Network system for simultaneously coupling pairs of nodes

A network system includes a plurality of low-order networks which each have a plurality of nodes coupled through data transfer paths and are mutually coupled by a repeater for data communication between the nodes. The repeater has a switching circuit system including a plurality of switching circuits for selectively coupling the low-order networks. The repeater further has a switch controller for controlling the switching operation of the switching circuits in accordance with a communication request from each node.

BACKGROUND OF THE INVENTION 
The present invention relates to a network system in which a plurality of 
low-order networks, each having a plurality of nodes coupled via data 
paths, are mutually coupled by repeaters and data communication is 
performed between the nodes. 
In a star network which uses a passive type optical star coupler as an 
optical distributor and executes data transmission between nodes by means 
of optical communication, it is inevitable that light attenuation is 
caused by the optical transmission path including the star coupler and the 
number of connectable nodes is limited. According to conventional network 
systems, therefore, network system expansion is realized by coupling a 
plurality of networks with optical repeaters that are each a relay device 
for system expansion. 
FIG. 1 illustrates an example of a network system that has been expanded 
using such repeaters. 
The network system comprises nodes N1 to N10, star couplers SC1 to SC5 and 
repeaters R1 to R4. A small or low-order star network is constituted 
around each of star couplers SC1-SC5, and a large or high-order star 
network is constituted around star coupler SC5. Repeaters R1-R4 are 
coupled between star coupler SC5 and the remaining star couplers SC1-SC4. 
In the system illustrated in FIG. 1, if the high-order star network is a 
non-multiplexed or single-wavelength network, it can permit data 
communication only between a single pair of low-order star networks. For 
instance, data transfer from node N2 to node N5 is effected through star 
coupler SC1, repeater R1, star coupler SC5, repeater R2 and star coupler 
SC2 in the named sequence. During the data transfer the high-order star 
network is occupied by the task so that another data transfer, for 
example, from node N6 to node N9 is not possible. In this case, therefore, 
the data transfer from node N6 to node N9 becomes possible only upon 
completion of the data transfer from node N2 to node N5. 
SUMMARY OF THE INVENTION 
As described above, conventional network systems expanded with repeaters 
entail a problem that only a single pair of low-order networks are allowed 
for data communication therebetween. 
With the above situation in mind, it is an object of this invention to 
provide a network system which allows data communication between plural 
pairs of networks by the use of improved repeaters. 
The repeater used in the network system of this invention comprises a 
switching circuit system including a plurality of switching circuits for 
selectively coupling low-order networks and a switch controller for 
controlling the switching operation of the switching circuits in 
accordance with a communication request from each node. 
According to the network system of this invention, the switch controller 
responsive to the communication request from each node connects data paths 
between different networks, thus ensuring simultaneous data communication 
between plural pairs of networks.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 illustrates the structure of a network system according to the first 
embodiment of this invention. 
This network system comprises nodes N1 to N16, optical star couplers SC1 to 
SC4 and an active repeater 50. 
Low-order star networks are constituted around the respective star couplers 
SC1-SC4 using optical fiber calbles for the transmission paths. Each star 
network is coupled with the center unit, i.e., star coupler SC1, SC2, SC3 
OR SC4, and nodes N1-N4, N5-N8, N9-N12 or N13-N16. Active repeater 50 has 
an active repeating circuit 6 for relaying the individual star networks 
and a controller 7 for controlling the active repeating circuit 6. 
FIG. 3 illustrates a detailed structure of active repeater 50. 
As illustrated, controller 7 has a repeat request detector 8 and a switch 
controller 9. Active repeating circuit 6 has an optoelectric (O/E) 
converters 10 to 13, a switching circuit 14 and electro-optic (E/O) 
converters 15 to 18. 
O/E converters 10-13, which are respectively coupled to star couplers 
SC1-SC4, has an ability to convert an optical signal transmitted through 
transmission optical fiber cables 1T to 4T into an electric signal. The 
converted outputs from individual O/E converters 10-13 are sent to 
switching circuit 14 and repeat request detector 8, which are both coupled 
to these O/E converters. Switching circuit 14 selectively connects the 
data transmission paths between star couplers SC1-SC4 of the individual 
star networks and may be constituted by a plurality of switches arranged 
and coupled in a matrix form. E/O converters 15-18 each convert an 
electric signal supplied through switching circuit 14 into an optical 
signal. The converted outputs of E/O converters 15-18 are transferred to 
the star networks through reception optical fiber cables 1R to 4R. 
Repeat request detector 8 of controller 7 detects a repeat request from the 
converted outputs of O/E converters 10-13. Based on the detection result, 
switch controller 9 of controller 7 controls the switching operation of 
switching circuit 14. 
The operation of the network system with the above arrangement will now be 
explained. 
When a repeat request is sent from any of nodes N1-N16, the request signal 
is applied to active repeating circuit 6 of active repeater 50, and is 
then transferred to repeat request detector 8 through one of O/E 
converters 10-13. Repeat request detector 8 detects the repeat request 
signal and sends a control signal corresponding to the detection result to 
switch controller 9. In response to the control signal, switch controller 
9 controls switching circuit 14 according to the detection result. More 
specifically, switching circuit 14 connects the associated data 
transmission paths together so as to permit data communication between the 
node at which the repeat request signal is generated and the node which is 
the target requested by that repeat request signal. 
