INTERNET-DRAFT A. Vaha-Sipila
Expires 28-Feb-1998 Nokia
26-Aug-1997
URLs for Telephony
<draft-antti-telephony-url-00.txt>
Status of This Memo
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Abstract
This document specifies a URL (Uniform Resource Locator) scheme
'callto' for specifying a location for an entity 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.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . 1
1.1 New URL Schemes . . . . . . . . . . . . . . . . . 1
1.2 Formal Definitions . . . . . . . . . . . . . . . . 2
1.3 Requirements . . . . . . . . . . . . . . . . . . . 2
2. URL Schemes for Telephone Calls . . . . . . . . . 2
2.1 Applicability . . . . . . . . . . . . . . . . . . 2
2.2 callto URL Scheme . . . . . . . . . . . . . . . . 2
2.3 Parsing a callto URL . . . . . . . . . . . . . . . 4
2.4 Examples of Use . . . . . . . . . . . . . . . . . 6
3. References . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . 6
5. Authors' Addresses . . . . . . . . . . . . . . . . 7
1. Introduction
1.1 New URL Schemes
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This specification defines a new URL scheme, callto. It is
intended for describing an entity that can be contacted using the
telephone network. This URL scheme caters for voice calls
(including DTMF based supplementary services), fax (facsimile)
calls and data calls. URLs that designate phone or fax numbers
that can be dialed have been brought forward in other (currently
expired) 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.
1.2 Formal Definitions
Rules are separated from definitions by an equal "=", literals are
quoted with double quotes "", parentheses "(" and ")" are used to
group elements, optional elements are enclosed in "[" and "]"
brackets, and a set of elements where order is not significant is
enclosed by "{" and "}" (note that this does not imply repetition;
only that the elements in that group can appear in any order).
Elements may be preceded with n* to designate n repetitions of the
following element; n defaults to 0. Single quotes '' are used to
indicate elements that are not formally specified and are
described in free text instead. Indentation indicates that the
definition continues from the previous line.
1.3 Requirements
Compliant software MUST follow this specification. Requirements
are indicated by capitalized words as specified in [RFC2119].
2. URL Schemes for Telephone Calls
2.1 Applicability
The callto URL scheme is 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. It is also possible to give
information about the capabilities of the remote entity.
2.2 callto URL Scheme
The callto URL does not have a 'path' in it - it is always
absolute. Everything is case-insensitive, expect for the
"user-name" and "password", which may be case-sensitive in some
environments.
Some characters are considered "reserved" and cannot be used in
the free text fields (such as "user-name" and "password") without
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escaping them using URL encoding.
reserved = " " | ":" | "?" | ";" | "="
The URL syntax is formally described as follows:
callto-url = scheme ":" scheme-specific-part
scheme = 'callto'
scheme-specific-part = subscriber-id [type-specifier]
subscriber-id = ["+"] phone-number
type-specifier = [";type=" call-type]
call-type = "voice" | "data" {[";params="
data-capabilities]
[";proto=" protocol-specifier]
[";user=" user-name] [";pass=" password]} |
"fax" [";params=" facsimile-capabilities]
phone-number = 1*phonedigit [pause-character
*(phonedigit | dtmf-digit |
pause-character)]
phonedigit = digit | "-"
pause-character = "p" | "w"
digit = "0" | "1" | "2" | "3" | "4" | "5" |
"6" | "7" | "8" | "9"
dtmf-digit = "*" | "#" | "A" | "B" | "C" | "D"
user-name = 'a user name for authentication;
in URL-encoded notation'
password = 'a password for authentication;
in URL-encoded notation'
protocol-specifier = "raw" | "ppp"
data-capabilities = modem-type ["?" data-bits parity
stop-bits]
data-bits = "7" | "8"
parity = "n" | "e" | "o" | "m" | "s"
stop-bits = "1" | "2"
modem-type = "V21" | "V22" | "V22b" |
"V23" | "V26" | "V32" |
"V32b" | "V34" | "V110" |
"V120" | "B103" | "B212" |
"X75"
facsimile-capabilities = "G1" | "G2" | "G3" | "G4"
"Subscriber-id" is the phone number to be dialed. This phone
number SHOULD be written in international notation with country
(CC) and area (NDC) codes, that is, both ITU-T CC and NSN elements
SHOULD be present.
International numbers MUST begin with "+", which indicates that
the number begins with a country code (CC). Hyphens are only to
aid readability; they MUST NOT have any other meaning. Numbers
that only work from inside a certain geographical area or from a
certain network MUST NOT start with a "+". For the meaning of "p"
and "w", see below.
"Type-specifier" specifies the call type (which kind of terminal
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equipment is used or what services are requested from the
network). If not defined, it defaults to "voice".
