Digital switching system

A digital switching system for establishing safety communications between N junctors is intended to guard against the potential danger of generalized failure which lies in the use of a central control unit and digital connection network for carrying out exchanges of information between junctors. Accordingly, each junctor is directly coupled to the N-1 other junctors of the system and is provided with its own control unit and its own digital connection network in order to enable said junctor itself to select the particular information which it is desired to receive from the N-1 other junctors. This system is primarily applicable to air and ocean traffic control.

BACKGROUND OF THE INVENTION 
The present invention relates to a system for digital switching between n 
junctors (n being a whole number greater than 1) and more particularly to 
a digital switching system for use in the field of safety communications 
such as air and ocean traffic control. In a digital switching system, the 
junctor serves as an interface for operator stations, different radio 
channels, telephone lines, and so forth. 
Systems of this type are already known in which all the junctors are 
connected to a central control unit and to a central connection network 
which are associated for receiving information from the different junctors 
of the system and controlling the junctor interconnections. As a result of 
the highly centralized structural arrangement of these switching systems, 
the complex assembly constituted by the central control unit and the 
central switching network are liable to result in total paralysis of the 
system whenever a failure occurs. 
SUMMARY OF THE INVENTION 
The object of the present invention is to prevent or at least considerably 
reduce the risk of total paralysis. 
This object is achieved by means of a switching system having a highly 
decentralized structure both in equipment and in logic circuitry, in which 
each junctor has its own control unit and its own switching network. 
According to the present invention there is provided a system for digital 
switching between n junctors (n being a whole number greater than 1) which 
deliver speech and signaling information, said system being provided with 
direct connections between the junctors so as to ensure that each junctor 
is capable of directly exchanging its information with the (n-1) other 
junctors and each junctor being provided with its own decision and 
switching unit formed by a control unit with fault detectors and by a 
digital connection network controlled by the aforesaid control unit.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a schematic view showing a switching system in accordance with 
the prior art. This system comprises n junctors J1' to JN' for delivering 
information D on the state of the junctors and digitized speech 
information P. The information D relating to the state of the junctors is 
transmitted without being processed to a control unit Uc derived from a 
computer which processes the information received and delivers output 
signals for controlling the state of the junctors. The speech information 
P of a junctor is transmitted to a connection network Rc having a 
space-time distribution matrix for carrying out under the control of the 
control unit Uc multiplexing of the speech information and retransmission 
of this information to the junctors. Communication between two junctors is 
established by the central unit which determines within the junctors the 
choice to be made in received speech information. In order to improve 
operational safety of a switching system of this type, it is a known 
practice to duplicate the outputs of the junctors and to duplicate the 
control unit Uc and the connection network. But in spite of the extensive 
equipment employed as well as the complexity of the control unit and 
connection network, there is a potential danger of total failure of the 
system as a result of failure of both control units or both control 
networks, thus leading to a major operational safety hazard. 
FIG. 2 shows how this risk of total failure may be reduced. FIG. 2 
illustrates n junctors J1 to JN which are distinguished from the junctors 
J1' to JN' of FIG. 1 by the fact that they each have their control unit 
and their connection network. The junctors J1 to JN can thus directly 
exchange digitized speech information P and signaling information S 
between each other or in other words information on the state of the 
junctors after such information has been processed by the control units 
relating to said junctors. Both in this specification and in the appended 
claims, direct exchange of information between the junctors is understood 
to mean a dialog between junctors in which the information delivered by 
one junctor is received unchanged by another junctor, that is to say 
without having been processed by means other than amplifiers. Thus a 
failure of the control unit or of the connection network of one junctor 
affects this junctor alone and the dialog may be continued between the 
other junctors. 
FIGS. 1 and 2 are highly simplified diagrams which show neither the 
duplication of certain elements and certain connections nor the duplicated 
clock which delivers the time-base signals. Similarly, FIG. 2 shows neither 
the interfaces placed between the junctors nor the supervision unit which 
collects information on the state of the system and the function of which 
is to facilitate maintenance. It is in any case worthy of note that these 
interfaces are transparent to the signals and that the supervision unit 
could if necessary be dispensed with except for the clock which it 
contains. 
