JPH0738643B2 - Accumulation type star net - Google Patents

Description

The present invention relates to a storage-type star network with guaranteed maximum propagation delay.

"Prior Art" An example of a conventional star net will be described with reference to FIG.

As shown in the figure, the conventional star network has a structure in which a plurality of terminal stations 2A to 2M are connected to a central station 1 through a transmission line 20 and a reception line 21 (Japanese Patent Publication No. 59-16453). Gazette).

Here, when the data packet is transmitted from the terminal station 2A,
The data packet is sent to the central station 1 via the transmission line 20. Upon receiving this data packet, the centralized station 1 transmits (broadcasts) this data packet to all the terminal stations 2A to 2M via the reception line 21. Each of the terminal stations 2A to 2M determines whether the received data packet is addressed to itself, and if it is addressed to itself, receives the data packet.

Each of the terminal stations 2A to 2M constantly monitors the signal received from the reception line 21, and cannot transmit from itself while any data packet is transmitted to the reception line 21. Therefore, the terminal station that has received any transmission request waits for the end of the transmission of the data packet on the reception line and then starts the transmission of the data packet.

However, when there is a transmission request to a plurality of terminal stations, data packet transmission is started at the same time, so that a data packet collision occurs. When two or more terminal stations transmit signals at the same time, the centralized station has a device for detecting the collision and notifies all the terminal stations of the collision. The transmitting terminal station stops sending data packets when it is informed of the collision by the central station. Then, processing for retransmission such as a retransmission algorithm is performed. This is shown in FIG.

First, station A among the terminal stations sends a data packet to the central station through the station A transmission line. In the figure, this is indicated as a transmission packet of station A. Upon receiving this, the central station broadcasts the data packet to stations A, B and C. In this example, the reception line length becomes longer in the order of A station, B station, and C station, and the transmission of the data packet from the central station to C station is the slowest due to the difference in signal and propagation time. . In the figure, these are indicated as A to C station received packets.

Here, when the data packet is transmitted from the B station at the next timing and the C station starts transmitting the data packet before the transmission is completed, the centralized station detects the packet collision at the hatched portion in the figure. When the central station converts this collision signal as it is or converts it into a collision detection signal and sends it to all terminal stations, stations B and C recognize the occurrence of collision and prepare for packet retransmission. In this star net,
Station B retransmits the data packet in a relatively short time,
This is broadcast as it is from the central station. Next, when the C station starts transmitting the data packet, the A station subsequently transmits the data packet, the data packet of the A station near the central station arrives at the central station first, and then the data packet of the C station. Arrives at the central station and a packet collision is detected. Therefore, the station A thereafter retransmits the data packet, which is broadcast to all the terminal stations as it is.

Conventionally, data packet collision processing has been generally performed by such a method.

When such a collision occurs, the central station 1 (Fig. 5)
In order to receive all the data packets without erasing each data packet, the present inventors provide a receiving memory for temporarily storing the data packets sent from each terminal station in the central station 1, and We have developed a storage-type star network that sequentially reads (polls) packets (Japanese Patent Application No. 61-226570). In this case, a certain time delay occurs after the data packet is transmitted from the terminal station until the central station broadcasts the data packet and the terminal station receives the data packet. This delay will be called a propagation delay.

In a storage-type star network that guarantees the maximum propagation delay, in order to guarantee the maximum propagation delay of the packets sent from the terminal station within a certain time, the amount of data packets stored in the central station is limited at the same time. There is. By doing this,
Even if packets are concentrated from each station for a period of time, the time to finish broadcasting the data packets from all the reception memories of the central station is within a fixed time. Therefore, the data packet sent from each terminal station to the central station is broadcast within a fixed time, and this becomes the maximum propagation delay of the system.

However, in such a system, there are terminals that do not have to guarantee the maximum propagation delay. Assuming that the maximum propagation delay is 10 msec, the voice transmission speed is 64 kbps (64 kbps
Since it is a kilobit), it is 10ms at the terminal station that handles voice.
80 bytes in ec, 10 including packet overhead
It is necessary to send a packet of about 0 bytes. Therefore, for a terminal station having one audio channel, 100 bytes are required for the receiving memory of the terminal station interface of the central station. On the other hand, for example, in an Ethernet system (a data communication network manufactured by Xerox Co., Ltd.), the maximum packet length is 15
It is 00 bytes, and in fact, such a packet length is absolutely necessary in such inter-computer communication.

Therefore, for a datagram terminal station sending such a packet, the receiving memory of the terminal station interface of the central station is required to have about 1500 bytes.

"Problems to be Solved by the Invention" The conventional star network shown in FIGS. 5 and 6 has the following problems. .

(1) When the lines are crowded, the probability of signal collision increases, which causes variations in delay time. Therefore, real-time transmission / reception relationships are emphasized, as in conversational voice communication. Not suitable for transmission.

