JPS61100041A - Csma communication system - Google Patents

Abstract

PURPOSE:To eliminate the need for detection of collision by transmitting a packet after it is confirmed that a carrier does not exist on a common transmission line over a time being a maximum reciprocating propagation delay time or over in the common transmission line. CONSTITUTION:In transmitting a data from a node A to a node B of plural taps 14 of a coaxial cable 12 terminated with a termination resistor 10, when the absence of a carrier is confirmed for basic waiting time tw>2tau (maximum reciprocating propagation delay time), the packet reaches the node B at points of time 1b, 2b with a delay of tau. When the node B receives this packet, a recep tion acknowledgement signal ACK is returned immediately to the node A at points of times 3b, 4b, then the 2nd long packet is transmitted immediately at points of time 5a, 6a and the node B receives the 2nd packet at points of time 5b, 6b. The node B returns immediately the signal ACK at points of time 7a, 8a. The node A receives the signal ACK at points of time 7b, 8b without collision.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to carrier detection multiple access (CSMA) communication systems.

In the conventional C3MA system, one packet is sent from the transmitting station.
Thereafter, the transmitting station does not know that a collision has occurred until an acknowledgment (ACK) signal is not returned from the receiving station within a predetermined period of time. Therefore, if the length of the message to be sent is long, a long time will have elapsed by the time the transmitting station identifies the occurrence of a collision.

Therefore, the iR packet length cannot be made too long. However, if the packet length is made too short, the proportion occupied by data portions such as the preamble, destination address, source address, control section, and CRC section in the kerato increases, and the transmission efficiency deteriorates due to the overhead. Also, by dividing into short nogkerats, the number of ACKs increases, which leads to overflow.

The number of signals increases, and the transmission efficiency decreases.

In the C5IIIA/CD method, by detecting a collision while sending a packet, it is possible to interrupt wasteful sending of E-kets due to a collision. Therefore, it is possible to increase the packet length at the initial stage of packet transmission, and the throughput can be increased.

CD (Collision Detection) is performed at the transmitting node by comparing received data and transmitted data bit by bit. If the communication channel is a bus type, a node that is transmitting can also receive data at the same time, and in this case the data transmitted from its own node should be received. When the two are compared and a mismatch occurs, it is determined that there has been interference by data transmitted from another node, that is, there has been a collision.

In general, in a local area network, S is sufficiently good and the probability of random data errors due to noise can be considered to be extremely small, so such collision detection is possible.

C3MA based on Ethernet (by DEC, Intel, Zero, CUS), IEF, E-802 standard
/CD In the baseband method, CD is relatively easy.

This is because the connection to the coaxial cable is made with a tag, and the transmitted data flows from the Tanof 0 to the coaxial cable in both directions, and is terminated at both ends, where the signal is absorbed. Received data is picked up by tapping. Since CD can be received simultaneously from the tap that is currently transmitting, there is almost no time delay between the received data and the transmitted data. Even if it is only a certain value, it will be determined from the circuit constants. Therefore, it is easy to compare transmitted and received data bit by bit.

However, in order to guarantee unambiguous detection of collisions, it is necessary that the signals from other taps are not attenuated by cables or the like. In other words, the transmission loss of the transmission line system is sufficient/
Must be reduced by 4%. For this reason, cables are required to be of high quality, which causes an increase in cable prices and construction costs.

On the other hand, when applying C3MA/CD to a wideband system,
The problem with De-Ai is that it is difficult to play with CDs. One reason is that in the broadband system, the transmitted data is sent to seven nodes at once, and then retransmitted from there to all nodes, so the transmitted data and the received data are Even for the node that sent the message, there is a large time delay. This delay is due to the round-trip propagation delay from the beginning to the end of the day. Furthermore, since the amount of delay varies depending on the tap, a rather complex configuration is required to compare transmitted and received data bit by bit.

Another reason is that in the wideband system, the transmission loss from the headband to the tag (and vice versa) is large, but the amount of loss varies depending on the time and day. If the variation in this loss is too large, CD cannot be performed reliably.

As described above, the C3MA/CD system has the advantage that the transmission delay time under heavy load is shorter than that of the C3MA system, and the efficiency of using the line capacity is also high.

However, as mentioned above, there are various problems caused by CD, so it is desired that a C3MA method be developed that avoids these problems, takes advantage of the characteristics of the CSMA method, and has almost the same characteristics as CDi.

Purpose The present invention does not have the disadvantages caused by CD, and also has C3MA/
It is an object of the present invention to provide a CSMA communication system that has almost the same characteristics as the CD system.

