In response to these problems, what measures has Japan taken to go to different sea areas?
What measures does the s-mac protocol take against these factors? S-MAC protocol is designed on the basis of SC9636-006 of IEEE 802. 1 1 protocol to meet the energy-saving requirements of sensor networks. S-MAC includes methods to save energy from various energy consumption modes, such as idle listening, collision, crosstalk and control overhead. Before describing the structure of S-MAC, we first summarize the concept and application of wireless sensor network.
Overview of S-MAC Protocol in MAC Protocol of Wireless Sensor Networks
Sensor networks are composed of multiple nodes, which use short-distance multi-hop communication to store energy, and most of the communication takes place between peer nodes. In-network processing is very important for network lifetime, which means that data will be processed as a whole message in the form of storage and forwarding. Finally, we assume that the application will have a long idle time and can tolerate the delay of network delivery timing.
1. Periodic monitoring and sleep
As mentioned above, in most sensor network applications, if no event is sensed, nodes will be idle for a long time. We assume that the data rate is very low during this period, so there is no need for the node to listen all the time. S-MAC reduces the listening time by putting nodes into periodic sleep state. Each node will sleep for a while, then wake up and listen to see if any other nodes want to communicate with it. During sleep, nodes turn off wireless devices, set timers, and then wake themselves up.
A complete period of listening and sleeping is called a frame. The listening interval is usually fixed, which is determined according to the parameters of physical layer and MAC layer (such as wireless bandwidth and contention window size). Duty cycle refers to the ratio of the listening interval to the whole frame length. The sleep interval can be changed according to different application requirements, which actually changes the duty cycle. Simply put, these values are the same for all nodes, and all nodes are free to choose their own monitoring/sleeping schedules. However, in order to reduce the control overhead, we prefer to keep the neighboring nodes synchronized, that is, they listen and sleep at the same time. It is worth noting that in multi-hop networks, not all neighboring nodes can keep synchronization. If node A and node B have to synchronize with different nodes C and D respectively, then node A and node B may have different schedules, and neighboring nodes A and B have different schedules, which keep synchronization with node C and node D respectively.
Nodes exchange their schedules by periodically broadcasting synchronization packets to their immediate neighbors. A node communicates with its neighboring nodes at a predetermined listening time to ensure that all neighboring nodes can communicate, even if they have different schedules. For example, if Node A wants to communicate with Node B, the time that Node A must wait until Node B is listening to the synchronization packet sent by Node C is called synchronization time. One of the characteristics of S-MAC is to form nodes into a planar peer-to-peer topology. Unlike the cluster protocol, S-MAC does not need to cooperate through the cluster head. Instead, nodes form virtual clusters in a common schedule and communicate directly with peer nodes. One advantage of this method is that it is more robust than the cluster-based method when the topology changes. The disadvantage of this mechanism is that periodic dormancy increases the delay, and the delay may accumulate at each hop.
2. Avoid conflicts
If multiple neighboring nodes want to communicate with a node at the same time, they will try to send messages when the node starts listening. In this case, they need to compete for the media. In the competition protocol, IEEE 802. II has done a good job in collision avoidance. S-MAC follows a similar process, including virtual carrier sense and physical carrier sense, and RTS/CTS (Request Transfer/Clear Transfer) exchange to solve the hidden terminal problem. Each transmission packet has a duration field to identify how long the packet will be transmitted. If a node receives a packet sent to another node, it can know how long the data cannot be sent from the duration field. The node records the value in the form of a variable, which is called the network allocation vector (NAV). NAV can be regarded as a timer. Every time the timer starts counting, the node decrements its NAV until it is reduced to 0. Before transmitting, the node first checks its NAV. If its value is not 0, the node thinks that the media is busy, which is called virtual carrier sense. Physical carrier sense is performed at the physical layer, and possible transmission is performed through the listening channel. Carrier sense time is a random value in the competition window to avoid conflict and hunger. If both the virtual carrier sense and the physical carrier sense indicate that the media is idle, the media is idle.
Before starting transmission, all transmitters perform carrier sense. If a node does not get the media, it will go to sleep and wake up when the receiver is idle and listens again. The transmission of broadcast packets does not need RTS/CTS, and unicast packets follow RTS/CTS/DATA/ACK sequence between sender and receiver. After RTS and CTS are successfully exchanged, the two nodes will use their sleep time to transmit data packets, and they will not follow their own sleep schedule until the transmission is completed. In each interception interval, due to duty cycle operation and competition mechanism, S-MAC can effectively identify the energy consumption caused by interception and collision.
4. The key technologies of S-MAC protocol are as follows.
Nested structure of (1) data packet
In S-MAC protocol, the upper layer packet contains the contents of the lower layer packet. To which layer the packet is sent, which layer only needs to deal with its part.
(2) Stacking structure and function
In the S-MAC protocol stack, when the MAC layer receives the data packet sent by the upper layer, it will start the carrier sense. If the result shows that the MAC layer is idle, the data is transferred to the physical layer; If the MAC layer is busy, it will go to sleep until the next available time and then send it again. When the MAC layer receives the data packet from the physical layer, it first indicates that there is no error through cyclic redundancy check (CRC), and then the MAC layer will pass the data packet to the upper layer.
