An article from
Post Office Telecommunications Journal
Autumn 1962

Towering over the Thames near Waterloo Bridge is a new building of considerable interest to the Post Office for inside it is ....
On the South Bank of the Thames at Waterloo, scene of the Festival of Britain some 10 years age, now stands a remarkable building which houses the biggest and most comprehensive Private Automatic Branch Exchange in Britain.
It is the new, 26-storey London headquarters of the Shell International Petroleum Company. Its Cordless PABX can serve 4,500 extensions, increased if necessary to 7,000, has 240 exchange lines, and 130 private wires, external extensions and inter-switchboard lines, six of which give direct communication with the Hague.
After two years of site exploration the building of the new Shell offices began in August, 1957, and for a short while the 26-storey tower block was the tallest building in London. That record has now been relinquished, and indeed it will soon again be outstripped by the Museum Tower (described in the Winter, 1961, issue). But the Shell Centre has other outstanding features which have yet to be surpassed.
The quantities of materials used in the construction could seldom have been encountered before in a project of this nature: 14 million bricks; 2 million feet of scaffolding; 18,000 tons of reinforcement; 200,000 cubic feet of concrete; nearly half a million feet super of facing stone; 23 miles of plastic pipe and so on. New methods of construction were of necessity developed to cope with the problems which emerged during the building operation. Closed circuit television was used to inspect the deep holes which were excavated to contain the foundation piers, sand for the building was blown through pipes to the upper floors and then fed down again by gravity, concrete was pumped to a height of 350 ft. with booster stages at the 9th and 18th floors, and a really modern technique - machinery and tanks for the top floor were flown in by helicopter.

The facilities to be enjoyed by the future occupants of the Centre (about 5,000 of them) will be unusually comprehensive. Both the 26-storey block and its flanking 10-storey building will be fully air conditioned with heating or cooling pipes in the ceilings which can be manually or thermostatically controlled, either individually or in groups. Windows are double glazed and mineral wool acoustic treatment has been given to partitions. Air tube mail distribution and tea and coffee conveyors serve all floors. A theatre and cinema, a swimming pool with electronic timing gear for racing events, a recreation area for badminton, table tennis and fencing, squash courts, a rifle range, changing cubicles, coffee lounges and a multiplicity of dining rooms are some of the amenities to be provided. There is even an entrance from the building to the Waterloo Underground Station on the Bakerloo line, so that the fortunate office worker has no need to brave the hazards of the London weather.  The buildings are connected by a subway which carries power cables, pedestrian traffic and other services.  The tower, on the 25th floor, has a public viewing gallery.

In recent years new designs of PABX have been introduced by manufacturers (to specifications approved by the Post Office) using cordless switchboards for the operators' positions. These cordless boards contain little more than keys and lamp indicators and, consequently, they can be designed with the pleasing lines of contemporary furniture. With the remainder of the PABX equipment relegated to the apparatus room it thus becomes possible for the operators to work in a room which has the appearance and the comfort of a modern office. Due in part to the switching techniques employed and also to the fact that they were developed at a later time, the modern cordless PABXs can offer facilities which are not provided by their predecessors. Shell has taken full advantage of these and of the improved appearance in the equipment which has been designed, made and installed for them by the Automatic Telephone and Electric Company.

The switchroom contains 19 operators' positions, a supervisor's desk and two inquiry desks. Deep carpeting and acoustic tiling on the ceiling give the room excellent acoustic characteristics and this treatment, combined with the absence of the noise associated with cord-type switchboard operating, provides excellent working conditions for the staff. The switchboards, specially designed for this installation by Mr. Richard Huws, are of a novel pattern which has been approved by the Council of Industrial Design. Loudspeakers are fitted unobtrusively in the ceiling and the supervisor has a microphone by means of which she can broadcast instructions to her operators. The justifiable pride of the architect in the design of the switchroom is shown by the provision of a semicircular glazed cubicle from which the staff may be observed at work.
Switch room at the Shell Centre on London’s South Bank.
The exchange opened for service on 16th October 1961, picture dated March 1962.

The apparatus room, which is more prosaic (though it has deep red walls and ceiling, black pillars and a buff coloured floor), is situated in the basement of the upstream building. Telephone cable risers connect with each floor of this building, while access to the downstream block is provided by way of a subway which also carries power cables, other services and pedestrian traffic. Under all floors of both blocks is a comprehensive system of trunking which enables outlets for individual extensions to be located virtually without restriction, thus providing full flexibility in the location of office furniture and of partitions.

