JP3725000B2 - Transmission data collision reduction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transmission data collision reduction method in which a transmission path of CSMA (Carrier Sense Multiple Access) such as Ethernet is connected between a plurality of stations and data is exchanged between them.
[0002]
[Prior art]
When data is exchanged between a plurality of stations, a medium access control method called CSMA represented by Ethernet is adopted as a protocol of a physical layer and a data link layer which are lower layers of the OSI reference model.
[0003]
This CSMA method has an advantage that the transmission delay is short when the load on the transmission line is low as compared with other transmission methods.
[0004]
[Problems to be solved by the invention]
However, in this CSMA scheme, when the transmission load increases, transmission data collision increases between a plurality of stations, and the probability that transmission data is lost increases.
[0005]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a transmission data collision reduction method that minimizes the collision of data exchanged between a plurality of stations even when the transmission load increases.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problem, a transmission data collision reduction method according to the present invention divides a plurality of stations into groups, sets the time until the next frame transmission of the first group to β1 (1), and transmits a predetermined number of next frames. And the slot time of β2 (1), the Kth group is
β1 (K) = β1 (1) + (K−1) · {β2 (1) +1 slot}
If the frame is transmitted after the β1 (K) time, it is possible to eliminate the collision of the frames between groups while following a predetermined protocol, and to greatly reduce the loss of data.
[0007]
In another invention, when a plurality of stations are grouped into n, and the time until the next frame transmission of the first group is β1 (1), β1 (K) time of the K (n> K) th group Is
β1 (K) = β1 (1) + (K−1) · set to 1 slot and the time β2 for transmitting the next frame of each group is a predetermined number of slot times for transmitting the next frame of the first group If set to β2 (1) · n and each group transmits the next frame alternately within β2 (1) · n time, the frame data can be transmitted in a state of being arranged between the groups. There is no collision of frames between groups, and data loss can be greatly reduced.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a transmission data collision reduction method according to the present invention will be described below with reference to the drawings.
[0010]
FIG. 1 is a schematic configuration diagram of a network system using a transmission data collision reduction method according to the present invention.
[0011]
In this network system, a plurality of stations 1a, 1b, 1c, 1d,..., 1n are installed, and a CSMA transmission line 2 is used to exchange data between these stations 1a, 1b,. It is connected.
[0012]
This system is based on the premise that a plurality of stations 1a, 1b,..., 1n exchange data with each other via a CSMA transmission line 2 such as Ethernet. , 1n are divided into a plurality of groups 3 ₁ , 3 ₂ ,..., 3n, and frame data is transmitted in consideration of delay time and the like for each group. Specifically, it will be described later.
[0013]
The network connection form of the system is a bus type network, but may be a ring type network or other connection form.
[0014]
(First embodiment)
In general, in this type of network, when the transmission load increases, the number of cases where data transmission starts simultaneously between the stations increases. In particular, in the case of a CSMA system such as Ethernet, when a frame of a certain station exists on the transmission path 2, the other station that is going to transmit data generates a random number from the random number generator after receiving the previous frame. The transmission of data is started after being delayed by the random number generation time. This is one measure for avoiding data collisions. However, based on past results and experience, the random delay time, which is a guideline for preventing data collisions, is considered to be 3 slots. The other stations transmit data after the delay time has elapsed.
[0015]
Here, the one-slot time means a time from when one station transmits frame data between any two stations until the other station receives the frame data and recognizes it as a frame.
[0016]
Next, normal transmission timing will be described with reference to FIG.
[0017]
If the station 1b makes a frame data transmission request during transmission of the previous frame 11 by the station 1a, the station 1b waits until the transmission frame of the station 1a completely disappears from the transmission path 2 or the frame 11 Is provided with a delay time until another station can receive the next frame, that is, a delay time until the station 1a transmits the next frame (hereinafter referred to as β1 time). Delayed by the number of slots determined by the number of occurrences, and the station 1b transmits a frame after this delay time.
[0018]
However, in the transmission timing method as described above, when, for example, four stations try to transmit data at the same time during the random delay time of three slots, nearly 50% of collisions occur.
[0019]
Therefore, as a method for reducing the data collision as described above, it is conceivable to make the delay time of the random number sufficiently longer than 3 slots. However, since the protocol has already been decided in many cases, the number of 3 slots can be changed. It may not be possible.
[0020]
Therefore, the transmission data collision reduction method according to the present invention is realized by taking the following measures.
[0021]
(1) First, a plurality of stations 1a, 1b,... Are divided into a plurality of groups 3 ₁ , 3 ₂ ,. This grouping method includes a grouping method in which the number of transmission messages in a group is equal among the groups, and a grouping method in which transmission timing is shifted between stations in the group.
[0022]
The number of stations in the group is set to be sufficiently smaller than “4” when the number of slots based on random numbers is “3”.
[0023]
(2) Further, as shown in FIG. 3, it is assumed that the frame is transmitted by changing the β1 time for each of the groups 3 ₁ , 3 ₂ ,. Although FIG. 3 shows two groups 3 ₁ and 3 ₂ , the β1 (1) time of the first group 3 ₁ is the same β1 time as before.
