Background
for Telephone Switching
2nd Edition (Revised and Expanded)
Chapter 6
Position Systems for Telephonists
Note:
Some photos from the print version of this chapter are not included
in this web edition, because the quality is poor. We hope to add
them if we can obtain copies of the originals.
OUTLINE
OBJECTIVES:
This chapter discusses position equipment provided
for telephone professionals (telephonists) who assist regular users
in dealing with various aspects of telephone calls.
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Basic requirements are illustrated
in terms of manual switchboards;
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Console access is described as
are
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Console functions and applications.
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Finally, replacements for
telephonists are introduced.
PREVIEW QUESTIONS: As you read,
watch for the answers to the following important questions:
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How did manual switchboards work?
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How do modern consoles make the
same results possible?
POSITION
SYSTEMS FOR TELEPHONISTS
Every five or six years, the
newspapers carry a story.about the "last" manual telephone
switchboard being replaced with a new, shiny automatic central
office (see, for instance, TE&M, August 15, 1990). Because of the
regularity of these reports, one may safely assume that there are
still a few manual systems in use, serving the customers of remote
telephone companies, in spite of the almost complete automation of
the industry. The passing of the manual switchboard, however, does
not mean that telephone systems are completely automatic; far from
it. There will always be situations in public telephone networks
where human assistance is required, while private business systems
and networks have additional and pressing needs.
Interfaces are required between
automatic telephone systems and people who have some sort of special
training for interaction. Usually, when these people are employed by
the telephone company, they are called "operators." When employed by
business customers, particularly in connection with PBXs, they are
usually called "attendants." As ACDs have increased in popularity,
the term "agents" is suitable to differentiate between their users,
usually the intended recipients of calls, as opposed to operators or
attendants who assist in setting up calls to others. We will use the
term "telephonists" to refer to all three, and investigate the
special positions needed by telephonists as opposed to regular users
of the telephone.
Although cord switchboards have given
way to consoles, they provide a convenient starting point for our
study: a telephonist at a console must be able to make a switching
system perform (almost) all of the services that were possible at a
cord board where most of the switching functions were carried out
directly by a human being.
Manual local offices
Manual switchboards were in general
use more recently than many younger people realize. In 1954, for
instance, Bell Laboratories in New York had a completely manual PBX,
and the then-new labs at Murray Hill and Whippany were served by
manual central offices. Over a period of some 70 or 80 years, manual
switching systems had developed considerable sophistication and
capability.
Smaller manual switchboards (up to
about 3000 lines) usually had a line jack and lamp at each line
appearance. The lamp indicated originations; when lit, it signaled
the operator to plug her back cord (cord nearest the face of the
switchboard) into the associated jack and request the called number.
Plugging in the cord extinguished the line lamp. Upon receipt of the
number, the operator would then find the called line's jack, check
for busy and, if the line was free, plug in the other cord.
Automatic ringing, in the more advanced systems, would then take
over. Answer and hang-up supervision were handled by lamps
associated with the particular cord circuit in the shelf in front of
the operator; the called party's lamp would go out upon answer and,
upon hang-up, the lamp associated with either or both cords would
light until the operator pulled them down. One could think of an
operator as a person who put out lamps.
In very small systems with one or two
positions, each line would have only one appearance; busy testing
was thus simplified because the presence of a plug in the jack could
easily be seen. Larger systems required multiple line appearances.
Because each operator could reach the jacks in front of the adjacent
operators, the multiple pattern repeated every three positions; any
appearance of a line could be used to terminate a call, so busy
testing at all appearances was necessary. Tip-testing, as described
in Chapter 5, was widely used for customer lines; trunks usually had
lamp signals including an ITI (idle trunk indicator) to show the
next trunk to be chosen in a given group.
In large switchboards, it was
necessary to remove the lamps from "the multiple" to make room for
10,000 jacks in front of each three operator positions. Each line
thus had several terminating appearances; originating appearances
were divided up among the operator positions so that a line had only
one originating jack and matching lamp. Each operator would handle
all the originations from a limited number of lines, but could
complete to all terminating jacks. Trunks to reach other central
offices also appeared on the switchboard.
Wiring a switchboard was relatively
complex. Line circuits consisting of the traditional line and
cut-off relays (see chapter 3) and trunk circuits (usually somewhat
more complex) were mounted in "relay racks," and tip, ring and
sleeve for each line along with such control wires as were needed
for lamps were extended to the operator positions. In large systems,
where the multiple consisted of just the tip, ring and sleeve wires,
various ways were found to simplify the wiring operation while
minimizing cross-talk among many wires in close proximity.
Originating line jacks and lamps as well as trunks required more
wiring, often custom built. Although the switching mechanism itself
was relatively simple (jacks and plug-ended cords manipulated by the
operator), the amount of copper was impressive.
In very large metropolitan centers,
the originating and terminating functions were completely separated
because few calls terminated in the office in which they originated.
"A" operators would respond to new calls, obtain the called number,
and select the appropriate outgoing trunk, either to tandem, toll or
the proper terminating office. "B" operators at terminating offices
would answer calls on trunks arriving at their positions, make the
busy test, and complete the call with a single cord. Note that only
B operators had a line multiple, while only A operators had
originating lamps and jacks; this specialization of both labor and
equipment was highly effective. As we have seen in Chapter 1, the
panel system, designed to replace cord boards in New York and other
big cities, copied this plan and had separate originating and
terminating halves.
Manual PBX switchboards
Manual PBX switchboards (see Fig. 1)
remained in wide use far longer than manual central offices.
Automatic (SXS) PBXs continued to use manual switchboards as
attendant positions until the mid-70s when small electronic
switches, incompatible with cord boards, became economically
attractive; stand-alone switchboards, because of their very low cost
when rented from the telephone company, were also widely used. Such
stand-alone systems were usually relatively small and non-multiple;
each line and trunk had its own lamp and jack, and calls were
completed as in a manual CO.
Boards associated with automatic
switches were multiple or non-multiple as size dictated; lines had
only jacks (no lamps) on the face of the board. Users accessed
attendants by dialing 0; dial 0 trunks had lamps and jacks like CO
and tie-trunks, and were answered in the usual way by plugging in a
back cord. The attendant then used the front cord to complete the
call to a line in the multiple.