Suppose that a repeat request signal for requesting data transfer from node 
N1 to node N9 is generated at node N1. This repeat signal is transferred 
to repeat request detector 8 sequentially through star coupler SC1, 
transmission optical fiber cable 1T and O/E converter 10. Switch 
controller 9 responds to the output from repeat request detector 8 and 
controls switching circuit 14 in accordance with the repeat request 
signal. Specifically, switching circuit 14 connects the output terminal of 
O/E converter 10 to the input terminal of E/O converter 17 so that data 
transfer from node N1 to node N9 can be executed. 
If, during the data transfer from node N1 to node N9, a new repeat request 
signal for data transfer between nodes that belong to other star networks 
(those having other star couplers than SC1 and SC3), e.g., data transfer 
from node N5 to node M13 is generated at node N5, the repeat request 
signal is transferred to repeat request detector 8 through the sequence of 
star coupler SC2, transmission optical fiber cable 2T and O/E converter 
11. Under the control of switch controller 9 based on the output of this 
detector 8, switching circuit 14 connects the output terminal of O/E 
converter 11 to the input terminal of E/O converter 18, thereby allowing 
for data transfer from node N5 to node N13. 
According to this network system, as described above, since switching 
circuit 14 that is controlled by switch controller 9 connects the data 
transmission paths between the source and destination star couplers of the 
star networks, it is possible to perform data communications between 
plural pairs of star networks at the same time. 
FIG. 4 illustrates the structure of a network system according to the 
second embodiment of this invention. 
The major difference between this network system of FIG. 4 and that of FIG. 
2 is that the former system uses a double network structure having a data 
network DN and a control network CN. The network system shown in FIG. 4 is 
constituted by three networks built around star couplers SC1 to SC3, 
respectively. 
As the data network DN for transferring data, e.g., image data, at a high 
speed, an optical transfer system having an optical fiber cable as a 
transmission medium is used, while a transmission system having a coaxial 
cable as a transmission medium is used as the control network system CN. 
Most part of an active repeater 51 of the system shown in FIG. 4 is 
basically the same as active repeater 50 shown in FIG. 3. Differences lie 
in that in active repeater 51 a repeat request is input to repeat request 
detector 8 via control network CN (via a data transmission path in 
repeater 50) and unlike active repeater 50, this active repeater 51 has a 
queue table memory in which generated repeat requests are sequentially 
registered in this queue table memory. 
Referring now to FIG. 5, the operation of the network system shown in FIG. 
4 will be explained. 
For instance, to perform data transfer from node N1 to node N5, a repeat 
request signal generated at node N1 is sent to active repeater 51 via 
control network CN where it is registered in a queue table stored in the 
queue table memory. Upon registering the repeat request signal, a request 
acknowledge signal is sent to node N1 via control network CN and a 
transfer request signal is sent to node N5 from active repeater 51 via 
control network CN. In response to this transfer request, node N5 sends a 
request acknowledge signal to active repeater 51 via control network CN. 
When the network system is ready to transfer data from node N1 to node N5, 
active repeater 51 sends a repeat permit signal to node N1. Upon receipt 
of the repeat request signal, node N1 returns a repeat permit acknowledge 
signal to active repeater 51. Needless to say, switching circuit 14 of 
active repeater 51 connects the necessary lines for the requested data 
transmission paths. When active repeater 51 receives the repeat permit 
acknowledge signal, data transfer from node N1 to node N5 via data network 
DN starts. Upon completion of this data transfer, node N1 sends a line cut 
request signal to active repeater 51 via control network CN. In response 
to this request signal, active repeater 51 returns a line cut request 
acknowledge signal to node N1 and cuts the line from node N1 to node N5. 
After the line is cut, active repeater 51 sends a line cut end signal to 
node N1 via control network CN and node N1 returns a line cut end 
acknowledge signal to the active repeater 51. 
In the above, data transfer from node N1 to node N5, i.e., data 
communication between star couplers SC1 and SC2, has been explained as one 
example; data communications between other nodes involving a plurality of 
star couplers are also performed in the above described manner. Since 
active repeater 51 has the same switch controller 9 and switching circuit 
14 as active repeater 50 of FIG. 3, the network system according to the 
second embodiment can also simultaneously perform data communications 
between plural pairs of star networks as per the system according to the 
first embodiment. 
FIG. 6 illustrates the structure of an active repeater 52 used in a network 
system according to the third embodiment of this invention. The network 
system of this embodiment is constituted as a double network system where 
a data signal and a control information signal are multiplexed using a 
wavelength (frequency) multiplexing system. 