[0024]
On the other hand, the second group 3 ₂ .beta.1 (2) times the first group 3 ₁ .beta.1 (1) Time and .beta.2 (1) time obtained by adding the further one slot time to time.
[0025]
That is, in this transmission data collision reduction method, the β1 (K) time of the K group is
β1 + (K-1) × (β2 + 1 slot)
If each station of the K group 3 _K transmits a frame after the β1 (K) time has elapsed, data collision can be reduced, and the possibility of transmission data being lost can be greatly reduced.
[0026]
Therefore, according to the above-described embodiment, the group 3 ₂ transmission frame group 3 ₁ Group 3 ₁ to the front frame 11 which is transmitted from the .beta.2 (1) time 1 slot time period added time after Since frames are transmitted, there is no collision of frames between group 3 ₁ and group 3 ₂ , data loss can be greatly reduced, and frame transmission in group 3 ₁ is given priority over frame transmission in group 3 _2. Therefore, data can be transmitted appropriately.
[0027]
Also, transmission can be performed while avoiding frame collision according to a predetermined protocol.
[0028]
(Second embodiment)
FIG. 4 is a transmission timing diagram for explaining another embodiment of the transmission data collision reducing method according to the present invention.
[0029]
This embodiment is an example in which not only the change in β1 time according to the first embodiment but also the β2 time is changed.
[0030]
In this transmission data collision reduction method, for example, when two groups 3 ₁ and 3 ₂ are described, the β1 (1) time of the first group 3 ₁ is the same as the conventional one. Set the period twice.
[0031]
Meanwhile, the second group 3 ₂ .beta.1 (2) times, the conventional .beta.1 (1) time obtained by adding the one slot time to time, further .beta.2 (2) time, like the first group 3 ₁ In consideration of expandability, the time is set to twice, and the frames of the first and second groups are alternately transmitted within the time of the double expansion slot.
[0032]
Accordingly, when there are n groups, the β2 (n) time is the conventional β2 (1) × n.
[0033]
On the other hand, the β1 (K) time of the K group is
β1 + (K−1) × 1 slot}
It becomes.
[0034]
Therefore, according to this embodiment, the timing of the transmission of group 3 ₁ transmission and Group 3 ₂ shifted by one slot, yet multiple groups, the number of groups into a predetermined number of slots time to send the next frame Since the next frame is transmitted alternately within the time β2 multiplied by, there is no collision between the frames of the group 3 ₁ and the group 3 ₂ , and the loss of data can be greatly reduced, and the transmission of the group 3 ₁ since it preferred on slight differences than the transmission of group 3 ₂ can transmit data appropriately.
[0035]
(Third embodiment)
In the first and second embodiments described above, even if there is a simultaneous transmission request of a plurality of stations in a no-signal time period when the load is low, the probability of occurrence of a collision in the group is significantly reduced. During a load, data collisions within the group can be high.
[0036]
Therefore, in this embodiment, in order to prevent a collision at a high load, a token passing system is adopted in the group, and a token is circulated in the group, thereby preventing a data collision.
[0037]
Note that the number of stations in the group is one or more. However, for example, when the group is composed of a single station, a token is not necessary. In this case, as a grouping method, for example, stations with low transmission frequency may be grouped into one group and tokens may be rotated, and stations with high transmission frequency may be separate groups of a single station.
[0038]
FIG. 5 is a diagram illustrating an example of a frame that flows in a transmission path when a single token is used.
[0039]
In this example, a group having four stations 1a, 1b, 1c, and 1d is connected to the transmission line 2, and the station 1b → 1c → 1d is turned in order from the station 1a ₁ and the station 1d receives the token. After transmitting the data, the token is returned to the station 1a again.
[0040]
Since the processing time of the protocol by the lower layer is shorter than that of the upper layer, it is less time consuming to circulate the token in the lower layer when viewed from the transmission path.
[0041]
FIG. 6 shows an example in which the stations 1a and 1b are one group, the stations 1c and 1d are one group, and tokens are circulated within each group.
[0042]
Therefore, according to such an embodiment, if data is transmitted while circulating a token within a group, transmission efficiency can be improved while preventing data collision.
[0043]
( Other embodiments )
(1) This embodiment is an example in which transmission requests are restricted at each station when the transmission load is high, thereby reducing data collisions.
[0044]
In this example, a confirmation frame (hereinafter referred to as Ack) is taken for each data frame, and FIG. 7 shows a general data flow using Ack. That is, in this figure, when the station 1a ₁ sends a data frame to the station 1b, the station 1b sends Ack back to the station 1a after receiving the data frame. If the station 1a does not receive Ack for a certain period of time, the station 1a retransmits the previous frame. The station 1a receives the Ack and transmits the frame when there is a transmission request.
