U.S. patent number RE30,037 [Application Number 05/875,660] was granted by the patent office on 1979-06-19 for data communications network remote test and control system.
This patent grant is currently assigned to Rockwell International Corporation. Invention is credited to Larry F. Bass.
United States Patent |
RE30,037 |
Bass |
June 19, 1979 |
Data communications network remote test and control system
Abstract
A remote test and control system for use with a data
communications network having primary and backup facilities
provides full network testing and switching capability from a
central location, thereby obviating the need for manual supervision
at the remote data terminal stations served by the network.
Inventors: |
Bass; Larry F. (Mission Viejo,
CA) |
Assignee: |
Rockwell International
Corporation (El Segundo, CA)
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Family
ID: |
24085748 |
Appl.
No.: |
05/875,660 |
Filed: |
February 6, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
523624 |
Nov 14, 1974 |
03920975 |
Nov 18, 1975 |
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Current U.S.
Class: |
714/716; 379/28;
714/4.2 |
Current CPC
Class: |
G06F
11/2294 (20130101); H04L 43/50 (20130101); H04B
1/74 (20130101) |
Current International
Class: |
G06F
11/273 (20060101); H04B 1/74 (20060101); H04L
12/26 (20060101); G08C 025/00 (); G06F
011/00 () |
Field of
Search: |
;235/302,304
;340/146.1BE ;364/200,900 ;179/175.2R,175.2C,175.3R |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
J R. Kelly, A Remote Test for Data Sets, Bell Laboratories Record,
vol. 42, No. 10, Nov. 1964, pp. 350-355..
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Primary Examiner: Atkinson; Charles E.
Attorney, Agent or Firm: Greenberg; Howard R.
Claims
What is claimed is:
1. A remote test and control system for use with a data
communications network interconnecting a central processing station
with at least one remote data terminal station, through a pair of
communication links either of which may be selected .Iadd.by a
command signal .Iaddend.for passing data information therebetween,
with each remote station containing a data terminal and a pair of
modems with the data terminal being adapted for connection to the
selected communication link through either modem, comprising:
command signal transmitter means for generating and transmitting
command signals over at least one of the communication links, each
command signal being addressed to a selected remote station;
individual command signal receiver means located at each remote
station for receiving the command signals addressed to its
associated station.Iadd., said receiver means being capable of
receiving command signals over whichever link they are
transmitted.Iaddend.; and
individual switching means located at each remote station
responsive to .[.one.]. .Iadd.a .Iaddend.command signal for
connecting the audio terminals and .[.another command signal for
connecting the.]. digital terminals of either one of the associated
station modems between the selected one of the two communication
links and the station data terminal, respectively.
2. The remote test and control system of claim 1 including
individual status signal transmitter means located at each remote
station for generating and transmitting over at least one of the
communication links a status signal indicative of various station
conditions following the receipt of a command signal and status
signal receiver means for receiving each status signal and
displaying the information contained therein.
3. The remote test system of claim 2 including individual modem
test means located at each remote station responsive to a command
signal for continuously monitoring via its associated individual
switching means a selected one of the associated station modems for
malfunctions and for providing an indication thereof via a status
signal.
4. The remote test system of claim 1 wherein each communication
link includes two sections, one for the central station to transmit
and the other for it to receive data information and wherein each
of said individual switching means is responsive to a command
signal for looping a communication link at its associated station
by connecting the transmit and receive sections of the
communication link together at the station and including an
individual test signal generator located at each remote station for
connection to the receive section via said individual switching
means in response to a command signal for applying to the receive
section test signals to measure the line characteristics thereof
and test signal generator and analyzer means for receiving and
analyzing the test signals over the communication receive section
and for also applying test signals to the transmit section.
5. The remote test system of claim 4 wherein each of said
individual switching means is responsive to a command signal for
placing either of its associated station modems in a digital loop
with either one of the two communication links and including
digital loop measurement means for applying a digital test signal
to the transmit section of the communication link, receiving the
transmitted signal over the receive section, and comparing the
received signal to the transmitted signal.
6. The remote test system of claim 3 wherein each communication
link includes two sections, one for the central station to transmit
and the other for it to receive data information and wherein each
of said individual switching means is responsive to a command
signal for looping a communication link at its associated station
by connecting the transmit and receive sections of the
communication link together at the station and including an
individual test signal generator located at each remote station for
connection to the receive station via said individual switching
means in response to a command signal for applying to the receive
section test signals to measure the line characteristics thereof
and test signal generator and analyzer means for receiving and
analyzing the test signals over the communications receive section
and for also applying test signals to the transmit section.
7. The remote test system of claim 6 wherein each of said
individual switching means is responsive to a command signal for
placing either of its associated station modems in a digital loop
with either one of the two communication links and including
digital loop measurement means for applying a digital test signal
to the transmit section of the communication link, receiving the
transmitted signal over the receive section, and comparing the
received signal to the transmitted signal.
