JPH0437345A - Lan communication system - Google Patents

Abstract

PURPOSE:To devise the system such that a trailing flag TF and a leading flag LF are overlapped partly without a time gap and the interference from other node is prevented by setting the LF immediately and sending it when the end of transmission is detected by the TF. CONSTITUTION:When a length RLEN of a reception data is smaller than a reception buffer length LEN, a reception data is subjected to DMA transfer to a memory, and when the end of a packet is detected by a trailing flag TF of the packet, a leading flag LF of an ACK packet is set. After the preparation of transmission, an ACK packet format in which a data is made complete is set during that time. Thus, the flag TF of the detected message packet 4 and the flag LF of the ACK packet 5 are partly overlapped. When the transmission of the ACK packet is finished, the flag TF of the packet 4 is sent and the transmission of the ACK packet is finished to make prescribed communication complete.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a CS MA/ACK system as an access system for a LAN (Local Area Network).

[Conventional technology]

In the C3MA (Carrier Sense Multiple Access) method, multiple nodes connected in a bus network are all equal, regardless of whether they are dependent stations or control stations, and can transmit when they confirm that the network is not in use. .

Among the C3MA systems, the C5MA/CD system is widely adopted. In this method, the transmitting station attempts to transmit, then monitors for collisions, and retransmits when a collision is detected, which is quite complex. C3M as another low-cost LAN
A/ACK method 2 has been developed for computer networks. This method transmits the packet after confirming that no packet is being transmitted on the medium, but does not sense the transmission medium while the packet is being transmitted. f of whether or not the packet sent by oneself correctly arrived at the other party.
I-acknowledgment is mainly an ACK packet sent from the other party.
).

[Problem to be solved by the invention]

In the C3MA/ACK method, a node detects a packet on the medium, and if there is a packet addressed to itself (the packet format is shown in FIG. 3), it returns an ACK packet according to the flowchart shown in FIG. When a packet is detected on the medium, its header information is read (Sl
), if it is a self-addressed address (B2), the received data length R
If LEN is smaller than the reception buffer length LEN and reception is possible (B3), the process advances to B4 and the ACK packet is sent.

However, if reception is not possible, the process advances to S12, and S13. S1
4, the NAC packet is sent.

At B4, DMA transfer the received data to memory (B4),
After receiving ends (35), prepare for sending (B6.S7)
and converts the ACK packet into cents (B
8) Do. Then, transmission starts (B9)L, and finally a trailing flag (SIO, 5ll) is transmitted and the process ends.

In this flowchart, the header information is sent to the CPU (not shown, but included in the circuit that implements this method).
does not transmit until it has analyzed and determined whether or not to transmit an ACK packet, and has sent the ACK packet according to the format (B8). Therefore, for example, three nodes Al, B2 . In a LAN consisting of C3, from node A1 to node B
If the data length of the message packet 4 sent to the message packet 2 is short, as shown in FIG.
The reception of the message packet 4 ends before the transmission of the ACK packet 5 for the message packet 5 starts, and there is a gap between the message packet 4 and the ACK packet 5.

If this free time is longer than a certain specific time, when node C3 sends a message packet 4 to node B2 during this free time, node B2 will send message packet 4 from node C3 to node B2 before sending ACK packet 5 to node A1. Message packet 4 is received from node B2, and node A1 is unable to correctly receive ACK packet 5 from node B2.

[Means to solve the problem]

The present invention has been made to solve the above problem, and when a message packet addressed to oneself is received, the leading flag of the acknowledge packet is immediately changed as soon as the trailing flag of the message packet is recognized. In this system, transmission is started, and then the packet is completed and transmitted.

[Effect]

As shown in the flowchart of FIG. 1, which will be described later in the embodiment, when the end of transmission is detected based on the trailing flag (TF) of the received packet (B5), a leap is immediately made without determining the data to be written in the ACK packet. The ink flag (LF) is sent out (B6). Therefore, the TF of the transmission packet and the LF of the ACK packet are in one line, so there is no gap and interference from other nodes can be prevented.

〔Example〕

Embodiments of the present invention will be described below with reference to the flowchart of FIG. When a packet on the medium is detected, its header information is read (SL). If the packet is addressed to itself (B2), if the reception data length RLEN is smaller than the reception buffer length LEN and can be received (B3),
34 or less, and sends an ACK packet.

However, if reception is not possible (B3), the process proceeds to step 313 and thereafter, and a NACK packet is sent.

Here, the received data length RLEN is the received puffer length LEN.
If it is smaller than the previous example, the received data is DMA transferred to memory (B4), and the end of the packet is detected by the trailing flag (TF) of the packet (B5). Unlike the conventional example, the leap ink flag (LF) of the ACK packet is immediately
) is set (B6), and after the transmission rate [(37, B8), the ACK packet format in which the data has been completed up to that point is sent (B9). Therefore, as shown in FIG. 6, the trailing flag (TF) of the detected message packet 4 and the leap ink flag (LF) of the ACK packet 5 are -Toden. When the transmission of the ACK packet data is completed (S10), the trailing flag (TF) of message packet 4 is sent (Sll, 51).
2) and ends the ACK packet transmission.

〔Effect of the invention〕

As explained above, according to the present invention, when the receiving station sends an ACK packet in response to a message packet, the trailing flag (TF) of the former is set and the leap ink flag (LF) of the latter is set to -Toden. be done. Therefore, the originating station can correctly receive an ACK packet from the intended receiving station and perform predetermined communication.

[Brief explanation of drawings]

Fig. 1 is a flowchart of an embodiment of the present invention, Fig. 2 is a flowchart of a conventional example, Fig. 3 is a packet format, and Fig. 4 is an example of nodes connected to a bus, with three stations A, B, and C. 5 is a diagram showing the timing relationship between message packets and ACK packets in the conventional system, and FIG. 6 is a diagram showing the timing relationship between message packets and ACK packets in the system of the present embodiment. 1.2.3- Nodes A, B, C. 4- Message packet from node A1 to node B2, 5- ACK bucket from node B2 to node A1

Claims (1)

[Claims] As a LAN CSMA/ACK method, when a message packet addressed to the self is received, as soon as the trailing flag of the message packet is recognized, the sending of the leading flag of the acknowledge packet is immediately started, and the packet is then completed. A LAN communication method characterized by transmission.