Users could access outgoing CO trunks
automatically by dialing 9; incoming trunks operated ringdown,
lighting a lamp associated with their jack in the switchboard.
"Combination trunks" handled incoming calls to the attendant, dial 9
outgoing calls from extensions, and attendant outgoing calls. The
attendant answered an incoming call with a cord and completed direct
to the extension, bypassing the automatic switching. Because about
25% of the calls in a PBX are incoming from the CO, this use of the
manual switchboard allowed an appreciable reduction in matrix size,
something frequently overlooked when early consoles were
substituted.
Tie-trunks could be arranged to have
switchboard appearances which permitted attendants to access them
directly while station users reached them via the automatic
switching equipment. Incoming tie-trunk calls could be arranged to
make dial-up connections to stations; incoming calls to the
attendant could be switched to the dial 0 trunks, but with a feature
sometimes called "zero level drop back," the SXS selector could be
released upon receipt of a dialed 0 and the attendant alerted to the
tie-trunk call at the tie-trunk's jack and lamp combination. This
approach allowed the attendant to identify the calling tie-trunk,
and reduced the number of dial 0 trunks required.
Functions performed by cord boards
From the brief survey above, it can be
seen that cord boards did, as a matter of course, a number of things
that were taken for granted but which, in a console design, had to
be implemented explicitly. Some of the more obvious follow.
Cord boards identified the line or
trunk involved on each end of each connection. Further, the path
from calling to called terminal could be traced via the cord. This
visual display was quite useful; for station lines on both manual
PBXs and CO switches, it was further enhanced by having
consecutively numbered jacks for hunt groups located adjacent to
each other and identified by an underline. Trunk groups (except for
the CO end of PBX trunks which appeared in the CO's line multiple)
were mounted in strips and labeled for easy identification. Busy
testing for lines and selection of the next available trunk were
made easy by the arrangement of the hardware and the use of
appropriate displays.
Direct access to each circuit
facilitated integrity testing, particularly in PBXs; a trunk,
tie-trunk or station line could be selected directly by an attendant
or operator and checked for proper operation. Lines or trunks
reached by automatic switching using hunting do not have this
advantage; without a no-hunt feature (see Chapter 5), one must take
whatever circuit the system chooses to deliver. With direct
switchboard appearances, a PBX attendant could test individual CO
trunks by plugging in, listening for dial tone, breaking dial tone
by dialing a digit, and then repeating the process on the next
trunk. A large network could be checked in a few minutes with such
procedures. Although such a test could easily be performed
automatically by a modern PBX, few actually have this capability.
Stations, like trunks, could be
accessed directly. Not only did this permit testing, it permitted
overriding a busy condition in emergencies. The attendant had to
know the rules for using "barge in" at any given company, but the
"feature" was available in the natural course of events. Transfer
was equally simple, particularly when assisted by "flashing recall."
The attendant (or operator) just moved the cord from one jack to
another. Because of the nature of switchboards, new calls could
readily be differentiated from an effort to recall the attendant.
Call forwarding was another feature an alert receptionist/attendant
could often supply, even without station activation.
"Splitting" a connection to talk
privately with either party (similar to consultation hold) was
easily done at a manual position. Call waiting and camp-on were also
easy: special pads of paper were provided to fit on the key shelf,
with marked off sections opposite each cord circuit; on detecting
busy, the attendant could note the called number, and other
information could be listed as required. The attendant was trained
to keep checking for busy on circuits with only one cord up.
When toll calls were recorded
manually, the attendant (or toll operator) would acquire the calling
and called number and make out a ticket. Slots were usually provided
next to each cord to hold the ticket for the duration of the call.
At answer, the answer time was marked down and the ticket placed in
the slot. At hang-up, the cords were pulled down, hang-up time was
noted, and the ticket was filed elsewhere for processing. Digital
clocks were available quite early; they made time recording much
easier than reading the big and little hands. The attendant could
queue calls for special facilities such as WATS, and the equivalent
of ARS could be wired into the idle trunk indicator lamps of a
switchboard.
In the days before voice mail,
attendants could take messages for station users who were away from
their desks. This was often much more convenient than leaving the
message with a secretary because a person retrieving messages had no
need to go beyond the switchboard. In large PBXs (1000 lines and
up), this kind of service at the switchboard was often impractical
but on smaller boards it worked well, facilitated by colored plugs
for insertion in the multiple to remind the attendants of the
service required.
Toll switchboards in the telephone
company were similar to attendant switchboards at a PBX, the
principal difference being the lack of a station multiple. In
general, toll operators handled only trunks; unlike PBX attendants,
they often had to deal with coin calls and other exotica related to
call charging.
The passing of the manual switchboard
The manual switchboard, even for PBXs,
is (almost) gone. Operator and attendant efficiency was often cited,
along with appearance, but other reasons can be found. As an
example, it was difficult to provide a station multiple when central
office equipment was used for Centrex switching. Further, while
progressive control systems such as SXS could easily compete with a
cord board position for access to the same circuits, common control
switches found this much more difficult. It was also difficult, in
large systems, to bring all lines and trunks to the attendant
positions when the automatic switching equipment was located
elsewhere. It is amusing, however, to see all the "new" features on
modern PBXs that do no more than duplicate the standard functions of
cord-boards, wrongly accused of being old fashioned devices.
Accessing Consoles
At the time of the breakup of the Bell
System (1982-4), most local central offices had been completely
automatic for decades. Further, at the apex of the AT&T toll
hierarchy, control switching points (CSPs) were also automatic,
implemented mostly by 4XBAR and later 4ESS 4-wire automatic trunk
switches. With no operators in Class 1, 2 and 3 CSPs and Class 5
local offices, it follows that operators, concentrated to provide
service for a large number of local switches, were associated almost
entirely with Class 4 offices or the toll connecting trunks between
them and local switching systems.
After the breakup, local telephone
companies were allowed to provide operator services; these had to be
associated with local or tandem switches because local operating
companies were not permitted to provide toll service. The several
competing toll companies then had the option of hiring the local
companies to provide operator services for them, doing it
themselves, or contracting with third-party operator service
suppliers. All this led to a certain amount of complexity.
