# Mạng và viễn thông P14

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## Mạng và viễn thông P14

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Operator Assistance and Manual Services Early telephone networkswere all manually operated.In the 1950s automatic networks began to take over, but even today they havefailed to supplant all manual ‘assistance services’. In the public network human operators provide a ‘safety net’ of assistance and advice for customers, and in some private networks human PBX operators are still employed to answer incoming calls from the public network and to connect them to the required extension.

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1. Networks and Telecommunications: Design and Operation, Second Edition. Martin P. Clark Copyright © 1991, 1997 John Wiley & Sons Ltd ISBNs: 0-471-97346-7 (Hardback); 0-470-84158-3 (Electronic) 14 Operator Assistance and Manual Services Early telephone networkswere all manually operated.In the 1950s automatic networks began to take over, but even today they havefailed to supplant all manual ‘assistance services’. In the public network human operators provide a ‘safety net’ of assistance and advice for customers, and in some private networks human PBX operators are still employed to answer incoming calls from the public network and to connect them to the required extension. In this chapter discuss we the operator assistance services which form a critical supplement to automatic switched services in meeting the high expectations of today’s telephone customer. 14.1 MANUAL NETWORK OPERATION In a manual network, the connection of caller to destination is carried out by human operator. This is done by plugging cords into individual line sockets or jacks, one jack corresponding to each possible destination user. Figure 14.1 illustrates an early manual switchboard,andFigure14.2atypicaltelephone used on sucha manualnetwork. Instead of anumbered dial there is just acradleforthehandsetandamagneto generator to call the operator. The routine for making a call on a manual network is as follows. The caller lifts the handset, and rings the magneto generator by turning the handle. This has the effect of alertingtheoperatorand lighting an opal (a light) ontheoperator’sswitchboard (Figure 14.1). In some cases, the operator was alerted merely by rattling the cradle. This had the effect of flashing the opal. There is an opal above each incoming line jack, indicating precisely which caller wishes to make a call. To answertherequest,the operator uses one of the cords mounted on console part of the switchboard, which is the pulled out and plugged into the relevant jack socket immediately below the opal. The operator is now able to speak to the caller and ask for the name of the person he wishes to call. The operator records the caller’s name, the destination number and the time of day, on a ticket for later billing of the caller. The destination party is then alerted by the operator, whorings his telephone with another hand-cranked generator. The connection 281
2. z=$&.$ 282 ASSISTANCE OPERATOR MANUAL AND SERVICES Opals and Destination 0 Caller Operator Schematic l I /‘ Generator signalling crank Actual Figure 14.1 Early manual, or ‘sleeve control’switchboard is completed by plugging the other end of the cord into jack of the destination party. the In this way the pair of plugs and the cord connect the two corresponding line jacks to caller and destination. At the end of call the caller replaces the handset, extinguishing the the opal. On noticing this, theoperator removes the plugs and cord from the jacks, ready for use on another call. To make calls to customers on other exchanges the operator has a number of trunk line jacks. To use them, the operator must relay the call details to the operator on the second exchange, and forward the connection. The second operator either completes the call or forwards it to another operator, as necessary. In manual networks, setting up telephonecalls is highly labour-intensive, and in theearlydaysthemajority of the workforce in public telephone companies were telephone operators. 14.2 SEMI-AUTOMATIC TELEPHONY Semi-automatic telephony is the term used to describe connectionswhich are set up by an operator across an automatic network. Semi-automatic telephony was common when telephone networks were first being automated, especially when some exchanges had been automated while others remained manual. Callers on the manual exchange, who wished to call others already connectedto an automatic exchange, would have their calls connected semi-automatically by theoperator.The caller would first contact the operator, and the operator would then connect the onward using special equipment call to control the automatic network rather than routing through further operators.