The concrete example described hereinafter relates to a digital switching 
system involving the use of digital junctors each provided with their 
control unit having a microprocessor base and their digital switching 
network. The junctors of the system each have two speech channels and are 
of three types: a junctor for an operator station which interfaces an 
operator station with two speech channels (one radio channel and one 
telephone channel), a telephone junctor employed for management of two 
telephone lines and a radio junctor for management of two radio channels. 
Apart from their control unit and their switching channel which are in any 
case of simpler design than the corresponding control unit and switching 
network of the prior art (shown in FIG. 1), the construction of these 
junctors is based on current practice in communications and will therefore 
not be described in order to avoid explanations which would overburden the 
description without being conducive to a clear understanding of the 
invention. Another point to be noted is that, since the signals exchanged 
between them are similar in the case of all three types of junctor, it 
will not be specified whether a junctor considered is of the operator 
station type, of the telephone type or of the radio type. 
Generally speaking, in the description of the specific construction which 
is considered by way of example, circuits within the capacity of those 
versed in the art and especially circuits which are more simple than in 
the prior art will not be discussed in detail for the sake of enhanced 
simplicity of the description. 
The example described hereinafter relates to a system formed by operational 
units of fifteen junctors each provided with their supply. This system can 
have up to fifteen operational units which therefore represent 
15.times.15=225 junctors or in other words can have a maximum capacity of 
2.times.225=450 channels. 
FIG. 3 shows in the case of a maximum capacity the arrangement adopted for 
wiring the speech multiplexing portion of the digital switching system 
considered by way of example. Only the first unit U1 and the fifteenth 
unit U15 of the fifteen operational units have been illustrated. In these 
operational units, only the first and fifteenth junctor out of the fifteen 
which constitute the unit are illustrated. These junctors are designated by 
the references J1 to J15 in all the operational units and therefore require 
that the operational unit to which they belong should be indicated in order 
to be designated with precision. Apart from the fifteen junctors, each 
operational unit has two interfaces designated by the references L and L' 
in all the units. In order to designate them with precision, the unit to 
which they belong must accordingly be indicated. 
In order to simplify the writing and utilization of references, only the 
elements shown within the junctor J1 and the interface L of the 
operational unit U1 have been indicated. Subject to differences which do 
not appear in FIG. 3 and which are due to the type of channel to be 
switched, the other junctors and the other interfaces have the same 
elements respectively as said junctor J1 and said interface L. Thus an 
element without any reference may accordingly be designated hereinafter by 
the reference of the corresponding element in J1 or L of U1 followed by the 
reference of the junctor or of the interface to which it belongs as well as 
that of the operational unit in which it is located. 
On the left-hand side of FIG. 3 are indicated the transmission accesses, 
namely two per junctor and corresponding to the two speech channels of 
each junctor. In the right-hand portion of FIG. 3 are indicated the 
reception accesses of the junctors corresponding to the two channels which 
each junctor is capable of selecting from the 2.times.15.times.15=450 
channels referred-to earlier. 
The two transmission accesses of a junctor correspond respectively to the 
inputs of two analog-to-digital converters A1/1, A1/2 which each create a 
digital time interval, this time interval being in most instances 
hereinafter denoted I.T. for the sake of conciseness. These two I.T's are 
therefore the images of the two channels specific to the junctor. By 
virtue of the duplicated time base specific to the system, thirty 
different time pulses are assigned to the 2.times.15=30 I.T. of each 
operational unit by the analog-to-digital converters. At the outputs of 
the two converters A1/1, A1/2, the two I.T's are transmitted to the same 
conductor and applied to the inputs of two controlled amplifiers B1 and 
B1' in order to be duplicated accordingly. 
