Communication network between user equipment

The invention concerns a network for communication between user equipments for the transfer of messages emitted by each user equipment to all the other user equipment. The network according to the invention has a tree-structured configuration (1-25) and operates with emission authorizations or tokens.

The invention relates to a communication network between user equipment for 
the transfer of messages emitted by each user equipment to all the other 
user equipment. 
The known communication networks of this type however have various 
drawbacks which detract from their optimum usage. 
A known network emits a systematic interrogation of all the user equipment 
in turn to determine if they desire to send a message. This interrogation, 
also called a token, can be transmitted by a bus to which are connected 
all the user equipment. There is thus a systematic transmission of the 
round robin or token to all the user equipment, which leads to poor 
efficiency due to the interrogation of user equipment with no message to 
send, and results in a maximum delay of transmission. This type of 
network, which offers the advantage of being able to use a passive 
support, does not permit the introduction of new user equipment except at 
the cost of great complexity. 
Another known network comprises user equipment interconnected in a ring. 
The interrogation or token circulates about the ring and stops only at a 
user equipment which has a message to emit. The output of this network is 
accordingly greatly improved but its fragility is considerable because all 
the user equipment is traversed by the data and by the interrogation. 
There is also known a network in which each user equipment continuously 
listens to the emissions of other user equipment, detection means after 
the fact guaranteeing the detection of simultaneous emissions of the 
message or collisions. This network has the drawback of not guaranteeing 
response time to an emission request by any user equipment whatever. 
Moreover, its efficiency is also low, given the collisions and the waiting 
procedures of uncertain duration prior to the consecutive reemission 
attempts upon detection of a collision, as the size of the network and its 
output increase. 
In this latter type of network, there is known in particular a so-called 
tree-structured configuration comprising main interconnection equipment 
which comprises at least two downstream terminals each connected by a 
connection to a single upstream terminal of a secondary interconnection 
equipment or to a user equipment, each secondary interconnection equipment 
comprising at least two downstream terminals each connected to a user 
equipment or to the upstream gate of another secondary interconnection 
equipment, all messages emitted by a user equipment being transmitted 
stepwise to all the interconnection equipment and thence to each of the 
user equipments connected thereto. 
The present invention aims to replace, in such a tree-structured 
configuration, the continuous listening and collision detection by a mode 
of interrogation of the user equipment which permits good performance of 
the overall network, even when its size and its output increase, which 
ensures a guaranteed response time, while not rendering delicate the 
network and permitting easy introduction of new user equipment. 
To this end, the network according to the invention is characterized in 
that: 
each user equipment emits a message only if it has first received an 
emission authorization signal, 
each user equipment emits, after having completed use of the authorization 
signal, an end of emission signal; 
the principal interconnection equipment emits an emission authorization 
signal to one of its downstream terminals only if, for each emission 
authorization signal which it has emitted from one of its downstream 
terminals, it has received an end of emission signal on the same 
downstream terminal, 
each secondary interconnection equipment emits an emission authorization 
signal to one of its downstream terminals only if it has itself received 
an emission authorization signal at its upstream terminal and if, for each 
emission authorization signal which it emits from one of its downstream 
terminals, it has received an end of emission signal at the same 
downstream terminal, 
each secondary interconnection equipment emits from its upstream terminal 
an end of emission signal only if, for each emission authorization signal 
which it has emitted from one of its downstream terminals, it has received 
an end of emission signal at the same terminal. 
It is thereby ensured that no more than one user equipment will be emitting 
a message at the same instant, without recourse to the detection systems 
normally used, this guarantee being given by the mode of transmission 
itself. 
According to an embodiment of the network according to the invention, 
each user equipment emits, when it needs to transmit a message, an 
authorization request signal, 
each interconnection equipment emits an emission authorization signal at 
one of its downstream terminals only if it has received at this same 
terminal an authorization request signal, 
each secondary interconnection equipment emits an authorization request 
signal at its upstream terminal only if each emission authorization signal 
which it has received at its upstream terminal has been followed by an end 
of emission signal emitted by itself at this same upstream terminal, and 
if there exists a downstream terminal at which has been received a new 
authorization request signal at at least one of its downstream terminals 
since the last emission authorization signal emitted from this downstream 
terminal. 
In this manner, an emission authorization signal is never transmitted to a 
user equipment which has not emitted an emission request, nor to another 
secondary interconnection equipment which has not received such a request 
at one of its downstream terminals. 
