Network Working Group E. Wilde
Internet-Draft Swiss Federal Institute of
Expires: July 25, 2002 Technology
A. Vaha-Sipila
Nokia
January 24, 2002
URI scheme for GSM Short Message Service
draft-wilde-sms-uri-01
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on July 25, 2002.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This memo specifies a URI (Universal Resource Identifier) scheme
"sms" for specifying a recipient (and optionally a gateway) for an
SMS message. SMS messages are two-way paging messages that can be
sent from and received by a mobile phone or a suitably equipped
computer.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 The Short Message Service . . . . . . . . . . . . . . . . . 3
1.2 Universal Resource Identifiers . . . . . . . . . . . . . . . 3
1.3 SMS Messages and the Internet . . . . . . . . . . . . . . . 3
1.3.1 SMS Messages and the Web . . . . . . . . . . . . . . . . . . 4
1.3.2 SMS Messages and Forms . . . . . . . . . . . . . . . . . . . 4
2. The "sms" URI Scheme . . . . . . . . . . . . . . . . . . . . 5
2.1 Applicability . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Formal Definition . . . . . . . . . . . . . . . . . . . . . 6
2.3 Parsing an "sms" URI . . . . . . . . . . . . . . . . . . . . 6
2.4 Examples of Use . . . . . . . . . . . . . . . . . . . . . . 7
2.5 Using "sms" URIs in HTML Forms . . . . . . . . . . . . . . . 8
3. "sms" URIs and SMS Web Services . . . . . . . . . . . . . . 8
3.1 Example . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . 9
5. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1 From -00 to -01 . . . . . . . . . . . . . . . . . . . . . . 10
Normative References . . . . . . . . . . . . . . . . . . . . 11
Non-Normative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 12
A. Where to send Comments . . . . . . . . . . . . . . . . . . . 12
B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
Full Copyright Statement . . . . . . . . . . . . . . . . . . 14
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1. Introduction
Compliant software MUST follow this specification. The capitalized
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 [RFC2119].
1.1 The Short Message Service
The Short Message Service (SMS) [SMS] is a rather simple service for
sending messages between SMS clients or, using so-called "Telematic
Interworking", from an SMS client through a gateway to a receiver
using a different service, such as fax or email. The SMS service is
described in more detail in the SMS service registration memo [draft-
wilde-sms-service-01].
1.2 Universal Resource Identifiers
One of the core specifications for identifying resources on the
Internet is RFC 2396 [RFC2396], specifying the syntax and semantics
of a Universal Resource Identifier (URI). The most important notion
of URIs are "schemes", which define a framework within which
resources can be identified (and possibly accessed). URIs enable
users to identify resources, and are used for very diverse schemes
such as access protocols (HTTP, FTP), broadcast media (TV channels
[RFC2838]), messaging (email [RFC2368]), or even telephone numbers
(voice [RFC2806]).
URIs often are mentioned together with Universal Resource Names
(URNs) and/or Uniform Resource Locators (URLs), and it often is
unclear how to separate these concepts. For the purpose of this
memo, only the term URI will be used, referring to the most
fundamental concept. The World Wide Web Consortium (W3C) has issued
a note [uri-clarification] discussing the topic of URIs, URNs, and
URLs in detail.
1.3 SMS Messages and the Internet
One of the important reasons for the universal access of the Web is
the ability to access all information through a unique interface.
This kind of integration makes it easy to provide information as well
as to consume it. One aspect of this integration is the support of
user agents (in the case of the Web, commonly referred to as
browsers) for multiple content formats (such as HTML, GIF, JPEG) and
access schemes (such as HTTP, HTTP-S, FTP).
The "mailto" scheme has proven to be very useful and popular, because
most user agents support it by providing an email composition
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facility when the user activates (eg, clicks on) the URI.
Accordingly, the "sms" scheme could be supported by user agents by
providing an SMS message composition facility when the user activates
the URI. Alternatively, in cases where the user agent does not
provide a built-in SMS message composition facility, the scheme could
still be supported by opening a Web page which provides such a
service. The specific Web page to be used could be configured by the
user, so that each user could use the SMS message composition service
of his choice.
This goal of this memo is to specify the "sms" URI scheme, so that
user agents (such as Web browsers and email clients) could start to
support it.
1.3.1 SMS Messages and the Web
SMS messages can provide an alternative to a "mailto" URIs [RFC2368],
or "tel" or "fax" URIs [RFC2806]. When a "sms" URI is activated, the
user agent MAY start a program for sending an SMS message, just as
"mailto" may open a mail client. Unfortunately, most browsers do not
support the external handling of internally unsupported URI schemes
in the same generalized way as most of them support external handling
of additional MIME type content for types which they do not support
internally. Ideally, user agents should implement generic URI
parsers and provide a way to associate unsupported schemes with
external applications (or Web services).