8. The remote test system of claim 1 wherein command signals are
transmitted over only one communication link and including
individual link selector means located at each remote station for
detecting that link and connecting thereto its associated station
command signal receiver means.
9. The remote test system of claim 3 wherein command signals are
transmitted over only one communication link and including
individual link selector means located at each remote station for
detecting that link and connecting thereto its associated station
command signal receiver means.
10. The remote test system of claim 7 wherein command signals are
transmitted over only one communication link and including
individual link selector means located at each remote station for
detecting that link and connecting thereto its associated station
command signal receiver means.
11. The remote test and control system of claim 1 wherein the
network includes an intermediate processing station containing
digital processing means interconnecting either one of the
communication links with either one of at least one pair of branch
circuits, said processing station including a pair of modems and an
individual associated terminal controller for the link pair and for
each branch circuit pair with the inputs to all the station
terminal controller command demodulation means being connected in
common.
12. The remote test and control system of claim 11 wherein the
outputs of all the station terminal controller status modulator
means are connected in common.
13. A remote test and control system for use with a data
communications network interconnecting a central processing station
with the data terminal of at least one remote terminal station
through a pair of communication links, either of which may be
selected .Iadd.by a command signal .Iaddend.for passing data
information therebetween, comprising:
command signal transmitter means for generating and transmitting
command signals over at least one of the communication links, each
command signal being addressed to a selected remote station;
individual command signal receiver means located at each remote
station for receiving the command signals addressed to its
associated station.Iadd., said receiver means being capable of
receiving command signals over whichever link they are
transmitted.Iaddend.; and
individual switching means located at each remote station
responsive to a command signal for connecting the associated
station data terminal to the selected one of the communication
links.
14. The remote test and control system of claim 13 including
individual status signal transmitter means located at each remote
station for generating and transmitting over at least one of the
communication links a status signal indicative of various station
conditions following the receipt of a command signal and status
signal receiver means for receiving each status signal and
displaying the information contained therein.
15. The remote test and control system of claim 13 wherein each
communication link includes two sections, one for the central
station to transmit and the other for it to receive data
information and wherein each of said individual switching means is
responsive to a command signal for looping a communication link at
its associated station by connecting the transmit and receive
sections of the communication link together at the station and
including digital loop measurements means for applying a digital
test signal to the transmit section of the communication link,
receiving the transmitted signal over the receive section, and
comparing the received signal to the transmitted signal.
Description
BACKGROUND OF THE INVENTION
The present invention generally concerns data communications
networks having primary and backup facilities and is specifically
directed to a remote test and control system for testing and
reconfiguring the facilities from a central location without the
need for manual supervision at the network remote data terminal
stations.
The wide acceptance and current popularity of data processing is
evidenced not only by the amount of data processing equipment
currently in use, but also by the marked interest of public and
specialized common carriers in providing data communications
networks for meeting the burgeoning data traffic demands arising
from the flow of data between distant locations. These traffic
demands and their dramatically increasing growth patterns are due
in no small part to the system design philosophy that it is often
economically expeditious, even if not absolutely necessary, to
process at one centralized location data from a number of
geographically separated data terminals. For example, necessity
might apply to the rapidly increasing point of sale transactions
wherein credit and inventory controls are executed from a central
memory bank for a number of commonly owned retail stores;
economical expediency might apply to the time sharing of an off
site single large computer by a number of remotely located
facilities rather than providing an individual small computer on
site at each one of those facilities.
In either case, the marriage of data communications with data
processing is a fact of commercial life and represents sizeable
capital investments by the business community. Because of these
investments it is essential that data communications systems,
comprising the networks which provide the communication links and
the data terminal stations connected thereto for transmitting and
receiving the data information, be utilized to the fullest extent
possible so as to most efficiently employ capitalized investment.
Consequently, it is imperative that the system operate with as
great a reliability as practicable to assure the greatest degree of
availability for data transmissions. Moreover, delays in the
acquisition of requested data may materially and detrimentally
impact or even prove critical to a business operation because of
the need for and emphasis on the continuity and speedy real time
retrieval of information, the airlines industry being one example
thereof. This provides even greater impetus for maximizing data
communications systems reliability.
In accordance with the foregoing, it is not uncommon to find
duplication of components in data communications systems so that
when one component fails because of some malfunction it can be
replaced by another to quickly restore service while the component
malfunction is diagnosed and corrected and the component is
restored to service, thereby maintaining service continuity in the
intervening period. For instance, a number of remote data terminal
stations might be interconnected with a central processing station
by two communication links, a link being defined herein as a half
or full-duplex two-way transmission path including all of the
associated equipment for passing signals between the remote and
central stations over any medium whether it be wire or air. The
link can be a dedicated one devoted to a particular customer or in
the case of the telephone system a dial circuit associated with the
normal telephone switched network which is accessed by conventional
telephone dialing. One link would be a primary, normally used for
data traffic with the other being a backup for emergency
contingencies in the event that the primary link develops a
malfunction. In that case upon learning of the malfunction, the
backup link would be placed into service in lieu of the primary
link until the malfunction was diagnosed and corrected and the
primary link restored to service. When the data communications
network is one designed for bandwidth limited voice communications
the backup link is quite often normally used for voice
communications so as to maximize the use of capitalized investment.