[0045]
As the Ack, as shown in FIG. 8, a code indicating an Ack similar to the conventional Ack composed of a partner station number, a code indicating Ack, a sequence number, and the like, and a newly added delay time are used. The The sequence number is a management number for managing transactions at the other station.
[0046]
The reason why the delay time is added to the conventional Ack as described above will be described with reference to FIG.
[0047]
The station 1a takes statistics of received frames, and determines a delay time variable n that increases the value when the number of received messages is large, and decreases the value when the number of received messages is small. To respond to the other station. The station that has received this Ack, that is, the station that has transmitted the request frame refers to the delay time variable n in Ack, and after receiving Ack, starts the timer for that time.
[0048]
When a transmission request is generated from the station 1b while the timer is activated, the transmission is performed after the timer expires. That is, after delaying n hours, the frame is transmitted. When there is a transmission request after the time is up, transmission is performed without a delay time.
[0049]
Note that the delay time when retrying at the station 1b remains the same as before.
[0050]
Therefore, according to the embodiment as described above, if the transmission load increases, the delay time increases at the transmission source station, so the number of transmission requests decreases, and as a result, the overall transmission load decreases, and a collision is also established. The number of retries is reduced because of lowering Therefore, transmission efficiency is improved and response time is faster than before. When the transmission load becomes low, the delay time is eliminated, so the response time is the same as before. In this way, processing that automatically avoids data collision according to the state of the transmission load can be performed, and transmission loss can be reliably prevented.
[0051]
(2) This embodiment is an example in which the total transmission load is reduced by reducing the number of Ack.
[0052]
That is, in FIG. 7, when the destination station that transmits the request message is a broadcast address, Ack is returned from a plurality of stations. In the case of a bus-type transmission line, when a message arrives at any one of the stations trying to deliver a broadcast message, there is a high possibility that the message is also delivered to the other station trying to deliver it. .
[0053]
Therefore, if the Ack returned from the plurality of stations can be reduced, the entire transmission line load can be reduced.
[0054]
One is that, after receiving a request message at each station, a different delay time is set before returning Ack, and Ack is returned after the delay time elapses. When uniform Ack is received, transmission of Ack is stopped regardless of the delay time.
[0055]
The other one is to reduce the Ack by receiving a plurality of request messages and transmitting a plurality of Ack so that the Ack message stays in one Ack message. Normally, when the transmission load is high, a waiting time occurs when trying to return one request message, but there is a high possibility that the next request message will be received during that time, but this is effective.
[0056]
By reducing the number of Ack messages in this way, the load on the transmission path is reduced and the occurrence of data collision can be reduced, and the Ack message can be saved to save the header size of the Ack message and the time between frames.
[0057]
In addition, this invention is not limited to the said embodiment, A various change can be implemented in the range which does not deviate from the summary.
[0058]
【The invention's effect】
As described above, according to the present invention, the establishment of data collision can be greatly reduced by grouping stations and changing the slot times of the groups.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a network to which a transmission data collision reduction method according to the present invention is applied.
FIG. 2 is a diagram for explaining general frame transmission timing of each station.
FIG. 3 is a diagram for explaining an embodiment of a transmission data collision reduction method according to the present invention.
FIG. 4 is a diagram for explaining another embodiment of the transmission data collision reducing method according to the present invention.
FIG. 5 is a diagram for explaining still another embodiment of a transmission data collision reducing method according to the present invention, and showing an example in which a plurality of stations in a group circulate a single token.
FIG. 6 is a diagram for explaining still another embodiment of the transmission data collision reducing method according to the present invention, and showing an example in which a plurality of stations in a group circulate a plurality of tokens.
FIG. 7 is a view for explaining still another embodiment of the transmission data collision reducing method according to the present invention.
FIG. 8 is a data array diagram of a new Ack to which a delay time used for a conventional Ack is added.
FIG. 9 is a diagram showing an example of data transmission using Ack shown in FIG. 8;
[Explanation of symbols]
1a, 1b, ... Station 2 ... Transmission path 31, 32 ... Group

Claims (3)

In a network system in which multiple stations are connected to the transmission path,
When the plurality of stations are grouped, and the time until the next frame transmission of the first group is β1 (1) and the predetermined number of slot times for transmitting the next frame is β2 (1), the Kth group is
β1 (K) = β1 (1) + (K−1) · {β2 (1) +1 slot}
A transmission data collision reduction method characterized by transmitting a frame after the β1 (K) time. In a network system in which multiple stations are connected to the transmission path,
When the plurality of stations are grouped into n, and the time until the next frame transmission of the first group is β1 (1), β1 (K) time of the K (n> K) th group is
β1 (K) = β1 (1) + (K−1) · set to 1 slot and the time β2 for transmitting the next frame of each group is a predetermined number of slot times for transmitting the next frame of the first group β2 (1) · n is set, and each group transmits the next frame alternately within β2 (1) · n time. In the transmission data collision reduction method according to claim 1 or 2,
A transmission data collision reduction method, wherein each group transmits a next frame while circulating a token in the group to avoid collision of frame data.

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