Configuration In order to achieve the above object, the present invention has the following features: - A node transmitting a message confirms that the carrier wave is not on the common transmission path for a time longer than the maximum round-trip propagation delay time on the common transmission path. The C3MA communication method is characterized by the fact that the node that sends the A-kerato and receives the confirmation packet immediately sends back the confirmation packet, and the sending node immediately sends the next A-kerato when it receives the confirmation packet. .

Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

To aid in understanding the present invention, simultaneous acknowledgment (ACK)
) Regarding the CSMA method with functions, conventional OMNI
C with immediate acknowledgment function, as is done in NET.
In the 3MA method, after sending the data backup, the A
If the CK is not returned from the destination node, it is determined that the data packet has been lost due to a collision or other cause. Assuming that the other node is operating normally and the transmission path is also normal, it would be reasonable to determine that the failure of an ACK to be a collision occurs in that network. That is, A
CK can be used as a type of collision detection (detection of non-collision). Therefore, FJther with ACK function
In instant acknowledgment methods such as ET and OMNINET, A
The priority of CK is set higher than that of data packets, thereby avoiding ACK collisions in advance. However, even if the data packet to be sent is long, it has the disadvantage that the presence or absence of a collision cannot be determined until after the entire data packet has been sent.

In the present invention, taking advantage of the characteristics of the immediate acknowledgment method, the ACK
In addition to avoiding collisions in advance, high priority is also given to the long data that follows the ACK, and collisions are avoided in advance. Furthermore, since there is a possibility of collision in the first packet, short data packets are used to minimize loss due to collision.

As shown in Figure 2, the maximum propagation delay time on the bus is τ
Then, the kerat length corresponding to the round trip propagation delay time 2τ is the minimum length of P in the C3MAlCD system. After starting to send the packet, a collision is detected and
The time γ1 until the channel becomes empty is approximately r = 2τ + α (1). Here, α is the sum of the time required for collision detection (delay) and the time required for collision enhancement.

α is generally not a very large value, but if we assume that α is smaller than τ and can be ignored, then r1#2τ (1a).

In C3MA/'CD and CSMA, transmission efficiency (throughput) changes depending on the packet length. Assume that the packet length is fixed and the transmission time is T. 'C3MA
/To detect a collision using the CD method, T≧2τ
(2) Must be.

In the C3MA system, T/τ is often set to 10 or more in order to reduce retransmissions due to collisions. Generally, it is set at 100th place. If T/τ is small, the throughput and therefore the channel capacity will be small. Further, the smaller a=τ/T (3) (therefore, the larger T/τ), the greater the throughput becomes.

In conventional C3MA with immediate acknowledgment function, data
The time γ2 from the start of transmission of AcK, *, to the end of receiving AcK, *, is given by r = T + 2τ + TACK (4). However, T is the transmission time of r-ta packets, 7ACK is the transmission time of ACK no.xi, and 2τ is the round-trip propagation delay time.

If the length of the ACK-9 packet is the aforementioned minimum packet length, TACK = 2τ (5), so r = T + 4τ (4a). If the AC is
If K is not received, it is considered that there has been a collision, so this γ2 is similar to γ□ in CSMA/CD. Collision is detected (indirectly) after all packets have been sent, Corresponds to the time it takes for the channel to become empty.

By the way, in a long packet, T)2τ (6), so r, =T+4 r))2 r (7)
Therefore, γ2 ) γ1(7a ). In other words, conventional C3MA wastes more transmission time when a collision occurs than C3MA/CD.

In the C3MA system according to the present invention, the time γ3 from the start of packet transmission until a collision is detected (indirectly) and the channel becomes empty is expressed as ' 3 = Tinit + 2τ+TACK
(8) becomes. Here, T init is the time required to send the first d' ke, g when trying to start sending r-yu, and this no'? The length of the get is set to the aforementioned minimum 2-bit length. Therefore, in this case, Tin1t”
'2τ, (9). By substituting equations (5) and (9) into equation (8), γ3-6τ αQ is obtained. This means that from γ2) γ3〉rl αυ, in the communication system according to the present invention, the transmission time wasted when a collision occurs is slightly longer than that by C3MA/CD, but
This means a drastic reduction compared to that achieved by conventional CSMA.

If the transmission of the first P and G is successful (by the ACK being returned), the ACK is followed by a long nine. The ACK-' get and the long get are configured to avoid collision in principle, as will be described later.

As seen in equation (6), in a long guget, T)2τ, so it can be said that the difference between equation (11) and equation (1) is small.