(2) Since a useless invalid signal flows on the line due to the collision, only the transmission capacity lower than the actual physical transmission capacity is guaranteed.

(3) If the system length is too long, there will be a large time difference between the terminal station located at a short distance from the central station and the terminal station located at a distance from the central station until the data packet reaches the central station. May not be able to detect packet collision. Therefore, it is necessary to specify the maximum system length that allows collision detection.

Although the storage-type star network that guarantees the maximum propagation delay avoids this data packet collision, it has a new problem.
That is, if the transmission speed of this system is 10 Mbps,
While 125 voice terminal stations can be connected, only 8 Ethernet-type datagram terminal stations can be connected. This is because the datagram terminal station guarantees the same maximum propagation delay as the voice terminal station. A characteristic of such a datagram terminal station is that it can transfer data without establishing a connection.

The duty factor is extremely small.

The transmission probability of the minimum length packet and the maximum length packet is high.

It is not necessary to guarantee the maximum propagation delay.

As mentioned above, it is not always necessary to treat it as a voice terminal station.

The present invention has been made by paying attention to the above points, and a storage-type star that improves the efficiency of a packet switching network by processing synchronous data packets and asynchronous data packets transmitted from each terminal station separately. The purpose is to provide a net.

"Means for Solving the Problems" The storage-type star network of the present invention comprises a plurality of terminal stations and a central station that receives data packets sent from each terminal station. In order to temporarily store the data packet sent from each terminal station, a first receiving memory and a love 2 receiving memory are prepared for each terminal, and the synchronous data packet is stored in the first receiving memory. And then the second
Asynchronous data packets are stored in the receiving memory of, the fixed time frame is set, the data packets stored in the first receiving memory are sequentially read out, and the free time is set within the range not exceeding the time frame. And reading the data packets stored in the second receiving memory and broadcasting these data packets to the respective terminal stations.

[Operation] In the storage-type star network of the present invention, the data packet transmitted from the terminal station is identified, the synchronous data packet is stored in the first receiving memory, and the asynchronous data packet is stored in the second receiving memory.
It is stored in the receiving memory of. Then, the synchronous data packets are read out in a predetermined order and broadcasted simultaneously, a fixed time frame is defined, and this is repeated to ensure communication with a guaranteed maximum propagation delay. On the other hand, the idle time in the time frame is used to read out and broadcast the asynchronous data packet. In this way, collision of data packets can be prevented and the communication network can be used efficiently.

(Outline of Central Station) FIG. 1 shows a block diagram of a central station of the storage-type star network of the present invention.

The transmission line 20 of each terminal station 2 (FIG. 5) is connected to a separation circuit 31 provided for each terminal, and each separation circuit 31 has a first reception memory 321 (synchronization reception memory).
And the second receiving memory 322 (asynchronous receiving memory) are connected.

Each of the reception memories 321 and 322 has a capacity equal to or larger than the maximum length of a packet transmitted from a terminal station, and is set so that a collision does not occur even if all terminal devices simultaneously transmit the packet. Each of the reception memories 321 and 322 has a function of turning on the empty signal when the data is empty and turning off the empty signal when the data is contained. This empty signal is connected to the control circuit 5 through the control bus 41. In addition, each of the reception memories 321 and 322 has a data bus 40 from the head of the data packet stored therein each time a read signal from the control circuit 5 arrives.
It has a function of sending the signal to the upper side and turning on the empty signal when the driving is completed. These are composed of, for example, a first-in first-out memory (FIFO). The transmitter 7 is a circuit that is connected to the data bus 41, receives the transmission timing signal 5a from the control circuit 5, and transmits the data packet read from each of the reception memories 321 and 322 to each station reception line 21.

In the circuit of FIG. 1, the data packet transmitted from each terminal device is classified into a synchronous data packet and an asynchronous data packet according to an identifier written in the data packet in advance. The latter is stored in the asynchronous reception memory 322.

The control circuit 5 receives the empty signals output from the reception memories 321 and 322, monitors the state of each reception memory, and sends a read signal to one reception memory selected according to a certain rule. At the same time, the transmission timing signal 5a is transmitted to the transmitter 7, and the data packet read from the reception memory which has received the read signal is transmitted to each station reception line 21 through the data bus 40 and the transmitter 7.

(Control Circuit) Next, the detailed configuration and operation of the control circuit 5 will be described.

FIG. 2 shows a detailed block diagram of the control circuit.

This circuit includes a frame counter 51, a transmission packet sequence storage memory 52, a synchronous control circuit 53, and an asynchronous control circuit 54.
And a read signal generator 55.

The frame counter 51 has a predetermined time frame T
This circuit generates a frame timing signal 51a once (hereinafter referred to as a frame). All the operations of the control circuit 5 are performed in units of this frame.

