INTERNET-DRAFT A. Vaha-Sipila
Expires 25-May-1998 Nokia
21-Nov-1997
URLs for Telephony
<draft-antti-telephony-url-03.txt>
Status of This Memo
This document is an Internet-Draft. Internet-Drafts are working
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Abstract
This document specifies URL (Uniform Resource Locator) schemes
''telephone'', ''fax'' and ''modem'' for specifying the location
of a terminal in the phone network and the connection types (modes
of operation) that can be used to connect to that entity. This
specification covers voice calls (normal phone calls, answering
machines and voice messaging systems), facsimile (telefax) calls
and data calls, both for POTS and digital/mobile subscribers.
Version History
| Changes to the previous versions are indicated by a bar in the
| left margin like in this section.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 New URL Schemes . . . . . . . . . . . . . . . . . . . . . 2
1.2 Formal Definitions . . . . . . . . . . . . . . . . . . . 2
1.3 Requirements . . . . . . . . . . . . . . . . . . . . . . 2
2. URL Schemes for Telephone Calls . . . . . . . . . . . . . 3
2.1 Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2.2 "telephone" URL Scheme . . . . . . . . . . . . . . . . . 3
2.3 "fax" URL Scheme . . . . . . . . . . . . . . . . . . . . 3
2.4 "modem" URL Scheme . . . . . . . . . . . . . . . . . . . 4
2.5 Parsing telephone, fax and modem URLs . . . . . . . . . . 4
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2.6 Examples of Use . . . . . . . . . . . . . . . . . . . . . 7
3. References . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . 8
5. Authors' Addresses . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
1.1 New URL Schemes
URLs that designate phone or fax numbers that can be dialed have
been brought forward in other Internet-Drafts. However, none of
these has reached the RFC status. This document tries to remedy
the situation. All interested parties are invited to submit
comments on this Internet-Draft. Contact information can be found
at the end of this document.
This specification defines three new URL schemes: "telephone",
"fax" and "modem". They are intended for describing a terminal
that can be contacted using the telephone network. The
description includes the subscriber (telephone) number of the
terminal and the necessary parameters for successfully
connecting to that terminal.
The "telephone" scheme describes a connection to a terminal that
handles normal voice telephone calls, a voice mailbox or another
voice messaging system or a service that can be operated using
DTMF codes. The name (scheme specifier) for the URL is
"telephone" as recommended by [E.123].
The "fax" scheme describes a connection to a terminal that can
handle telefaxes (facsimiles). The name (scheme specifier) for
the URL is "fax" as recommended by [E.123].
The "modem" scheme describes a connection to a terminal that can
handle incoming data calls. The term "modem" refers to a device
that does digital-to-analog and analog-to-digital conversions;
in addition to these, a "modem" scheme can describe a fully
digital connection.
The notation for phone numbers is the same which is specified in
[FAX-ADDR]. However, the syntax definition is a bit different due
to the fact that this document specifies URLs whereas [FAX-ADDR]
| specifies electronic mail addresses. For example, "/" (used in
| URLs to separate parts in a hierarchical URL [RFC1738]) has been
| replaced by ";".
1.2 Formal Definitions
Formal definitions follow [ABNF]. This specification uses
elements from the 'core' definitions (Appendix A of [RFC2234]).
1.3 Requirements
Compliant software MUST follow this specification. Requirements
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are indicated by capitalized words as specified in [RFC2119].
2. URL Schemes for Telephone Calls
2.1 Applicability
In this document, "user agent" means software that can detect and
parse one or more of these URLs and place a call to the remote
terminal using hardware at its disposal.
These URL schemes are used to direct the user agent to place a
call using the telephone network. The network in question may be a
landline or mobile phone network. If the phone network
differentiates between (for example) voice and data calls, or if
the user agent has several different telecommunications equipment
at its disposal, it is possible to specify which kind of call
(voice/fax/data) is requested. The URL can also contain
information about the capabilities of the remote entity, so that
the connection can be established successfully.
