Xem mẫu
- 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
- 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.
- SEM1;AUTOMATIC TELEPHONY 283
- <
’ 284 ASSISTANCE
OPERATOR SERVICES
AND MANUAL
Figure 14.3 Inside of a hand generator signalling set, showing the magneto coils. (Courtesy of
BT Archives)
- SEMI-AUTOMATIC TELEPHONY 285
Figure 14.4 Early operator switchboard. (Courtesy o British Telecom)
f
- 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.
- 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)
- 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
- 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
- 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
- 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
- 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
- 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.
- 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
- 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.
nguon tai.lieu . vn