In historical context, the 3CL toll
switchboard had supported Bell System operator functions very well
for many years; one simply dialed 0 into the local CO which then
made a connection to an operator trunk. The operator, often miles
away, would answer the call and provide the functions needed. For a
toll call, the operator would make out the billing ticket, seize an
outgoing toll trunk, and dial the call directly. When AMA made DDD
possible (and took over what had previously been multi-message-unit
bulk-billed calls as well), direct trunks bypassed the 3CL
switchboard and went directly to a tandem or class 4 toll switch.
AMA interfaced with these trunks at the 5XBAR end to facilitate
obtaining the calling equipment-number from the outgoing sender; the
Dimond ring translator, which converted equipment to directory
number, was part of the AMA equipment (see Chapter 2). Dial 0 trunks
still reached the 3CL, of course, to handle collect, credit card,
person-to-person and third party calls, to say nothing of ONI for QZ
billing as well as billing for early Centrex CU.
After initial efforts by New York Tel
and AT&T to develop a standard console to work with 5XBAR, AT&T
introduced the Traffic Service Position System (TSPS) in the late
1960s, a console system supporting a variety of switches and not
just 5XBAR. Like AMA, it had access paths bridging onto
toll-connecting trunks, one access path per trunk, as shown in
Figure 2. The TSPS switching matrix connected these access paths
from many local COs to various groups of operator positions and,
indeed, performed all the functions of a large ACD. In this way,
operator positions could be located convenient to the desired work
force, independent of the location of local, toll and TSPS switches.
With large amounts of information to
be exchanged between the TSPS switch and its consoles, the early
version of T-carrier, which had one supervisory bit for each channel
in each frame, proved to be a good vehicle. By accessing these
supervisory bits directly, 8000 24-bit control words per second (192
kBps) in each direction were transmitted between the system control
and groups of remote consoles. By repeating signals and using
several kinds of checking, very high reliability was obtained long
before today's sophisticated data techniques became commonplace.
It should be noted that a TSPS did not
switch trunks; it simply provided operator access to trunks already
homing on tandem or toll switching systems. Indeed, the purpose of a
TSPS was to add operator capability to automatic trunks without
interfering with existing trunk switching. This arrangement,
although suitable for regions of high telephone density with trunks,
CSPs and Class 4 offices already in place, was not necessarily ideal
where new automatic tandem or toll switches would have to be
installed. Further, it was not suitable for large business tie-trunk
networks where centralized attendants could be used effectively.
A contrasting approach was
demonstrated by tandem and toll switches such as Northern Telecom's
SP-1 which incorporated operator positions. With TOPS (for Traffic
Operator Position System, circa 1974), any trunk could be switched
to any operator, or any operator position could be inserted into an
existing connection as shown in Figure 3. Further, the switch
controlled an operator position over a simple TTY (data) link. This
allowed remote operator positions to be located singly as well as in
groups, and eliminated, with considerable saving in cost and
floor-space, the separate switching system used by TSPS to
interconnect large numbers of trunk access paths to operators and to
control operator positions. Because all trunks had access to TOPS
operators, separate groups of trunks for operator calls were not
needed (compare Fig. 2 with Fig. 3.) When Northern Telecom advanced
beyond the SP-1, a computer-controlled crossbar system, to
all-digital CO switches such as the DMS series, TOPS was upgraded to
go along (1981).
After divestiture of AT&T's local
operating companies, Northern Telecom almost immediately expanded
the DMS TOPS to TOPS MP (for multi-purpose), an improved version
designed specifically to allow local switches to add back operator
functions and also provide directory assistance. AT&T waited until
ISDN standards had stabilized enough for use, and then introduced
OSPS, or operator services position system, as a part of the 5ESS
development. Like Northern Telecom's TOPS, OSPS is a function of
software on a tandem/toll switch which can also act as an ACD for
operator positions; operator positions are connected to the 5ESS via
standard ISDN 2B+D BRI channels. To meet the post-divestiture market
for adding operators to local switching, the OSPS can be part of a
5ESS configured as an "access tandem," or can act as a stand-alone
ACD with trunks to various nearby local COs. However, initial
descriptions exclude the use of OSPS with a 5ESS configured as a
local switch.
It is interesting to note that, in an
age of LANs running at 10 mBps and faster to deliver data-base
information to VDTs associated with ACD positions, AT&T does not
even find the use of a 64 kBps B channel necessary for the exacting
requirements of directory assistance and similar telephone company
needs. Rather, the 16 kBps D channel, also used for signaling to the
OSPS position, is quite adequate, and the second B channel is left
as a spare.
Access to PBX attendant positions went
through an evolution similar to that of telco operator positions.
First, manual switchboards were replaced with rudimentary consoles
making direct connections to trunks; later, an access matrix
connected attendants to trunks as required. With the coming of
electronic telephone sets controlled by separate D-like signaling
channels (starting in 1975), it soon became evident that a console
need not be different from an electronic telephone, and access
matrices could be eliminated in favor of the main switching matrix
where consoles and electronic telephone sets where handled in almost
exactly the same way. Eventually, PBX proprietary phones and
consoles will give way to ISDN standards.
It should be noted that direct
connections and access matrices allowed attendants to answer
incoming calls even during periods of heavy traffic when the main
switching matrix might have no available paths. However, advances in
switching components and matrix organization generally make the
possibility of such blocking extremely remote.
Centrex, now provided only by CO
switches, allows customers to obtain consoles working in a variety
of ways, sometimes going back to the days of early PBXs where
bridged connections are actually made, either directly or via an
access matrix, to customer lines. The requirement that equipment on
the customer's premises be owned by the customer causes some
difficulties here. However, both AT&T and Northern Telecom, with
their OSPS and TOPS MP systems, enable local telephone companies to
offer console service (with telco operators at telco positions) to
Centrex clients.
Console functions.
A console can be considered a data
terminal that enables the switching system to display pertinent
information to an operator or attendant, and to accept instructions
from the telephonist for use by the switching system in the
disposition of telephone calls. The console also provides one or
more talk paths to permit the telephonist to communicate with
calling and/or called parties, although a completely separate but
program-related telephone can be provided instead.