None of the URL schemes do have a 'path' in them - they are
always absolute. The URLs are always case-insensitive.
2.2 "telephone" URL Scheme
The URL syntax is formally described as follows:
telephone-url = telephone-scheme ":"
telephone-subscriber
telephone-scheme = "telephone"
telephone-subscriber = global-phone-number / local-phone-number
global-phone-number = "+" 1*phonedigit [isdn-subaddress]
[post-dial]
local-phone-number = 1*(phonedigit / dtmf-digit /
pause-character) [isdn-subaddress]
[post-dial]
isdn-subaddress = ";isub=" 1*phonedigit
post-dial = ";postd=" 1*(phonedigit / dtmf-digit
/ pause-character)
phonedigit = DIGIT / visual-separator
visual-separator = "-" / "."
pause-character = one-second-pause / wait-for-dial-tone
one-second-pause = "p"
wait-for-dial-tone = "w"
dtmf-digit = "*" / "#" / "A" / "B" / "C" / "D"
2.3 "fax" URL Scheme
The URL syntax is formally described as follows (the definition
reuses nonterminals from the definition above):
fax-url = fax-scheme ":" fax-subscriber
fax-scheme = "fax"
fax-subscriber = fax-global-phone / fax-local-phone
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fax-global-phone = "+" 1*phonedigit [isdn-subaddress]
[t33-subaddress] [post-dial]
fax-local-phone = 1*(phonedigit / dtmf-digit /
pause-character) [isdn-subaddress]
[t33-subaddress] [post-dial]
t33-subaddress = ";tsub=" 1*phonedigit
2.4 "modem" URL Scheme
The URL syntax is formally described as follows:
modem-url = modem-scheme ":" remote-host
modem-scheme = "modem"
remote-host = telephone-subscriber *modem-params
modem-params = ";type=" data-capabilities
| data-capabilities = accepted-modem ["?" data-bits parity
| stop-bits]
| accepted-modem = "V21" / "V22" / "V22b" /
"V23" / "V26" / "V32" /
"V32b" / "V34" / "V110" /
"V120" / "B103" / "B212" /
"X75"
data-bits = "7" / "8"
parity = "n" / "e" / "o" / "m" / "s"
stop-bits = "1" / "2"
2.5 Parsing telephone, fax and modem URLs
A. The type of call is specified by the scheme specifier.
"Telephone" means that a voice call is opened. "Fax" indicates
that the call should be a facsimile (telefax) call. "Modem" means
| that it should be a data call. Not all networks differentiate
| between the types of call; in this case, the scheme specifier
| indicates the telecommunications equipment type to use.
B. <telephone-subscriber> and <fax-subscriber> indicate the
phone number to be dialed. The phone number can be written in
either international or local notation. All phone numbers SHOULD
always be written in the international form if there is no good
reason to use the local form.
Any telephone number must contain at least one <DIGIT>, that is,
| subscriber numbers consisting only of non-numbers are not allowed.
International numbers MUST begin with the "+" character. Local
numbers MUST NOT contain that character. International numbers
MUST be written with the country (CC) and national (NSN) numbers
as specified in [E.123] and [E.164]. Local numbers MAY be used
if 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.
C. All <visual-separator> characters MUST be removed from the
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phone number by the user agent before using it do dial out.
These cracaters are present only to aid readability: they MUST
NOT have any other meaning. Note that although [E.123]
recommends the use of space (SP) characters as the separators,
spaces MUST NOT be used in these URLs.
D. After the telephone number has been extracted, it is
converted to the format that the user agent can use to place the
call. (For example, the "+" character might be replaced by the
international call prefix, or the international and trunk
prefixes might be removed to place a local call.) Numbers that
have been specified using <local-phone> or <fax-local-phone>
MUST be used by the user agent "as is", without any conversions.
E. The number may contain a <post-dial> sequence, which MUST be
dialled using Dual Tone Multifrequency (DTMF) in-band signalling
after the call setup is complete. If the user agent does not
support DTMF, <post-dial> MUST be ignored. In that case, the
user SHOULD be notified.
