CN110300028B - Ethernet model design method based on time slot non-adherence CSMA - Google Patents
Ethernet model design method based on time slot non-adherence CSMA Download PDFInfo
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Abstract
The invention relates to an Ethernet model design method based on CSMA protocol, in particular to an Ethernet model design method based on time slot non-persistent CSMA. The method comprises the steps of establishing an industrial Ethernet network channel transmission structure model, a transmission protocol improvement model and a network data transmission capture effect model. The existing time slot non-persistent CSMA protocol is taken as a main research protocol, a new time slot required by data transmission is obtained by dividing the time slot in the existing protocol again, and a capture effect is applied to the new protocol, so that an Ethernet network model is established, and transmission characteristic analysis is carried out on the Ethernet network transmission data; compared with the CSMA protocol model which is not adhered to by the original time slot, the established model is more real-time and reliable. Meanwhile, the established model not only reduces the defects of channel conflict, non-utilization and the like, improves the real-time performance of the industrial Ethernet network, and greatly improves the transmission effect of data borne by the industrial Ethernet network.
Description
Technical Field
The invention relates to an Ethernet model design method based on CSMA protocol, in particular to an Ethernet model design method based on time slot non-persistent CSMA, which can be used for solving the problem that the reliability and the real-time performance of an industrial Ethernet network system are reduced due to the defects of channel transmission conflict, channel idle and non-utilization and the like of the industrial Ethernet communication network system, and provides a basic platform for the application and the theoretical research of the industrial Ethernet communication network.
Background
Ethernet (Ethernet) is a network which follows IEEE802.3 standard and can be transmitted on optical cables and twisted pair wires, is also the most common communication protocol standard adopted by the existing local area networks at present, has the transmission rates of 10Mbit/s, 100Mbit/s, 1Gbit/s and 10Gbit/s, can meet the requirements of fast, real-time and reliable control of Ethernet, and is widely applied to the industrial control field with higher real-time requirements such as motor train units, subway trains, urban rail vehicles and the like. Currently, ethernet mainly adopts a star-type and bus-type structure, each station can independently determine frame transmission, and if two or more stations transmit frames to a bus at the same time, medium access collision (without channel multiplexing) occurs, resulting in collision and discarding of the transmitted frames. Therefore, in such ethernet networks, the success of a user data transmission depends largely on whether the data transmission will generate bus medium contention with data transmitted by other users.
In order to solve the problem of bus occupation, a CSMA (carrier sense multiple access) protocol is provided, which can effectively ensure that when each station transmits data to the bus, other stations do not transmit data, and meanwhile, each station can detect whether the bus medium is idle as soon as possible. The CSMA technology firstly monitors a channel to be accessed, avoids random time if the channel is busy, does not transmit data, and transmits the data only when the monitored channel is idle. However, because the ethernet employs a medium Access mechanism of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), and the 1-adherence to CSMA protocol and the binary exponential backoff BEB algorithm are used to handle packet collisions, it is determined that the ordinary ethernet has uncertainty in real-time.
The data transmission method improves the real-time performance and the reliability of the Ethernet network data transmission by analyzing the theory of the data transmission strategy, the influence factor of the real-time performance and the performance index, thereby achieving the purpose of improving the performance of the Ethernet network system. Based on the research background, researches on key technologies such as a redundancy technology, a reliability technology, bus power supply, an industrial Ethernet real-time guarantee mechanism, functional safety and the like are derived.
The key to optimizing network performance and designing system is to raise the real-time performance of Ethernet network. Currently, the mainstream methods for studying the real-time performance of the ethernet mainly include topology-based, real-time scheduling policy-based, ethernet conventional protocol-based improvement, logic-based, and the like. However, the existing methods have some disadvantages that the real-time performance of data transmission is reduced, for example, high-speed ethernet cannot be completely supported, the stationarity is not enough, and cross communication cannot be performed, so that they all have certain limitations. In summary, improving the real-time performance of the ethernet network is the core of improving the performance of the whole network communication system
Disclosure of Invention
The invention aims to solve the technical problem of data transmission conflict and the like in the existing Ethernet network and provides a time slot non-persistent CSMA-based Ethernet model design method. The method comprises the establishment of an industrial Ethernet network channel transmission structure model, a transmission protocol improvement model and a network data transmission capture effect model. The existing time slot non-persistent CSMA protocol is taken as a main research protocol, a new time slot required by data transmission is obtained by dividing the time slot in the existing protocol again, and a capture effect is applied to the new protocol, so that an Ethernet network model is established, and transmission characteristic analysis is carried out on the Ethernet network transmission data; compared with the CSMA protocol model which is not adhered to by the original time slot, the established model is more real-time and reliable. Meanwhile, the established model not only reduces the defects of channel conflict, non-utilization and the like, improves the real-time performance of the industrial Ethernet network, and greatly improves the transmission effect of data borne by the industrial Ethernet network.