Most consoles are constructed with a
flat or slightly sloping panel similar to the key shelf of a cord
board on which are located the major controls and their related
displays. On a vertical panel, comparable to the jack field of a
cord board although usually much lower, additional displays and
specialized controls are placed. Consoles may be free standing, as
in TSPS, Figure 4, or designed to sit on a desk. Today, many
consoles consist of a keyboard (with many extra "function keys"),
CRT display, and varying levels of internal intelligence and memory;
an example is the early TOPS system, shown in Figure 5. Such
positions have data access to the associated switching system's
control, and voice access to its switching matrix.
PBX consoles with their buttons and
flashing lights are the switching system as far as users and
attendants are concerned. But the small, sleek console, the
"cordless switchboard" that is such a potent sales tool, adds
considerable complexity to the PBX and increases switching matrix
size. An early advantage claimed for the cordless switchboard,
almost an obsession with designers, was the way it eliminated a
manual operation: with no cords to pull down, the system could
release a connection set up by an attendant as easily as one dialed
direct. This was not an unmixed blessing, however; automatic release
did not provide the attendant with the information necessary to
record hang-up time on a toll ticket or to seize a newly released
trunk for the next call in a manual queue. As a result, such
features had to be provided automatically.
Because a console must interface a
telephonist to an automatic switching system without the assistance
of traditional jacks, lamps, cords, message pads, etc., and in such
a way that traditional features and services are not degraded, it
must be designed with great attention to "human factors"
considerations. Displays, buttons, keyboards, headsets, handsets,
etc., must be carefully planned and tested to be sure they are easy
to use and minimize fatigue and discomfort. The functions of PBX
consoles often differ considerably from those needed within the
telephone industry, and these differences must be reflected in
design.
In CO operator systems and large PBX
systems, where several consoles are needed, the system must perform
a UCD function and distribute the traffic, more or less evenly, to
appropriate groups of telephonists. Some autonomy in call selection
should be provided so that, for example, skilled personnel can
handle complex calls while others can choose the simpler ones. On
recall, it is often necessary to return to the position that handled
the call the first time around. Provisions for training and
supervisory operations are also required.
Because the load on console systems
varies with time of day, day of week, etc., it must be possible to
take unoccupied consoles out of service; this is often done by
simply unplugging the handset or headset. In PBX design, taking all
consoles out of service activates night and through connections, and
UNA if provided. Connections that are up at the time of the transfer
operation should be unaffected; only when a facility goes idle
should the night condition take over. Because operator position
systems, like stand-alone customer ACDs, are usually quite large,
redistributing the load may involve several different locations,
routing modifications, and other approaches taking full advantage of
common channel signaling and intelligent routing.
In general, console displays indicate
the presence of calls needing the services of a telephonist. The
telephonist, using console controls, causes the selected call to be
connected to the console, finds what is needed, and keys in the
signals that will enable the switching system to carry out the
appropriate action. During call set-up, the telephonist can talk
privately to the calling or called party if necessary, or to both at
the same time. After the call is established, it can be released
from the console or kept associated if the need for further
assistance is anticipated.
Controls.
In many early switchboards, "lever keys" were used to control
various functions such as splitting or ringing. These keys were
actually switches with three positions, one with the handle or lever
sticking straight up, one with the lever pushed forward, and one
with it pulled back. The lever operated a number of switching
elements, constructed very much like the contacts of flat-spring
relays, permitting the opening and closing of a number of circuits.
Lever keys, when moved away from the center position, could be
arranged to stay in the operated position, or else to return
automatically to center when released. Wonderfully complex circuits
could be built with lever keys and operated easily by human beings.
Later, push-button switches, also
called keys (as in 1A2 key systems, Chapter 5), gained favor on
telephone sets, switchboards and consoles. These push-buttons, too,
could be arranged to lock operated or to return to normal when
released. Complex spring and contact assemblies were eventually
underpriced by electronics, and today, most control buttons used on
consoles and telephone sets do not latch, but make a single
momentary closure which causes electronic logic to carry the
required actions and activate suitable displays.
To relate stimulus and response
unequivocally, control buttons are usually put close to related
lamps or other displays; indeed, many control buttons today have
lamps or LEDs built in. This makes for a very compact array that can
offer both control and display functions. An early use of this
capability was a console feature called DSS (Direct Station
Selection), developed primarily for non-SXS electromechanical PBXs.
The idea behind DSS was to speed up the completion of incoming PBX
calls by letting the attendant see at a glance if the desired
extension was busy (lamp lit) and, if free, connect the trunk to it
by pushing a single button. When the only alternative was to use a
rotary dial to insert the extension number, DSS made a console
almost fast as a cord board.
Classic DSS is illustrated in Figure
6a, a console used with electromechanical PBXs. The DSS field,
across the vertical panel at the rear, dominates with 200
illuminated push-buttons. This kind of console is called key per
trunk, or KPT, because each trunk (up to 30) has its own appearance
on the left of the horizontal shelf. When ringing, a lamp associated
with the particular trunk-button flashes; the attendant pushes that
button to trip ringing and connect to the incoming call. After
obtaining the extension number, the appropriate button in the DSS
field is pushed (if its lamp is not illuminated) and the call is
completed.
Each DSS lamp/button is connected
directly to the matching line circuit, just as each trunk button and
lamp connects to its associated trunk circuit. A cable of about 300
pairs is required between the console and the switching equipment.
Installing a 300 pair cable is relatively expensive, and discourages
relocating the console. However, use of many pairs of wires
simplified control circuitry prior to the coming of inexpensive and
reliable electronics.
A second kind of console, illustrated
in Figure 6b (as well as in Figure 7), typical of those used with
many of today's stored program control electronic PBXs, is called
"switched loop;" trunks are switched to one of several "loops" on
the console, either by an access matrix or by the main switching
matrix itself where each loop appearance is very much like a station
line. Control and display information is sent between console and
switch control via a data link, eliminating the need for a 300 pair
cable to support DSS lamps and trunk control. With switched loop
operation, the console imposes no limits on the number of trunks in
the system, even when it is physically quite small.