3. SEM1;AUTOMATIC TELEPHONY 283
4. < ’ 284 ASSISTANCE OPERATOR SERVICES AND MANUAL Figure 14.3 Inside of a hand generator signalling set, showing the magneto coils. (Courtesy of BT Archives)
5. SEMI-AUTOMATIC TELEPHONY 285 Figure 14.4 Early operator switchboard. (Courtesy o British Telecom) f
6. 286 ASSISTANCE OPERATOR SERVICES AND MANUAL THE EXCHANGE AT WORK. A Museum A-side opaator answers and gets into toucll with a Hop B-side operator. who finds out if An explanation whlch will prevent Hop 3000 is free and helps the Museum operator to many common misunderstandings. connect the lina. If conversely Hop 3000 wants The telephone lines in a large city are divlded Museum 605. it i5 a Hop A-side operator who answers and gets into touchwith a M w u m B-de into groups, called Exchanges. Operator. the B-s;dc. ne of M Exchange d& a Central A-side operator gets into touch with a directly only with Ringers up in that &change ; Central B-side operator. In every call. therefore, two Post Office operators. B d e with those rung-up in that Exchange : - . -- ____ In reality. d c o y r . ~ l h s t U I four -la . - . . -. . . : 1-0 Po.1 o(Lrr rnma e.g.. Muscum 6 0 5 wants Hop 3000. ud 1-0 .ancun-th.! i.. t k WO s m h r r i b s . - . d We. m I.-. . n d. u m ~ P- 06ec I&+ d the d ud. H- llrr m a e. 4 S Figure 14.5 The exchange at work. An extract from an early British Post Office publication providing an explanation which will prevent many common misunderstandings. (Courtesy o f B T Archives) Ironically, in the reverse direction, any caller who was connected to an automatic exchange would have to dial a code to get hold of an operator to obtain a manual connection to any destination customer still connected to a manual exchange. Manual exchanges have progressively given way to today’s predominantly automatic networks, but even today callers resort to dialling for assistance from the operator in a number of instances 0 to call a user on aresidual manual exchange(particularly remote in overseas locations) 0 to receive assistance following difficulty on an automatic connection 0 to receive the answer to a general enquiry 0 to enquire for the directory number of another user 0 to make a call to the emergency services (fire, police or ambulance) 0 to make a special service call, such as a reverse-charge call (also known as a collect call), or a personal call, etc.
7. CALLING THE OPERATOR 287 Inaddition,manycompanyswitchboardsandhotels still retainoperatorsforthe connection of incoming calls to individual extensions or hotel room numbers, despite the fact thatdirect diul-in (DDI, also direct inward dialling, DID) nowadays makes direct dialling possible. 14.3 CALLING THE OPERATOR If allwe want is to get through to the operator and him we need assistance, the tell effect of cranking the magneto is very much the same as dialling the right number on an automatic network. On a sleeve-controlled switchboard (one using plugs, cords and jacks,asillustratedinFigures 14.1 and 14.4), incomingcallsareindicatedtothe Figure 14.6 Switchboard operators at work. A picture giving an idea of the tangle of hands and leads - the frenetic operation of manual exchanges. (Courtesy of British Telecorn)
8. 288 ASSISTANCE OPERATOR MANUAL AND SERVICES operator by lighting the opals. In modern ‘cordless’ operator switchrooms the call is administered by call queueing equipment or automatic call distribution ( A C D ) equipment. This equipment stacks up calls in the order in which they are received, and allocates them to telephone operators in the switchroom as they become free from dealing with previous calls. Operators simply press a button to indicate that they are ready to handle another call. While waiting in the queue foran operator to become free, thecaller may hear ringing tone, or may instead be given a recorded message, something like ‘this is the assistance service: an operator will deal with your enquiry shortly’. Recorded messages have the benefit of confirming that callers have ‘got through’, giving reassurance that they are not waiting in vain. The recorded message also allows callers who have accidentally dialled the number for the operator service (when meaning to dial some other number), to hang up their calls up and try again. Because connections made via the operator are multi-link rather than single link connections, special measures are required, to ensure that the end-to-end quality of the connection is acceptable, and to charge the customer correctly. Callers are normally connected to the nearest switchroom. This ensures that the endsection connection is of the best available quality. Thispart of the connection (i.e. from caller to operator)is not normallyautomaticallymeteredforchargingpurposes;the call charges are derived either from paper tickets written by the operator, or from electronic tickets produced on the operator’s computer consoles. Operator switchrooms aredesigned to be efficient workplaces, and staff numbers and rosters are planned to meet customers’ call demand. Just as an automatic telephone network must be provided with sufficient circuits to meet the traffic, so must the number of positions manned by operators at any given time of day match the traffic demand at that time. A useful quality target for staff providing an operator service is to aim to answer all calls within a given time (say 25 seconds), or perhaps to aim to answer 90% of calls within say 15 seconds. Thelatter statistic is oftenwritten in shorthand as PCAl5 = go%, i.e. the percentage of calls answered in 15 seconds=90%. PCA25 can also be used as a performance statistic (measuring the percentage calls answered in 25 of seconds), but the average caller on a public