F. A local phone number or a post-dial sequence may contain
<pause-character> characters which indicate a pause of 1 second
while dialing ("p"), or a wait for dial tone ("w"). User agents
SHOULD support this method of dialing. If it is not supported,
user agents MUST ignore everything in the dial string after the
| first <pause-character> and the user SHOULD be notified. The user
| or the user agent MAY opt not to place a call if this feature is
| not supported.
Any <dtmf-digit> characters and all dial string characters after
the first <pause-character> or <dtmf-digit> MUST be sent to line
using DTMF (Dual Tone Multifrequency) in-band signaling, even if
dialing is done using direct network signaling (a digital
subscriber loop or a mobile phone).
G. A phone number MAY also contain an <isdn-subaddress> which
indicates an ISDN subaddress. User agent SHOULD support ISDN
subaddresses. These addresses are sent to the network by using a
method available to the user agent (typically, ISDN subscribers
send the address with the call setup signalling). If ISDN
subaddressing is not supported by the caller, <isdn-subaddress>
| MUST be ignored and the user SHOULD be notified. The user or the
| user agent MAY opt not to place a call if this feature is not
| supported.
H. A fax number MAY also contain a <t33-subaddress>, which
indicates the start of a T.33 subaddress [T.33]. User agents
SHOULD support this. Otherwise <t33-subaddress> MUST be ignored
| and the user SHOULD be notified. The user or the user agent MAY
| opt not to place a call if this feature is not supported.
| I. <modem-params> indicate the minimum compliance required from
| the user agent to be able to connect to the remote entity. The
| minimum compliance is defined as being equal to or a superset of
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| the capabilities of the listed modem type.
| The user agent MUST call out using compatible hardware, or request
| that the network provides such a service.
| For example, if the user agent only has access to a V.22bis modem
| and the URL indicates that the minimum acceptable connection is
| V.32bis, the user agent MUST NOT try to connect to the remote host
| since V.22bis is a subset of V.32bis. However, if the URL lists
| V.32 as the minimum acceptable connection, the user agent can use
| V.32bis to create a connection since V.32bis is a superset of
| V.32.
| This feature is present because modem pools often have separate
| numbers for slow modems and fast modems, or have different numbers
| for analog and ISDN connections, or may use proprietary modems
| that are incompatible with standards. It is somewhat analogous to
| the connection type specifier (typecode) in FTP URLs [RFC1738]: it
| provides the user agent with information that can not be deduced
| from the scheme specifier, but is helpful for successful
| operation.
This also means that the number of data and stop bits and parity
MUST be set according to the information given in the URL or to
default values, if the information is not present.
The capability tokens are listed below. If capabilities
suggest that it is impossible to create a connection, the
connection MUST NOT be created.
If new modem types are standardized by ITU-T, this list can
be extended with those capability tokens. Tokens are formed by
taking the name of the standard and joining together the first
letter, number and the first letter of the postfix. New
capabilities SHOULD then be documented in an RFC. New non-ITU-T
capabilities (such as vendor-proprietary modem types)
MUST be specified in a separate RFC.
Capability Explanation
V21 ITU-T V.21
V22 ITU-T V.22
V22b ITU-T V.22bis
V23 ITU-T V.23
V26t ITU-T V.26ter
V32 ITU-T V.32
V32b ITU-T V.32bis
V34 ITU-T V.34
V110 ITU-T V.110
V120 ITU-T V.120
X75 ITU-T X.75
B103 Bell 103
B212 Bell 212
Data bits: "8" or "7" The number of data bits. If not
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specified, defaults to "8".
Parity: "n", "e", "o", Parity. None, even, odd, mark or
"m", "s" space parity, respectively. If
not specified, defaults to "n".
Stop bits: "1" or "2" The number of stop bits. If not
specified, defaults to "1".
