defined with this memo SHOULD be parsed successfully by software implementations complying with [11]. Minimal SMS address format in Internet Mail May 1999 All implementation supporting this SMS over e-mail address format MUST support as a minimum the specification described in this document. 2. Terminology and Conventions used in this document In this document, the formal definitions are given using the ABNF syntax [3]. Certain basic rules are in uppercase, such as SP, HTAB, CRLF, DIGIT, ALPHA, etc. 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 RFC-2119 [4]. The following terms are also defined: sms-email: The complete Internet e-mail address structure, which is used to transport an SMS address over the Internet e-mail service. mta-I-sms: The Internet domain name that identifies uniquely an I-sms device over the Internet I-sms device: A device, which has an Internet domain name and is able to send directly or indirectly SMS messages. The following abbreviations are frequently used: GSM : Global System for Mobile communications SMS : Short Message Service SMSC : Short Message Service Centre 3. The sms-email The complete structure of an SMS-to-Email address is defined by the element. This object is a valid Internet mail address, based on the rules defined in [6] and [7]. It's structure allows the SMS number to be identified. sms-email = ["/"] sms-address ["/"] "@" mta-I-sms The "/" characters may result from other mail transport service gateways, such as X.400. Implementers' Note: The "/" characters SHOULD be accepted but SHOULD NOT be generated. Gateways are allowed to strip them off when converting to Internet mail addressing. Minimal SMS address format in Internet Mail May 1999 It is essential to remind that element MUST strictly follow the quoting rules specified in the relevant standards [6], [7]. 4. The e-mail address of the I-sms device: mta-I-sms An I-sms device has a name, which identifies it by the Internet Mail system. This is the right hand side (RHS) part of the address, i.e. the part on the right of the "@" sign. This part is defined by the element as follows: mta-I-sms = domain For strings used in SMTP transmissions, the string MUST conform to the requirements of the specifications [5], [7]. For strings used in message content headers, the string MUST conform to the requirements of the standards [6], [7]. 5. The element The element identifies the individual recipient (human or server) of the message, within the supported by the domain. This is the left-hand side (LHS) part of the address, i.e. the part on the left of the "@" sign. When the message is produced by an X.400 gateway of other device, MAY have a prefix and/or a suffix with the "/" character. sms-address = sms-mbox [ via-qualifier ] [ net-qualifier ] [1*( qualif-type1) ] The and the SHOULD NOT appear more than once in a single . The element is defined in [1], paragraph 2. The element definition allows new service qualifiers to be defined in the future, in order to support additional functionality provided by the Short Message Service. However, new elements MUST be defined by separate RFCs or submitted to the author of this memo for inclusion in next versions of the document, and MUST be registered with the appropriate IANA form template, which can be found in [11], appendix B.2. The definition for sms-mbox is: sms-mbox = "SMS=" gstn-phone The element definition complies with the element, which is defined in [11]. Minimal SMS address format in Internet Mail May 1999 The syntax for is given in [11] and supports the global phone scheme, as well as local phone schemes. If a local phone or a proprietary schema is used, it MUST NOT use the leading "+" between the "=" sign and the dialling string. The "+" sign is strictly reserved for the standard "global-phone" syntax. Implementation requirements: It is REQUIRED that the values are supported by software implementations, in order to comply with this specification. Global phone numbers MUST be properly parsed and converted to the local phone scheme when this is required, in order to send the message. It is REQUIRED that gateways and other software implementations are capable of processing any valid string. When an optional element is not supported by a software implementation or a element, which is defined for use with other values, is found: a) this element SHOULD be ignored, b) the process of parsing the SHOULD proceed as normal and, c) the user SHOULD be notified about the unsupported element by an e-mail message. 