The industrial Ethernet communication network channel transmission structure model mainly considers the path loss caused by the distance between an access point and a terminal and the shadow fading caused by the shielding of a building and other obstacles, and models the path loss and the shadow fading respectively.
The received signal power decreases monotonically as the distance between the access point and the terminal increases, which is referred to as path loss. Propagation models based both on theoretical and actual measurements show that in indoor or outdoor channels, the average received power (dBm) is inversely proportional to the logarithm of the distance between transmitter and receiver, i.e.:
meanwhile, the signal is randomly changed due to the fact that the signal meets an obstacle in channel propagation, so that the power of the received signal at a given distance is randomly changed, and the power of the received signal is also randomly changed due to the change of the reflector and the scatterer. Therefore, a model is needed to describe the random signal attenuation caused by these factors. The most common model is the log normal shadowing model, with the standard deviation of fading between 6-10 dB.
The improved model of the industrial Ethernet network transmission protocol is used for solving the problems of data transmission conflict and retransmission of the original time slot non-persistent CSMA protocol, and a new time slot non-persistent CSMA protocol is established by adopting a time slot re-segmentation method. Because the data packet can only start to be transmitted in the subdivided time slot, the data packet generated in the current time slot can only start to be transmitted in the next time slot, thereby reducing the probability of data packet collision.
The industrial Ethernet network data transmission capture effect model utilizes the characteristic of capture effect, namely in a network system, when two signals have almost equal amplitudes at a receiving end, the stronger one of the two signals is dominant due to a small difference of relative amplitudes, and the other signal is replaced at a demodulation output end. Therefore, when the data packets collide, the collided data packets are respectively processed differently according to whether the capture effect is considered, so that the success rate of data transmission is improved.
Compared with the existing design method for constructing the industrial Ethernet communication network data transmission communication modeling, the method has the following advantages.
The invention relates to an industrial Ethernet network control system conforming to TCP/IP standard, namely an Ethernet model design method based on CSMA protocol, in particular to an Ethernet model design method based on time slot non-adherence CSMA, which analyzes parameter change caused by channel change of data transmission of an industrial Ethernet network under multi-time slots through an established model, keeps floating change of parameter indexes such as channel capacity, waiting time, data generation interval and the like, reduces data collision, loss and the like, and ensures transmission reliability, real-time performance and the like. And a basic platform is provided for industrial Ethernet network application and theoretical research thereof, and the research and development period is shortened.
Drawings
FIG. 1 is a design diagram of an industrial Ethernet network model according to the present invention
FIG. 2 is a schematic diagram of an industrial Ethernet network communication system model according to the present invention
FIG. 3 is a diagram showing the simulation results of the throughput of the industrial Ethernet network according to the present invention
FIG. 4 is a diagram illustrating delay simulation results of an industrial Ethernet network according to the present invention
FIG. 5 is a diagram showing the simulation results of time slot of industrial Ethernet network according to the present invention
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings. As shown in fig. 1, the design method of the present invention is mainly divided into three parts: the industrial Ethernet network communication system model is built by the industrial Ethernet network channel transmission structure model, the industrial Ethernet network transmission protocol improvement model and the industrial Ethernet network data transmission capture effect model.
Firstly, the invention models the path loss and shadow fading in a channel model, thereby ensuring the stability of the change caused by distance and obstacles during data transmission; after the channel is ensured to be stable, the original time slot is concerned to not adhere to the CSMA protocol, the original time slot is subdivided, the data packet can only start to be transmitted in the subdivided time slot, and the data packet generated in the current time slot can only start to be transmitted in the next time slot, so that the probability of data packet collision is reduced, and the protocol is improved; finally, when the data packet transmission conflicts, different processing is respectively carried out on the collided data packets according to whether the capture effect is considered: when there is no capture effect, all the colliding packets are discarded and the data packet is treated as a transmission failure. If no conflict exists, the generated data packets are sequentially transmitted to the destination; when there is an acquisition effect, if the data packets collide, the data packet with the maximum receiving power may still be correctly received.
The industrial Ethernet network communication system model is formed by combining an industrial Ethernet network channel transmission structure model, an industrial Ethernet network transmission protocol improvement model and an industrial Ethernet network data transmission capture effect model.
