JPS6331243A - Local area network communication system - Google Patents

Abstract

PURPOSE:To multiplex and transfer the message of different logical links to a line to one terminal by setting constantly a physical link to the terminal stored in a private branch exchange and setting the logical link for every transferred message. CONSTITUTION:The physical link is constantly estabilshed between the exchange 100, a work station 16, a file station 18 and a print station 20. For instance, the terminals of the respective stations 16, 18, 20 are constituted to transmit an ENQ signal to the exchange 100 in response to the energization of a power source to the terminal. The exchange 100 establishes the physical link with the terminal in response to the ENQ signal. To the message such as the ENQ signal, LI data, an ACK signal; a logical link number corresponding to the destination address and a transmission source address of the message is given for every transferred message.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to data communication systems, and more particularly to local area network communication systems.

BACKGROUND OF THE INVENTION For example, in local area network communication systems using private branch exchanges, circuit switching systems are often used in which physical links are established between originating and receiving terminals. The terminating terminal is thus monopolized by the calling terminal as long as a physical link is established to it. Therefore, during that time, other terminals cannot access those terminating or originating terminals.

For example, a call arrives from a public telephone line to a certain file station housed in a private branch exchange, and a physical link is established between the two. Even if such a physical link is established via a private branch exchange, communication is not necessarily performed during the entire period of the connection.

In this example, if you use a computer to access the file station from a public line via a private branch exchange and enter search conditions such as document creator, year of creation, and classification into the computer, they will be combined into one message. The data is organized and transferred to a file station via a private branch exchange. When the file station receives this message, it accesses the index file and searches for documents that meet the search conditions. This search time is considerably longer than the message transfer time, but during this time not only does the physical link between the computer and the file station remain established, but communication information is not transferred to it.

Further, when the search is completed at the file station, the file station transfers the bibliographic information of the relevant document to the personal computer that requested the search via the physical link.

The user then determines a desired document from the bibliographic items displayed on the screen of the personal computer, and requests the file station to transfer the text of the document in the form of a message. The time from the completion of reception of bibliographic items in this personal computer to the start of transfer of the request message to the file station is also considerably longer than the transfer time of the request message. However, during this time, the physical link between the personal computer and the file station remains set, and communication information is not transferred to it.

In circuit switching systems, originating and terminating terminals are basically connected in a one-to-one manner, so conventional exchanges can connect other terminals to one terminal even when no communication information is actually transferred to the communication link between them. The overlapping is designed to avoid this from the perspective of interference. However, if a physical link continues to be occupied by a specific terminal without transfer of communication information, there is a high probability of encountering a busy state when there is a lot of traffic, and the traffic may not be able to be processed effectively.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a local area network communication system that eliminates the drawbacks of the prior art, reduces the probability of encountering a busy state, and shortens waiting time.

Configuration In order to achieve the above object, the present invention provides a local area network communication system including a private branch exchange accommodating a plurality of terminals, in which the private branch exchange always establishes a physical link with at least one of the terminals, This system is characterized by a local area network communication system in which a logical link is established for each message sent and received to a terminal with which a physical link has been established. A detailed description will be given below based on one embodiment of the present invention.

Referring to FIG. 2, there is shown an example of a local area network in which the present invention may be advantageously applied. In turning,
A private branch exchange (PBX) 100 connected to the public telephone network 10 by a line 12, a plurality of general telephones 14, and a workstation (WS) 113. File Stitchion (FS) +8. In-house terminals such as a print station (PS) 20 are accommodated. The private branch exchange 100 is
This embodiment basically uses a line switching system, and is configured to avoid overlapping, where two or more lines or terminals are physically connected to one line or terminal at the same time.

The workstation 1B is a processing system, such as a personal computer or an office computer, by means of which other types of workstations, such as a file station 18, a print station 20, and other processing systems connected to the public telephone network 10 are connected. be able to access the system.

The file station 18 is a database in which various document data are filed, and the workstation 16
It can also be accessed from other workstations housed in the public telephone network IO. The print station 20 is a printing system that prints out various document data.

