ERICSSON BULLETIN
No. 49 PAGE No. 63


ET4H Cordless PABX for Hotels
E. C. DYSON - Circuit Development Engineering Department
JULY 1964

The ET4H private automatic branch exchange makes a significant contribution to hotel efficiency and service. Designed originally for the Mayfair Hotel, London, it offers a wide range of facilities for both guests and staff and its basic design is such that it can be adapted to meet the diverse service requirements of other hotel managements.

To be successful, hotel telephone installations must cater for a number of special requirements not covered by the standard facilities of an automatic system. While the merits of the modern cordless PABX, as typified by the ET4,1 are becoming increasingly recognized by hotel managements, such systems are designed primarily for industry or commerce and lack the personal service features desirable for hotel use.

The engineering problems vary in detail between different installations but always there is the need to combine two quite different categories of service in a single efficient system; communications for the staff and service to the guests.

Staff require enquiry and transfer facilities, direct access to exchange lines and, in fact, all the features provided by a modern cordless PABX.

Guest extensions on the other hand have little need of transfer facilities and generally little community of interest with other guests. Thus, calls between guest extensions are comparatively rare and the management will usually wish to exercise some degree of supervision over those that do take place. The majority of internal calls are to staff outlets such as Room Service and, by permitting direct dialling, the guest receives a faster service, whilst the hotel reaps the benefit of lower operating costs as the switchboard is bypassed.

None the less, a guest is confronted with an additional complication, the telephone dial, which some may tend to regard as an encumbrance. Operation should therefore be as simple as possible and in the interests of guests who object to dialling a digit sequence at all, assisted access to all services via the 0 level is available as an alternative. The need for the phrase “what is your room number?“ with its suggestion of impersonality and the risk of misunderstanding must be eliminated; calling-line identification and a simple room/telephone number relationship are essentials.

While these features help to reconcile some guests to the presence of a dial, other guests will demand a dial for unrestricted local and STD access in secrecy to the public exchange. These services are of considerable value to businessmen and, other things being equal, will often determine the choice of hotel. Growing familiarity with automatic facilities, and particularly with STD or its equivalent abroad, make direct access a necessary feature for any new luxury hotel. Given facilities for meter pulse recording and billing of effective calls, its provision is in the interests of the hotel management, because the load on the switchboard is reduced, with consequent savings in operating costs, and requests for separate exchange lines by long-term guests can often be eliminated.

Apart from these general features, hotel managements usually require provision in the telephone system for handling special requests from guests. The two most common requests are to prevent calls to those guests who for some reason wish to remain undisturbed, and to arrange for the filtering of calls to VIP guests.

With a P.M.B.X the usual procedure is to insert dummy plugs in the relevant jacks, thus furnishing a positive reminder to the operator to consult her list of special requests before extending a call. On a cordless installation a similar degree of protection can be given by means of a form of interception on the MDF or, if the number of special requests justifies it, by a barring facility that the operator alone can over-ride by trunk offering procedure.

Fig 1
Simplified Trunking diagram of the ET4H PABX

THE ET4H CORDLESS SWITCHBOARD
A modified version of the ET4 cordless switchboard, known as the ET4H, incorporates the features described in this introductory outline. Much of the development work was carried out in close consultation with the management of the Mayfair Hotel where installation of the PABX was completed in June, 1962.

EQUIPMENT DETAILS
The Extensions

Trunking arrangements can be seen from the simplified Trunking diagram in Figure 1. Although this generally follows standard ET4 practice, the equipment layout has been modified to segregate guest and staff extensions. An IDF is included to give numbering flexibility and permit guest extension numbers to comply with room numbers prefixed by the digit ‘2‘, the actual numbering allocation being between 2100 and 2799. But as none of the seven guest floors at the Mayfair will ever have more than 70 guest rooms, the numbers from 70 - 00 can be used for staff extensions when it is convenient to number them on a floor basis.

Dialling is permitted from staff extensions to guest extensions but not between guest and guest, and appropriate marking conditions are applied to bar call-back enquiries by guests to any extension or service other than the cordless manual positions, leaving staff extensions unrestricted.

Staff extension line circuits are routed to a separate grading of Local 1st Selectors and the main group of staff extensions is numbered between 800 and 899.

Barring of direct exchange access can be applied to any extension by strapping in the equipment, either permanently or under control of a lock in the telephone instrument, the authorized user alone holding the key. On all extensions, whether lock control is provided or not, incoming exchange calls, and calls to or from other services, are unaffected by barring. Actually, in the conditions obtaining at the Mayfair Hotel, the use of lock control is confined solely to safeguarding staff extensions from access by unauthorized persons and is not provided at guest extensions because of the high ‘nuisance value’.