The equipment provided at extension points varies in complexity from simple 700 type instruments, of which there are over 2,000, through plan extensions (150 plans 1A, 1,200 plans 2 and 400 plans 107) to special apparatus connected not only to the PABX but also to an independent key calling network. The key calling system provides rapid communication between members of groups of personnel who have a high community of interest. The main station of each group (called the "master" station) can make a call to any of its associated (or "side") stations merely by throwing a key. The "side" station may speak to its "master" in the same manner, and may in itself act as master to a series of lesser side stations. By operating more than one key at a "master" station conferences may be held.

Each of the 110 "master" stations incorporates a loudspeaking telephone (it can be used optionally instead of the handset which is also provided) and keys which vary in number from 10 to 30, the whole of the equipment being housed in a cabinet specially designed for the Shell installation. The 632 side stations have no loudspeaking facilities, but also have their keys (20, 10 or 2) mounted in a specially designed cabinet. There is no central equipment required for this system: only multiple cable connects the various stations which are all mains operated.

Other well known methods of providing key calling at PABX extensions exist which use centralised switching equipment associated with the PABX for establishing the connections and thereby may prove more economical in initial capital outlay at the expense of flexibility. The independent system, however, was chosen by Shell because they require the answering of exchange calls to take priority over internal traffic, a view that the Post Office will endorse. By adopting the independent key calling system they have arranged that two connections, one from the PABX and one from the key calling network, are terminated on each extension instrument so that incoming exchange calls can be signalled at the extension even if the user is speaking on the other network.
The Shell Organisation has paid special attention to the problems relating to exchange access. The 240 exchange lines are connected to Waterloo exchange which has been converted to STD working. It was decided that access to the trunk network should be possible only through an operator and that auxiliary services normally available by a local call should not be allowed to extension users. This embargo also covers the 999 call since Shell Centre has its own local emergency service. The following grouping of exchange lines thus emerge: 103 are allocated for incoming calls only, 97 are used for outgoing calls only, but have barring equipment located at the PABX which forbids the use of 0, 100, 999, INF and TEL and other similar codes, while the remaining 40 are full facility lines for use on trunk calls only, with access only through the operator (by dialling 87). By means of facility discriminators which are seized whenever an extension telephone handset is lifted the class of service allowed at each station can be varied in accordance with the status of the extension. For example, cleaners, office boys and the like are allowed only extension to extension calls and are barred all exchange access.
For technical reasons all trunk calls obtained through the operator on large cordless PABXs are "reverted", that is, the extension user calls the operator, requests the call and then hangs up his handset. The operator then obtains the required number and rings the calling extension in order to connect the call. This procedure is adapted in the Shell installation for giving a record of trunk calls for accounting purposes in the following manner. Associated with each exchange line of the full facility type is a recording meter which prints figures on a continuous roll of paper tape. When the operator keys the digits to obtain a trunk call the corresponding numbers are recorded on the meter tape. The operator then keys the extension number to revert the call and this number also is recorded. For the duration of the call the meter responds to the STD pulses received from the exchange and when the call ends their total is added to the record. The tape then automatically steps on to leave a space in readiness for the next recording.

These arrangements give the Shell Organisation full control of trunk calls and comprehensive accounting information relating to them, but special arrangements have to be made to provide service when the manual positions are not staffed. For this purpose each of the 200 restricted exchange lines has teed to it at Waterloo Exchange a second line, the number of which is published for night service. When the night service key is operated on the Supervisor's desk in the switchroom, the 200 exchange lines are connected through to zoo selected extensions which can then receive incoming exchange calls from the teed night service numbers.

To enable the selected 200 extensions to make outgoing calls, 20 of the 40 full facility exchange lines are switched, together with their recording meters, to level 87 of the PABX, and access to them is obtained by dialling these digits as for operator assistance during the day. When the extension hears the exchange dialling tone the required number is dialled and this, with the metered units, is duly recorded as before. Since, however, there is no reversion of the call under night service conditions, special arrangements have to be made to record the number of the calling extension. This is done by Calling Line Identification equipment which, at the end of an outgoing exchange call hunts for the extension and passes the required information into the recorder before the call is released.

This review of the Shell installation has necessarily been incomplete and facilities such as operator recall, enquiry and transfer and so on, which are common practice in large cordless PABXs, can only be mentioned in passing. It should, however, be said that from the start of the project discussions have been held between the Inland Telecommunications Department, the Engineering Department, the Regional and Area Staff, the contractor and the Shell management, and there is no doubt that this co-operation has contributed largely to a satisfactory interpretation of the complex requirements of the customer and to the successful completion of the project.
This, then, is the PABX at Shell Centre. There is no doubt that it will adequately fulfil the present requirements of the Shell Organisation and will set the pattern for some time to come.
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