Therefore, the CSMA scheme according to the present invention is cSMA
/Has almost the same characteristics as CD. Performance deteriorates compared to CSMA/'CD only under extremely heavy loads.

The C3MA method according to the present invention will be explained with reference to FIG. In this model, a plurality of nodes including nodes A and B are connected to a plurality of taps 14 of a coaxial cable 12 terminated with a terminating resistor 10, respectively. When sending data from node A to node B, when node A detects that there is no Ktw time carrier on the coaxial cable 12,
Send out ini/yaru ega, g. This is shown in FIG. 1 at time 1a. Here, tw ) 2τ is taken as α. This tw corresponds to the so-called basic waiting time (BWT) in Ethernet and the like.

The ini/yarupakenote is sent from time 1a to time 2a, and reaches node B after a delay of τ.
b). As soon as node B completely receives the initial number P, it sends an ACK i get back to node A (3a-4a).

The first time any node attempts to send out a ``no'' or ``get,'' it must do so after ensuring that there is no carrier for a period of time tw. By doing this, since the ACK-get is received within 2τ at the sending node and starts f′L, the AC
K-e and g will have high priority. Furthermore, since this ACK)4' packet is sent only immediately after receiving a specific .xi.get, it is impossible for a collision to occur.

In the communication method according to the present invention, long data is divided into a short (minimum length) initial packet and a long second packet, and if the initial packet is successfully transmitted, the subsequent By reserving the transmission of the second 7 (get), collision of the second 7 (get) is avoided.Specifically, if node A has finished receiving the ACK packet (4b), then The transmission node A sends the signal to the second node B (5a to 6a).

Similar to the reception of ACK-p, t at node A, node B starts receiving the second 0, t within 2τ after sending ACK 7', t, so that the coaxial cable 12
No other node connected to the node can begin sending out the initial node. This is because, according to this method, it is determined that any other node can transmit an initial paget only when it detects that there is no carrier wave greater than or equal to tw()2τ).

Therefore, this second packet has all the high priority rankings, and in principle, it is impossible for a collision to occur.

Once the second packet is received at Node B (5b-6b
), immediately the second A, CK-'? The message is returned to node A (7a to 8a). As before, this ACK/'P cannot cause a collision. Node A receives this ACKd,
By receiving the packets (7b to 8b), it is known that the series of packet transfers has been successful (it has definitely reached the node B).

Furthermore, if the transmitted data is long, node A may transmit all of the third data (9th get) following reception of this second ACK-P get. As before, this third ``p'' and ``g'' cannot cause a collision. Node B sends out a third ACK packet immediately after receiving this third packet. This ACK packet cannot cause a collision either. The same applies to the 4th section below. Fifth.・You can send out all of the data.

Note that the second ACK packet and subsequent ACK packets are not essential in the communication system according to the present invention. These ACK-9s are not necessary if there is a guarantee that the destination node (Node B in this example) can reliably accept the second packet and subsequent data packets.

In other words, only the first ACK is required.

Transmission line 1 is an extremely high-quality transmission system with very few transmission errors.
If used as 2, it is the second package.

Since a collision between data g and g after g cannot occur, the data reaches the destination node reliably without causing any errors. In this case, after the third ``get'', the immediately preceding data ``get'' will be followed (i.e., at least within tw).
Start sending.

In the previous explanation, the data to be sent is input/displayed.

Is it divided into two packets (third packet, etc. if necessary)? It may be configured such that data as transmission information is not included in the get, and data is included only in the second packet (and subsequent data/get). In this case, I/Y, E, and G will be used exclusively for the purpose of collision detection. By getting the first ACK and getting the first ACK, you have reserved the use of the channel for the second get.
When CKI Kenoto did not return, it meant that the reservation could not be made, and the collision is thought to be the main cause.

FIG. 3 shows an example of the device configuration of a node that implements the CSMA communication system according to the present invention. This applies to nodes A or B connected via taps 14 to the coaxial cable 12 shown in FIG.
1 Node A host machine (computer) io.

When the host device 100 of Node B wants to send data, the host computer 100 of Node A sends the data and commands to the host device 102 of Node A.

This instructs the transmission control section 110 to transmit. The transmission control unit 110 decodes the command, sends the destination address (node B in this case), and sends it to the nostar 112.