6. The "VIA" service qualifier Short Message Services usually rely on a middleman to deliver the messages. For GSM-based networks this is called the Short Message Service Centre and it is identified by a address. When specifying the phone number of this middleman is required, the element MUST be used. via-qualifier = "VIA=" message-centre-id message-centre-id = gstn-phone An alternative definition, based on the element definition [11], is the following: Qualif-type1 "keyword" name: VIA Qualif-type1 "value" ABNF definition: value = message-centre-id message-centre-id = gstn-phone Minimal SMS address format in Internet Mail May 1999 If the "VIA" qualifier is present, the gateway MUST send the message via the specified SMSC or not send it at all. 7. The "NET" service qualifier This qualifier specifies the type of the network in use. "GSM" means a GSM-based network of any frequency band. net-qualifier = "NET=" network-type network-type = "GSM" / other-type other-type = string An alternative definition, based on the element [11], is the following: qualif-type1 "keyword" name: NET qualif-type1 "value" ABNF definition: value = network-type network-type = "GSM" / other-type other-type = string The element may be extended by registering the appropriate value. Any value MUST be specified by an RFC document and be registered using the appropriate IANA registration template. 8. Examples of SMS e-mail addresses SMS=+448957375644@smsgateway.org /SMS=+44342385874/@smsworld.org SMS=+44-5869-318945@smsservice.org SMS=07044573897@smsservice.org SMS=07044573897/VIA=+358-50-123-1234@smsservice.org SMS=+44-8934-349856/VIA=+358-50-123-1234/NET=GSM@smsgateway.org 9. Additional implementation considerations This memo provides a compact definition for the SMS address format in internet mail, which facilitates the development of email-to-sms gateways. The grammar specified in this memo defines email Minimal SMS address format in Internet Mail May 1999 addresses, which are valid elements [11] and MUST be used ONLY for the "SMS" value. Gateways supporting multiple services, by identifying different "service-selector" values, MUST use the full specification defined in [11]. 10. Conclusion By using the standard extension mechanisms of the GSTN address format in Internet Mail, this proposal defines new elements that facilitate the transmission of SMS messages through Internet Mail. A new service selector is defined, namely "SMS" and two service qualifiers, the "VIA" and the "NET", which provide the Short Message Service Centre address and the network type of the recipient's network. The "GSM" network type was defined, to provide support for GSM-based networks. The extension proposed in this memo does not affect or require any changes to the existing e-mail software. 11. Collected grammar sms-email = ["/"] sms-address ["/"] "@" mta-I-sms mta-I-sms = domain sms-address = sms-mbox [ via-qualifier ] [ net-qualifier ] [1*( qualif-type1) ] sms-mbox = "SMS=" gstn-phone via-qualifier = "VIA=" message-centre-id net-qualifier = "NET=" network-type message-centre-id = gstn-phone network-type = "GSM" / other-type other-type = string qualif-type1 = "/" keyword "=" string keyword = 1*( DIGIT / ALPHA / "-" ) string = PCHAR gstn-phone = ( global-phone / local-phone ) global-phone = "+" 1*( DIGIT / written-sep ) Minimal SMS address format in Internet Mail May 1999 local-phone = [ exit-code ] [ dial-number ] exit-code = phone-string dial-number = phone-string phone-string = 1*( DTMF / pause / tonewait / written-sep ) DTMF = ( DIGIT / "#" / "*" / "A" / "B" / "C" / "D" ) written-sep = ( "-" / "." ) pause = "p" tonewait = "w" 12. Security Considerations The extension proposed in this memo is based on the existing e-mail mechanisms; thus it is vulnerable to the same type of attacks found for the Internet Mail System. The routing of e-mail messages is determined by Domain Name System (DNS) information, therefore a successful attach on this service could force the mail path via some particular gateway or message transfer agent, where mail security can be affected by compromised software. DNS security mechanisms are defined in [9] and, as they become more widely supported by software implementations, clients MAY employ those mechanisms to verify the authenticity and integrity of mail routing records. Junk email is also considered to be an important threat to the system, because it may flood the mobile network with SMS messages. When SMTP servers process Internet mail messages with the addressing format presented in this memo, they SHOULD be configured to restrict the messages sent to or from a source, based on some heuristic. 