In this arrangement, voice communications would be forced to yield
to data communications whenever the link was required as a
replacement for its primary.
Once a backup arrangement is decided upon for the data
communications network, in order to maintain the same consistency
of reliability throughout the system, it is usually desirable to
also provide backup components within each of the data terminal
stations themselves. When the communications network is designed
for bandwidth limited voice communications, as is the telephone
system, it is not uncommon to supplement the requisite modem at
each station required for interfacing the data terminal with the
network with a back up modem. Consequently, if the primary modem
malfunctions, the other modem acts as a replacement so as not to
disable the data terminal during the period needed to diagnose and
correct the malfunction and restore the primary modem to
service.
Although the use of backup facilities ameloriates the longer term
detrimental effects of malfunctions in data communications network,
there still remains the problem of first, determining that there is
a system malfunction; second, locating the malfunctioning component
so that it can be isolated from the rest of the system; and third,
replacing it with its backup counterpart to restore service while
the malfunction is diagnosed and corrected. Since the time that the
system or any part of it is down because of a malfunction is
economically wasteful, it is imperative that this three-step
operation be performed as expeditiously as possible. Once the
presence of a malfunction is recognized, usually through some
difficulty encountered by a user or a preventive maintenance
program, the malfunctioning component is normally located through
the cooperation of two people, one at the central processing site
and the other at the data terminal stations for applying and
interpreting the results of various tests which are performed. Not
only does this entail delays since personnel have to be dispatched
to the remote stations (although personnel could be stationed on
site on a permanent basis this is not usually a viable economical
alternative in view of the many stations which may comprise a
system), but also the specialized training and employment of
numerous people since in many cases the terminal stations which
comprise a data communications system may be spread over an
expansive area. With the dramatic growth of the data communications
field and the great sums of money devoted thereto this is a serious
problem. Recognizing the problem, remote test systems have been
developed for testing data communications systems from a central
location thereby obviating the need for personnel at the data
terminal stations. However, these systems are not comprehensive in
that they do not provide the full battery of tests needed to
quickly and accurately detect and isolate malfunctioning components
nor thereafter to expeditiously restore service by remotely placing
the required backup facilities into operation.
With the foregoing in mind, it is a primary object of the present
invention to provide a new and improved remote test and control
system for use with data communications networks for determining
and locating system malfunctions from a central location.
It is a further object of the present invention to provide such a
remote test and control system having capability for reconfiguring
the communications network facilities from the central location as
required by replacing identified malfunctioning components with
their backup counterparts.
It is still a further object of the present invention to provide
such a remote test and control system which is easily and
inexpensively made compatible with all portions of data
communications networks despite their various configurations and
equipment.
These as well as other objects may be readily appreciated by
referring to the Detailed Description of the Preferred Embodiment
which follows hereinafter together with the appended drawings.
BRIEF DESCRIPTION OF THE INVENTION
The remote test and control system of the invention provides remote
testing and switching capability for a data communications network
having primary and backup facilities through a network controller
located at a central location which contains standard test
equipment for generating and analyzing the test signals that are
applied to the network for troubleshooting as well as generating
and transmitting to the individual network remote data terminal
stations command signals for effectuating switching changes thereat
to reconfigure the network by switching between primary and backup
facilities and also establish various test modes. The network
controller may include additional equipment for receiving status
signals from the terminal stations indicating various station
conditions which may be of interest to an operator at the central
location.
Each network data terminal station is provided with a terminal
controller responsive to the command signals for implementing the
switching directives by switching the station to one or the other
of the communication links serving it and selecting between the two
station modems when the network is voice bandwidth limited as is
the telephone system. The terminal controller may include
additional equipment for generating and transmitting to the network
controller status signals when desired as well as various test
signals used in troubleshooting of the network.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a typical data communications network with which the
remote test and control system of the invention is intended to
function.
FIG. 2 is a functional block diagram of the invention.
FIG. 3 is a symbolic representation of the audio and digital
switches which comprise the system terminal controller together
with the command signals to which the switches are responsive.
FIG. 4 shows the various tests which the remote test and control
system performs.
FIG. 5 is a functional block diagram of the command encoder in the
system network controller.
FIG. 6 is a functional block diagram of the status decoder in the
system network controller.
