# 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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## Nội dung Text: Mạng và viễn thông P14

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)