13. IANA considerations New values for the element MUST be registered with IANA. To register a value, the form template given in B.1 [11] MUST be used. All IANA considerations mentioned in appendix B [11] apply to the . Minimal SMS address format in Internet Mail May 1999 14. References [1] Allocchio, C., "Minimal PSTN address format in Internet Mail", RFC 2303, March 1998. [2] Allocchio, C., "Minimal FAX address format in Internet Mail", RFC 2304, March 1998. [3] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, Internet Mail Consortium and Demon Internet Ltd., November 1997. [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [5] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, August 1982. [6] Crocker, D., "Standard for the format of ARPA Internet text messages", STD 11, RFC 822, August 1982. [7] Braden, R., "Requirements for Internet hosts - application and support", RFC 1123, October 1989. [9] Eastlake, D. and C. Kaufman, "Domain Name System Security Extensions", RFC 2065, January 1997. [10] TS 100 901 V6.1.0 (1998-07); GSM 03.40 version 6.1.0 Release 1997; Technical realization of the Short Message Service (SMS); Point-to-Point, European Telecommunications Standards Institute (ETSI). [11] Allocchio, C., "GSTN address element extensions in e-mail services", Internet Draft (Work in progress), April 1999, 15. Acknowledgements The following people have participated with their feedback in the realisation of this memo: Vaha-Sipila, A., NOKIA Allocchio, C., GARR-Italy Karakostas, V., UMIST Wing, D., CISCO The author would also like to thank the members of the IETF Internet Fax working group, for their contributions in extending the functionality and the scope of Internet Mail. Minimal SMS address format in Internet Mail May 1999 16. Author's address Nikolaos Tsarmpopoulos Ulysses Maritime Electronic Market Ltd. 10 Ely Place, London ECIN 6RY Internet mail: Tsarb@acm.org Tsarb@excite.com 17. Full Copyright Statement "Copyright (C) The Internet Society (1999). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organisations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. The document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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 MECHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Appendix A. IANA registration templates A.1 "SMS" Service Selector To: IANA@isi.edu Subject: Registration of new values for the GSTN address service-selector specifier "SMS" Service Selector Name: SMS Description of Use: Minimal SMS address format in Internet Mail May 1999 SMS - SMS, an acronym for Short Message Service, is a (possibly bidirectional) alphanumeric paging message found in several mobile phone systems. The recipient of the Short Message is identified by a phone number. The Service Selector and its Qualifiers are defined in RFC[]. Security Considerations: It should be noted that the user agent SHOULD NOT send out Short Messages without the knowledge of the user because of associated risks, which include sending masses of Short Messages to a subscriber without her consent and the costs involved in sending a Short Message. The user agent SHOULD provide a mechanism to restrict the messages sent to or from a source, based on some heuristic. Person & Email Address to Contact for Further Information: To be added to the final version. A.2 "VIA" Qualifier To: IANA@isi.edu Subject: Registration of new values for the GSTN address qualif- type1 element "VIA" qualif-type1 "keyword" name: VIA qualif-type1 "value" ABNF definition: value = message-centre-id message-centre-id = gstn-phone Description of Use: This Qualifier specifies the phone number of the Short Message Centre, which acts as an intermediary when delivering the Short Message. Use Restriction: This qualifier element is only meaningful for the "SMS" Service Selector. This qualifier element SHOULD NOT be used more than once in a single e-mail address. Security Considerations: The security considerations are the same as for the "SMS" Service Selector. Minimal SMS address format in Internet Mail May 1999 Person & email address to contact for further information: To be added to the final version. A.3 "NET" Qualifier To: IANA@isi.edu Subject: Registration of new values for the GSTN address qualif- type1 element "NET" qualif-type1 "keyword" name: NET qualif-type1 "value" ABNF definition: value = network-type network-type = "GSM" / other-type other-type = string Description of Use: This Qualifier specifies the recipient's network type. "GSM" means any GSM-based network (independent of the frequency band used). If there is a requirement for other network types, the names for those MUST be specified by another RFC and registered using another IANA registration template. Use Restriction: This qualifier element is only meaningful for the "SMS" Service Selector. This qualifier element SHOULD NOT be used more than once in a single e-mail address. Security Considerations: The securiry considerations are the same as for the "SMS" Service Selector. Person & email address to contact for further information: To be added in the final version.