Synchronous turn generation section 126, CRC generation section 120
Once the collision control unit 104 and other units are initialized, transmission begins, but before that, it must be confirmed that there is no carrier wave tw on the cable 12 for a certain period of time. This carrier wave detection is performed by the transceiver 150. To avoid complicating the diagram, the carrier wave detection signal line (not shown) is connected to the transceiver 15.
0 to the transmission control section 110. When it is determined by carrier wave detection that the time carrier wave of tw does not exist continuously, the transmission control unit 110 starts transmission. If a carrier is detected, the subsequent action of checking for free channels and retrying involves the so-called non-/J? -7 stunt, l-no, 17 stunt, p-no e-7 stunt, it varies somewhat depending on the method, but after the carrier wave disappears and the time t
Transmission starts when w or more elapses.

The transmission is started by generating a synchronization signal from the synchronization/gutter generator 126. The synchronization signal is sent to the modulator 12
4, appropriate encoding is performed. , for example, Manchester encoding. This encoded signal is sent to the transceiver 1
50 onto cable 12. This example is Et
Pace bar using coaxial cable sound like hernet/
This is a code method.

When the synchronization signal has been sent, the transmission control unit 110 sends the data to the destination and sends the contents of the nostar 112 to the parallel/serial conversion unit 118, where it is converted into a serial bit string. This bit string signal is passed through a CRC generator 120 to a modulator 124, where it is encoded and transmitted onto the cable 12 by a transceiver 150. After sending the contents of the send destination register 112, ie, the destination address, the contents of the send destination register 114+7), ie, the source address, are sent in the same way.

Next, in this case, the type of ini/yalpaget is sent from the g-type putter 7 generation unit 116. next(
If so, then (a portion of) the data in buffer 102 is sent in a similar manner. A data length is set in the counter 108, and data of a length corresponding to the count value of the counter 108 is sent out in response to a command. After sending the data, the transmission control unit 110 sends the CRC generator 120
Instructs to add a CRC code to the end of the nosoget. When the transmission of the CRC is finished, the transmission control unit 110 causes the transceiver 150 to stop transmitting the carrier wave and enters the reception mode.

Node A will now wait to receive an ACK packet from node B.

Now, while node A is transmitting, other nodes that are not transmitting are receiving signals on cable 12.

For example, in the node B, when the transceiver 150 detects a carrier wave, the reception control unit 134 is notified through a signal line (carrier detection) not shown.

When the carrier wave is detected, the reception control section 134 activates the synchronization pattern/detection section 148 and initializes the CRC check section 144 and the counter 132. Therefore, the synchronization/P-turf detection section 1
48 detects a synchronization signal, and when synchronization is established, the reception control section 134 starts the operation of the CRC inspection section 144 and activates the destination detection section 138. When the destination detection unit 138 detects its own address (node B in this example), it notifies the reception control unit 134 of this fact, and the control unit 134
After that, the tray holder begins to move as if it were to be inserted. If the address is different from the own address, the reception of Kerato will be ignored. That is, the node does nothing until the carrier runs out.

In this way, if it is a 1,000-get address addressed to the user, it is accepted, and then the sender address is received, and this is entered in the sender's noster 136 for the receiver.

Next, I receive the packet type, which is NOKUKE.

It can be placed in a toyprenosta. Then (if any),
Data is received and stored in the buffer 102. At this time, the length of the data is counted by the counter 132.

When the reception of the data is completed, the reception control section 134 causes the CRC inspection section 144 to check the validity of the CRC code. If there is no transmission error including collision, the CRC is correct; if there is an error, the CRC is incorrect.

If there is an error, the reception control unit 134 ignores the received packet. If there is no error and the /F packet type recorder 140 determines that the packet is initial/e, then the reception control unit 13
4 is a transmission control unit 110 so as to immediately send out an ACK-E signal as soon as there is no carrier wave on the transmission path lz.
command.

The transmission control unit 110 of this Node B is the same as the transmission of Ini/Yar Gukerat of Nol'A Kara.

However, the difference is that as soon as there is no more carrier wave on the cable 12, the transmission of ACK-e kerato starts. That is, child A at time tw
I won't wait until The destination address of the ACK・ηkerato that node A”s returns from node B is due to a reception bug when receiving the initial message.
This corresponds to the source address stored in G and is used. That is, in node B, synchronization/e-turn generation unit 1
48, the destination address of node A is sent from the receiving packet source node star 136, and the source address of node B is sent from the sending source V node star 114. The unit 116 sends out an ACK type as a noget type. At this time, if there is data to be sent to node A in the buffer 102 of node B, that data may be sent successively. In general, status information such as air blockage information from the reception path and fa 102 and air blockage information from the host machine 100 is sent as necessary. Finally, the CRC generator 120 generates a
A C code is added, and the transmission of hcK-p is completed.