network who wants operator assistance, is not satisfied with such a long wait. There is a relationship between the measured value ofPCAandthe staffing level oftheswitchroom,the use of more staff generally increasing the PCA value. Going to one extreme, to employ a very large number of operators queueing up to answer calls would ensure almost instantaneous answer. At the other extreme, with too few operators it is the caller who does the queueing and waiting. A modification of the Erlang formula presented in Chapter 30 is called the Erlangwaiting-timeformula. Itcan be used to calculatethenumber of operators required in a switchroom to keep the waiting time down to a target figure (i.e. to cal- culate PCA values) 14.4 OPERATOR PRIVILEGES Intheonwardconnection of calls, operators may be given anumberof special networking privileges. They may have exclusive use of particular routes or of certain
9. TYPICAL 289 circuits within a route, to give their callers a better chance of getting through than normal customers (especially when the network is busy). This enables theoperator tobe of real assistance tothe caller in cases of difficulty, andfurthermore reducesthe likelihood of wasted operator timespentinfutilerepeatattempts.Other privileges explained below include manual hold, circuit monitoring and interruption, and forward transfer. However, with the increasing development and automation of networks, and the small number of human operators available for network policing, these features are becoming obsolete. Manual holdallowsthe operatorto hold theconnection even afterthe calling subscriber has replaced the handset. This makes it possible to trace the origin of a malicious call in a case when a caller has given a false identity. It also prevents thecaller making any further calls. This use of the facility is now largely susperseded by calling line identity (CLZ) information in automatic networks and many networks today no longer have thefacility. An alternative use of the manual hold facility permits tracing the cause of faulty connections. The ability to trace emergency service calls (e.g. fire, police, ambulance) is of special importance. Circuit monitoring and interruption: sometimes the operator is given the facility to monitor or interrupt customers calls while in progress. This can be useful in investi- gating customer complaints, including account discrepancies. It can also be used to breakin onconversationalreadyinprogress, when an important incoming call is received, and this would have been done historically if a trunk call was received while only a local was in progress (hence the term for this facility, trunk ofer). Forward transfer: another facility becoming largely obsolete, the forward transfer facility allows the operator who has previously established a semi-automatic connection for the call, to request assistance from the operator at the destination exchange; inter- national operators used it to provide language assistance (i.e. translation). The oper- ators mightspeak anintermediate language (typically Frenchor English) between themselves and their mother tongue to their own customers to resolve any difficulties duringcallset-up.(Exampleforperson-to-person calls). The desired language of assistance is indicated by a special digit called the language digit, which is inserted by the originating operator’s exchange into the called customer’s dialled digit string during the signalling at call set-up. This is discussed in more detail later in the chapter. 14.5 TYPICAL ASSISTANCE SERVICES As most calls are made automatically nowadays, operators to provideonly a range need of assistance services to complement the automatic service; here are some of the more common ones. ‘Station call’ service A station call is the name given to an ‘ordinary’ call between two telephone stations, when it is made via the operator. A station call may be made (via the operator as opposed to automatically) either because the call cannot be dialled directly, or because customers prefer it, or perhaps because customers have had difficulty in getting
10. 290 ASSISTANCE OPERATOR MANUAL AND SERVICES through. Another reason maybe that the customerwishes to be rung back immediately after the call has finished to be advised of the duration and charge ( A D C ) (also called time and charges). ‘Reverse charge’ or ‘collect call’ service For any of a variety of reasons, callers when travelling may not wish to pay for calls themselves, preferring to transfer the charges to the call recipients. The service which does this for them is the reverse charge or collect call service. The reason for trans- ferring the charge may be shortage of change when using a payphone, or to avoid leaving ones host with a large telephone bill when staying away from home. Whatever the cause, collect call service must always be madevia the operator. Before receiving a collect call, recipients are asked by the operator whether they are willing to accept the call charges. If so, the call is connected and an operator ticket records the call details in the normal way, except that the bill is sent to the recipient rather than to the caller. A similar service, self-explanatory, is also sometimes available: ‘Bill call to third party’ (this might allow a payphone caller to charge the call to his home account). ‘Personal call’ service (Also called a person-to-person call.) Sometimes callers may wish to contact particular people who share their telephone with a number of others. A caller may not want to make an automatic call and pay for a connection, but to find out that the desired individual is not available. In these circumstances it is appropriate to make a personal call, via