2.6 Examples of Use
telephone:+358-55-1234567
This URL instructs the user agent to place a voice call to the
specified number in Finland. The hyphens are included to make the
number more human-readable: country and area codes have been
separated from the subscriber number.
fax:+358.55.1234567
The above URL instructs the user agent to place a fax call to
the specified number. It uses dots instead of hyphens as
separators, but they have no effect on the functionality.
| modem:+358551234567;type=v32b?7e1;type=v110
This URL instructs the user agent to place a data call to the
specified number. The user agent may opt to use either a ITU-T
| V.32bis modem (or a faster one, which is compatible with V.32bis),
using settings of 7 data bits, even parity and one stop bit, or an
ISDN connection using ITU-T V.110 protocol.
telephone:+358-55-1234567;postd=pp22
The above URL instructs the user agent to place a voice call to
+358-55-1234567, then wait two seconds and emit two DMTF dialing
tones "2" on the line (for example, to choose a particular
extension number).
telephone:0w00358551234567
This URL places a voice call to the given number. The number
format is intended for local use: the first zero opens an
outside line, the "w" character waits for a second dial tone,
and the number already has the international access code
appended to it ("00"). This kind of phone number MUST NOT be
used in an environment where all users of this URL might not be
able to successfully dial out by using this number directly.
However, this might be appropriate for pages in a company
intranet.
3. References
[RFC2234] Augmented BNF for Syntax Specifications: ABNF.
November 1997. D. Crocker et al. RFC 2234.
<URL:ftp://ftp.ds.internic.net/rfc/rfc2234.txt>
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[FAX-ADDR] PSTN and Fax Address Format in E-Mail Services. 1997.
C. Allocchio. An Internet-Draft (work in progress).
<URL:ftp://ftp.ds.internic.net/internet-drafts/
draft-ietf-fax-addressing-02.txt>
[RFC1738] Uniform Resource Locators (URL). December 1994. T.
Berners-Lee et al. RFC 1738.
<URL:ftp://ftp.ds.internic.net/rfc/rfc1738.txt>
[RFC2119] Key Words for Use in RFCs to Indicate Requirement
Levels. March 1997. S. Bradner. RFC 2119.
<URL:ftp://ftp.ds.internic.net/rfc/rfc2119.txt>
[E.123] ITU-T Recommendation E.123: Telephone Network and ISDN
Operation, Numbering, Routing and Mobile Service: Notation for
National and International Telephone Numbers. 1993.
[E.164] ITU-T Recommendation E.164: Telephone Network and ISDN
Operation, Numbering, Routing and Mobile Service: Numbering Plan
for the ISDN Era. 1991.
[T.33] ITU-T Recommendation T.33: Facsimile Routing Utilizing
the Subaddress. 1996.
4. Security Considerations
It should be noted that the user agent SHOULD NOT call out without
the knowledge of the user because of associated risks, which
include
- call costs (including long calls, long distance calls,
international calls and prime rate calls)
- wrong numbers inserted on web pages by malicious users
- making the user's phone line unavailable (off-hook) for a
malicious purpose
- opening a data call to a remote host, thus possibly opening a
back door to the user's computer
The user agent SHOULD have some mechanism that the user can use to
filter out unwanted numbers. The user agent SHOULD NOT use rapid
redialing of the number if it is busy to avoid the congestion of
the (signaling) network. Also, the user agent SHOULD detect if the
number is unavailable or if the call is terminated before the
dialing string has been completely processed (for example, the
call is terminated while waiting for user input) and not try to
call again, unless instructed by the user.
5. Authors' Addresses
Contact person for this specification:
Nokia Mobile Phones
Antti Vaha-Sipila
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P. O. Box 68
FIN-33721 Tampere
Finland
Electronic mail: antti.vaha-sipila@nmp.nokia.com
Please include your name and electronic mail address in all
communications. If you want to receive the newest version of this
specification electronically, send mail to the address above.
This document expires on the 25th of May, 1998, or when a
new version is released.
A. Vaha-Sipila URLs for Telephony November 1997