As per Relevance of the word elements, we have this rfc below:
Network Working Group C.
Request for Comments: 2303 GARR-
Category: Standards Track March 1998
Minimal PSTN address format in Internet
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
Copyright
Copyright (C) The Internet Society (1998). All Rights Reserved
IESG
This memo describes a simple method of encoding PSTN addresses in
local-part of Internet email addresses, along with an
mechanism to allow encoding of additional standard attributes
for email gateways to PSTN-based services
As with all Internet mail addresses, the left-hand-side (local- part
of an address generated according to this specification, is not to
interpreted except by the MTA that is named on the right-hand-
(domain).
1.
Since the very first e-mail to PSTN services gateway appeared,
number of different methods to specify a PSTN address as an e-
address have been used by implementors. Two major objectives for
- enable an e-mail user to access these services from his/
e-mail interface
- enable some kind of "PSTN over e-mail service" transport,
reduce the costs of PSTN long distance transmissions, and use
existing e-mail infrastructure
Allocchio Standards Track [Page 1]
RFC 2303 Minimal PSTN in Internet Mail March 1998
This memo describes the MINIMAL addressing method to encode
addresses into e-mail addresses and the standard extension
to allow definition of further standard elements. The
problem, i.e. to allow a traditional numeric-only PSTN device user
access the e-mail transport service, is not discussed here
All implementations supporting this PSTN over e-mail service
support as a minimum the specification described in this document
The generic complex case of converting the whole PSTN addressing
e-mail is out of scope in this minimal specification: there is
work in progress in the field, where also a number of
optional extensions are being defined
In this document the formal definitions are described using
syntax, as defined into [7]. We will also use some of the "
DEFINITIONS" defined in "APPENDIX A - CORE" of that document.
exact meaning of the capitalised
"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", "OPTIONAL
is defined in reference [6].
2. Minimal PSTN
The minimal specification of a PSTN address in e-mail address is
follows
pstn-address = pstn-mbox [ qualif-type1 ]
pstn-mbox = service-selector "=" global-
service-selector = 1*( DIGIT / ALPHA / "-" )
; note that SP (space) is not allowed
; service-selector
; service-selector MUST be handled as a
; INSENSITIVE string by implementations
Specifications adopting the "pstn-address" definition MUST define
unique case insensitive "service-selector" element to identify
specific messaging service involved
These specifications MUST also define which minimal "qualif-type1"
extensions, if any, MUST be supported for the specified service
Implementations confirming to these minimal
specification are allowed to ingnore any other non-minimal
address element which can be present in the "pstn-address". However
Allocchio Standards Track [Page 2]
RFC 2303 Minimal PSTN in Internet Mail March 1998
conforming implementations MUST preserve all "qualif-type1"
elements they receive
The generic "qualif-type1" element is defined as
qualif-type1 = "/" keyword "="
keyword = 1*( DIGIT / ALPHA / "-" )
; note that SP (space) is not allowed in
string =
; note that printable characters are %x20-7
As such, all "pstn-address" extensions elements MUST be defined
the "qualif-type1" form
2.1 Minimal "global-phone"
We now define the minimal supported syntax for global-phone
global-phone = "+" 1*( DIGIT , written-sep )
written-sep = ( "-" / "." )
The use of other dialling schemas for PSTN numbers (like
numbering plans or local dialling conventions) is also allowed
However, this does not preclude nor remove the minimal
requirement to support the "global-phone" syntax as defined above
Any non "global-phone" dialling schema MUST NOT use the leading "+"
between the "=" sign and the dialling string. The "+" sign
strictly reserved for the standard "global-phone" syntax
Note
The specification of these different dialling schemas is out
scope for this minimal specification
User specification of PSTN e-mail addresses will be facilitated
they can insert these separators between dial elements like
etc. For this reason we allow them in the syntax the written-
element
Implementors' note
Use of the written-sep elements is allowed, but not recommended
Any occurences of written-sep elements in a pstn-mbox MUST
ignored by all conformant implementations. User Agents
remove written-sep elements before submitting messages to
Message Transport System
Allocchio Standards Track [Page 3]
RFC 2303 Minimal PSTN in Internet Mail March 1998
2.2 Some examples of a minimal "pstn-address
VOICE=+3940226338
FAX=+12027653000/T33S=6377
SMS=+33-1-88335215
3. The e-mail address of the I-pstn device: mta-I-
An "I-pstn device" has an e-mail address, or to be more exact, a
which enables a mail system to identify it on the e-mail
system
In Internet mail, this is the Right Hand Side (RHS) part of
address, i.e. the part on the right of the "@" sign. We will
this "mta-I-pstn
mta-I-pstn =
For "domain" strings used in SMTP transmissions, the string
conform to the requirements of that standard's
specifications [1], [3]. For "domain" strings used in
content headers, the string MUST conform to the requirements of
relevant standards [2], [3].