As shown in fig. 2, the model includes an access point and a plurality of terminals, the terminals have the same performance and are provided with buffers, and after the data packet is generated, the data packet is firstly stored in the buffer and is transmitted according to the algorithm principle in the data link layer. When the buffer capacity is limited, the newly generated packet will be discarded after the packet fills the buffer, which is called congestion. If the data packet has been buffered but not successfully transmitted to the access point, the transmission is said to be failed.
Each terminal in the communication model assumes mutually independent randomly generated data packets, and the packet generation process obeys the Possion distribution, namely, the following characteristics are satisfied:
independence: the number of the data packets generated in the time slot intervals which are not overlapped with each other is mutually independent in statistics;
and (3) stability: the number of data packets generated in a segment of time slot interval is only related to the segment of time slot interval and is not related to the starting time of the segment of time slot interval;
sparsity: in a very small time slot interval, the probability of generating two or more data packets is very small and can be ignored.
The improved model of the industrial Ethernet network transmission protocol is used for solving the problems of data transmission conflict and retransmission of the original time slot non-persistent CSMA protocol, and a new time slot non-persistent CSMA protocol is established by adopting a time slot re-segmentation method. Because the data packet can only start to be transmitted in the subdivided time slot, the data packet generated in the current time slot can only start to be transmitted in the next time slot, thereby reducing the probability of data packet collision.
In the improved industrial Ethernet network transmission protocol model, the data transmission rate is assumed to be R (bps), and the number of bits of data to be transmitted is TtThe generated traffic G is the sum of the newly generated packet and the retransmitted packet per unit time, that is, if the packet is 0, G is 0.
Assuming that the number of information bits contained in each data packet is T, the number of successfully transmitted data packets in unit time is n, and the normalized throughput S is the sum of the successfully transmitted data packets to the access point in unit time, the method for determining the throughput of the access point in the access network is described in the following
If no data packet is generated or all transmission data packets are discarded due to collision, the throughput Smin0; throughput S if all data packets are successfully transmitted in all unit timesmax＝1。
If the load is greater than a certain threshold, the average transmission delay will increase sharply. If the total transmission delay time Tw of the successfully transmitted data packets and the unsuccessfully transmitted data packets is set to 5000, the average transmission delay T is calculateddelayIs composed of
Meanwhile, in the original slot non-persistent CSMA protocol, the slot length is defined to be the same as the slot length in the slot ALOHA, and is slot ═ Plen/Srate, where Plen is the packet length, i.e., the number of symbols, and Srate is the symbol rate. However, the original time slot length is too large, and the channel cannot be effectively utilized, so the time slot length slot is determined by adopting the following method when the time slot is subdivided:
wherein t is the propagation delay, i.e. the quotient of the distance between the transmitter and the receiver and the signal propagation speed; n is the number of terminals, tdelayDelay for access, tzdBoth of these depend on the channel capacity C and the packet size for the terminal delay. The channel capacity is obtained according to the Shannon channel capacity, i.e.
C＝W*log(1+SNR)
Where SNR is the signal-to-noise ratio and W is the channel bandwidth (Hz).
After the time slot is determined, if data is known to arrive, the packet generation interval is (n is the number of terminals)
When the channel is busy, the packet waits for a random time to be retransmitted, which is expressed as:
Tsj＝-Tint×log(1-m),0≤m≤1
in order to verify the effectiveness of the present invention, the scheme of the present invention is compared with the original time slot non-adherence to CSMA, as shown in fig. 3, as the traffic volume increases, the network throughput initially shows an upward trend, and after the throughput reaches the maximum, the network throughput shows a downward trend as the traffic volume increases, wherein the improved time slot non-adherence to CSMA protocol throughput is higher than that of the original time slot non-adherence to CSMA protocol no matter the upward trend or the downward trend. Also, as can be seen from fig. 5, when there is an acquisition effect, the throughput of the slotted non-persistent CSMA protocol is higher than when there is no acquisition effect. This is because when there is no capture effect, all packets are discarded as long as the packets collide; when the capturing effect is available, if the data packets collide, the data packets with the maximum power and larger than the power threshold of the received signal can still be correctly demodulated.
As shown in fig. 4, the transmission delay is different for different traffic. The transmission delay of the improved time slot non-adherence CSMA protocol based on the traffic is obviously lower than that of the original time slot non-adherence CSMA protocol. Meanwhile, when the capture effect is available, the delay is low, and when the capture effect is unavailable, the delay is high and is increased exponentially. This is because the time slot re-division makes the length of the transmission time slot short, thereby making the packet transmission timing earlier. Therefore, the present invention has lower transmission delay.