As shown in FIG. 3, one frame is divided into a synchronous data area and an asynchronous data area. The boundary 50 between the two changes dynamically. Of these, the sync data area is the sync reception memory 32
1 is used to poll the data packet stored in it by polling 1 in a predetermined fixed order. Information on the polling sequence is registered in the transmission packet sequence storage memory 52. For example, in the case of FIG. 3, stations A and C in the synchronous data area.
Station ... The reception memory for synchronization is polled in the order of station K. In this case, the synchronization reception memories of all the terminal stations are not polled. Only specific terminal stations from the stations A to M are selected. Then, for the other terminal stations, only the asynchronous reception memory is used and polled in the asynchronous data area. The station that can be used is not specified for the asynchronous data area, and any station can be used if there is a space.

Specifically, in the central station, a synchronization reception memory 321 and an asynchronous reception memory 322 are prepared for each terminal station, but only a specific terminal station sends the synchronization data to the synchronization reception memory 321. Is allowed. Other terminal stations will always use only the asynchronous reception memory 322.
Of course, the above-mentioned specific terminal station can also send asynchronous data.

The synchronization control unit 53 is a circuit for polling the empty signal from each synchronization reception memory 321 in that order based on the information regarding the polling order registered in the transmission packet order recording memory 52. If the polled empty signal is turned off, the data packet stored in the reception memory is read and the data packet is transmitted to the transmitter 7.
To each station reception line 21 through. If the empty signal remains on, there is no data packet from the terminal, so the empty signal of the receiving memory registered in the next entry of the sending packet sequence recording memory 52 is polled. This operation is performed by the transmission packet sequence recording memory 52.
Repeat for all registration information in. When the polling process of the synchronous reception memory 321 is completed for all stations registered in the outgoing packet sequential recording memory 52, the synchronous data area is moved to the asynchronous data area, and the control is transferred to the asynchronous control unit 54.

In this embodiment, the transmission packet sequential recording memory 52
The content of is fixed, and the station that can send the synchronous data is determined in advance. However, it is possible to change this dynamically. Asynchronous data packets may be used to change the contents of the outgoing packet sequential recording memory 52, or a special data packet type for notifying the central station may be created in addition to the synchronous / asynchronous data packet. A dedicated receiving memory may be separately allocated for data packets.

On the other hand, when the control is transferred from the synchronous control unit 53, the asynchronous control unit 54 polls the empty signal from each asynchronous reception memory 322 this time. If the empty signal is off, a read signal is sent to read the data packet in the reception memory, and if it is on, the next memory is polled. This operation is repeated for each station until the end of the frame. That is, the synchronization reception memory 32
1 is polled one by one in a fixed order and moves to the asynchronous data area, but the asynchronous reception memory 322 can be repeatedly polled in a predetermined order as many times as it is in the idle time.

At this time, if the polling order of the asynchronous data packets is constant, the priority among the terminal stations that output the asynchronous data will be determined. That is, when the idle time (asynchronous data type) is short, a terminal station with a low priority is not easily polled. Therefore, if there is a terminal station with a high priority, it suffices to set polling for that station first,
On the contrary, when it is not desired to give priority to each terminal transmission, the polling order may be shifted every time or the polling order may be determined by a random number. This polling order is also output from the transmission packet order recording memory 52 to the asynchronous control unit 54.

Further, it is possible to provide a plurality of types of asynchronous data reception memories and realize packet exchange with different priorities for the respective reception memories. That is, the types of receiving memories for asynchronous data are increased, and the priorities are made different in the above areas. A packet identification circuit (not shown) provided in the input unit of the central station identifies the priority of the input data packet and inputs the data packet to the corresponding receiving memory. The polling may be performed in the asynchronous data area, for example, in order from the reception memory having the highest priority.

The read signal generator 55 receives the synchronization reception memory 321 according to a command from the synchronization control circuit 53 or the asynchronous control circuit 54.
Alternatively, it is a circuit that outputs a read signal to the asynchronous reception memory 322. This circuit sends the read timing signal 5a to the transmitter 7 at the same time when the read signal is output. The read signal generator 55 is
It is assumed that one control line is connected to all the reception memories and a read signal is transmitted through this control line. For example, the synchronous control circuit 53 or the asynchronous control circuit
An address signal specifying each receiving memory is supplied from 54 to a read signal generator 55, and a selector provided in the read signal generator 55 selects a corresponding control line to select a read signal.

(Operation) The storage-type star network of the present invention having the above-described configuration operates as follows. An example of this operation will be described with reference to the time chart of FIG.