Active repeater 52 has a switching circuit 14, a controller 30, an optical 
separator group 20, an O/E converter group 24, an optical multiplexer 
group 27 and an E/O converter group 28. Controller 30 has a switch 
controller 9, an O/E converter group 21, a packet processor group 22, a 
processor 23, a packet generator group 25, an E/O converter group 26 and a 
queue table memory 29. Active repeater 52 is used in the network system 
that has substantially the same structure as is shown in FIG. 2. That is, 
this active repeater 52 can replace active repeater 50 in the network 
system shown in FIG. 2. In this case, however, each node N1, N2, . . . has 
a separator at its input section for separating a control information 
signal from a data signal and has a multiplexer at its output section for 
multiplexing the control information signal and data signal. At each node, 
the control information signal and data signal are distinctly treated. 
A control information signal including schedule information is transmitted 
in a wavelength of .lambda.1 while a data signal is transmitted in a 
wavelength of .lambda.2. The control information signal is transmitted in 
the form of a packet and is processed by packet processor group 22 in 
active repeater 52, so that individual pieces of information are separated 
from the packet and are supplied to processor 23. Processor 23 manages 
queue table memory 29 in which a source and a destination is registered, 
and controls switch controller 9 based on the table information. Switching 
controller 9 controls the line switching operation of switching circuit 
14. The outputs from packet generator group 25 are converted into optical 
signals with a wavelength of .lambda.1 which are in turn transmitted to 
the respective star couplers through optical multiplexer group 27. O/E 
converter group 24 converts an optical signal with a wavelength of 
.lambda.2 into an electric signal. E/O converter group 28 converts an 
electric signal sent through switching circuit 14 into an optical signal. 
The converted outputs of E/O converter group 28 are transmitted to the 
respective star couplers through multiplexer group 27. 
FIG. 7 illustrates a format of a packet. 
In each packet, a preamble, a repeat request flag, the number of a 
destination network (repeat network), a destination address, a source 
address, data and a CRC (cyclic redundancy check) code as an error 
detection code are arranged in the named order. 
The operation of the above system will now be explained with reference to 
the flowchart of FIG. 8. 
For instance, data transfer from star coupler SC1 to star coupler SC2 is 
performed in the following manner. 
Processor 23 determines whether or not the repeat request flag is on (step 
S1), and loads the number of a destination network (step S2) when the 
decision is "YES," i.e., when the repeat request flag is on. Processor 23 
then determines whether or not the destination network is empty (step S3). 
If the decision is "YES" (i.e., if the destination network is empty), 
switching circuit 14 is switched to the destination network under the 
control of switch controller 9 to connect the necessary lines (step S4). 
Data is added with a preamble and the number of a source network and is 
output from the repeater (step S5). In the subsequent step (step S6), it 
is determined whether or not the data is received without contention. If 
the decision is "YES," an acknowledge signal is returned to the source 
(step S7). If the decision in step S3 or S6 is "NO," an acknowledge signal 
indicating the decision is returned to the source (step S8). 
In this manner, the line switching of the data transfer paths by switching 
circuit 14 can be controlled and the data can be properly transmitted 
using a wavelength multiplexing system with wavelengths .lambda.1 and 
.lambda.2. Also, the use of the queue table is advantageous to manage the 
scheduling of the data transfer. 
Further, an interrupt flag may be prepared in the packet such that upon 
detection this interrupt flag, the requested data transfer can be queued 
with the highest priority. In addition, the priority may be determined in 
advance by the type of transfer data, the nodes of the source and/or the 
destination, or a combination of the two methods. 
FIG. 9 illustrates a network system according to the fourth embodiment of 
this invention in which one of nodes coupled to a star coupler is provided 
with a function of an active repeater. 
A repeater/node 53, which is a node capable of serving as an active 
repeater, is coupled to star couplers SC1 to SC4 to which the other nodes 
N1 to N10 are also coupled. These star couplers SC1-SC4 are coupled to a 
star coupler SC5 through existing repeaters R1 to R4, respectively. 
In this case, the network that is coupled to star coupler SC5 through 
repeaters R1-R4 serves as a control network for transferring control 
information and data is transferred between star couplers SC1-SC4 through 
repeater/node 53. 
According to this network system, a particular node of an existing system 
can simply be replaced with repeater/node 53 and no additional node is 
required to the existing system. 
FIG. 10 illustrates a network system according to the fifth embodiment of 
this invention in which the control network of the network system 
according to the second embodiment shown in FIG. 4 is replaced with the 
one that uses an optical fiber cable transfer path in place of a coaxial 
cable. 
According to this embodiment, star couplers SC1 to SC3 are coupled to a 
star coupler SC0 through existing repeaters R1 to R3, thus constituting a 
control network, while the star couplers SC1-SC3 are coupled to an active 
repeater 54 to constitute data networks. Optical multiplexers 61 to 63 and 
optical separators 71 to 73 are provided respectively between star 
couplers SC1-SC3 and existing repeaters R1-R3 and active repeater 54 so 
that a data signal transferred through active repeater 54 and a control 
information signal transferred through star coupler SC0 are multiplexed or 
separated from each other with different wavelengths. The cooperative 
operation of active repeater 54 and star coupler SC0 is controlled by a 
system manager 80. 
This invention is not limited to the aforementioned particular embodiments 
in terms of the number of nodes, the number of low-order networks and the 
mode of each network. This invention can be modified in various manners 
without departing from the scope of the invention.