The outputs of the amplifiers B1 and those of the amplifiers B1' of the 
fifteen junctors of an operational unit are connected respectively to the 
input of the interface L and to the input of the interface L'. In 
consequence, these two interfaces each receive the 30 I.T's relating to 
the thirty transmission accesses. Each interface has fifteen input 
amplifiers C1 to C15 and fifteen output amplifiers D1 to D15. The outputs 
of the amplifiers C1 to C15 of the interface L of the unit U1 are 
connected respectively to the input of the amplifier D1 of the interface 
of the unit U1, to the input of the amplifier D1 of L of U2 (not shown) 
and so on in sequence up to the input of the amplifier D1 of L of U15. The 
same connections exist between the amplifiers C1 to C15 of the interface L' 
and the inputs of the amplifiers D1 of L' of U1, D1 of L' of U2, . . . , D1 
of L' of U15. Similar connections serve to couple the input amplifiers C1 
to C15 of the interfaces L and L' of the operational units U2 to U15 to 
the output amplifiers D1 to D15 of the interfaces L and L' of the units U1 
to U15. Thus the outputs of the amplifiers C1 to C15 of L' of U15 are 
connected respectively to the input of the amplifier D15 of L' of U1, D15 
of L' of U2, . . . , D15 of L' of U15. 
In each operational unit, the outputs of the amplifiers D1 to D15 of L and 
of L' therefore deliver respectively in duplicate the thirty I.T's of the 
units U1 to U15. Each of the fifteen junctors of each of the fifteen units 
has its own digital connection network constituted by a space-time matrix M 
having fifteen accesses which are respectively coupled to the outputs of 
fifteen controlled OR-gates E1 to E15. These OR-gates have two inputs and 
these inputs are connected in the case of the gate E1 to the outputs of D1 
of L and L', . . . , and in the case of the gate D15 to the outputs D15 of 
L and L'. Thus each matrix M receives from the OR-gates D1 to D15 the 450 
I.T's corresponding to the 450 speech channels of the system and is 
capable of selecting any two of these latter in order to deliver them on 
its output. 
As shown in FIG. 3, each junctor has its own control unit based on a 
microcomputer and detectors as designated by the reference Pr in the 
junctor J1 of the operational unit U1. Each interface also has its own 
control unit based on a microcomputer and detectors as designated by the 
reference Pc within the interface L of the operational unit U1. It is the 
control unit Pr of the junctor which, as a function of the state of the 
system and of the two channels to be received in the junctor considered, 
determines in the case of each OR-gate E1 to E15 of the junctor which of 
the two duplicated inputs of this gate is to be connected to the matrix M 
of the junctor. The two time intervals thus selected are processed 
respectively in two digital-to-analog converters F1/1, F1/2 which each 
select one of the two I.T's by means of a time pulse delivered by the time 
base of the system and under the control of the control unit which is 
specific to the junctor considered. The output of the converters F1/1, 
F1/2 restitutes in analog form the signal of the selected speech channel. 
Again in the case of the example which we have begun to describe with 
reference to FIG. 3, FIG. 4 shows the wiring arrangement relating to the 
local signaling network of the system which permits a dialog between the 
different control units of the system by exchange between the different 
junctors and interfaces of the system and a supervision unit Us mentioned 
earlier, of information on the state of the different junctors and of the 
different interfaces. Each junctor and each interface delivers the 
information on its state after having processed this information in its 
own control unit as shown in FIG. 3 but not reproduced in FIG. 4. 
As in the case of the speech multiplexing wiring system, the local 
signaling network is duplicated in a first network and a second network 
which are identical, thus making it necessary to describe only one of 
these networks hereinafter. For the sake of enhanced clarity and 
simplicity, only those elements which need to be designated individually 
are given a reference in FIG. 4. Moreover, as in the case of FIG. 3, the 
15.times.15=225 junctors of the system do not exhibit any differences and 
the same applies to the 15.times.2=30 interfaces, at least in regard to 
the local signaling network, all that will be said in connection with the 
junctor J1 and the interface L of the operational unit U1 will apply 
respectively to the other junctors and to the other interfaces. 