FIG. 7 is a functional block diagram of the relevant portions of
the terminal controller used in a network intermediate processing
station for implementing the control and status extension feature
of the invention.
FIG. 8 shows the details of the link selector circuit for selecting
the link over which command signals are to be received.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 depicts a typical data communications network with which the
remote test and control system of the invention is intended to
operate. The network serves a central processing station 10 and a
plurality of remote data terminal stations 12 which are all
geographically separated from each other but are interconnected via
a communication link 14 which may take any appropriate form such as
wire, microwave, etc. The communication link 14 may comprise a
single path for both transmitting and receiving data signals in
half-duplex fashion or two paths, one for transmitting and the
other for receiving signals if full-duplex operation is desired.
Each remote station 12 connects to the communication link 14
through its own individual branch portion of the link, the
connection to the common portion of the link 14 being made as
dictated by the system; for example, at a central switching office
in the case of the telephone network. Although the communication
link 14 is shown in a multidrop arrangement (one path shared by two
or more stations 12), the invention will hereinafter be seen to be
equally compatible with a point-to-point network wherein each
remote station 12 is directly interconnected with the central
station 10 by its own individual link.
Each of the remote stations 12 contains a data terminal 16 for
generating data sigals in digital binary form which are transmitted
over the communication link 14 to a central processor 18 located in
the central station 10. After processing the data, the central
processor 18 transmits the appropriate data response back to the
terminal 16 from whence the input data originated. Since the data
communications network, as depicted herein for exemplary purposes
only, is voice bandwidth limited, for example as the telephone
network would be, a plurality of modems 20 are included to provide
the well known function of transforming the data digital signals to
and from a format which is suitable for transmission over the
bandwidth limited network. Since the central processor 18 may
interconnect with other communication links, the central station 10
also includes a concentrator 22 as an interface therebetween.
In order to minimize capital costs, our typical data communications
network also serves an intermediate processing station 24 which
interconnects with a plurality of remote data terminal stations 26
via their individual branch circuits 28. Remote stations 26 are
exactly like remote stations 12 except that data signals from their
respective data terminals 30 are processed by a digital processing
means 32 located in intermediate station 24 in lieu of or in
addition to the central processor 18 located in the central station
10. The type of processing done by processing means 32 will of
course depend upon the nature and configuration of the particular
data communications network. For example, the processing means 32
could be merely a concentrator thereby avoiding the need for
extending the communication link directly to all of the remote
stations 26. In such case, data signals passing between the remote
stations 26 and the central station 10 would be reformatted and
resequenced as they pass through the digital processing means 32.
Alternatively, the digital processing means 32 could be another
processor for processing data from the remote stations 26 under the
control and in conjunction with the central processor 18 located at
the central station 10. In any event, it is to be realized that the
digital processing means 32 can take any one of well known forms
dependent upon the particular functions it is to provide. As with
the central and remote stations, the intermediate station 24
includes modems 20 for interfacing with the bandwidth limited data
communications network.
Although for the sake of simplicity, they are not shown in FIG. 1,
our typical data communications network does provide backup
facilities for maintaining service continuity in the event of
equipment failures. For example, each modem 20 has an exact
duplicate which can be switched to replace it should an operating
problem develop therein. Similarly, the communication link 14, and
branch circuits 28 are afforded backup capability should operating
problems develop therein. The backup link 14 and branch circuits 28
may be either dedicated, viz. in parallel with their primary
service counterparts but disconnected from the remote station
equipment until required for backup service by closing the switches
at the stations (the common and branch portions of the backup link
14 would already be connected at the connection centers such as the
central office in the telephone network) or dial backup circuits in
the case of the switched telephone network in which case separate
telephone connections would be established between each remote
station 12 or 26 and the central station 10 for passing signals
therebetween over the telephone voice network. In either case, as
presently exists, all of the required switching would be done
manually once the problem was identified and isolated through
various tests performed with the aid of skilled personnel located
at all of the remote stations of the network.
As will be appreciated hereinafter, the particular data
transmission arrangement used with the data communications network
is not germane to the invention. Thus, the remote test and control
system disclosed herein may be made compatible with any type of
signalling system whether it be strictly a polled arrangement
wherein each remote station is sequentially addressed by the
central processor or a multiplex arrangement, frequency or time
division, permitting more than one communication to take place
simultaneously.
As shown in FIG. 2, the remote test and control system of the
invention employs two major components, namely, a network
controller 34 located at a central site, preferably central station
10 and a terminal controller 36 located at each of the remote
stations 12 and 26 and the intermediate station 24. Each pair of
station modems 20 providing primary and backup service requires its
own individual terminal controller 36. The network controller 34 is
connected to the primary and backup communication links 14 through
an interface circuit 38 which may be merely a patch field or if
desired a more sophisticated switching means for accessing the
links and which also includes the standard coupling bridge, filters
and amplifiers normally found in a communications system. The
network controller 34 includes equipment for applying test signals
to the data communications network and for measuring the results
thereof. The network controller 34 further includes equipment for
applying command signals to the data communications network to
effect switching changes at the remote data terminal stations 12
and 26 as well as intermediate station 24. These command signals
are applied to the network not only to reconfigure it for operating
purposes by switching over to backup facilities, but also to place
the different network elements into various test modes.