The invention also provides, according to a particularly advantageous 
embodiment, that the exchanged signals are in the form of transitions 
between conditions which are signalled throughout on the connections, and 
that, when a condition is signalled, it is maintained at least until the 
received return signals indicate that the considered condition has been 
taken into account. 
This embodiment is particularly simple and also is resistant to 
disturbances resulting from momentary transmission conditions in the 
connections. 
In this case, preferably, the emission request condition is equivalent to 
the absence of end of emission condition and the end of emission condition 
is equivalent to the absence of emission request condition. The resultant 
savings in the number of conditions to be transmitted permit simpler 
network arrangements. 
Preferably, in the case of this embodiment, it can be provided that 
a single transmission circuit, in each direction of a connection, is used 
to transmit the messages and the conditions of authorization, absence of 
authorization, end of emission and absence of end of emission, 
in each transmission circuit three types of signals are transmitted from 
the emission side and distinguished from the receiving side, namely the 
rest condition, the messages and the ineffective messages. 
the authorization conditions and the end of emission conditions are 
represented by the rest condition, 
transmission of the authorization condition on a downstream connection is 
if necessary deferred until the end of emission of a current message. 
The terminals of the interconnection element are each constituted by a 
module comprising: 
a receiver which signals at its output the detections of the rest 
condition, 
an emitter which emits a rest signal if the control is activated, 
a connector which connects to the bus if its control is actuated, the 
interconnection element comprising also a regenerator which regenerates 
the messages and, in the absence of a message to regenerate, emits 
ineffective messages and signals that it does so on the output.

In the example shown in FIG. 1, the network comprises a principal 
interconnection equipment (PIE) 1 whose downstream terminals 2 and 3 are 
connected by connectors 4 and 5, respectively, to upstream terminals 6 and 
7 of secondary interconnection equipment 8 and 9 (SIE). A third downstream 
gate 10 of the principal interconnection equipment is connected by 
connector 11 to user equipment 12. 
A downstream terminal 13 of SIE 8 is connected by a connector 14 to user 
equipment 15 and its second downstream terminal 16 is connected, via 
connection 17, to the upstream terminal 18 of secondary interconnection 
equipment 19. The three downstream terminals 20 of SIE 19 are connected 
respectively by three connections 21 to three user equipments 22. 
The two downstream terminals 23 of interconnection equipment 9 are 
connected, via two connections 24, respectively to two user equipments 25. 
Each interconnection equipment, which is a multiterminal repeater, 
therefore comprises at least two downstream terminals. Each secondary 
interconnection equipment comprises also a single upstream terminal. 
All the messages (M) emitted by the user equipments on their respective 
connections are disseminated stepwise by the secondary and principal 
interconnection equipment so as to be received by all the other user 
equipments. 
The structure which has been described is a classical tree-structured 
configuration. 
According to the invention, each user equipment (12, 15, 22, 25) emits a 
message (M) (or a series of messages) only when it has first received an 
emission authorization signal A. 
Each user equipment (12, 15, 22, 25) emits an end of emission signal F 
after having finished utilizing the signal A. It must then receive a new 
signal A before emitting a new message. 
Each SIE (8, 9, 19) emits a signal A from one of its downstream terminals 
only if it has itself received a signal A at its upstream terminal, and 
if, for each signal A which it has emitted from a downstream terminal, it 
has received a signal F at the same downstream terminal. 
Moreover, each SIE (8, 9, 19) emits at its upstream terminal a signal F 
only if, for each signal A which it has emitted from a downstream 
terminal, it has received a signal F at the same terminal. 
Therefore, no more than one user equipment (12, 15, 22, 25) can emit a 
message M at the same instant. 
The invention also provides, in a preferred embodiment, that each user 
equipment (12, 15, 22, 25) comprises means for emitting an authorization 
request signal (D) when it is in need of a signal A, that is, when it is 
ready to emit a message M. 
In this case, each principal (1) or secondary (8, 9, 19) interconnection 
equipment transmits a signal from a downstream terminal only if it has 
first received a signal D at this same downstream terminal. The emission 
of a signal A is therefore subordinated to the reception of a signal D. 
Moreover, each SIE (8, 9, 19) emits from its upstream terminal a signal D 
only if each signal A which it has received at its upstream terminal has 
been followed by a signal F emitted by itself at this same upstream 
terminal and if it has received a signal D at at least one downstream 
terminal since the last emitted signal F. 