The recipient of an SMS message need not be a mobile phone. It can
be a server that can process SMS messages, either by gatewaying them
to another messaging system (such as regular electronic mail), or by
parsing them for supplementary services.
SMS messages can be used to transport almost any kind of data (even
though there is a very tight size limit), but the only standardized
data formats are character-based messages in different character
encodings. SMS messages have a maximum length of 160 characters
(when using 7-bit characters from the SMS character set), or 140
octets. However, SMS messages can be concatenated to form longer
messages. It is up to the user agent to decide whether to limit the
length of the message, and how to indicate this limit in its user
interface, if necessary. There is one exception to this, see Section
2.5.
1.3.2 SMS Messages and Forms
The Hypertext Markup Language (HTML) [HTML401] provides a way to
collect information from a user and pass it to a server for
processing. This functionality is known as "HTML forms". A filled-
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in form is usually sent to the destination using the Hypertext
Transfer Protocol (HTTP) or email. However, SMS messages can also be
used as the transport mechanism for these forms. As SMS transport is
"out-of-band" as far as normal HTTP over TCP/IP is concerned, this
provides a way to fill in forms offline, and send the data without
making a TCP connection to the server, as the set-up time, cost, and
overhead for a TCP connection are large compared to an SMS message.
Also, depending on the network configuration, the sender's telephone
number may be included in the SMS message, thus providing a weak form
of authentication.
2. The "sms" URI Scheme
Syntax definitions are given using the Augmented BNF for Syntax
Specifications [RFC2234].
2.1 Applicability
This URI scheme is intended for sending an SMS message to a certain
recipient(s). The functionality is quite similar to that of the
"mailto" URL, which (as per RFC 2368 [RFC2368]) can also be used with
a comma-separated list of email addresses.
In some situations, it may be necessary to guide the sender to send
the SMS message via a certain SMSC. For this purpose, the URI may
specify the number of the SMSC.
SMS messages may be sent through gateways to other services. These
gateways are operated inside SMS centers. An "SMS" URI may specify
that a certain gateway should be used.
The notation for phone numbers is taken from [draft-allocchio-gstn-
01]. Refer to this document for information on why this particular
format was chosen.
How the SMS message is sent to the SMSC is outside the scope of this
specification. SMS messages can be sent over the GSM air interface,
by using a modem and a suitable protocol, or by accessing services
over other protocols, such as a Web service for sending SMS messages.
Also, SMS message service options like deferred delivery and delivery
notification requests are not in the scope of this document. Such
services MAY be requested from the network by the user agent if
necessary.
SMS messages sent as a result of this URI MUST be sent as class 1 SMS
messages, if the user agent is able to specify the message class.
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2.2 Formal Definition
The URI is case-insensitive. The syntax of an "sms" URI is formally
described as follows, where the base syntax is taken from RFC 2396
[RFC2396]:
sms-uri = scheme ":" scheme-specific-part
scheme = "sms"
scheme-specific-part = 1*( sms-recipient ) [ sms-body ]
sms-recipient = gstn-phone sms-qualifier
[ "," sms-recipient ]
sms-qualifier = *( smsc-qualifier / pid-qualifier )
smsc-qualifier = ";smsc=" SMSC-sub-addr
pid-qualifier = ";pid=" PID-sub-addr
sms-body = ";body=" *urlc
The syntax definition for "gstn-phone" is taken from [draft-
allocchio-gstn-01], allowing global as well as local telephone
numbers.
The syntax definition for "SMSC-sub-addr" and "PID-sub-addr" is
derived from [draft-wilde-sms-service-01], please refer to that
document for the syntax of the qualifier values.
The "sms-body" is used to define the body of the SMS message to be
composed. It consists or URL-encoded characters. Only characters
from the 7-bit SMS character set [SMS-CHAR] are allowed.
It should be noted that both the SMSC as well as the PID qualifier
may appear only once per sms-recipient. If multiple qualifiers are
present, conforming software MUST interpret the first occurrence and
ignore all other occurrences.
2.3 Parsing an "sms" URI
The following list describes the steps for processing an "sms" URI:
1. The "gstn-phone" of the first "sms-recipient" is extracted. It
is the phone number of the final recipient and it MUST be written
in international form with country code, unless the number only
works from inside a certain geographical area or a network. Note
that some numbers may work from several networks but not from the
whole world - these SHOULD be written in international form.
According to [draft-allocchio-gstn-01], all international numbers
MUST begin with a "+" character. Hyphens and dots are only to
aid readability. They MUST NOT have any other meaning.
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2. The "smsc-qualifier" of the first "sms-recipient" is extracted,
if present.
3. The "pid-qualifier" of the first "sms-recipient" is extracted, if
present.