Referring to FIG. 1, an example of a specific configuration of a private branch exchange 1 (10) that realizes the local area network communication system according to the present invention is shown.The private branch exchange 100 includes a central processing unit (CPU) 102, A control system of the exchange 100 is configured with a ROM 10B and a RAM 108 on a system bus 104 connected to the ROM.
10B stores various processing programs and fixed data for realizing connection link control processing, which will be described later.
108 is a storage device in which connection processing status tables and data are temporarily stored.

As shown in the figure, the system bus 104 includes a serial/parallel converter (
Down line 1 from the public telephone network 10 via SP) 110 and receiver & I/F (interface) 112
2R, -1 ni line 22 from workstation 16
-1-redirect line 24 from file station 18
Ding.

and 1-way line 2 from print station 20 [
fT are connected to each other. Receiver & I/F1
, +2 receives signals from these lines and sends them to the exchange 10.
This is a receive boat circuit that interfaces with the internals of 0. The serial/parallel converter 110 is a receiver & I/F 112
This is a signal conversion circuit that converts a signal received in the form of a serial signal from a line into a parallel signal and outputs it to the bus 104.

The system bus 104 also includes a parallel to serial converter (PS) 114 and a transmitter & I/F1 as shown.
12 uplinks to the public telephone network 10 via 1B.

A down line 22R to the work station 1θ, a down line 24R2 to the file station 18, and a down line 28R to the print station 20 are connected, respectively. The transmitter & I/F IIEI is a transmission boat circuit that interfaces the exchange 100 with these lines and transmits signals to the lines. The parallel-to-serial converter 114 converts the parallel signal transferred from the system bus 104 into a serial signal and sends it to the transmitter & I/F 1.
This is a signal conversion circuit that outputs to 1B.

Note that the general telephone set 14 is not shown in the figure because it is not directly related to the understanding of the present invention. Also, the number of equipment elements may be any number commensurate with the traffic and is not essential to an understanding of the invention.

In this embodiment, the private branch exchange 100 employs a multi-logical link system in which multiple logical links are formed between one private terminal and two or more lines or terminals. Therefore, the control operation of communication from an off-premises terminal, for example, a personal computer housed in the public telephone network 10, to an on-premises terminal such as a workstation 16, file station 18, or print station 20 is controlled by the PC communication system shown in FIG. A non-procedural GFU (controlling functional element) sequence will be explained as an example.

In this embodiment, the CPU 102 of the private branch exchange 100 is configured to execute a non-procedural CFU sequence for personal computer communication. In this embodiment, there are a switch 100 and a network station 18. A physical link is established between file station 18 and print station 20 at all times. Therefore, there is no need to perform the sequence of ENQ signal transmission from the exchange, return of the ACK signal from the terminal, and transmission of the SOH signal, which are performed when establishing a physical link in normal personal computer communication.

For example, terminals such as workstation 1B, file station 18, and print station 20 are configured to send an ENQ signal to exchange 100 in response to power being turned on to the terminals. The exchange 100 is
In response to this ENQ signal, a physical link is established with that terminal.

For example, the ENQ signal from the file station 18 is received by the receiver & I/F 112 from the line 24T, and converted into parallel data by the serial/parallel converter 110. This data is stored in a predetermined storage area of the RAM 10B from the system bus 104 under the control of the CPU 102. This causes the CPU 102 to send this data to EN.
It is determined to be a Q signal.

In this embodiment, the RAM 108 is as shown in FIG.
It has an area for storing a terminal status table 120 for managing the status of the terminal. When CPU 102 determines that an ENQ signal has been received from a specific terminal, it sets a waiting indicator REAIIY in the corresponding entry. In this way, a physical link is always established between exchange 100 and terminals 16, 18 and 20. When a terminal is not operational, the entry indicates that the terminal cannot be used, that is, it is inactive or a failure indicator DOWN is displayed.

In the example shown in FIG. 4, a personal computer adapter (
A call connection from a personal computer (PC) connected via ADP to the file station 18 housed in the private branch exchange 100 is established by multi-logical links. The telephone network 10 is connected to the private branch exchange 100 according to the telephone number of the file station 18 sent from the personal computer PC.
Connect to the network. After setting up the network connection, the adapter ADP
A CN signal is sent from the private branch exchange 100 through the telephone network. The CN signal is received by the receiver &r/F 112 from the line 12R of the telephone network 10 and sent to the serial/parallel converter 11.
0, it is converted to parallel data. This is CPU 10
2 from the system bus 104 to the RAM 108 under the control of
The CPU 102 determines this data to be a CN signal.