the operator. The caller gives the operator the name and telephone number of the individual required, and the operator then makes the call and checks that the right recipient is available to come to the telephone. If so, the caller is charged from the moment when the operator allows conversation commence. to Usuallyeither a surcharge or a higher charge per minute of conversation is levied on personal calls. If the person wanted is not available, the connection is cleared without conversation and the caller is not charged. ‘Directory enquiry’ service (Also called directory assistance.) To make an automatic call a caller must have the number of the destination telephone station. Without that number the network has no indication of what connection the caller wants. If the caller does not know it, perhaps because he has not called that particular person or company before, then one way of ‘looking-up’ numbers is to use the paper directory, issued to telephone customers. This gives an alphabetic list of the names of all customers with their numbers. However, the sheer number of customers nowadays has tempted many telephone companies to issue only a telephone directory covering the immediately surrounding geographical area. The operator directoryenquiry (De) service provides a more comprehensive nationwide service. Accessto the service in the normal way is by dialling an access code and waiting in a queue at the nearest directory enquiry switchroom. The operator looks up the num- ber in the appropriate paper directory or by querying a computerized directory system. When the number is found it is given verbally to the caller, who then presumably follows up theenquiry by placing a call over the automatic network.Alternatively the operator
11. TERNATIONAL ATORS BETWEEN COOPERATION 291 can immediately put a call through. Some network companies charge customers for each directoryenquiry; others give a free service, which they believe stimulates more automatic calls anyway. General enquiry service Whether publicized directly or not, the operator is also often called upon by customers to answer general enquiries about the telephone or another service. A typical enquirer mightaskforthe areacodeto be used for aparticulartown, or an international operator may be asked for the time-of-day difference in hours between originating and destination countries. The answers these enquiries, and further reference information to to help operators in the undertaking of all their services is usually provided in the form of a visual index \$le (VZF). This is a handy reference book, kept on each operator’s console. Operator tickets may or may notbe made out torecord general enquiries, and charges may or may not be levied. 14.6 COOPERATION BETWEEN INTERNATIONAL OPERATORS: CODE 11 ANDCODE 12 SERVICE When networks belonging to more than one company are interconnected, there are times when the operator in one network requires assistance from the operator in the other. This usually comes about because neither of the operators has quite the same privileged control over the other network, as they have over their own. Alternatively, in inter- national networks operatorsmay require no more thanlanguage assistance (i.e. transla- tion of the distant end mother tongue intoa comprehensible intermediate language). To give operators of different networks a means of calling one another, ITU-T’s telephone signalling systems are provided with three signals specifically for the use of operators; these are code I 1 signal code 12 signal language digit signal The code I 1 signal is used by theoperator of theoriginatingnetworktoobtain assistance from the operator of the terminating network, incases where the call cannot be connected semi-automatically because the terminating network is a manual one. The signal gives access to appropriately equipped operators in the terminating country. In countries where the network is already fully automatic, code I 1 service will have been withdrawn. Thecode I 1 signal itself is single digit signal, just as thevalues 1,2,3,4, 5 6 , 7, 8, 9, 0 are. The difference is that code 11 cannot be dialled by ordinary telephone customers. This precaution prevents ordinary telephone subscribers from masquerading as telephone operators, and from using this privileged role to defraud overseas network companies. The code I2 signal, like the code l 1 signal, is also used by theoperator of an originating network toget assistance from an operatorin the terminating network. Also
12. 292 OPERATOR ASSISTANCE AND MANUAL SERVICES like the code 11 signal, the code 12 signal is a single digit signal which cannot be dialled by ordinary telephone customers. Code 12 is to be used when difficulty has previously been experienced in establishing an automatic or semi-automatic connection, and it gives access to an appropriately equipped operator in the terminating country. Unlike the code I 1 signal, code 12 is often used with extra digits. e.g. (Code 12) + ABCD The extra digits ABCD may be used to identify an individual or particular group of operators within a switchroom, so helping overseas operators to return to the same assisting operator. Code 11 and code 12 signals are always sent immediately following the country code and language digit of the international number. The language digit is an extra digit, inserted into the digit train of all semi-automatic operator controlled telephone calls to indicate the language that the calling operator would prefer distant operator to speak in, should language assistance be required. Not all countries’ telecommunications companies offer language assistance appropriate to all the language digits, but the following values are allocated. 