Historical telephone sets
This section of the website is about historical telephones
that are mentioned or featured elsewhere on this website. These pages are
by no means intended to give a complete overview of historical telephone
sets, but act merely as a placeholder for background information on them.
For telephones with cryptographic features, please check our
page about crypto-telephones.
Telephone sets featured on this website
Pulse signalling is the oldest standard for dialling a
number over a subscriber line on an automatically switched exchange. The telephones have a rotary dial that
– when operated – interrupts the line current at 10 pulses per second.
For this reason it is also known as a loop disconnect system .
In the 1970s and 80's, when button-operated telephone sets became mainstream,
many of them simulated the loop disconnect pulses.
In 1963, the Bell System (USA) introduced push-button dialling by means of
Dual-Tone Multi-Frequency signalling (DTMF)
under the name Touch-Tone .
It allowed faster dialling and was less prone to mistakes.
In Europe it was known as DTMF
or MF4, but was not introduced until the 1970s and 80s.
And even then, many push-button phones still simulated pulse-dialling
as the exchanges had not yet been converted to DTMF.
ISDN was a set of digital communications standards that could be implemented
over existing PSTN (copper) wiring. The signalling was sent over the
network as part of one of the digital protocols.
ISDN was short-lived and was succeeded by ADSL and VoIP.
With the arrival of wideband internet, many telecom operators have
converted their networks to IP-based communications, using the
Voice-over-Internet Protocol (VoIP).
With this protocol, signalling
information is typically sent as out-of-band data, using the
Session Initiation Protocol (SIP).
Old analogue telephone lines (POTS) commonly only need two wires for the
connection between a telehone set and the telephone line. Power, signalling
and audio is passed over these two wires. Although there are many different
designators for these wires, the most common European name for them is
(A) and (B). In the US, they were known as Ring (R) or (-)
and Tip (T) or (+). Furthermore, each country used to assign its own
colour scheme to the wiring.
To avoid confusion, we will use the European designators
(A) and (B) here,
and colour them red
and blue respectively.
Modular jacks — also known as
Registered Jack (RJ) connectors —
are a relative simple yet
reliable way to connect (analogue) telephone equipment to a telephone line.
The connector was initially developed in the United States, but has since
been adopted worldwide. They exist in many forms:
Although there are many variations, the most popular ones are shown above.
The specified pin-numbering is when looking into the female socket,
(i.e. not the plug).
At the centre are the contacts that are used for connection to old analogue
telephone lines (POTS), with the official modular designator at the
bottom. It shows the number of positions (P) and the number of actual
contacts (C). To avoid confusion, the official designator should be used
instead of RJ-something.
At the right is the
RJ45 or 8P8C ethernet connector,
which is shown here for comparison only.
➤ More about Registered Jack (RJ) connectors
In the US, 6P2C, 6P4C and 6P6C connectors were used for single-line,
two-line and three-line configurations respectively, as shown in the
diagram below. The most common wiring is for a single-line, which is
always connected to the middle two contacts, regardless the connector
type. The single-line US standard was adopted by most countries
in the world, with some exceptions.
In Europe, the situation was much more complicated, as each country
traditionally had its own type of connector and wall socket. The
introduction of the Registered Jack
did not take place until the mid-1970s,
when foreign equipment was gradually being allowed on European networks.
Although most countries have meanwhile adopted the American standard –
shown on the left – the UK uses the outermost two contacts of a 6P4C
connector, whilst Belgium uses the rightmost two contacts. This leads
to compatibility issues when connecting foreign equipment to a line.
To avoid confusion, Crypto Museum suggests to wire the wall socket as
per rightmost diagram.
With analogue lines (POTS) gradually disappearing and ethernet cabling
becoming much more common, we have been looking for a simple way to distribute
old analogue lines throughout the premises, using modern cabling
standards, such as Cat-3,
and RJ45 jacks.
Above is the wiring scheme we use at Crypto Museum for the connection of up
to four analogue telephone lines via regular
ethernet wiring, taking the
common twisted-pair wiring order into account. We have created small breakout
boxes to provide upto 4 analogue lines, some of which we have modified
by shorting lines 3-5 and 4-6, so that one of the sockets will accept any type
of 2-wire equipment, regardless the connection variant (American, European,
British or Belgian).
Below is the wiring for a standard handset as it is used on most modern
POTS telephone sets. It uses the smaller RJ9 (4P4C) connector that is in
most cases wired with a coiled cable.
Below is the pinout of a Dutch analogue subscriber line, as endorsed
by the (then) state monopolist PTT. This is the pinout when looking
into the wall socket, which is the same as looking at the screw terminals
inside the instrument's plug (shown here). When no external bell is connected,
a wire strap should be placed in the wall socket, between the B and EB contacts.
aSubscriber line (A) red
bSubscriber line (B) blue
EBExternal bell (normally strapped to b) 1
The (EB) terminal is normally strapped to (b) terminal inside the
wall socket. It is removed when an external bell set is connected to
these terminals. If the phone doesn't ring, check whether
this strap is present.
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© Crypto Museum. Created: Thursday 30 March 2017. Last changed: Saturday, 12 August 2023 - 11:21 CET.