At a switched loop console, the
attendant, upon seeing on a display that a call is coming in, causes
the trunk to be connected to one of the loops to the console where
it can be answered. The console of Figure 6b has six switched loops,
each with a control button and five status LEDs, located above the
4x3 signaling pad in the center of the horizontal shelf. The general
idea was to allow the attendant to retain physical access to certain
connections by just pushing a console button rather than signaling
the matrix to provide the desired connection. Eventually, it became
evident even to R&D management, brought up in the age of
electromechanical switching, that with suitable displays and
controls, only one switched loop was required for a console. Thus
eventually positions for both telco operators and PBX attendants
became little more than glorified electronic telephone sets, or PCs
with a built-in telephone, connected to a parent switch by either a
BRI or some proprietary equivalent.
As an optional feature, the console of
Fig. 6b has a DSS field for 100 extensions on the sloping panel,
along with six buttons to select a particular group of 100 lines.
The attendant can complete a call by selecting the proper hundreds
group and then, if the desired line is free, pushing its DSS button.
As an alternative, the extension number can be keyed in from the
signaling pad. Clearly, pushing two DSS buttons in order is not much
faster than using the keypad to send two-, three- or even four-digit
extension numbers to the system control, eliminating the need for
DSS and saving a good deal of space and complexity.
When the cost of DTMF receivers fell
low enough to allow them to be used with PBXs, some designers opted
for DTMF on consoles. Unfortunately, most attendants became so
skilled at keying in numbers that the various talk-off properties of
DTMF receivers (see Chapter 3) made them too slow and led to errors.
As a result, console key pads, including the one in Figure 6b, used
a form of digital signaling instead. However, vendor sales and
training personnel, to say nothing of experienced attendants, were
so convinced that DSS was necessary that eliminating it was nearly
impossible.
From a human factors point of view,
attendants seem to prefer a one-to-one relation between lines or
trunks and control buttons. When the DSS panel works via a data
link, it can be added easily when wanted. However, some designers
used the same principle with trunk controls, particularly in small
systems with 12 trunks or less. Such consoles were sometimes called
"software KPT."
DSS, even when provided, is not
equally useful for every extension, and the limitations it imposes
on numbering plans can be quite severe in modern systems with
completely flexible translation. Thus some systems provide a limited
number of DSS buttons for the most frequently called lines, and
allow them to be assigned alphabetically by name rather than by
number. Repertory dialers can also be used for one-button selection
of specific extensions, but lack the busy-idle status display which
is part of a small, programmable DSS field.
Displays.
Initially, switchboard lamps were favored in console
displays, transmitting information by being on, off, or blinking at
various rates; later, they illuminated text messages inscribed on
back-lit glass panels. Because lamps were relatively short-lived, a
means was usually provided for applying a test signal to light all
lamps for a check. Later, light emitting diodes (LEDs) and liquid
crystal displays (LCDs) provided much more effective and reliable
information presentations. Although "dumb" video display terminals
were also used for a time, the coming of the PC with built-in memory
and intelligence has opened almost unlimited possibilities for
presenting information stored locally as well as in the memory of
the switching system or a supporting mini- or main-frame computer.
When the PBX has a built-in directory,
a VDT can call up a DSS display whenever needed, showing not only
extension numbers and their status, but also names associated with
extensions (and trunks). Another possibility is to show, in
numerical order on the screen, only the extension numbers in use.
Because most lines are idle most of the time, such a display can
leave most of the rest of the face of the tube for other functions.
On small systems, individual trunks
may have busy lamps; however, when there are many trunks in several
trunk groups, "exception" reporting is more useful. For instance,
each trunk group may have a lamp which flashes slowly as use
increases beyond a certain percentage, the flash rate increasing as
the percent busy grows until the lamp is on, steady, when all trunks
are busy.
When a particular extension or trunk
requests service at a console, its identity (number and identifying
name) are often shown in a CALLING display, along type of call (dial
0, recall, etc.) and class of service. When the console initiates or
extends a call, a CALLED display shows identity as keyed in with the
system supplying the called name, class mark, and status (idle,
busy, ringing, on hold or forward, etc.). This capability is
particularly important with unanswered calls; the attendant can
decide whether to let the call hunt on ring-no-answer, be forwarded
to voice mail, or return to the console or a manual message center.
When the attendant splits the call, information pertinent to this
operation is also shown. Positions for telephone company operators
must also show information related to charging, routing, etc.
The use of displays to clarify and
simplify controls has only just begun on consoles as well as
electronic telephone sets. Soft function keys, labeled appropriately
and modified as required on the display during the course of the
call, can guide the telephonist or user through complex feature
operations, can identify lines or trunks as encountered, and can
help find names and numbers in a telephone directory. We can expect
to see software to enable a PC, already present, to provide advanced
displays for a telephone on the same desk, particularly when a
signaling channel independent of the speech path is available. There
is almost no limit to what can be done when one can start with a
display of such power. Even so, the ability of LCDs to display both
text and graphics inexpensively makes a PC unnecessary for the great
majority of advanced displays a telephone system might need.
The major uses of consoles within the
telephone industry are for operator assistance in setting up or
billing calls, and directory assistance. For telephone customers,
consoles are used in connection with PBX and Centrex systems,
largely to complete incoming calls to the desired party. There are a
number of other customer functions, however, that have traditionally
used switchboards or consoles rather than standard telephone sets.
Among the most important are telephone answering bureaus and various
hotel functions. Automatic call distributors have widely ranging
needs, but frequently use conventional telephones, perhaps with
headsets rather than handsets, for agent positions. Because agents
usually relate callers to a computerized data base, the elaborate
display terminals they require are often part of the computer rather
than the telephone system; there are many ways of linking the two
systems to expedite service.
Because the telephonist has, as a
primary function, voice interaction with the calling and/or called
party, the actual mounting of the microphone and receiver are of
more than passing importance. When an operator needed both hands to
plug in and pull down cords, a headset was the only possibility; PBX
consoles generally needed only one hand to manipulate push-buttons,
so handsets were frequently used, allowing the attendant, who also
often doubled as a receptionist, greater freedom of movement. Both
handsets and headsets plugged into jacks with additional contacts
which permitted activating the console or taking it out of service
automatically. Modern VDT-based telephone company consoles, where
both hands are needed to use the qwerty keyboard, have continued to
use headsets plugged into jacks with additional control capability.
In the early 1980s, the advantages of
headsets for people who spent a lot of time on the phone, even when
they used regular telephone sets, interacted with "fully modular"
telephone set construction then becoming available to produce
headsets that could be plugged in in place of the regular handset.