Fig 2
Message waiting lamp panel for guests

Level ‘7‘ gives access to a suite of special manual positions, equipped to deal with requests for Room Service and manned by multi-lingual operators to provide maximum assistance to guests of all nationalities. These operators are also responsible for the hotel message service, and extensions notified of awaiting messages are asked to call on this suite via level ‘3‘, which is assigned for message collection.

Notification that a message is awaiting a guest is by a message lamp on each telephone. This lamp is controlled from a panel (see Figure 2) adjacent to the Room Service positions. There is one push key per extension, the operation of the key causing a continuous flashing of the lamp on the extension telephone and also a steady glow of a guard lamp in the panel. In addition, there is a parallel lamp appearance in the guest’s pigeon-hole in the hotel foyer.

The use of separate key circuits for each message lamp imposes no restriction on the number of extensions capable of being signalled simultaneously, and separate line wires avoid cessation of the lamp signals when the handset is lifted, a feature often wrongly interpreted by the guest.

Exchange Lines and Meter Pulse Recording
Incoming exchange calls are normally extended by the manual operators to the required guest, staff, or service extension via the final selectors, and the standard ‘Park on Busy’ facility is retained. The same provisions apply to service extensions, but for Enquiry Desk and Reception where exchange-line traffic is much heavier, calls can also be extended via the first selectors.

Exchange lines are divided into two separate groups, one group being used for incoming calls and for calls originated from the manual positions. The other group is associated with level ’9‘ and gives direct and secret access to the exchange; its use is shared by guest extensions and non-barred staff extensions alike.

The relay-sets associated with the level ‘9‘ group of exchange lines, store the called number up to a total of 10 digits, and also prevent access to all chargeable codes, such as telegrams, and trunk demand where STD meter pulses are not received.

Up to 999 STD pulses may be stored, but to avoid the possibility of a guest running up an embarrassingly high account on a single call, the equipment is arranged so that calls are automatically disconnected at an arbitrary lower total of pulses. The figure adopted is 500, but other values may be selected by strapping.

When the extension replaces his handset, the exchange line is released if the call has not involved a charge, but if one or more meter pulses have been received, start and mark signals are extended to a control relay set whose finder hunts for the exchange line. The control relay set comprises a buffer store for the information held in the exchange-line relay set; this information is transferred in substantially parallel mode and assembled in such a manner that it can be read out by ICT card punching equipment or by a standby printer.

Simultaneously with the collection of information from the exchange-line relay set, Calling Line Identification (C.L.I.) equipment is set in operation, resulting in the last three digits of the extension number being recorded in a relay store.

The exchange-line and extension are freed as soon as the respective transfers of information are completed. At this stage, the control circuit indicates that it is ready for the read-out cycle.

Fig 3
Typical punch card record for Room No. 151. The call charge of eight pence may be seen at the bottom right-hand corner

The ICT equipment or the standby printer circuit then causes the various relay trees in the buffer and C.L.I. stores to be examined, extracts the relevant information and produces a record of the call, including the time and date.

Figure 3 illustrates a typical punched card for room 151 where the charge is shown in £ s. d. as eight pence. The conversion from meter units is effected with the aid of a small ICT computer. This automatically adds a sliding scale hotel surcharge.

The system of charge recording for guest calls made with manual-operator assistance is similar to that for dialled calls, ICT punched cards again being the basis.
Since ADC (advise duration and charge) information is always subject to some delay, the procedure is for the operator to make out a temporary docket on completing the call and, when full ADC information is later received, a ‘Punch Seize‘ key is pressed to seize a ‘Call Data Store‘. This is analogous to the Control R/S associated with the direct-access exchange lines. Information concerning the call is keyed into the store using the normal keysender keys, the stored information being displayed for check purposes on in-line projection-type indicators on the switchboard.

When the operator has verified that the details shown are correct, depression of the keysender ‘start’ key causes the ICT cycle to commence. After the card has been punched, the Call Data Store automatically releases and the keysender is restored to its normal function.

Accounting
Punched cards are used for telephone calls in the Mayfair Hotel since all other hotel charges are recorded on similar punched cards, remote control keysets for instance being used in the restaurants to prepare cards for meal charges. Details of all charges can thus be rapidly collated in a central billing office, and the inclusion of charges for telephone calls made by a guest just before departure (ordinarily a subject of special difficulty) is readily achieved. When a guest asks for his account, the relevant cards are taken from a pigeon hole, fed into a tabulator, and the account automatically prepared in a few seconds.

Fig 4
Part of the manual suite with two of the room positions on the left

 

Fig 5
Face equipment of the general traffic position

The Switchboards
Figure 4 shows part of the manual suite with two of the Room Service positions on the left. The other positions, dealing with normal telephone traffic, incorporate a number of features for hotel application in addition to the data store access and the message arrangements already mentioned, and can be seen in greater detail in Figure 5.

