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.
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
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
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.
Two distinctive types of ringing enable extensions to differentiate between internal and external 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.
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.
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.
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
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.
A waiting-call display is provided on each switchboard and indicates the approximate total of calls awaiting answer.
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.
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.
This facility enables the switchboard operator to recall the public-exchange operator into manually set-up exchange calls.
The operator can speak to either the calling or called parties of an external call without the other overhearing.
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.
An incoming caller wishing to speak to several extensions in succession can receive special routing and supervision by the operator.
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.
The desk enables a supervisor to call, monitor and instruct switchboard operators and also indicates the number of calls awaiting answer on the suite.
This facility enables an operator to connect her speaking circuit to an adjacent unstaffed switchboard.
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.
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.
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.
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.
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.
See 'out-of-order cabinet'.
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.
A limited amount of tandem traffic can be catered for, provided the total tandem/ extension traffic does not exceed 330e.
By keying/dialling an appropriate code an extension user can call the operator and an emergency telephone. Three simultaneous calls permissible.
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.
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.
Ringing and Tones
Reliability and Maintenance
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.
Dimensions and Weights (approx.)
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.
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
Last revised: October 01, 2019