The terminal controller 36 includes equipment responsive to the
command signals for effecting the switching changes and for
generating test signals for testing network elements to detect
faults as well as status signals to permit the network controller
34 to monitor conditions at its associated remote station. As
shown, the primary and backup modems 20 are connected between an
audio switch 40 and a digital switch 42, the former for connecting
the audio terminals of either of the modems 20 to either of the
communication links 14 and the latter for connecting the digital
terminals of either of the modems 20 to the data terminal 16. As
will be apparent from FIG. 3, these switches 40 and 42 include
individual switches 43, shown symbolically, for performing the
foregoing switching functions as well as others, to be described
shortly, in response to various command signals from the network
controller 34. The individual switches 43 of audio and digital
switches 40 and 42, respectively, may be electronic or
electromechanical whichever is preferred with their control
circuitry (considered part of the switch 43, but not shown)
assuming any one of various schemes well known in the art. Each
switch 43 closes in response to the designated command signal shown
in FIG. 3 in order to accomplish the switching directive
transmitted from the network controller 34 over the transmit
portion of link 14. Status and test signals are transmitted back to
the network controller 34 from the terminal controller 34 via the
receive portion of link 14.
Before continuing with a description of the invention, it would be
well to pause at this point to present the various standard network
tests which can be performed by the remote test and control system
herein. These tests are directed to various parts of the data
communications network and are designed to measure parameters
affecting the audio and digital signal performance of the network.
As shown in FIG. 4(a), transmission characteristics of the full
duplex communication link 14 can be measured through an audio loop
test by connecting the transmit and receive portions of the link 14
together via the audio switch 40 at the desired remote station
location and applying to the transmit portion various complex
frequency signals generated by a test signal generator (TSG) 44
located in the network controller 34. After passing through the
loop via the desired remote station, these test signals are
received by a test signal analyzer (TSA) 46 located in the network
controller 34 which allows one to determine how the original
complex frequency signals generated by TSG 44 have been changed by
transmission through the communication link 14 and consequently the
various circuit characteristics associated therewith. For example,
it will be readily apparent to those skilled in the art that such
characteristics as line loss, frequency response, envelope delay,
harmonic distortion, phase jitter, frequency offset, etc., can be
and are in fact measured in this fashion. The TSG 44 and TSA 46,
being readily available commercial devices from such companies as
Hewlett Packard and Collins Radio, need no further explanation
here. If further technical information is desired, however, the
reader is referred to two Bell System Technical Reference
publications (numbers 41000 and 41009) which present the pertinent
underlying theory. By comparing the measured parameters with
established standards, or better yet, actual predetermined
operating parameters for the actual data communication link 14, one
is able to ascertain the existence of some problem in the tested
portion of the data communications network through unacceptable
deviations therefrom.
Having determined from the audio loop test that some problem does
exist in the communication link 14, one can further determine
whether the problem exists in the transmit or receive portion
thereof by a one-way test (FIG. 4(b)) wherein complex frequency
signals are applied to the receive portion of the communication
link 14 by a test signal generator (TSG) 48 located in the remote
station at which the audio loop test was performed and measuring
the received signals at the network controller 34 with the TSA 46.
This one-way test will indicate if there is a problem in the
receive portion of the communications link 14, or if not, by
comparing the characteristics of the receive portion with the
characteristics of the communication link 14 if there is a problem
in the transmit portion. Thus, the combination of the audio loop
and one-way tests provides information for completely analyzing the
data communications link 14 with respect to both its transmit and
receive portions. When the communications link 14 is used for
half-duplex operation then only the one-way test is required for
ascertaining the characteristics thereof.
As shown in FIG. 4(c), a digital loop test can be performed with
either the primary or backup modem 20 at the desired remote station
by properly switching the audio and digital switches, 40 and 42,
respectively, associated therewith. In this test, the digital
terminals of the modem 20 are short circuited via the digital
switch 42 so that signals received over the transmit portion of the
data communication link 14 are passed through the audio receive
terminals of the modem 20 and are immediately fed back via the
audio transmit terminals thereof. These digital test signals which
contain a pattern of some pseudo-random oriented bits are generated
by a test pattern generator (TPG) 50 and applied to the transmit
portion of the communication link 14 via a modem 52, both located
in the network controller 34. A comparator 54 located in the
network controller 34 receives the digital signals over the receive
portion of the communication link 14 for comparison with the
signals as originally transmitted. Detected changes therebetween
provide information for the entire digital loop. Since the TPG 50
and comparator 54 are well-known commercial devices available as
Modem Test Sets from a number of companies such as Bowmar and
International Data Sciences they require no further explanation
here.