The ‘0‘ level circuits are used for booking exchange calls and for extending guests’ extension-to-extension calls on demand and thus have access to the call-back selector gradings. If the wanted extension happens to be busy on the first attempt, the operator can later employ a Revertive relay set to establish a call between two extensions.

It will be seen that the general traffic positions are equipped with four edge-lit identification indicators instead of the normal provision of three, so that circuits, as well as extensions dialling ‘0’, can be identified. Every connecting circuit can be equipped with an STD meter for ascertaining charges on operator-originated calls.
The Room Service positions, handling messages and requests for room services, also have calling-line identification but the position circuitry is of a comparatively simple nature since the only circuits required in addition to the answering levels ‘3‘ and ‘7‘ are for making calls to extensions and for extending occasional calls to a special head waiter’s telephone.

Miscellaneous Services
All the other various services provided by the hotel, such as Reception, Foyer Enquiry Desk, Restaurants, Valet Service and Hairdressers, terminate on telephone instruments with conventional final-selector access. They also have access from group-selector levels by one or two digit codes, since guests cannot dial the final-selector number. A guest can also be extended to any service via the ‘0‘ level operator as there will always be occasions when operator assistance is necessary.
Dependent on the exchange barring facility, service extensions have direct access to exchange lines with one C.L.I number per service group, and incoming calls are normally extended by operators via the final selector.

Other operational features include means of diverting calls to other locations for services not continuously staffed, such as restaurants. Discriminating ringing of all extension bells as on standard ET4 equipment is retained and, although of no particular advantage to guests, it indicates to staff extensions and services those calls which can be transferred.

A special staff-call system is installed for the operators to attract the attention of valets, housekeepers and certain managerial staff. After dialling the necessary code into relay sets, accessible from the manual-position connecting-circuit finders, the appropriate mains-operated lamps flash in hotel corridors on the required floors or, in certain circumstances, on all floors. Up to three calls can be established simultaneously and, in addition, there is a personal induction ‘ bleep ‘ system controlled from the manual room and a call bell system from guests’ rooms. Neither of these auxiliary systems forms part of the telephone equipment.

Fig 6
Section of the apparatus room

Switching Equipment
A section of the apparatus room is shown in Figure 6. The switching equipment conforms generally to ET4 practice in that the minimum number of uniselectors and selectors are employed, and ‘relay’ circuitry is used wherever feasible. For example, most of the information stored in exchange-line relay sets is transferred to ratchet relays, and reading-out by intermediate (buffer) stores is accomplished by relays alone. These count the number of pulses required to drive the ratchets to the next home position.

Two-motion selectors are of BPO 2000 type, and the call-back selectors operate on digit-absorbing principles. Absorption is effected entirely by relays. The selector does not step at all when the initial digits ‘1‘ or ‘2‘ are dialled; digit ‘1‘ causes NU tone to be returned to the caller and ’2‘ prepares the selector for subsequent switching in the lower bank, whose levels are associated with guest extensions.

Higher initial digits, e.g. 3, 4, 5, cause the selector to move up 1, 2 or 3 steps correspondingly, where it switches into the upper bank on a level which is physically two levels lower than the digit dialled.

The use of relays in this manner permits digit absorption to be achieved on a 2000-type selector without limiting hunting time or affecting the inter-digital pause margin, and mechanical wear is less than with conventional non-absorbing group selectors.

Separate racks are used for line circuits and final selectors.

ALTERNATIVE FACILITIES
Considerable variation is possible within the general framework of ET4H design to cover different service arrangements and operating methods.

For example, in another ET4H installation now in progress at the Royal Garden Hotel, London, the room service positions will be merely small key and lamp units located on teleprinter tables. Meal orders from guests will be received via the units and transmitted to the kitchens from the teleprinters, thus providing a permanent record of orders. At night, service calls will be diverted to a Coffee Shop telephone also with an associated CLI display.

In addition, for the benefit of conventions and similar parties, it will be possible to provide direct dialling facilities between guest extensions on selected floors by switching controlled from the manual positions.

Certain functions or facilities can be omitted or simplified according to requirements. In this case, where individual billing of exchange calls is not required, bulk-billing extension meters will be installed in the accounts office.

CONCLUSION
Since the Mayfair Hotel installation opened in June, 1962, a 40-line extension has been added and the system has now been in service sufficiently long to satisfy the hotel management that the basic concepts have been justified in practice. Calling-line identification has proved invaluable.

Always there will be some guests who prefer a simple manual system but, if this were provided, other guests would complain because they were unable to dial numbers themselves. The compromise the ET4H offers has been favourably received by the vast majority of guests because the system has been designed specifically for hotels, delicately balancing the rival claims of low operating cost and personal service with a not excessive capital outlay.

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