Internet Draft N. Tsarmpopoulos May 10, 1999 UMEM Expires: October 1999 draft-tsarmpopoulos-sms-address-mail-00.txt Minimal 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 Short Messaging System (SMS) is widely used by GSM mobile phones for the transmission of text messages. This memo extends the "Minimal GSTN address format in Internet Mail" with a new "service-selector" value, which allows the interaction of Internet addressing with Mobile Terminated (MT) SMS addressing. The purpose of the memo is to facilitate the transmission of SMS messages using the familiar e-mail client application. 1. Introduction The interaction of Global Switched Telephone Network (GSTN) addressing with Internet Mail, which is defined in [1], allows the development of gateways with other messaging systems, such as Fax [2] and SMS. Tsarmpopoulos Internet Draft 1 Minimal SMS address format in Internet Mail May 1999 This memo describes the MINIMAL addressing method and extensions to encode the SMS addresses in e-mail addresses, as required in [1]. There are two major objectives: - enable an e-mail user to send Mobile Terminated (MT) SMS messages from the familiar e-mail client interface. - facilitate the use of Internet Mail as a transport mechanism for SMS messages. This method for sending SMS messages through Internet mail allows mobile network operators to install and publish the addresses of Email-to-SMS gateways, to facilitate the exchange of messages between the GSM-SMS and the Internet Mail messaging systems. 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]. 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: I-sms device: A device, which has an Internet domain name and is able to send directly or indirectly SMS messages. mta-I-sms: The Internet domain name that identifies uniquely an I-sms device over the Internet sms-email: The complete Internet e-mail address structure, which is used to transport an SMS address over the Internet e-mail service. 3. Minimal SMS address The minimal SMS address is defined in accordance with RFC 2303 [1]. The string ôSMSö is assigned to the ôservice selectorö element. The formal definitions follow: service-selector = "SMS" Tsarmpopoulos Internet Draft 2 Minimal SMS address format in Internet Mail May 1999 Therefore, the minimal specification of an SMS in e-mail address is: sms-address = sms-mbox and sms-mbox = "SMS=" global-phone The Minimal supported syntax for "global-phone" is defined in reference [1]. We give the definition also here: global-phone= "+" 1*( DIGIT , written-sep ) written-sep = ( "-" , "." ) The use of other dialling schemas for PSTN numbers is also allowed, but support for the "global-phone" syntax is compulsory. If a proprietary dialling 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. Note: The specification of alternate dialling schemas is out of the scope for this minimal specification ImplementersÆ Note: Although using the "written-sep" element facilitates users, implementers are not encouraged to include them when submitting messages to the Message Transport System. 3.2 Examples of a minimal "sms-address" The following addresses are valid "sms-address" values: SMS=+441612327220 SMS=+30-421-30600 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 will be referred to as "mta-I-sms". mta-I-sms = domain For "domain" strings used in SMTP transmissions, the string MUST conform to the requirements of the specifications [5], [7]. For Tsarmpopoulos Internet Draft 3 Minimal SMS address format in Internet Mail May 1999 "domain" strings used in message content headers, the string MUST conform to the requirements of the standards [6], [7]. 5. The sms-email The complete structure of an SMS-to-Email address is called "sms- email". This object is a valid e-mail address, based on the rules defined in [6] and [7]. It's special 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. It is essential to remind that ôsms-addressö element MUST strictly follow the ôquoting rulesö specified in the relevant standards [6], [7]. 5.2 Some examples of minimal "sms-email" addresses SMS=+448957375644@smsworld.org /SMS=+44342385874/@smsworld.org SMS=+44-5869-318945@smsworld.org 6. Conclusion By using a standard extension mechanism of the Minimal PSTN address format in Internet Mail, this proposal defines a new element and facilitates the delivery of SMS messages to mobile phones through the Internet Mail system. The extension proposed in this memo does not affect or require any changes to the existing e-mail software. 7. Collected Formal Syntax sms-address = sms-mbox sms-mbox = "SMS=" global-phone global-phone= "+" 1*( DIGIT , written-sep ) written-sep = ( "-" , "." ) Tsarmpopoulos Internet Draft 4 Minimal SMS address format in Internet Mail May 1999 8. 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. In particular, 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 SHOULD employ those mechanisms to verify the authenticity and integrity of mail routing records. Junk email is considered important threat to the system, because it may flood the mobile network with SMS messages. For this reason, it is strongly recommended that SMTP servers are configured to validate the identity of the sender and possibly to restrict the number of messages posted from a specific email address in a "per day" or "per hour" basis. 9. 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, ôDomain Name System Security Extensionsö, RFC 2065, January 1997. Tsarmpopoulos Internet Draft 5 Minimal SMS address format in Internet Mail May 1999 [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). 10. Acknowledgements The format of this specification has been based primarily on the work of C. Allocchio, including RFC2304 [2]. The author would also like to thank the members of Internet FAX Working Group of the IETF, for their contributions in extending the functionality of Internet mail. 11. Author's Address Nikolaos Tsarmpopoulos Ulysses Maritime Electronic Market Ltd. 10 Ely Place, London ECIN 6RY E-mail: Tsarb@acm.org Phone: +44-161-2327220, +44-171-2960296 Fax: +44-161-2260191 12. Full Copyright Statement "Copyright (C) The Internet Society (1999). All Rights Reserved. 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