Private Automatic Branch Exchanges

The Plessey EPB2000 private electronic branch exchange (PEBX) combines high performance and reliability with features that offer both initial and long-term cost savings. Its highly flexible design makes it capable of meeting the communication needs of any organisation with capacity requirements between 300 and 2000 extension lines and up to 300 exchange-line/inter-PBX circuits.

Design Highlights
Operationally compatible with all existing telephone exchange systems.

Reliable fast common-control of switching network by discrete electronic components and integrated circuits Optimum voice transmission characteristics switching network equipped with Plessey well-proven sealed contact crosspoint switches

Comprehensive up-to-date facilities including press button or mixed dial/press button operation High traffic handling capability (nominally 0.17 erlang per extension)

Attractive styling for equipment cabinets and operator consoles

Quiet operation

Small floor space compared with electromechanical systems

Fast economic installation by use of plug-in cables and standardised plug-in equipment modules

Quick commissioning - complete exchange assembled, pre-wired and factory tested before delivery Inexpensive modular expansion with minimum operational disturbance - by adding plug-in equipment modules and/or cabinets

Simple maintenance - in-built and plug-in diagnostic aids reduce maintenance effort to location and renewal of faulty plug-in module

Easily adaptable to future requirements. High intrinsic reliability built in at all levels of system design and backed by stringent quality control standards throughout every phase of manufacture

Extension Facilities

Call restrictions.

Various call restrictions can be applied to selected extensions by allocation of appropriate class-of-service (COS) options such as 'barred trunks' and 'barred direct access to external lines and special services'. Such options can be readily re-arranged within the PEBX to suit the changing requirements of an organisation and to keep operating costs to the minimum. Up to 25 classes of service can be provided. Extension calling Extension-to-extension calls are unrestricted and keyed/dialled directly by the calling extension.

Discriminating ringing

Two distinctive types of ringing enable extensions to differentiate between internal and external calls.

Enquiry calls

By pressing the enquiry key once, an extension can hold an external call and, on receiving dial tone, make an internal enquiry. The enquiring extension is reconnected to the external caller automatically on clear down of the called extension.

Third-party co-option (add-on conference)

A second operation of the enquiry key by the enquiring extension allows entry of the external caller into the enquiry connection, thereby permitting a 3-way conference.

Automatic transfer

Having established an enquiry call the originating extension can offer the external call to the called extension and transfer it automatically by replacing the handset. If transfer fails, either the enquiring extension is re-rung or the external call is automatically transferred to the operator's switchboard.

Operator assistance

An extension can obtain assistance from the switchboard operator by keying/dialling the digit '0'. Assistance can be given in the setting up and transfer of exchange-line and inter-PBX calls.

Operator Facilities

Press button operation

Full press button operation is provided at the switchboard for the setting up of both internal and external calls.

Standby rotary dial

Selective answering

Illuminated 'answer' press buttons enable the operator to distinguish between various classes of incoming call, i.e. from the public exchange, remote PBX or internal extensions.

Waiting-call display

A waiting-call display is provided on each switchboard and indicates the approximate total of calls awaiting answer.

Call supervision

Visual signals are provided on a LED (light-emitting diode) display and inform the operator of call progress. For example, when the operator connects an incoming call to an extension the WAITING LED glows during set-up and the RINGING LED glows when the extension is rung; if the extension is engaged the BUSY LED glows.

Delay Recall

The operator is automatically recalled if an extended call is not answered within a predetermined time.

Ring when free

This facility (also called 'camp on busy') is automatically applied on calls from the switchboard operator to engaged extensions. Only one call can be camped on at any time.

Public-exchange-operator recall

This facility enables the switchboard operator to recall the public-exchange operator into manually set-up exchange calls.

Call splitting

The operator can speak to either the calling or called parties of an external call without the other overhearing.

Trunk offering

The operator can intrude into any established connection, with a superimposed intrusion signal.

Route/group busy display

A 'busy' LED is provided for each group of lines/circuits, illuminating the appropriate number on the indicator panel when the particular group is busy.

Group and trunk identification

Four projector-type indicators provide a display for identification of trunks or other operator-associated groups of circuits.