(Fully modular meant that both the cord from base to handset and the
one from base to wall could be unplugged at both ends.) The jacks
used in fully modular sets are very simple, with no extra contacts
or switching capability. Thus plugging in a handset or headset does
not tell the switching system anything. ACDs, which make extensive
use of regular telephone sets, usually require a code to be keyed in
for activation and deactivation, but, because they also require the
particular agent to transmit an identity code, a few more digits are
not usually a problem.
Operator and directory assistance
positions.
Both AT&T and Northern Telecom have
gone to VDTs with qwerty keyboards and many additional function
keys, including soft keys (see Fig. 5, for example). Because these
VDTs (often actually PCs) have software support from the switches on
which they home as well as intelligence and memory of their own,
they provide the operator with a powerful and flexible interface for
accessing and controlling the network in which they are embedded,
displaying directory information, etc. Further, by being completely
general, their internal and external programming can be upgraded as
future needs dictate.
PBX Consoles
The cost of a VDT is still fairly
high, and PBXs are often provided with less expensive consoles using
only telephone controls and displays and a numeric key pad. In most
instances, these are adequate, particularly if the console is simply
a member of the system's family of electronic telephone sets. Both
consoles and electronic sets today typically have at least some soft
function keys, as well as 40 or 80 characters of alpha-numeric
display. In addition, different overlays can be made available to
provide labels for controls and displays required by specialized
functions.
Main-Satellite Systems and CAS for
PBXs
Many business customers have a number
of locations in the same general vicinity; better service can be
rendered and savings in personnel can be realized if one group of
centralized attendants can serve all locations rather than providing
each location with its own attendants. Two approaches have become
fairly standardized: satellite systems, where one directory number
reaches the attendants who then use tie-trunks to complete calls to
remote locations, and CAS, or centralized attendant systems, where
each location has its own directory number, and "release link
trunks" are used to make a switched connection to centralized
attendants. With a large percentage of incoming calls completed via
DID, the number of PBX attendants needed is quite small;
centralizing those who remain greatly improves efficiency.
A main-satellite system, usually
called a satellite system in spite of the confusion with
communication satellites in space, offers callers the convenience of
a single directory number for a multi-location company, although, of
course, several different incoming trunk groups can be provided if
intra-company divisions are to be segregated; features such as DNIS,
of course, allow one physical trunk group to act as though it were
many, with the number dialed by the caller, transmitted over the
control channel, providing the identity of the desired destination.
Only the main switch supports
attendants. It is usually the location which receives the most
calls; as a result, a large number of incoming calls are simply
conventional PBX calls. However, tie-trunks are provided between the
main location and each of the satellites so that attendants can use
them to complete calls; these same tie trunks can also be used for
desk-to-desk dialing within the system.
CAS may or may not have regular
tie-trunks between locations, but it must have tie-trunks
class-marked as release link trunks (RLTs); see Figure 8. An
incoming directory number call at any satellite is connected to an
RLT, and at the other end, a connection is made to an attendant
position. When the attendant answers, off-hook supervision goes back
over the RLT, CO ringing is tripped, and the connection is
established. The attendant greets the caller as usual, obtains the
name (or, with luck, the extension number) of the called party, and
signals the control of the switch where the call entered the system.
That switch then releases the RLT to handle another call, and
establishes the connection from the CO trunk to the called party.
CAS obviously needs far fewer RLTs
than satellite systems need tie-trunks, because the RLT is only
associated with the call momentarily while the tie-trunk is used by
the call for its entire duration. However, without tie-trunks, desk
to desk dialing or transfer of calls from a user on one switching
system to a user on another is not practical.
Special programming, similar to that
used with an electronic key system to send a flash to the system on
which it homes, is needed so that the attendant on the main
switching system can attract the attention of the control at the
distant switch where the incoming call awaits transfer. Once that
switch supplies recall dial tone, the attendant can send DTMF digits
or feature codes via the RLT; standards have been established for
such analog signaling so that different brands of PBX can be
combined in a CAS system. Systems with electronic telephones and
separate signaling channels can, in principle, be designed to carry
out such functions more easily; unfortunately, such digital
signaling is usually proprietary, and seldom works with other brands
of PBX. Another motivation for ISDN.
Centracall, a very early
(pre-electronic) version of CAS, was tariffed by the New York
Telephone Company in response to the request of department stores.
In the late 1940s, shopping centers sprang up around most major
cities, and new stores had to be there in addition to the "big
store" downtown. It was expensive to make suburban customers call
into the main with multi-message-unit or toll calls, and then carry
their calls back to their local store on tie-trunks. However, once
CAS became available, its use spread far beyond chains of department
stores.
Switching through to an attendant can
be particularly useful in large companies with tie-trunk networks
operating in different time zones. West Coast attendants can handle
incoming calls after East Coast attendant positions have closed for
the night, changing class marks of selected tie-trunks, normally
unused after hours, to RLTs. Similarly, East Coast attendants can
answer early-bird calls for West Coast extensions. Clearly,
switching to a console which is actually one of a family of
electronic telephone sets has much to recommend it, assuming overall
compatibility. With LCD or other displays, and separate signaling
channels as with ISDN, the attendant can see which PBX a call is
entering and access the directory at that PBX if necessary.
Although main-satellite and CAS
systems are firmly established, the distributed switching made
possible by modern technology offers an even more general approach
for business customers and telephone companies alike. Remote
switching units and subscriber loop carrier allow a main switch at
one location to serve groups of distant users economically. PBXs
such as the InteCom have developed separate switching matrices which
can be controlled over a data link from a distant PBX. Such remote
matrices may or may not have tie trunks connecting them to the
controlling switch, but system management is greatly facilitated by
having only one data base and administration center, and only one
program to update when new releases come out.
Hotel/motel PBX consoles
The hospitality industry, as discussed
in Chapter 5, has often required several special types of console in
addition to the main console that handles incoming calls. These have
included a front desk console, used to show room status and to
change class of service as the room is rented or vacated, to display
telephone usage for billing purposes, to enter wake-up times, etc.