As shown in fig. 5, similar to fig. 3 and 4, the traffic-based improved slotted non-persistent CSMA protocol has a significantly lower transmission delay than the total amount of slots required for the original slotted non-persistent CSMA protocol transmission. Meanwhile, when the capturing effect is available, the required time slot is lower, and when the capturing effect is unavailable, the time slot is higher and exponentially increased.
The invention relates to an Ethernet model design method based on CSMA protocol, in particular to an industrial Ethernet model design method based on time slot non-adherence CSMA, which establishes an industrial Ethernet communication model by researching the time slot non-adherence CSMA protocol, analyzes the characteristics of path loss, shadow fading, traffic, transmission delay and the like based on the industrial Ethernet communication model, and aims to reduce the delay of a data packet in industrial Ethernet data transmission, improve the throughput, further improve the real-time property of the industrial Ethernet network and ensure the stability of the industrial Ethernet network.
Claims (3)
1. A time slot non-persistent CSMA-based Ethernet model design method is characterized in that: the method comprises the establishment of an industrial Ethernet network channel transmission structure model, a transmission protocol improvement model and a network data transmission capture effect model, wherein a new time slot required by data transmission is obtained by dividing the time slot in a time slot non-persistent CSMA protocol again, and meanwhile, the capture effect is applied, so that the Ethernet network model is established, and the transmission characteristic analysis of the Ethernet network transmission data is carried out; the improved model of the industrial Ethernet network transmission protocol is used for solving the problems of data transmission conflict and retransmission of the time slot non-persistent CSMA protocol, a new time slot non-persistent CSMA protocol is established by adopting a time slot re-segmentation method, and because a data packet can only start to be transmitted in a re-segmented time slot, the data packet generated in the current time slot can only start to be transmitted in the next time slot, thereby reducing the probability of data packet collision; the industrial Ethernet network data transmission capture effect model utilizes the characteristic of capture effect, namely in a network system, when two signals have almost equal amplitudes at a receiving end, a stronger signal of the two signals occupies a dominant position due to a small difference of relative amplitudes, and the other signal is replaced at a demodulation output end, so that when data packets collide, different processing is respectively carried out on the collided data packets according to whether the capture effect is considered, and the data transmission success rate is improved.
2. The Ethernet model design method based on time slot non-persistent CSMA as claimed in claim 1, wherein: the industrial Ethernet network communication system model is formed by combining an industrial Ethernet network channel transmission structure model, an industrial Ethernet network transmission protocol improvement model and an industrial Ethernet network data transmission capture effect model.
3. The Ethernet model design method based on time slot non-persistent CSMA as claimed in claim 2, wherein: the industrial Ethernet network communication system model comprises an access point and a plurality of terminals, wherein the terminals have the same performance and are provided with buffer areas, after a data packet is generated, the data packet is firstly stored in the buffer areas, the data packet is transmitted according to an algorithm principle in a data link layer, when the capacity of the buffer areas is limited, after the data packet is filled in the buffer areas, the newly generated data packet is discarded, so the data packet is called as a block, if the data packet enters the buffer areas and is not successfully transmitted to the access point, the data packet is called as a transmission failure, wherein each terminal in the communication model assumes that the data packet is randomly generated independently, and the packet generation process obeys Possion distribution, namely the following characteristics are met:
(1) independence: the number of the data packets generated in the time slot intervals which are not overlapped with each other is mutually independent in statistics;
(2) and (3) stability: the number of data packets generated in a segment of time slot interval is only related to the segment of time slot interval and is not related to the starting time of the segment of time slot interval;
(3) sparsity: in a very small time slot interval, the probability of generating two or more data packets is very small and can be ignored.
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| US7826474B2 (en) * | 2006-07-13 | 2010-11-02 | Harris Corporation | P-persistent carrier sense multiple access (CSMA) for non-packetized wireless digital voice networks |
| US7792136B2 (en) * | 2007-01-31 | 2010-09-07 | Harris Corporation | Carrier sense multiple access (CSMA) for non-packetized wireless digital voice networks using intelligent conversation boundary detection |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101163076A (en) * | 2006-10-09 | 2008-04-16 | 华为技术有限公司 | Method and system of determining and optimizing throughput of short distance wireless network |
| CN103874233A (en) * | 2014-02-14 | 2014-06-18 | 长江勘测规划设计研究有限责任公司 | Synergy slotted ALOHA protocol based on capture effect |
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