Serial calls

An incoming caller wishing to speak to several extensions in succession can receive special routing and supervision by the operator.

Extension-number identification

The operator can display the identity of an extension originating an assistance call. The 4-digit number is displayed on projector-type indicators.

Inter-switchboard call transfer

This facility enables an operator to offer waiting unterminated external calls to other switchboards.

Prompt and deferred alarms

Both the alarm conditions can be extended to the switchboard from the exchange equipment.

Supervisor/enquiry desk

The desk enables a supervisor to call, monitor and instruct switchboard operators and also indicates the number of calls awaiting answer on the suite.

Switchboard coupling

This facility enables an operator to connect her speaking circuit to an adjacent unstaffed switchboard.

Exchange Facilities

Extension parking

This occurs if a call does not proceed within the permitted time following handset pick-up. It also occurs if the permitted time between keying/dialling digits is exceeded or if the extension fails to clear after a call.

Inter-PBX working

Calls can be made to or from other private exchanges automatically or via the switchboard operator. The same facilities can be applied to inter-PBX lines as are available on public-exchange lines.

Group hunting

This facility is of value where it is desired to speak to any one of several people located, for example, in the same department. Any call made to a group number rings the first free telephone in that group.

Secretarial hunting

Any line in an extension-hunting group, other than the first, can also be connected to other groups, enabling a secretary to be party in two or more hunting groups.

Night service

Incoming calls during the night-service period can be either routed to selected extensions or signalled by special bells and answered by any extension by keying/dialling 8.

Press button/dial extensions

The exchange caters for MF press button telephones and/or the standard rotary-dial type.

Calling or first-party release

Extension-to-extension calls can be released either by the calling or first party, dependent on strapping.

Faulty-line isolation

See 'out-of-order cabinet'.

Power-failure transfer

In the event of an exchange power failure, selected extensions can be switched directly to public-exchange lines and function as direct subscribers to the public exchange.

Tandem switching

A limited amount of tandem traffic can be catered for, provided the total tandem/ extension traffic does not exceed 330e.

Emergency reporting

By keying/dialling an appropriate code an extension user can call the operator and an emergency telephone. Three simultaneous calls permissible.

Equipment Cabinets
The automatic equipment is accommodated in free-standing, all-steel cabinets of standard size and construction equipped with lift-out doors front and rear, and surmounted by enclosed cable channelling. Air-intake grilles are provided in the base of the cabinets together with concealed outlets at the top to allow heat removal by natural convection. The complete cabinet assembly carries an attractive dual smooth/textured finish in Wedgwood and Steel Blue.

epb2000x.jpg (25217 bytes)Each cabinet can accommodate five or six shelves of slide-in units (typical slide in unit is shown to the right), which contain one or more epoxy-glass component cards using conventional or printed wiring as appropriate. The units rest on extruded aluminium runners and connect to the cabinet wiring via gold-plated connectors that ensure positive electrical contact and allow insertion and withdrawal of a unit under minimum pressure. Sockets are provided on the front of units for monitoring and routine measurements.

Both single and multiple-width units are employed according to the size of circuit and components to be accommodated. Miniature components and assemblies are used wherever possible.

Shelf wiring is carried on rear frames using PVC-covered wire and gun-wrapped terminations.

Interconnections between cabinets are by plug-ended cables.

Equipment strapping is facilitated by providing cabinets with a convenient slide-out framework, on which is mounted the strapping field.

Operator's Switchboard
epb2000y.jpg (8333 bytes)The operator's switchboard is of the floor-pattern type and matches the exchange equipment cabinets in colour scheme and finish. It is designed to ensure simple and speedy operation by reducing the functional part of the switchboard (dealing essentially with the control and supervision of incoming and assistance calls) to little more than an assembly of keys and lamps.

Control keys are provided with inbuilt supervisory lamps, simple press-to-release and non-locking actions, and press buttons in contrasting colour to facilitate selection. A Keyset is provided for use on both internal and external calls. The dial, concealed by a lift-off metal cover, is for emergency use only. Because there is no answering or outgoing multiple, en-suite arrangement of switchboards is not essential. Instead a switchboard can be sited singly or arranged with others in small groups of two, four or six positions across the width of a room.