In the case of this embodiment, it is assumed that four terminal stations from station A to station D are connected to the central station. And station A, B
It is assumed that the station and the station C send both synchronous data packets and asynchronous data packets, and the station D is set to send only asynchronous data packets. Here, in the transmission packet order recording memory 52 shown in FIG. 2, it is assumed that the polling order of the synchronous receiving memory is written in the order of A, B, and C, and the polling order of the asynchronous receiving memory is described. Is written in the order of A, B, C, D. Note that the time chart of FIG. 4 is different from that of FIG. 6 in that the delay of the signal generated when propagating through the signal line is ignored.

First, in the first frame, it is assumed that the data packets 101 and 102 transmitted from the station A and the station C before the start of this frame are stored in the respective reception memories 321 (FIG. 1). To do. Here, the frame timing signal 51a (FIG. 2) for starting the first frame is input to the synchronization control circuit 53. The synchronization control circuit 53 includes a synchronization reception memory 321.
(Fig. 1) is polled in the order of A, B, C, and the reception memory 32 of stations A and C in which the empty signal is turned off.
A read signal is sent to 1, and as shown in FIG. 4, the synchronous data packet 101 of station A and the synchronous data packet 102 of station C are sent to the receiving lines of each station.

This completes the sync data area in this frame. Therefore, the synchronous data packets 103, 104, and 105 sent from the A station, B station, and C station after the start of this frame have not been processed in this frame because polling is completed before they are stored in the receiving memory. , Will be processed in the next frame.

Next, when the asynchronous data area starts, since the asynchronous data packet 106 sent from the station C immediately before that is stored in the asynchronous reception memory, this is read by the asynchronous control circuit 54 and received by each station reception line. Sent to. Since the asynchronous data packet is exclusively processed until the end of one frame after the end of the synchronous data area of this frame, the data packet 107 sent from the D station during this period is also immediately sent to the receiving line of each station. Sent out. In this case, the asynchronous data area is sufficiently long so that all asynchronous data packets sent from each terminal station during this frame are broadcast immediately. However, if there are many synchronous data packets and the synchronous data area becomes long, even if the asynchronous data packet is stored in the asynchronous reception memory, it may not be polled in this frame.

By the way, in the next frame, station A, station B,
Synchronous data packets 103, 105, 104 sent from station C
Are sequentially polled and broadcast, and thereafter, asynchronous data packets 108, 109, 110 and 111 transmitted from the A station, B station, C station and D station in this frame are broadcast. Further, the synchronous data packets 112, 113 and 114 transmitted from the A station, B station and C station in this frame are processed in the next frame.

On the other hand, when the terminal station finishes sending the packet, the terminal station is in the packet sending prohibited state, and when the terminal station confirms that the packet sent by the own station is returned, the terminal station is again in the packet sending enabled state. However, because there are multiple receiving memories,
Different types of packets can be sent simultaneously.

"Advantages of the Invention" With the configuration as described above, the storage-type star network of the present invention can realize a hybrid switching network without being given strict system timing by a central station. Further, the terminal station can immediately start the transmission without judging whether or not the other station is transmitting, as long as the communication line is ready for transmission at the time of transmitting the data packet. That is, it is not necessary to stop the packet transmission at the time of collision or to perform the re-transmission processing (backoff algorithm etc.). Of course, the central station does not need to detect a collision or send a collision signal.

On the other hand, since invalid data due to collision does not flow on the line, the line can be efficiently used up to near the physical capacity. Also, there is no limit on the maximum system length for collision detection. The maximum system length depends exclusively on the capabilities of the drivers and receivers at both ends of the transmission / reception line, but it is possible to install a terminal device at a distant place via a three repeater or the like even at a long distance beyond that capability. Therefore, there is no practical maximum system length limit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a central station of a storage-type star network of the present invention, FIG. 2 is a detailed block diagram of its control circuit, and FIG. 3 is a time chart showing the structure of one frame thereof. FIG. 4 is a time chart showing the operation of the storage-type star network of the present invention, FIG. 5 is a block diagram of a general star network suitable for implementing the storage-type star network of the present invention, and FIG. 6 is its star. It is a time chart which shows the operation of a grid. 1 ... Centralized station, 2 ... Terminal station, 321 ... First receiving memory, 322 ... Second receiving memory.

Claims (1)

[Claims] 1. A plurality of terminal stations and a central station for receiving data packets transmitted from the respective terminal stations, the central station for temporarily storing the data packets transmitted from the respective terminal stations. , A first receiving memory and a second receiving memory are prepared for each terminal, the first receiving memory stores a synchronous data packet, and the second receiving memory stores an asynchronous data packet. Then, after setting a fixed time frame and sequentially reading the data packets stored in the first reception memory, the data packets are stored in the second reception memory in the free time within a range not exceeding the time frame. The storage-type star network, which reads out the data packets, and broadcasts these data packets to each of the terminal stations.