"Data-capabilities" is an optional field which indicates what kind
of entity is answering at the other end. The "modem-type" field is
present to indicate the line speed or protocol. The "modem-type"
listed should be the one that offers the fastest connection. If
several, incompatible modem types are connected to the same
number, each of these is listed. Possible modem types are
described below. Also, optional information on data bits, parity
and stop bits may be provided for each "modem-type".
"Proto" is the definition of the protocol that is spoken over the
data connection. If not specified, it defaults to "raw", which
implies no higher-level protocol at either end (for example a
terminal connection). "PPP" tells the user agent (client, caller)
to start negotiating a PPP connection with the server.
"User-name" and "password" are the credentials used for
authenticating the user. These direct the upper-level protocol or
session that utilitises the newly created data connection. Use of
this information is left to the user agent. When specified in a
URL that directs the user agent to create a PPP connection this
information SHOULD be used for PPP authentication. In a normal
terminal ("raw") connection, this information MAY be utilised by
automatic login scripts or a similar purpose.
"Facsimile-capabilities" inform the user agent about the remote
fax capabilities. These are described below.
2.3 Parsing a callto URL
A. The "subscriber-id" is extracted. If it begins with a "+", it
is an international number. This kind of a number is converted to
the user agent's local format (for example, if the agent is a
browser component that dials out, the "+" is replaced by the
international call prefix, or if the country code matches the
country code of user agent's home country, the "+" and the country
code are replaced by a domestic call prefix).
A phone number may contain "p" or "w" characters which indicate a
pause of 1 second while dialing, or a wait for user input,
respectively. User agents SHOULD support this method of dialing.
If it is not supported, user agents MUST ignore everything after
the "p" or "w" characters. All digits after the first "p" or "w"
character 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).
B. If there is no "type-specifier" after the "subscriber-id", the
user agent MUST open a normal voice call, and if the true nature
of the call type can be defined later (for example, modem/fax
autodetection), user agent MAY opt to change to the detected mode.
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C. If there is a "type-specifier" after "subscriber-id", the user
agent MUST call out using either a suitable terminal equipment
(modem, telefax) or request that the network provides such a
service. If call type is specified, calls MUST NOT be done in such
a way that is incompatible with the recipient entity (such as
calling a voice number with a modem, or calling a modem number
with a telefax). Type specifiers are "voice" for normal voice
call, or a call to a voice mailbox, or a voice messaging service;
"fax" for a facsimile (telefax) call; "data" for a data call, with
no processing of transferred data implied at either end by
default; and data with a "ppp" protocol specifier for a data call
where the caller (client) and the callee (server) should begin
negotiating a PPP connection after the call has been established.
What protocols are negotiated at this phase depends on the user
agent's and server's capabilities and configuration. What happens
after the call has been established is outside of the scope of
this document.
D. If there are any parameters after "call-type", the user agent
SHOULD parse the remote capabilities, such as the data
bits/parity/ stop bits and remote user name and password and
adjust itself appropriately. The capability tokens are listed
below. If listed capabilities have been parsed and suggest that it
is impossible to create a connection, the connection MUST NOT be
created.
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
G1 ITU-T T.2 (G1) facsimile
G2 ITU-T T.3 (G2) facsimile
G3 ITU-T T.4 (G3) facsimile
G4 ITU-T T.6 (G4) facsimile
Data bits: "8" or "7" The number of data bits. If not
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".
Protocol specifier: The higher level protocol to be used
"ppp" or "raw" over the raw data stream. If not
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specified, defaults to "raw" which
implies that the data stream does not
contain any higher level protocol (for
example, a terminal connection). "ppp"
implies that PPP handshake should be
started over the data stream.
2.4 Examples of Use
callto:+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.
callto:+358-55-1234567;type=fax
The above URL instructs the user agent to place a fax call to the
specified number.
callto:+358-55-1234567;type=data;params=v34?7e1;params=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.34 modem (or a slower one, which is compatible with V.34), using
settings of 7 data bits, even parity and one stop bit, or an ISDN
connection using ITU-T V.110 protocol.
callto:+358-55-1234567pp22
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). (Most Hayes AT compatible modems accept commas
"," as the pause characters.)
3. References
[RFC1738] Uniform Resource Locators (URL). December 1994. T.
Berners-Lee et al. <URL:ftp://ftp.ds.internic.net/rfc/rfc1738.txt>
[RFC2119] Key words for use in RFCs to Indicate Requirement
Levels. March 1997. S. Bradner.
<URL:ftp://ftp.ds.internic.net/rfc/rfc2119.txt>
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)
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- 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
(signaling) network. Also, 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
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 28th of February, 1998, or when a
new version is released.
A. Vaha-Sipila URLs for Telephony August 1997