After sending the initial packet (point 2 in Figure 1), node A
a), ACK-P is waiting for the arrival of ACK-P. If there are no collisions or transmission errors, ACK-P should start to be received within 2τ time (3b).
If the length of the kerat is the above-mentioned minimum packet length, as can be seen from FIG. 1, the reception should be completed within 4τ time (4b).

Node A sends ACK A in the same manner as Node B received earlier.
Receive Kerat. Here, if there is an error in the CRC, if the /F ticket addressed to the self does not arrive, if none of the packets and packets are returned, and if the ACK packet is not received within a certain time ta, there may be a collision or some kind of transmission. It is possible that there was an error. As explained above, here the collision causes the ACK-'? It is presumed that Keget was not returned. Here, 4τ(ta(tw+2τ) 9 mouths (here, t
w) 2τ1 (from 0).

If the ACK A kerat is not received within ta, the collision control unit 104 of node A backlogs the initial ACK get and retransmits this initial e kerat according to a pack-off algorithm that reduces the retransmission probability. It works like that.

When ACK A and G are received normally, the transmission control unit 1
10 immediately transmits the second signal when there is data to be transmitted. This transmission starts immediately after the carrier wave runs out without waiting for tw. Also,
- Similar to the previous two nokerato transmissions, except that the gugettide indicates that it is the second packet. This second packet, like the ACK packet, does not, in principle, cause a collision. In this method, only the initial ξ kerato has a high possibility of causing a collision.

If Node B has received the second Kerato and the CRC is complete, it immediately sends an ACK-e to Toono-Kichido A. Node A knows that the series of data transfers was successful by receiving the second ACKA. If necessary, node A forwards the third and subsequent kerats in the same manner.

If there is data to be sent by a node other than node A,
It is only when the channel is active for more than a time tw, that is, when there is no carrier wave on the cable 12 for more than tw, that it is possible to send out an initial/l get. When an ACKA digit or a second sekerat is transferred between node A and node B, the channel is free for less than 2τ. In other words, since the channel is never vacant for a time longer than 2τ, and since tw)2τ, it is not possible to transmit Nokget from any node other than these two nodes A and B.

Note that although the present invention has been described with reference to specific embodiments, the present invention is not limited thereto. For example, although a coaxial cable is used here as the couple 12, other cables, such as a twisted nine-wire pair cable, may be used.

Furthermore, although baseband transmission has been described, wideband transmission using an RF modem may also be used. In this case, a tree-structured cable hierarchy with roots at DO/DO is advantageously applied. Further, the present invention can be advantageously applied to optical communication elements and trunks using optical fibers using optical coupling circuit networks such as optical star couplers, and can also be applied to wireless systems using light or radio waves.

Effects According to the present invention, after confirming that there is no carrier wave on the transmission path for a predetermined period of time, the packet is transmitted, and thereafter, the confirmation packet and the data packet are sent as necessary. I try to send them in sequence and alternately. Therefore, even if collision detection is not performed as in the CSMA/CD method, it is basically the C3MA method, and the C3
It is possible to achieve almost the same performance as the MA/CD method.

[Brief explanation of the drawing]

Fig. 1 is a communication flow diagram for explaining the principle of the C3MA communication system according to the present invention, Fig. 2 is a flow diagram showing an example of collision in a channel, and Fig. 3 is an example of the configuration of a node realizing the present invention. It is a block diagram. Explanation of symbols of main parts 12-Common transmission path 14... 104 Collision control section 108.132 Counter 110 Transmission control section 112 Sending packet destination relay station 114 Sending P number, To sending source node 116・・・・・・
e, Toquip pattern generation section 120, CRC generation section 134, reception control section 136, received packet source renostar 138, destination detection section 140, guget type renostar 144...C
RC inspection section 150 Transmitter/receiver A, B ・Node Patent Applicant '691° Knee 1. ,. Agent Takao Katori 11: :-:ni≦ Ward 1, Figure 2, Figure 3

Claims (1)

[Claims] In a CSMA communication system, a plurality of nodes are commonly connected to a common transmission path, and the plurality of nodes transmit packets to the transmission path when there is no carrier wave on the common transmission path, The first node among the nodes transmitting the packet confirms that the carrier wave is not on the common transmission path for a time longer than the maximum round-trip propagation delay time on the common transmission path, and transmits the packet, The second node that received the packet among the plurality of nodes immediately sends the confirmation packet to the first node after receiving the packet.
The CSMA communication system is characterized in that, after receiving the confirmation packet, the first node immediately sends the next packet if there is a packet to be sent.