4. The "sms-body" is extracted, if present.
5. The user agent should provide some means for message composition,
either by implementing this itself, or by accessing a service
providing it. Message composition SHOULD start with the body
extracted from the "sms-body", if present. If the "pid-
qualifier" is set to "pid=SMTP:...", then the user agents must
make sure that the email address is correctly set (as defined by
the SMS specification [SMS]) in the message being composed.
6. After message composition, a user agent SHOULD try to send the
message first using the SMSC set in the "smsc-qualifier" (if
present). If that fails, the user agent MAY try another SMSC.
7. If the URI consists of a comma-separated list of recipients (ie,
contains multiple "sms-recipient" parts), all of them are
processed in this manner. Exactly the same message SHOULD be
sent to all of the listed recipients.
2.4 Examples of Use
sms:+41796431851
This indicates an SMS message capable recipient at the given
telephone number. The message is sent using the user agent's default
SMSC.
sms:+41796431851;via=+41794999000
This indicates that the SMS message should be sent using the SMSC at
the given number.
sms:+41796431851,+4116321035;pid=fax
This URI should result in two SMS messages being sent, one to the
recipient number as shown in the example above, the other one being
sent as a fax to the second number (the fax is sent by the SMSC
performing the gatewaying, not by the user agent).
sms:+41796431851;pid=smtp:ietf@dret.net;body=hello%20there
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In this case, a message (initially being set to "hello there", which
may have been modified by the user before sending) will be sent via
SMS using the SMS to email functionality in the SMSC, so that it will
eventually result in an email being sent to the specified email
address. In this case, the phone number will not be interpreted.
2.5 Using "sms" URIs in HTML Forms
When using a "sms" type URI as an action URI for HTML form submission
[HTML401], the form contents MUST be packaged in the SMS message just
as they are packaged when using a "mailto" URL [RFC2368], using the
"application/x-www-form-urlencoded" MIME type, effectively packaging
all form data into URI compliant syntax [RFC2396]. The SMS message
MUST NOT contain any HTTP headers, only the form data. The MIME type
is implicit. It MUST NOT be transferred in the SMS message.
The character encoding used for form submissions MUST be UTF-8
[RFC2279]. It should be noted, however, that user agents MUST URL-
encode form submissions before sending them.
The user agent SHOULD inform the user about the possible security
hazards involved when submitting the form (it is probably being sent
as plain text over an air interface).
If the form submission is longer than the maximum SMS message size,
the user agent MAY either concatenate SMS messages, if it is able to
do so, or it MAY refuse to send the message. The user agent MUST NOT
send out partial form submissions.
Form submission via an "sms" URI can be combined with Telematic
Interworking to result in form submissions being submitted via an SMS
message and finally being sent to an email account. In this case,
all provisions for using the email "pid-qualifier" and using "sms"
URIs with HTML forms must be followed.
3. "sms" URIs and SMS Web Services
In many cases, user agents will not be able to directly compose and
send SMS messages (because this requires that such a service is
accessible to the system the user agent is running on). However, it
is likely that the user has access to a Web service that provides an
SMS service, such as a Web site offering form-based SMS composition.
Ideally, the user agent should access this Web service when
activating an "sms" URI, thus enabling the user to use the Web
service.
One problem with this approach is that the Web service should somehow
get the "sms" URI, in order interpret it and set the required
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parameters (such as the receiver's phone number). The easiest way to
implement this is for the user agent to add the "sms" URI as query
string to the Web service's URI. Consequently, user agents
supporting SMS Web services identified by URIs SHOULD append the
"sms" URI as query string to the Web services URI when accessing the
Web service. Web services providing SMS composition facilities
SHOULD expect to receive an "sms" URI as query string and should
process it as described by this memo. This method only can be
applied for Web service URIs which permit query strings (such as
"http" and "https" URIs). For other Web service URIs (such as "ftp"
and "mailto"), user agents as well as Web services MUST NOT use the
query string.
It should be noted that RFC 2396 [RFC2396] defines that within query
strings, the characters ";", "/", "?", ":", "@", "&", "=", "+", ",",
and "$" are reserved. It is therefore necessary to encode the "sms"
URI accordingly before appending it as query string.
3.1 Example
A document contains this piece of (X)HTML:
Send me an SMS!
The user agent interpreting this document does not internally support
SMS message composition, but has configured to access a Web service
for handling "sms" URIs. This Web service has the following URI:
http://sms.example.com/sms-form
When the user activates the "sms" URI (eg, by clicking on the text
"Send me an SMS!"), the user agents acts as if the activated URI had
been:
http://sms.example.com/sms-form?sms%3A%2B41796431851
The Web service is then responsible for parsing the query string and
providing an approriate interface, for example by already filling in
the recipient address with the number provided in the "sms" URI.