Full access is gained to the switchboard interior for inspection of key wiring and cable connections on releasing two fascia-panel screws and swinging the panel forward.

Out-of-order Cabinet
epb2000z.jpg (11898 bytes)A floor-mounted out-of-order cabinet (shown to the right) is provided primarily to isolate faulty trunk and operator assistance circuits and is situated in the switchboard room. The cabinet also provides emergency fall-back facilities whereby up to four exchange lines can be switched to special emergency telephones for incoming and out going calls.

Press button telephones employing MF (CCITT recommended 1/4 + 1/4 VF) signalling are recommended for use in fast-switching networks. Alternatively, the conventional BPO Type 746 rotary-dial telephone can be used in Strowger-dominated networks. Both dial and press button telephones can be accommodated on the same EPB2000.

Ringing and Tones
Both ringing current and tones are generated electronically in plug-in units. The tones oscillator is crystal controlled and the continuous ringing is appropriately interrupted by a cadence unit. Two sets of ringing equipment are provided: one as the regular and the other as the standby.

Line Limits
Maximum extension-line loop resistance (including the telephone) is l300 ohms). Exchange and inter-PBX line limits can be up to 1000 ohms), depending upon the limits imposed by the remote exchange.

Reliability and Maintenance
System switching is continually monitored and any adverse degradation of service due to switching failure is automatically alarmed and the relevant fault information printed. However, owing to the multiple-path choice of call set-up, single faults do not deprive extensions of the ability to make calls, though the grade of service is slightly reduced.

Faults are subjected to a reset, where appropriate, to clear the fault condition (if transient) or temporarily 'lift' the condition to allow other calls through. It the fault persists, it is alarmed and remains subject to a reset every few seconds.

LED alarm panels and appropriate maintenance aids enable speedy location of the faulty/alarmed unit which is simply unplugged and replaced with a serviceable spare, thereby considerably reducing out of commission time.

Duplicated and distributed sub-systems of common control ensure continuity of service during fault conditions and make the probability of complete system failure negligible.

The exchange operates from a dc supply of nominally 54V negative. A fully automatic duplicate-battery power plant is provided with capacity to provide adequate reserve in the absence of the mains supply. One or more charger units is provided to produce an output sufficient to maintain full float condition during the exchange busy-hour, and each has the facility to boost-charge the battery in the event of a prolonged mains failure. Local 5V and 25V positive dc supplies are derived from the 54V negative supply.

Dimensions and Weights (approx.)
Equipment cabinets (installed) Height 2320 mm, Width 1250 mm, Depth 616 mm, Weight 715 kg.

Operator's switchboard Height 935 mm, Width 900 mm, Depth 790 mm, Weight 50 kg.

Out-of-order cabinet Height 11 04 mm, Width 984 mm, Depth 660 mm, Weight 68 kg.

Technical Data
Extension lines 300-2000 (total traffic not greater than 330e)

Trunks 300 max.

Operating voltage 54V dc 0. 5V)

Input power400-44OV ac, 50Hz, 3 phase: 200-25OV ac, 50Hz, single phase (dependent upon exchange size) Loop resistance 1300c) (including telephone)

Extension signalling: Press button CCITT recommended 1 out of 4 plus 1 out of 4 VF signalling

Rotary dial 10 p/s with 2:1 break/ make ratio

Environmental limits: Ambient temperature 0' - 50'C (10'-20'C recommended)

Relative humidity up to 95% (40% -50% recommended) Heat dissipation 100W/ M2

Ringing: Frequency 25Hz

Cadence (secs) 0.4 on, 0.2 off, 0.4 on, 2.0 off (internal calls)

0.75 on, 2.25 off (external calls)

Dial tone 200Hz (7.5ms on, 12.5ms off)

Ring tone: Frequency 400/450Hz

Cadence (secs) 0.4 on, 0.2 off, 0.4 on, 2.0 off

Busy tone: Frequency 400Hz

Cadence (secs) 0.375 on, 0.375 off NU tone (continuous) 400Hz

Note: Other ring and tone periodicity's can be provided to particular administration requirements.

PUBLICATION NO. 7625, 10/75

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Last revised: November 03, 2021