Another specialized console, little more than a numeric display
program-paired with a telephone, has been used to provide the room
number of the caller to the bell captain, room service, and other
locations with a need to know (note the similarity of this early PBX
feature to the public network's "Calling Number ID," available much
later). Adding the name of the person registered in the room,
possible with a built-in directory, updated in real time, can make
this feature more valuable.
Today, most of the functions of
specialized hotel consoles can actually be performed better by
regular electronic telephone sets, but the need to keep costs low
sometimes excludes their consideration. Small hotels and motels
often use nothing but conventional single-line telephones, with the
one console, located at the front desk, performing all special
functions directly. With the coming of inexpensive PCs, even very
small motels can use them to handle billing, directory, etc., and to
interface the PBX control to obtain information automatically from
which telephone charges can be calculated.
Answering bureaus
Telephone answering bureaus, although
buffeted by the recent deluge of answering machines and voice mail,
continue to provide service for physicians and others whose callers
need a human response rather than a recorded message. Originally,
answering bureaus used regular cord boards for their agents; a
customer's line would be bridged at the central office and appear on
a jack at the answering bureau; the CO would thus ring both in
parallel, and if the customer did not pick up after (typically)
three rings, the agent would answer with the appropriate greeting
(jacks were labeled with both name and greeting desired).
An answering bureau, as supported by
the telephone company before deregulation, would have a large
multi-pair cable installed to the CO, allowing a specific jack on
one of its switchboards to be connected to the customer's line by
jumpers at the CO's MDF (see chapter 7). Under the circumstances,
telephone answering services tended to be located near the CO.
However, in metropolitan areas, where there were many central office
switches in the same general area, a concentrator-identifier (CI)
system was developed (mid-1950s) to reduce the number of pairs
needed from each CO to as few as four per hundred lines. With or
without the CI, the agent could only enter the call during the
ringing interval to insure privacy.
With the coming of stored program
control, call forwarding became an obvious way to divert a call to
the answering service, and answering services could distribute such
calls via an ACD or PBX with suitable programming. However, the
called party has to be identified to answering service personnel to
make possible the correct greeting. This can, of course, be done by
having a line for each customer from the answering service to the
nearest telephone office, providing an appropriate call forwarding
target. However, an ISDN PRI, with 23 shared channels and a
signaling link over which the DNIS feature can be used, will work as
well for an answering service as for a reservation or telemarketing
system. Note that DNIS, unlike Calling Number ID, does not require
something new such as adding the calling number to the call set-up
information.
As an alternative, the called number
could be sent to the answering service via frequency shift keying
after each ring (like Calling Number ID), via DTMF or a variety of
other pre-ISDN means if the serving telephone company wished.
However, the obvious solution, from the telephone company's point of
view, is to rent the answering service ISDN phones in an ACD
configuration, each phone making full use of its BRI signaling
channel and built-in display.
When answering services (or PBX
message centers) take messages which are to be called for later, it
should be possible to type them into a computer rather than use
hand-written notes. Indeed, some systems have this capability, but
it appears that using the human being at the answering service to
bridge on a voice mail system and obtain verbally the required
responses from the caller makes recording easier and allows the
customer to access his or her messages directly by simply calling
the voice mail system. Such an approach could violate regulations
which are intended to insure privacy, but has much to recommend it
when properly controlled.
ACD positions.
Today, telephone company operators,
whether they assist a caller in establishing a call to someone else
or are the recipient of the call themselves, use consoles that, for
all practical purposes, are ISDN telephone sets, with or without VDT
capability. For reasons of economy, these operator positions are, as
has been discussed, located where a suitable labor force is
available, often remote from the switches they support. To take full
advantage of this operator force, the controlling switching system
must, of necessity, be an ACD in addition to the other functions it
performs. Because the number of positions involved is usually quite
large, and several specialized functions may be handled by different
groups, the ACD function has to be quite sophisticated.
An operator position can cause the
related switch to establish connections as required, but can equally
well be used to terminate calls. In the latter instance,
particularly with regard to directory assistance, the operator must
have access to a large data base to provide the caller with
appropriate information. Although the entire white pages for the
United States will fit on two CD-ROM disks and could thus be mounted
within a PC-based terminal, the need for continual updating means
remote access is necessary. The ISDN BRI appears the ideal way to do
this, and a voice-data terminal working over the same network to
callers and data base alike would seem to have some advantages.
The other main use of large ACDs is in
connection with reservation systems, notably for airlines, and
telemarketing, both incoming and outgoing. Outgoing telemarketing is
currently based on what is called a "predictive dialing system," a
data base and automatic dialer associated with the PBX or ACD; the
dialer calls phone numbers from its data base and arranges to
transfer a ringing call to the next available agent; at the same
time, pertinent information about the called party is displayed on
the agent's VDT. This approach allows the machine to do the dull,
repetitive work, leaving the human free to deal with more complex
matters such as selling, collecting, etc.
Incoming telemarketing delivers the
call to the next available agent, queuing calls if necessary until
an agent comes free. Again, the agent must often be provided with
pertinent customer information from a data base. Initially, the
agent would obtain verbally the calling party's name, phone number,
or zip code, and use it to cue the data base response. With calling
number ID, however, the calling phone number is delivered directly
to the system. If the caller is using someone else's phone, or is
calling from behind a PBX, further clarification may have to be
obtained.
In general, the customer data base for
either incoming our outgoing calls is kept on a separate computer;
although for years an effort has been made to use PBXs to provide
data access to main-frame computers (AT&T and Northern Telecom
introduced DMI and CPI respectively in mid 1980s), this kind of
multi-channel digital link, a precursor of the ISDN PRI, did not
become popular until Calling Number ID became available. Then
telemarketers began to visualize their PBXs or ACDs as peripherals
for their computers, so that company-specific software could be
developed to handle the entire operation. "Open architecture" was
developed for PBXs to permit outside control, and a new (if not
completely standardized) approach to such operations began.
The PBX answers the incoming call as
usual, obtains the calling number from the telephone company (most
easily done via the signaling channel associated with a PRI), and
sends it to the computer. The computer then assigns the call to a
particular agent, tells the PBX to make the appropriate voice
connection, and delivers the customer's profile to that agent's VDT,
more often by a LAN than via a proprietary or ISDN BRI data channel.