This embodiment permits sending a signal A only to a user equipment which 
has emitted a signal D, the signal F following the latter signal A having 
been received. 
According to a particularly simple embodiment of the invention, the signals 
A, F and if desired D are embodied in transitions between conditions which 
are manifested along the corresponding connection. When a condition is 
signalled, it is maintained at least until the received return signals 
indicate that the condition in question has been taken into account. 
The signal A is materialized by a change from condition (a) to condition 
(a), the signal F by a change from condition (f) to condition (f) and, in 
the case of signal D, by the change from condition (d) to condition (d). 
There is thus obtained a particularly simple and practical structure which 
is insensitive to disturbances resulting from temporary conditions during 
transmission on the connections. 
The structure can be further simplified by thus regrouping the conditions 
f, f, d and d according to the equation: 
EQU f=d (and f=d). 
Preferably, in this case, there is utilized a single transmission circuit, 
in each direction of a connection, to transmit the messages M and the 
conditions a, a, f, f and three types of signals which are transmitted 
from the emission side and distinguished from the reception side: rest 
condition R, messages M, and ineffective messages I, the distinction 
between rest condition R and the other signals M and I being easy to 
effectuate at each of the terminals. 
The conditions (a) and (f=d) are materialized by signals R and, as a 
result, the conditions (a) and (f=d) by the signals M or I. 
In this case, the transmission of condition (a) on a downstream connection 
is, if necessary in an appropriate case, deferred until the end of the 
emission of a concurrent message M because the simultaneous emission of 
the signal S which characterizes the end of the message and the last 
portion of this message itself is impossible. 
The fact that the change from condition (a) to (a) is the only means for 
signalling to the other end of the connection that the condition (f=d) has 
been recognized, so as to permit it to change to condition (d=f), thus 
implies that the condition (a) will be maintained at least until reception 
of the condition (f=d). 
This embodiment permits the use of particularly economical transmission 
means. 
According to one embodiment, the transmission means uses the coding of 
messages in synchronous mode by the HDLC procedure, with the following 
definitions: 
rest condition R, sequence of 1 of length greater than 6, or when using a 
modem, absence of signal at the physical level (absence of carrier), or 
transmission of ineffective messages I, sequence of flags (01111110), and 
proper messages M, constituted of trams to the HDLC direction. 
Referring to FIG. 2, which shows an interconnection equipment having (n) 
downstream terminals constituted of (n) modules numbered from 1 to n and a 
module numbered 0 connected to the upstream terminal. 
Each module comprises: 
a receiver (A) which signals on an output (s) the detections of the 
non-rest condition, and which is connected to the bus if its command (c) 
is activated, 
an emitter (B) which emits a rest signal if the command (s) is activated. 
The interconnection equipment also comprises a regenerator (D) which 
regenerates the messages (M) and, in the absence of messages (M) to be 
regenerated, emits ineffective messages (I) and signals that it has done 
so on the output (i). 
Each of the modules 1 to n-1 is controlled by a logic E whose equations 
are: 
EQU set d if a and (d.sub.1 or d.sub.2) 
EQU reset d if d.sub.2 and (d.sub.1 or a.sub.2) 
EQU set a.sub.1 if d and a and d.sub.1 and a.sub.2 and i 
EQU reset a.sub.1 if d or a or a.sub.2 
EQU set a.sub.2 if d and a and d.sub.2 and d.sub.1 
EQU reset a.sub.2 if d or a. 
When a is received, a.sub.1 is emitted until d.sub.1 is received, then 
a.sub.2 is emitted until d.sub.2 is received, then d ceases to be emitted. 
Emission of a.sub.1 is deferred until the regeneration and transmission of 
any message M is terminated. 
The module .phi. comprises a control combination logic whose equations are: 
EQU a=s 
EQU c=s 
EQU g=d and s 
A generator G forces emission of ineffective messages (I) in the direction 
of the emitter B of the module .phi., when its terminal g is activated. 
This assembly assures that the interconnection equipment IE, if it disposes 
of an authorization received at its terminal .phi., attributes it in turn 
to each of its downstream terminals which is requesting, when its turn 
comes, then signals an end of use of its authorization. 
The connection 26 in dashed lines illustrates the direct connection d-a. In 
the principal interconnection equipment, the module .phi. may be omitted 
and replaced by a direct d-a connection 26 at the level of the logic 
E.sub.1.