PABX No. 4

Whilst the BPO maintained the large PABX's, they were never allowed to make or install them.

Customers would purchase a PABX from the manufacturer of their choice who would design a system to suit the customers needs.

The BPO would oversee the installation and then take on maintenance responsibility for the equipment.

The PABX 4 has virtually an unlimited capacity and uses the same standard types of automatic equipment, power plant and extension telephones as the PABX 3. The capital cost - which must be met by the customer - is greater than that of a PABX 3 of the same size, but it offers more facilities and uses a desk-type, cordless, manual switchboard in contemporary styling.

It incorporates several novel features which will, if fully utilised, produce a marginal saving in operator time, but with some loss of personal service to the extension users. The differences in facilities and degree of personal service between the PABX 3 and 4 need careful assessment and consideration before a choice is made. The Telephone Manager will gladly help and advise on the relative merits of the two systems in particular circumstances.

As with the PABX 3, the customer must buy the equipment from an approved contractor who will also be responsible for installing it. The Post Office provides the extension wiring and telephones, and maintains the whole installation.
Apart from the operator’s switchboard the PABX 4 is similar in design and construction to the PABX 3 already described; the automatic apparatus is mounted on the same type of open racks, and a similar type of power plant is provided. The main difference is the provision of the cordless, desk-type switchboard, and for this reason the PABX 4 is often called the cordless PABX. Dependent automatic installations in separate premises can be associated with a PABX 4, as with a PABX 3.

GENERAL FACILITIES
In common with the other systems described in this booklet, the PABX 4 provides a normal range of PABX facilities, including extension-to-extension dialling; extension-to-exchange dialling; connexion of incoming exchange calls by the PABX operator; through clearing; hold for enquiry; operator call-in for assistance; automatic transfer of calls; and night-service arrangements. Some special features are:
Selected extensions can be given priority calling to ensure that their calls are dealt with by the operator before calls from other extensions.
Incoming calls are put through to extensions by the PABX operator by the use
of press-buttons. If a called extension is engaged the operator can leave the incoming call to be connected automatically when the extension is free.
The operator can speak to an exchange-line caller or to the called extension without being overheard by the other person.
Selective restriction on calls can be applied so that particular extensions can be prevented from making and/or receiving exchange calls, or having exchange calls transferred to them
from other extensions. Inter-PBX line barring can also be arranged.
Facilities are usually provided for the operator to use press-buttons instead of a dial for outgoing exchange calls.
Calls over inter-PBX lines from other switchboards may be received by the PABX operator or, when signalling conditions permit, may be received direct by the extension required. Conversely, in most cases extensions can dial directly to other switchboards, and sometimes - if the distant switchboard is another PABX - directly to the required extension.
Night-service can be provided in one of the following ways:

Switchboard
One or more positions are provided, depending upon the size of the PABX. They are cordless, desk-type, floor-standing, contemporary in appearance, with compact styling, and adaptable for use in any shape of room since they do not have to be assembled in line as a suite. Maximum use is made of automatic techniques to reduce the amount of manual operating work.
The switchboard has a small desk with a sloping face panel on which are press-buttons, switches and either display lights or a translucent screen. Each approved contractor may produce his own version of the manual switchboard and although these conform to certain basic requirements, they may differ considerably in appearance. When making an outgoing call from the PABX switchboard the operator is automatically connected to a free exchange line by pressing a button. The call is set up through the automatic equipment and when established is disconnected from the switchboard. The PABX is designed to meet the needs of offices where extensions are allowed to dial their own exchange calls, and it is not as easy for the operator to obtain them as it is on a PABX 3: the operator cannot connect an out going call, on behalf of an extension, until the extension handset has been replaced, and the extension therefore has to be rung back.

Presentation of calls to the switchboard
All calls to the switchboard are presented approximately in their order of arrival to operators. Under one system there are separate lights to indicate an exchange call, a call from an extension, a call from another PBX, etc, and if more than one light shines operators can select which type of call to answer. In another system all incoming calls share the same light and the type of incoming call is indicated by another light after the operator has answered the call.

Numbering arrangements and dialling codes
These are similar to those used on the PABX 3 except that 8 is usually reserved for night service.

Alarms
These are similar to those on the PABX 3.

Tones
Standard dialling, ringing, engaged and number unobtainable tones are used and, in addition, there is a ticking tone which indicates that the operator has come in on an engaged line. Exceptionally, a distinctive ringing tone may be used for internal calls if required.

Accommodation
The same considerations apply to PABX 4 accommodation as for the PABX 3. There is some saving in the size of the room needed for a multi-position switchboard because the cordless boards can take up to 30 per cent less floor space than that needed for a similar number of PABX 3 switchboard positions, but the automatic equipment will usually need more room. A table showing typical room sizes is given overleaf.

Optional Facilities
As with the other types of PABX there are various optional facilities that can be readily provided. Some of these are
Conference telephone calls between up to ten extensions, or between one exchange line and up to five extensions.

Key callers to enable selected extensions to call up to twenty pre-determined extensions by pressing the appropriate key.

Staff location systems under the control of the operator. Call queuing for calls to busy extensions. Reception of incoming exchange line calls direct on to selected extensions. Remote controlled dictation systems.

Typical room sizes for PABX 3 and PABX 4 installations
The dimensions shown are intended to be a guide only; the sizes quoted are approximate and some adjustment may be necessary following a more detailed investigation of requirements.

Number of extensions Not exceeding	Dimensions of switchroom (ft)	Dimensions of equipment room (ft)	Dimensions of battery room (ft)	Total floor area (sq. ft)
PABX 3
100 extensions with 2 positions	12 x 11	14 x 13	-	314
200 extensions with 3 positions	14 x 11	16 x 14	-	378
400 extensions with 4 positions	16 x 11	22 x 18	-	572
500 extensions with 4 positions	16 x 11	24 x 18	13 x 6	686
600 extensions with 5 positions	18 x 11	25 x 22	14 x 6	832
800 extensions with 7 positions	23 x 14	27 x 26	16 x 6	1120
1200 extensions with 10 positions	29 x 14	32 x 27	17 x 6	1372
PABX 4
100 extensions with 1 position	12 x 10	22 x 14	-	428
200 extensions with 2 positions	15 x l0	24 x 18	-	582
400 extensions with 3 positions	18 x l0	28 x 2l	-	768
500 extensions with 4 positions	21 x 10	26 x 24	19 x 6	948
600 extensions with 4 positions	21 x 10	26 x 26	19 x 8	1038
800 extensions with 5 positions	24 x 10	31 x 26	19 x 8	1198
1200 extensions with 6 positions	27 x 12	43 x 36	28 x 8	2096