As shown in FIG. 4(d), a fourth test is possible for analyzing the
performance of a modem 20 in a remote station. This modem test is
performed by shorting out the audio transmit and receive terminals
of the modem 20 via audio switch 40 and connecting its digital
terminals between a TPG 56 and a comparator 58 both being located
at the remote station. These function the same as their
counterparts in the network controller 34 thereby providing
information for evaluating the digital performance of the modem 20.
Since it is desired, if not imperative, for reliability purposes
that the backup modem 20 be fully operational if called into
service to replace its primary counterpart this modem test can be
continuously performed with respect thereto. The detection of a
malfunction can be reported to a human operator at the network
controller 34 by means of a status signal like all other status
signals so that the malfunction can be cured before the backup
modem 20 is required for service.
As may well be appreciated, the foregoing tests can be performed on
either the primary or backup facility, dependent upon what the test
is intended to accomplish, namely, fault finding for the data
communications network after a problem has been identified or
preventive maintenance. By performing the audio and digital loop
tests at the various terminal stations served by the network the
particular section or sections of the communication link 14 in
which a problem has developed can be located by process of
elimination, each station affording a different section of the link
for testing. The testing flexibility is only limited by the
complexity and expense one wishes to go to in the audio and digital
switches 40 and 42, respectively, to permit various switching
combinations.
Returning now to FIG. 2, it will be seen that operator commands for
transmission to the remote stations 12 and 26 as well as
intermediate station 24 are entered into a command encoder 60
located in the network controller 34. The command signals are in
the form of digital bits which comprise a command digital word,
there being a sufficient number of bits in the data field for
performing all the requisite functions, with the location of each
bit therein being associated with a particular function to be
performed. The command word would, of course, have a preamble for
recognition and synchronization purposes as well as an address
field for directing the command word to the appropriate
station.
The output of command encoder 60 is applied to a command modulator
62 which transforms the digital information in any one of
well-known ways to a proper format for transmission over the
communication link 14 via the interface circuit 38. In a preferred
embodiment, the use of phase shift keying modulation using a
carrier signal frequency of 300 Hz. and a data rate of 50 baud
permits the command signals to be transmitted in the lower portion
of the voice bandwidth so as to avoid interference with the data
signals being transmitted over the data communications network or
unnecessarily interrupting data signal transmissions when
transmitting command words.
Status signals in the form of digital words are received over the
communication link 14 via the interface circuit 38 in a status
demodulator 64 located in the network controller 34. After the
status signal is demodulated in accordance with whatever modulation
technique is employed, the information is applied to a status
decoder 66 where the status digital word is converted to an
appropriate display format along with the outputs of comparator 54
and TSA 46. The display format can be any conventional type such as
light indicators, CRT, teletype, etc.
In addition to the equipment previously discussed, each terminal
controller 36 includes a command demodulator 68 for receiving the
command signals from the network controller 34 via its associated
audio switch 40 and the communication link 14. After extracting the
command digital word in accordance with the type modulation used,
the command demodulator 68 applies it to a command decoder 70 which
routes the control bits to their intended destinations. For
example, signals for controlling the connection of the primary and
backup communication link 14 to the associated controller's TSG 48
or the station's modems 20 as well as interconnecting the transmit
and receive portions of the link 14 for audio loop testing are
applied to the audio switch 40. The command signal for controlling
which of the station modems 20 is to be connected to its associated
data terminal 16 is applied to the digital switch 42. The signal
for controlling the TSG 48 transmission is applied by the command
decoder 70 thereto.
Each terminal controller 36 also includes a status encoder 72 for
structuring status digital words to be transmitted back to the
network controller 34 for providing information about the remote
station to a human operator stationed at the network controller 34
site. As shown in FIG. 2, this information could include the
outputs of the station comparator 58 and the command decoder 70 for
respectively indicating the results of the modem tests (previously
discussed) and confirming that the command digital word transmitted
to the terminal controller 36 by the network controller 34 was
properly received. If one desired to ascertain the proper operation
of the audio and digital switches 40 and 42, respectively, in
response to command signals from the network controller 34, that
data could also be applied to the status encoder 72. The output of
the status encoder 72 is applied to a status modulator 74 for
proper formatting before being transmitted to the network
controller 34 via the communication link 14 and the associated
audio switch 40.
A problem in the primary communication link 14 preventing the
passage of normal data signals to and from the central station 10
would also prevent the transmission of command signals from the
network controller 34. Thus, if the command demodulator 68 of the
terminal controller 36 was connected only to the primary
communication link 14, there would be no way to remotely switch the
remote station 12 over to the backup communication link 14 when
required. Although the command demodulator 68 could be connected to
both the primary and backup communication link 14 to avoid this
problem, signals on the backup link could conceivably interfere
with the command signals being received over the primary link. For
example, noise could prove to be troublesome and more than that
audio signals when the backup link is normally used as a voice
communication path.