Note: in both cases, the standards permit use of "domain names"
"domain literals" in addresses
4. The pstn-
The complete structure used to transfer a minimal PSTN address
the Internet e-mail transport system is called "pstn-email".
object is a an e-mail address which conforms to RFC822 [2]
RFC1123 [3] "addr-spec" syntax, with some extra structure
allows the PSTN number to be identified
pstn-email = ["/"] pstn-address ["/"] "@" mta-I-
Implementors' note
The optional "/" characters can result from other mail
services gateways, where it is also an optional element
Implementations MUST accept the optional slashes but SHOULD
generate them. Gateways are allowed to strip them off
converting to Internet mail addressing
Allocchio Standards Track [Page 4]
RFC 2303 Minimal PSTN in Internet Mail March 1998
It is essential to remind that "pstn-address" element MUST
follow the "quoting rules" spcified in the relevant standards [2],
[3].
4.1 Multiple
In case a particular service requires multiple subaddresses (in
form defined by the specific standard specification for
service), and these subaddresses need to be given on the same "pstn
mbox", multiple "pstn-email" elements will be used
Implementors' note
The UA could accept multiple subaddress elements for the
global-phone, but it must generate multiple "pstn-mbox"
when passing the message to the MTA
4.2 Some examples of "pstn-email
VOICE=+3940226338@worldvoice.
FAX=+1.202.7653000/T33S=6377@faxserv.
/SMS=+33-1-88335215/@telecom.
5.
This proposal creates a minimal standard encoding for PSTN
within the global e-mail transport system and defines the
extension mechanism to be used to introduce specific new elements
The proposal requires no changes to existing e-mail software.
specific PSTN service using this proposal MUST define its
"service-selector" specification and MUST define the eventual
"qualif-type1" elements to be supported for its minimal
specification. An example is in reference [13].
6. Security
This document specifies a means by which PSTN addresses can
encoded into e-mail addresses. As routing of e-mail messages
determined by Domain Name System (DNS) information, a
attack on this service could force the mail path via some
gateway or message transfer agent where mail security can be
by compromised software
There are several means by which an attacker might be able to
incorrect mail routing information to a client. These include: (a
compromise of a DNS server, (b) generating a counterfeit response
Allocchio Standards Track [Page 5]
RFC 2303 Minimal PSTN in Internet Mail March 1998
a client's DNS query, (c) returning incorrect "
information" in response to an unrelated query. Clients SHOULD
that mail routing is based only on authoritative answers. Once
Security mechanisms [5] become more widely deployed, clients
employ those mechanisms to verify the authenticity and integrity
mail routing records
7. Author's
Claudio
Sincrotrone
SS 14 Km 163.5
I 34012
RFC822: Claudio.Allocchio@elettra.trieste.
X.400: C=it;A=garr;P=Trieste;O=Elettra
S=Allocchio;G=Claudio
Phone: +39 40 3758523
Fax: +39 40 3758565
8.
[1] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
August 1982.
[2] Crocker, D., " Standard for the format of ARPA Internet
messages", STD 11, RFC 822, August 1982.
[3] Braden, R., "Requirements for Internet hosts - application
support", RFC 1123, October 1989.
[4] Malamud, C. and M. Rose, "Principles of Operation for
TPC.INT Subdomain: Remote Printing -- Technical Procedures",
1528, October 1993.
[5] Eastlake, D. and C. Kaufman, "Domain Name System
Extensions", RFC 2065, January 1997.
[6] Bradner, S., "Key words for use in RFCs to Indicate
Levels", RFC 2119, March 1997.
[7] Crocker, D. and P. Overell, "Augmented BNF for
Specifications", RFC 2234, November 1997.
[8] ITU F.401 - Message Handling Services: Naming and Addressing
Public Message Handling Service; recommendation F.401 (
1992)
Allocchio Standards Track [Page 6]
RFC 2303 Minimal PSTN in Internet Mail March 1998
[9] ITU F.423 - Message Handling Services:
Between the Interpersonal Messaging Service and the
Service; recommendation F.423 (August 1992)
[10] ITU E.164 - Numbering plan for the ISDN era;
E.164/I.331 (August 1991)
[11] ITU T.33 - Facsimile routing utilizing the subaddress
recommendation T.33 (July, 1996)
[12] ETSI I-ETS 300,380 - Universal Personal
(UPT): Access Devices Dual Tone Multi Frequency (DTMF)
for acoustical coupling to the microphone of a handset
(March 1995)
[13] Allocchio, C., " Minimal FAX address format in Internet Mail",
RFC 2304, March 1998.
[14] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay):
between X.400 and RFC 822/MIME", RFC 2156, January 1998.
Allocchio Standards Track [Page 7]
RFC 2303 Minimal PSTN in Internet Mail March 1998
9. Full Copyright
Copyright (C) The Internet Society (1998). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Allocchio Standards Track [Page 8]
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