In response, CPU 102 assembles and transfers the AC data from system bus 104 to parallel to serial converter 114 . This is converted into a serial signal by the converter 114, and transmitted as an AC signal from the corresponding line 12T to the telephone network IO by the transmitter & I/F 11B. However, when receiving a CN signal requesting access to a terminal in the DOWN state, for example, the CPU 102 returns an RFC signal to the source that made the request in a similar manner.

In this embodiment, the data signal DT sent to and received from each terminal IEi, 18 and 20 is assembled into the format shown in FIG.
2 the address of the destination terminal and the address of the source terminal 13
6 is included. These addresses allow workstations WSI, WS2, filestation FS,
A print station PS or the like is designated. telephone network 1
When the DT double signal arrives from the personal computer PC via 00,
GPU 102 checks the header 132 to recognize the destination terminal.

Therefore, the CPU 102 refers to the status table 120 in the RAM 108 according to the recognized destination address, and checks whether the READY status is displayed in the entry corresponding to the address. If it is READY,
Rewrite the status 7!1 display of that entry to BUSY, and send ENQ to file station 18.
Send a signal. ACK from file station 18
When the signal is returned, the STX and Ll data included in the data 130 already received from the personal computer PC are sent to the file station 18. When the sending is completed, the status display of the entry is rewritten to READY.

Next, when it receives the ENQ signal from the file station 18, it rewrites the status display of that entry to BUSY and sends an ACK signal to the file station 18. Therefore, from file station 18 to STX,
When the LI data is received and the reception is completed, the status display of the entry is rewritten to READY.

By the way, the ENQ signal, Ll data, and AG signal transferred from the exchange 100 to the file station 18 in this way
Various messages such as K signals also have headers,
The header includes elements similar to the header shown in FIG. 5, namely a destination address 134 and a source address 138.
is included. Alternatively, the message's destination address 134 and source address 13
The configuration may be such that a logical link number corresponding to B is assigned.

When a method of assigning logical link numbers is adopted, an area is provided in the RAM 108 to store a logical link number correspondence table 140 as illustrated in FIG. In this example, a logical link number is assigned corresponding to the combination of destination address and source address.

The logical link number may be uniquely assigned within a common destination address group, for example, as shown in FIG. If the configuration is such that the same logical link number is assigned, for example, when a message arrives from the on-premises workstation 16 to the file station 18 during communication between the file station 18 and an off-premises PC, the file station 18 , it would be impossible to tell which computer or workstation the message originated from. However, for example, even if the logical link number for communication with file station 18 and the logical link number for communication with print station 18 are the same, no problem will arise for file station 18. Of course, the logical link number may be unique within the entire logical link number correspondence table 140.

As described above, when the private branch exchange 100 starts communication with the file station 18, the CP of the private branch exchange 100
U 102 sets a BUSY indication in the corresponding entry in status table 120. Therefore, for example, when the private branch exchange 100 receives a DT double signal addressed to the file station 18, if BUSY is displayed in the corresponding entry of the file station 18, the CPU 102
is a queue in RAM 108 (not shown)
Wait by setting this to .

When changing the display of the status table 120 from READY to BUSY, as described above, immediately before the private branch exchange 100 transmits the ENQ signal to terminals in the premises such as the workstation 1B, the file station 1B, and the print station 20, This is immediately after receiving the ENQ signal from the local terminal, and this time point is indicated by rBJ in FIG. Also, the display of the status table 120 can be changed from BUSY to RE.
The ADY is set immediately after the private branch exchange 100 finishes transmitting Ll data to the local terminal and immediately after receiving LI data from the local terminal, as shown by ``rl'i'' in the figure.