It is not clear how this trend will develop, but it has interesting
possibilities. By separating voice from the data distribution
system, ACD agents need little more than a conventional 2500 type
telephone, perhaps with a headset.
The whole purpose of automatic
switching is to replace operators. Today, the final frontier in this
process is to automate the more complex functions where humans have
held out for the longest because of the difficulty of the tasks and
the need for complex interactions with callers.
Centrex and DID
Centrex was designed to give each
business user a private CO telephone line which could be dialed
directly, bypassing the attendant. Thus DID, or direct inward
dialing, became an important feature. PBXs, accepting the extension
number outpulsed by the telephone company, could also complete calls
directly and bypass the attendant. Callers were not always pleased
with this approach. Many preferred to remember only one number for
each company, and ask the PBX attendant for the called party.
Indeed, the need to remember a great many new telephone numbers was
an obvious by-product of DID. To remedy this problem, Automated
Attendants were developed, as will be discussed later.
DIL and DDC
In addition to DID, there are two
other ways of bypassing the PBX attendant: DIL and DDC, discussed in
Chapter 5, and DISA, to be discussed below. Direct-in lines or
direct department calling use a CO trunk or trunk group to the PBX,
program-related to a particular extension or hunt-group pilot
number. When the CO rings the trunk, the PBX detects that ringing
and repeats it to the extension. When the user answers the phone,
ringing from the CO is tripped and the connection is established.
Clearly, an ISDN PRI will be able to render such services faster and
more economically.
DISA and the Automated Attendant.
DISA, or direct inward system access,
requires callers to have a DTMF telephone. They dial the number of a
CO trunk or trunk group which, as usual, rings toward the PBX. The
PBX then trips ringing and returns dial-tone from one of its own
DTMF receivers. The caller now uses DTMF to tell the PBX which
extension or service is desired. Obviously, the caller has to know
what to do once PBX dial-tone is obtained. To improve the utility of
DISA, it is possible to replace dial-tone with a recorded
announcement or synthesized speech. Elaborate voice menus can be
provided to help the caller find the right destination. A feature
(or system) of this sort is called an Automated Attendants (AA).
Very often, an automated attendant can find the called party if the
caller spells out the name using the letters associated with the
DTMF push-buttons.
Whether DISA uses dial-tone or an AA,
it represents a formidable security risk to the entire system.
Unauthorized callers can use it to gain access to long distance
services, the company computers, etc. Once inside, there is almost
no end to the havoc they can cause. The simplest approach is to
require the caller to enter an unlocking code (and disconnect if the
right code is not entered in three tries at most). Codes with only
four or five digits are useless, because hackers can program their
computers to keep trying. But much longer codes, while harder to
guess, are also harder to remember, and produce louder complaints
from the legitimate DISA community when they are changed (as they
should be, frequently).
Another approach is to give all DISA
users their own identity codes. Now, however, the hacker only needs
to find one code out of many that will open the system. If this
approach is used, great care should be taken to have valid numbers
machine-generated in such a way that they have no connection to
birth dates, department numbers, etc.
Perhaps the best approach is a
variation of the callback principle (see Chapter 1). Here the caller
gives the system an unlocking code and/or an identity code, followed
by the telephone number from which the call is being placed; the
caller then hangs up. If the switch finds the unlocking/ identity
code to be valid, it calls back to the specified number, entered
into the call record, using a different trunk. Even if it reaches a
someone attempting illegal entry, the switch knows where he or she
is calling from and has a basis for tracing, even if call forwarding
is used to hide the caller.
Calling back on a different trunk
serves two purposes. First, it greatly reduces the size of the DISA
trunk group (perhaps to a single trunk), and then allows WATS or
other low-cost facilities to be used for the actual call. Second, it
foils a hacker trick of NOT hanging up and then supplying bogus
dial-tone to fool the PBX into thinking the DISA trunk has been
released at the CO and then, upon reseizure, has returned a new
dial-tone. With calling party hold (see Chapter 3), the PBX's DISA
trunk could hang up but still reseize the old connection.
In all situations involving DISA, AA,
Voice Mail, etc., the system manager should remember that anything
which makes the system more "user friendly" will almost certainly
make it more vulnerable. Unauthorized access can be enormously
expensive.
Automated attendants, like
restrictors, ARS and CDR, were originally add-on devices. They
appeared to the PBX or Centrex as a group of 2500 sets reached via
DDC or DID, able to flash and send extension numbers or feature
codes to transfer the incoming call as desired; in alternative
designs, they were inserted in the PBX's trunks to intercept and
then complete incoming calls (note the similarity to switched loop
and KPT console operation). Today, of course, PBX and Centrex
designers often include AA in their designs.
It should also be noted that TSPS,
OSPS and TOPS all have an array of voice prompts to assist in
reducing the number of human attendants needed by automating coin
calls and other procedures which require the telephone system to
instruct the caller in the proper approach. Even person-to-person
calls are being automated in this ongoing attempt to increase
efficiency.
When a switch and AA are related to a
computer, a number of additional functions, under control of the
computer, become possible. These functions include registering
students for college classes or handling telephone shopping or
banking transactions. Voice prompts eliciting DTMF digits from the
caller permit a variety of meaningful dialogues to take place
between callers and robots. There have even been a few instances
where caller robots have talked to telephone robots, although the
results are seldom satisfactory.
When voice recognition systems advance
somewhat, and voice-print identification systems are improved, they
will doubtless expand the capabilities of telephone systems to
provide functions formerly the exclusive province of humans, and
even go beyond what can be expected of a human in the area of
security. There are, however, many who find this advance of the
robots unpleasant, and who would prefer human contact. It is
unlikely that human telephonists will ever be completely replaced,
but at the moment, they seem to be an endangered species.
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Switchboard
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Console
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DSS
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CAS
Click Here for
Answers
1. Distinguish among three types
of Telephonists.
2. Did manual switchboards have
common controls?
3. List some functions performed
on cord boards that had to be built into automatic switches.
4. List four ways for a local CO
switch to deliver a caller to an operator.
5. What is DSS?
6. What is the difference between
a switched loop and a key per trunk PBX console?
7. What is the main advantage of a
switched loop console?
8. What is a console?
9. Discuss the future of the
console.
10. What is the difference between
a satellite system and CAS?
11. How can DISA be made safer?
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