FIG. 4 shows the operational unit U1 with the interfaces L, L' and the 
junctors J1, J15 with an operator station K which employs the two speech 
channels of the junctor J1 and two radio assemblies N1, N2 which employ 
respectively the two speech channels of the junctor J15. FIG. 4 also shows 
the operational unit U15 and the supervision unit Us. 
The first local signaling network has a bus topology and has two lines: a 
data line Bs and an occupation line Bo which indicates whether the local 
network is utilized or not, thus making it possible to limit the risk of 
simultaneous presence of data having different origins on the line Bs. 
When a junctor is required to transmit a message, it must therefore wait 
until the occupation line Bo is free. The lines Bs and Bo are connected in 
identical manner to the fifteen operational units U1 to U15 and to the 
supervision unit. 
The junctor J1 is connected by two lines to the line Bs and by two lines to 
the line Bo: a data transmission line with a controlled amplifier Fe, a 
data reception line with a controlled amplifier Sr, a transmission 
occupation line with a controlled amplifier Oe and a reception occupation 
line with a controlled amplifier Or. These lines, at the output of the 
junctor J1, are common to the fourteen other junctors of the operational 
unit. The lines related to the amplifiers Se, Sr, Oe, Or traverse the 
interface L respectively through four controlled amplifiers Hde, Hdr, Hoe 
and Hor in order to be connected to the data line Bs in the case of the 
first two and to the occupation line Bo in the case of the other two. In 
the interface L, four lines equipped with four operational amplifiers Gde, 
Gdr, Goe, Gor are shunt-connected respectively to the lines equipped with 
amplifiers Hde, Hdr, Hoe, Hor. 
The control unit of the junctor J1 is provided with fault detectors which 
serve to changeover to the other network if a fault or failure is detected 
on one of the two duplicated networks and to isolate the junctor from the 
remainder of the system in the event of a fault condition. Changeover from 
one network to another or isolation of the junctor are performed by control 
of the OR-gates E1 to E15 (FIG. 3) and by blocking of the controlled 
amplifiers of the junctor, namely the amplifiers B1, B1' of FIG. 3 and the 
amplifiers Se, Sr, Oe, Or of FIG. 4. In the event that a short-circuit 
appears at the output of an amplifier, the control unit of the junctor 
cannot inhibit this latter, in which case the interfaces L, L' of the 
operational unit intervene. Their control unit Pc (FIG. 3) is provided 
with detectors for detecting faults in the messages. These detectors serve 
to determine whether the messages obtained from the fifteen junctors of the 
operational unit are all coherent and, should this not be the case, to 
block the amplifiers Hde, Hdr, Hoe and Hor (FIG. 4). 
As will be noted with reference to FIG. 4, it is in order to ensure a 
higher degree of reliability and easier fault location of the signaling 
networks that each interface L, L' ensures isolation and separation into a 
transmission bus and into a reception bus within the operational unit with 
respect to a single transmission-reception bus between the different units 
for exchanges of signaling information. 
It is also worthy of note that the time-base signals delivered by the 
supervision unit Us to each junctor in a duplicated manner through the 
interfaces are controlled by detectors at the level of the interfaces and 
of the junctors. Again by virtue of the control units of the junctors and 
interfaces, this makes it possible to operate a junctor with either of the 
two time-base signal distributions when they are both in a normal state but 
to choose automatically the better of the two distributions when a fault 
condition has been found in the other. 
The present invention is not limited to the example hereinbefore described. 
From this it follows in particular that the number of junctors per 
operational unit may be different from fifteen and may even be reduced to 
one. Similarly, the number of operational units of a digital communication 
system can be different from fifteen and may be reduced to one if 
necessary. As has already been mentioned, the supervision unit may be 
reduced to a time-base circuit and therefore may no longer have a 
supervision function but simply a synchronization function. Similarly, the 
interfaces can be replaced by simple conductive connections without 
controlled amplifiers and without a control unit with detectors although 
it will be understood that, all other things being equal, operational 
safety will be distinctly lower than that of the system described with 
reference to FIGS. 3 and 4.