4. Security Considerations
The "Security Considerations" section of the SMS service registration
memo [draft-wilde-sms-service-01] MUST be consulted.
A user agent SHOULD NOT send out SMS messages without the knowledge
of the user, because of associated risks, which include sending
masses of SMS messages to a subscriber without his consent, and the
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costs involved in sending an SMS message.
The user agent SHOULD have some mechanism that the user can use to
filter out unwanted destinations for SMS messages. The user agent
SHOULD also have some means of restricting the number of SMS messages
being sent as the result of activating one "sms" URI.
If an "sms" URI contains a pid-qualifier and the user agent supports
the qualifier and its value, then the user agent MUST set the SMS
message's PID as specified by the qualifier. User agents MAY inform
users about the value and the functional consequences of PID
qualifiers (eg, by notifying users that sending the SMS effectively
will result in a fax message being delivered, rather than an SMS
message).
The method described in section Section 3 adds another level of
indirection to the handling of "sms" URIs. If this method is
combined with the pid-qualifier gateway functionality, SMS
composition and reception will probably be distributed over three
different protocols (the Web service, SMS transport itself, and the
service selected by the pid-qualifier). User agent SHOULD make this
clear to users (either when the Web service is being configured, or
when it is accessed).
The Telematic Interworking functionality of the SMSC addressed by the
pid-qualifier is not necessarily implemented by the SMSC being used,
and SMSC providers are known for not or not correctly supporting some
or all pid-qualifier values. User agents SHOULD take into account
that the success rate of SMS messages being sent using pid-qualifiers
is lower than that of "plain" SMS messages.
5. Change Log
5.1 From -00 to -01
o Added the "sms-body" field and its processing rules.
o Added Section Section 3 about using "sms" URIs as query strings
for SMS Web services.
o Fixed typo in ABNF (said "global-phone" instead of "gstn-phone").
o Added some explanatory text about form submissions using email
Telematic Interworking.
o Added some text about character encoding in form submissions.
Normative References
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[HTML401] Raggett, D., Le Hors, A. and I. Jacobs,
"HTML 4.01 Specification", W3C REC-
html401, December 1999, .
[RFC2119] Bradner, S., "Key words for use in RFCs
to Indicate Requirement Levels", RFC
2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented
BNF for Syntax Specifications: ABNF",
RFC 2234, November 1997.
[RFC2279] Yergeau, F., "UTF-8, a transformation
format of ISO 10646", RFC 2279, January
1998.
[RFC2396] Berners-Lee, T., Fielding, R. and L.
Masinter, "Uniform Resource Identifiers
(URI): Generic Syntax", RFC 2396,
August 1998.
[SMS] European Telecommunications Standards
Institute, "Digital Cellular
Telecommunications System (Phase 2+);
Technical realization of the Short
Message Service (SMS); Point-to-Point
(PP)", December 1998, .
[SMS-CHAR] European Telecommunications Standards
Institute, "ETSI TS 100 901 (GSM 03.38
version 7.2.0 Release 1998): Digital
Cellular Telecommunications System
(Phase 2+); Alphabets and language-
specific information", July 1999,
.
[draft-allocchio-gstn-01] Allocchio, C., "Text string notation
for Dial Sequences and GSTN / E.164
addresses", draft-allocchio-gstn-01
(work in progress), November 2001.
[draft-wilde-sms-service-01] Wilde, E., "Registration of GSTN SMS
Service Qualifier", draft-wilde-sms-
service-01 (work in progress), January
2002.
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Non-Normative References
[RFC2368] Hoffmann, P., Masinter, L. and J. Zawinski, "The
mailto URL scheme", RFC 2368, June 1998.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC
2629, June 1999.
[RFC2806] Vaha-Sipila, A., "URLs for Telephone Calls", RFC
2806, April 2000.
[RFC2838] Zigmond, D. and M. Vickers, "Uniform Resource
Identifiers for Television Broadcasts", RFC
2838, May 2000.
[uri-clarification] World Wide Web Consortium, "URIs, URLs, and
URNs: Clarifications and Recommendations 1.0",
W3C uri-clarification , September 2001, .
Authors' Addresses
Erik Wilde
Swiss Federal Institute of Technology
ETH-Zentrum
8092 Zurich
Switzerland
Phone: +41-1-6325132
EMail: ietf@dret.net
URI: http://dret.net/netdret/
Antti Vaha-Sipila
Nokia
EMail: antti.vaha-sipila@nokia.com
Appendix A. Where to send Comments
Please send all comments about this document to Erik Wilde.
Appendix B. Acknowledgements
This document has been written using the IETF document DTD described
in RFC 2629 [RFC2629].
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Thanks to Claudio Allocchio for his comments.
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