This problem is overcome by the present invention through a link
selector circuit 76 located at each remote station which monitors
both the primary and backup communication link 14 to determine over
which one command control signals are being transmitted. Upon
determining which one, the link selector 76 selects that link for
connection to its associated terminal controller 36 by applying a
signal to the associated audio switch 40 which then connects the
associated command demodulator 68 thereto. Thus, when a primary
communication link 14 in service develops a problem requiring the
switchover to the backup link, the operator at the network
controller 34 would begin transmitting command signals via the
command modulator 62 over the backup link which upon detection by
the link selector 76 would cause its associated audio switch 40 to
switch its associated command demodulator 68 over to the backup
link. Any initial command signal, including a dummy signal not
addressed to any particular station would suffice since it is only
the detected signal level (as will be explained later) that
matters. Thereafter, the command signal ordering an addressed
remote station 12 to switch its modem 20 over to the backup circuit
would be received by the associated command demodulator 68 which
would then cause audio switch 40 to make the switchover.
Details of the network controller command encoder 60 are shown in
FIG. 5. The command digital word is formed in a shift register 78
by parallel entry therein of the command, address and preamble bits
in their proper locations via a gate circuit 80. The preamble bits
which are fixed, are generated in a preamble generator 82 while the
command and address bits are generated by command and address
generators 84 and 86, respectively, in response to human controls
by the operator (for example, by flipping console switches). Thus,
the operator is able to select the command he wishes to implement
together with the remote station for receiving that command by
appropriately setting the bits of the command and address
generators 86 and 84, respectively. Once the command and address
information has been entered into shift register 78, (gate 80 being
enabled at this time) the operator initiates transmission of the
command word by applying a momentary start signal to the S input of
an RS flip-flop 88 which sets it, causing its Q output to go high.
This Q output is applied to an AND gate 90 to enable it at this
time to pass pulses from a clock circuit 92 to a counter 94. The
counter 94 is designed to provide a count equivalent to the number
of bits in a command digital word whereupon it then applies a
momentary signal to the R input of flip-flop 88 via its output lead
to reset that flip-flop. At that time, its own count is reset to
zero. The low Q output of flip-flop 88 following a full count by
counter 94 partially inhibits AND gate 90 thereby preventing the
clock pulses from passing therethrough until the next start signal
is received. In addition to incrementing the count of counter 94,
the output of fully enabled AND gate 90 is applied to shift
register 78 so that during this time the digital command word is
shifted out via command modulator 62 whose output is connected to
the interface circuit 38 via an AND gate 96. A second input to AND
gate 96 is received from the Q output of flip-flop 88 so that that
gate is inhibited from passing the carrier signal generated in
command modulator 62 when no command word is being transmitted from
the network controller 34 (Q output law). During command word
transmissions gate 80 is inhibited by the high Q output of
flip-flop 88.
The status digital word, which has the same bit structure as the
control digital word, is received in the network controller status
decoder 66, the details of which are shown in FIG. 6. After
separating the clock and data information from one another, the
status demodulator 64 applies both to a shift register 98 so that
data is serially entered into the register at the same rate that it
is being transmitted. The bits in the preamble field location
within the shift register 98 are continuously compared with the
fixed preamble code in a comparator 100 so that when a match is
detected an enable signal is applied at that time by the comparator
100 to a gate circuit 102 thereby permitting the status bit
information located in the data field of the status digital word to
be parallel entered into a register 104 whose output is connected
to any appropriate type of indicators. A preamble code match occurs
of course only when the status word is fully entered into shift
register 98. Once new data begins entering shift register 98, the
comparator 100 disables gate 102 until the new data is likewise
completely entered and a preamble code match is again detected.
The terminal controller command decoder 70 and status encoder 72
function exactly the same as their network controller counterparts
just described and shown in FIGS. 5 and 4, respectively. The only
difference between the command decoder 70 and the status decoder 66
is that the comparator in the former seeks a match in address code
as well as preamble code before the shift register information is
entered into a parallel entry register thus assuring that only the
properly addressed station responds to the intended command. The
only difference between the status encoder 72 and the command
encoder 60 lies in the means by which the signal transmission is
initiated. Whereas, a command signal transmission from the network
controller 34 is initiated through a start signal triggered by a
human operator, the status signal transmission is begun either
automatically in response to the receipt of a command signal if
such is the system design or alternatively in response to a
specific command signal requesting the status condition of the
addressed remote station.