1 = French 2 = English 3 = German 4 = Russian 5 = Spanish 6 to 9 (spare) (0 = dimensioning digit for automatic working) The language digit ( L D ) is always inserted immediately after the country code of the number dialled, or in the alternative position demanded by the international signalling system. Thus on a call to the number 44 171 234 5678 (a number in Central London, UK) the train 44 (1) 171 234 5678 might be used by an operator overseasrequiringlanguageassistancefromthe UK operator in French. The digit is not inserted by the operator manually, but rather is systematically added by the exchange on a route by route basis. Thus LD = 2 for English might set on the route to Japan and LD = 1 for French might be appropriate on a route to a French African colony. When the language digit is set at value 0, it is called the discriminating digit, and it is used to identify automatic (i.e. non-operator- controlled) calls. The discriminating digit (value 0 of the language digit) is inserted systematically by automatic telephoneexchanges. Thusthe receiving networkcan
13. ATOR A MODERN 293 distinguish between automatic origin calls and operator controlled(i.e. semi-automatic) calls. If necessary, and in response to either a code 11, code 12, or forward transfer signal, language assistance can be given. Having examined the language digit, and in so doing performed appropriate routing and accounting, the international exchange call in the destination country (but not an international transit exchange) will removethe language digit before sending out the destination national number into the network of theterminatingcountry.The languagedigitthereforeonly exists on international telephone links. 14.7 AMODERN OPERATOR SWITCHROOM Since the early days operator-controlled manualtelephone networks, operator switch- of room equipment has moved through several phases of technology, first to cordless boards and latterly to fully computerized systems. It may seem ironic that a computer system should be designed to work in a mode requiring human intervention rather than setting out toeliminate the human element; but the fact is, telephone customers still find comfort in spoken assistance. Today, computerized operator exchanges give optimized ergonomic conditionsfor the human operators without compromising the networkefficiency. Some of these exchanges have a central switching equipment, where the switching and control of circuits takes place; but in addition, more luxurious remote switchrooms where the operators sit are connected via computers and computer data links. From their remote switchroom (or maybe even from a workplace at home) the operators can issue commands, using the keyboard of a computer terminal, to instructthe centralswitch what call routing, or other control action should performed. Meanwhile the computer can automatically generate be its own electronic tickets, storing the number (callers number), B number (destination A number), call duration, time of day, etc. Someof the information can be typed in by the operator when talking to the caller (A party) (e.g. the B number), and some of the information canbe derived automatically (e.g.time of day and duration). Figure14.7 call illustrates schematically the network arrangement of this type of computer-controlled operator exchange. As well as the ergonomics and comfort benefits of this type of switchroom (more like an office, and less like the factory-like switchrooms of the past), there are a number of other benefits. 0 The operator time required to handle individual calls is reduced. 0 Callre-attemptscan be mademore easily (by pressing a ‘last number re-dial’ button). 0 The accuracy of operator tickets is improved,andtheinformation is directly available in a computer format for subsequent computerized bill calculation. 0 The central switchingequipment can be located with other automatic exchanges, and maintained by a common technicial staff, while the switchrooms maybe located near an available workforce.
14. 294 ASSISTANCE OPERATOR SERVICES AND MANUAL - - - E w i t c h location 7 Onward Central switching - I connectio Caller Computer Telephone control clrcuit link r 7 I I I Operator I I I I / I I I Switchroom location l L _ _ - - - ---_ J Figure 14.7 Network schematic of modern computer operator exchange 0 If more than one remote switchroom or homeworking operators are connected to the same central switching equipment better staff rostering can be achieved, say by closing some switchrooms at night, and handling all the overnight traffic at one switchroom. This was not generally possible in the past. 14.8 OPERATOR ASSISTANCE ON TELEX NETWORKS The principles of telex operator assistance networks are similar to those of telephone operator assistance networks. The difference is that the operator has to ‘speak’ to the caller through a telex machine and not by voice. Other slight differences exist in the actual menu of services offered; for example, the telex operator might offer a multiple destination service to telex callers. 14.9 OPERATOR ASSISTANCE ON DATA NETWORKS Operator assistance is not normally available on packet-switched and other data net- works. However, for the purpose of point-to-point data connection over thetelephone
15. ASSISTANCE OPERATOR NETWORKS DATA ON 295 network, some companies (declining in number) allow their telephone operators,when asked by callers, to select particularly high grade circuits designed specifically for the transmission of voice band data. The customer uses such circuits in conjunction with data modems located on the customer premises at either end of the connection.

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