The CPU 102 always updates the status table 12 at a predetermined period.
Checking 0. If there is data queued in the queue, that data is transmitted to the terminal when the corresponding entry in the status table 120 becomes REAI)Y. Similarly, when the private branch exchange 100 receives a message from a terminal within the premises, the CPo 10
2 checks the status table 120. If the corresponding entry in the status table 120 is READY, the data is transmitted to that terminal, and if BUSY is displayed, it is queued in a queue.

When multiple logical links are set up as in 1, one terminal may receive mixed messages from multiple senders. However, as described above, since the logical link number in the header section is uniquely assigned at least within a common destination address group, they can be distinguished by the logical link number. Furthermore, the exchange 100 that receives the message back from the terminal can also identify the destination from the same header section.

When the cpo 102 sends a message to a terminal within the premises, it monitors the response from the terminal for a predetermined period of time. If a response is not received even after monitoring for a predetermined period of time, the terminal may be configured to try again. If a reply is not received from the terminal due to a terminal failure or the like even after monitoring for a predetermined period of time or after retrying a predetermined number of times, an unusable indication DOWN is set in the corresponding entry in the status table 120. For example, when a fault in a terminal is recovered and an ENQ signal is sent from the terminal to exchange 100, CPU 102 sets the corresponding entry to READY.

Connection with a personal computer PC outside the premises through the telephone network 10 is established by the CPU 102 in response to reception of an FM signal from the telephone network 10.
The network is disconnected by sending back a DN signal, and the exchange 100 performs restoration processing. As can be seen from this, in this embodiment, the standard protocol for normal personal computer communication can be advantageously used as is.

Although the illustrated embodiment is a local area network connected to a public telephone network, the present invention is not limited thereto and can be effectively applied to other communication networks, such as digital data switching networks.

Effects According to the present invention, a physical link is always set up for a certain type of terminal housed in a private branch exchange, but a multi-logical link method is used in which a logical link is set up for each transferred message. There is. Therefore, messages of different logical links can be multiplexed to the line to one terminal, and the efficiency of line usage in which information is actually transferred to the line is high, and waiting time is small. Therefore, the user can obtain a quick response.

[Brief explanation of drawings]

Figure 1 shows a local area network communication system that implements the local area network communication system according to the present invention. g! FIG. 2 is a relay system diagram showing an example of a local area network to which the present invention is advantageously applied. FIG. 3 is a flow diagram showing an example of multi-logical link setting in the non-procedural CFU connection sequence of the private branch exchange shown in FIG. 1, and FIG. 4 shows an example of a status table of a private branch terminal managed by the private branch exchange. Figure 5 is a diagram showing an example of the format of messages sent and received in the same private branch exchange, Figures 6 and 7 are
FIG. 3 is a diagram showing an example of a logical link number correspondence table managed in the same private branch exchange; Explanation of symbols for main parts: Workstation 18, File station 100, Private branch exchange 102, CPU 10B, ROM 10B, RAM

Claims (1)

[Scope of Claims] 1. In a local area network communication system including a private branch exchange accommodating a plurality of terminals, the private branch exchange always establishes a physical link with at least one of the terminals, and the physical link A local area network communication method characterized in that a logical link is set up for each message sent to and received from an established terminal. 2. In the communication system according to claim 1, the private branch exchange has a state management means for managing the state of the terminal to which the physical link has been established, and the state management means includes:
When the private branch exchange receives a message to be sent to a terminal with which the physical link has been established, it transmits the message to the terminal if the terminal is in a standby state, and waits if the terminal is in use. communication method. 3. In the communication system according to claim 2, the state management means has a state table that stores the standby state and busy state of the terminal to which the physical link has been established, and 1. A communication system characterized in that when a message to be sent is received, the transmission or waiting is performed by referring to the status table. 4. In the communication system according to claim 3, the state management means monitors the response from the terminal to which the physical link has been established, and when it is determined that the terminal is unable to respond, A communication method characterized in that the terminal is displayed as unusable in the status table until a response is received later. 5. In the communication system according to claim 3, the private branch exchange controls the connection link according to a non-procedural CFU sequence, and upon receiving a connection signal, refers to the state table and determines whether the physical link is established. A communication method characterized in that if the terminal is in an unusable state, a rejection response is returned, and if the terminal is in a state other than unusable, an affirmative response is returned.