The presence of an intermediate digital processing station 24 of
FIG. 1 poses problems in passing the command and status digital
signals between the network controller 34 on one side thereof and
the remote stations 26 on the other side. Since each pair of modems
20, primary and backup, located in the intermediate station 24
requires its own terminal controller 36 (to perform the same
functions including switching as performed by the remote station
counterpart) there is the further problem of passing the command
and status signals between the network controller 34 and those
terminal controllers 36 associated with the intermediate station
modems 20 separated therefrom by the digital processing means 32.
Although these signals like the regular data signals passing
through the data communications network could obviously be passed
through the digital processing means 32 this would add to the
complexity of the circuitry therein as well as impose the time
delays associated with the modems 20 and digital processing means
32 unnecessarily on the speed of the remote test and control system
operation. These undesirable effects are obviated by the control
and status extension feature depicted in FIG. 7. FIG. 7 shows the
relevant portions of the individual terminal controllers 36
associated with the modem pairs of intermediate station 24 with the
same pictorial relationship as that depicted in FIG. 1. The input
leads to all of the terminal controller command demodulators 68 are
connected together while the input leads to all of the terminal
controller status modulators 74 are likewise connected together.
Thus, a command signal transmitted from the network controller 34
via the communication link 14 and the audio switch 40 of the upper
left terminal controller 36 is accessible to any one of the command
demodulators 68 located in the intermediate station 24 directly or
by any located in the remote stations 26 via the communication
branch circuits 28 and the audio switches 40 connected thereto in
the intermediate station 24. The command demodulator 68 whose
terminal controller address corresponds to that of the command
digital word will be the one which receives the command signal to
the exclusion of the other demodulators. Similarly, each status
modulator 74 within intermediate station 24 has direct access to
link 14 via the interconnecting audio switch 40 (upper left) while
each station modulator 74 at a remote station 26 likewise has
access thereto via its branch circuit 28 and the intermediate
station audio switch 40 connected thereto. But in no event are any
of the command and status signals passing through the network over
link 14 required to pass through digital processing means 32 and
its associated modems 20.
As shown in FIG. 8, the link selector 76 comprises a level
comparator 106 having two inputs, each being connected to one of
the communication links 14 through an individual bandpass filter
(BPF) 108, an envelope detector 110 and an RC charge/discharge
circuit 112 consisting of a resistor 114 in parallel with a diode
116 and in a series with a capacitor 118. The input signals to
level comparator 106 are derived from the capacitors 118. The level
comparator 106 has two outputs, each being associated with one of
its inputs arranged so that a switching signal appears on that
output whose corresponding input has a larger signal thereon.
Envelope detector 110 is merely an AM detector which provides a
D.C. output that is a function of the magnitude of the modulation
information.
The link selector 76 takes advantage of the different
characteristics between the desired command signal for detection
and all the other types of undesired signals such as noise, data,
voice, etc. The command signal has a narrow bandwidth (around 100
Hz.) centered around a frequency in the lower frequency spectrum
(as mentioned earlier preferably 300 Hz.) so that most undesired
signals are merely filtered out by BPF 108 which is designed
accordingly. Voice signals which pass through BPF 108 and which
normally have a high peak to average energy ratio are distinguished
from the command signal which has a low peak to average energy
ratio by the voltage developed across capacitor 118 which has a
long charge period via resistor 114 and a short discharge period
via diode 116. Thus, normal speech patterns will prevent capacitor
118 from maintaining a high signal level since during random speech
pauses capacitor 118 will discharge very rapidly through diode 114.
A command signal on the other hand having a duration which is
ordered and much greater than the charge time constant of the RC
circuit 112 will permit capacitor 118 to charge to its maximum
value and hold it during the presence of the command word thus
causing level comparator 106 to generate an output signal on the
output lead associated with the input lead connected to that
capacitor. Consequently, the link selector 76 will respond to a
command signal even in the presence of a voice signal whose
magnitude greatly exceeds that of the command signal. As mentioned
previously any command word, even a dummy word not addressed to any
station will suffice to effectuate a switchover to the desired link
14 by charging the capacitor 118 connected thereto to the
appropriate level.
As demonstrated by the foregoing preferred embodiment, the
invention disclosed herein provides a means for easily and
expeditiously testing and reconfiguring data communications
networks, including station modems when required, from a central
site without the need for any human supervision at the remote data
terminal stations served by the networks. Thus, facilities which
develop operating problems or present future problems via a
preventive maintenance program can be quickly and efficiently
identified and isolated while their backup counterparts are
activated to maintain service continuity even during the period of
time that is required to diagnose and correct the problems. This
greatly enhances overall system reliability and customer
satisfaction while optimizing the utilization of capitalized
equipment.
Since various modifications to the system described herein are
undoubtedly possible by those skilled in the art without departing
from the scope and spirit of the invention, the detailed
description is to be considered illustrative and not restrictive of
the invention as claimed hereinbelow:
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