(3) Select and maintain the schedule.
Before starting periodic listening and sleeping, each node needs to choose a sleep scheduling mechanism and keep consistent with its neighbors. How to choose and maintain the scheduling mechanism can be divided into the following three situations.
① During the listening time, if a node does not listen to the sleep scheduling mechanism of other nodes, it immediately chooses a sleep scheduling mechanism.
② When a node receives a sleep scheduling mechanism broadcast by a neighbor node before selecting and announcing its own scheduling mechanism, it will adopt the sleep scheduling mechanism of the neighbor node.
③ When a node receives several different sleep scheduling mechanisms after selecting and broadcasting its own sleep scheduling mechanism, the following two situations should be considered: when a node has no neighbors, it will abandon its current sleep scheduling mechanism and adopt the newly received sleep scheduling mechanism; When a node has one or more neighboring nodes, it will adopt different scheduling mechanisms at the same time.
(4) Time synchronization
In the S-MAC protocol, a node and its neighbors need to keep time synchronization in order to listen and sleep at the same time. S-MAC protocol uses relative time stamp instead of absolute time stamp, and at the same time makes the listening time much longer than clock error and drift to reduce synchronization error. Nodes will update their time according to the packets received from neighboring nodes, thus keeping time synchronization with neighboring nodes.
(5) Carrier Sense Multiple Access with Collision Avoidance
The basic mechanism of CSMA/CA with collision avoidance is to establish a handshake mechanism between the receiver and the sender to transmit data.
Handshaking mechanism is that the sender sends a request for transmission (RTS) packet to its receiver, and the receiver replies a ready to receive (CTS) packet after receiving the CTS packet. The handshake between RTS and CTS is to let the neighbor nodes of the sender and receiver know that they are transmitting data, thus reducing transmission conflicts.
(6) Network allocation vector
In S-MAC protocol, each node keeps a network allocation vector (NAV) to indicate the activity time of its neighbor nodes. In the S-MAC protocol, each packet contains a duration indicator value, which indicates the current duration of the communication. Neighboring nodes can know how long they need to sleep when they receive the data packet sent by the sender or the receiver to other nodes, that is, update the NAV value with the time in the data packet. When the NAV value is not zero, the node should enter the sleep state to avoid crosstalk. When NAV becomes zero, it will wake up immediately and be ready for communication.
Compared with IEEE 802. 1 1 MAC, S-MAC protocol prolongs the sleep time of other nodes as much as possible, reduces the collision probability and reduces the energy consumed by idle listening. Through the traffic adaptive interception mechanism, the transmission delay of messages in the network is reduced; Adopt in-band signaling to reduce retransmission and avoid monitoring unnecessary data; In order to reduce the overhead of control messages and the delay of message transmission, message segmentation and burst transmission mechanisms are adopted to process in-band data. Therefore, the S-MAC protocol has good energy-saving characteristics and meets the requirements and characteristics of wireless sensor networks. However, due to the fixed duty cycle in S-MAC, it can not adapt to the change of network traffic, and the implementation of the protocol is very complicated, which requires a lot of storage space. This is especially prominent for sensor nodes with limited resources.
Faced with these problems, what measures did Feng Taihou and Wendi Deng take? 1. Promulgate the salary system (that is, rectify the official management);
In the Northern Wei Dynasty, hundreds of officials were unpaid, and officials searched the people. After Feng Taihou and Emperor Xiaowen Luban, officials were not allowed to pay their own salaries. Those who take a horse full of bribes will be put to death.
2, the implementation of land equalization system:
Because of years of war, people are in exile. * * * controls a large number of wasteland. Feng Taihou and Emperor Xiaowen practiced the system of land equalization and distributed the wasteland to farmers for cultivation. It promotes the recovery and development of social economy.
3, ternary system, rent modulation
Implement the three-long system and the household system that are compatible with the equal land system. Bo Gu set up party, village and neighborhood, implemented the system of equal land, and imposed corvee.
Rent modulation requires a couple to pay a certain amount of rent to the state every year. So that in order to escape the tax of * * *, the households who sheltered the patriarch turned to * * * to become the establishment households of * * *.
Abstract: Feng Taihou presided over the reorganization of the official system, the establishment of the three systems, the land equalization system and the new rent modulation, which laid the foundation for the prosperity of Emperor Xiaowen after he moved to Luo, and initially sinicized Xianbei people.
What are the hidden concerns of double eleven logistics enterprises and e-commerce?
On the day of "Double 1 1", the express delivery order reached1.300 million pieces. At that time, according to the statistical data of "Analysis Report on Development Trend and Investment Planning of Express Industry" released by Forward Industry Research Institute, on the day of 1 1, major e-commerce companies * * generated express logistics orders 1.352 billion pieces throughout the day, a year-on-year increase. Throughout the day, postal and express delivery enterprises handled 4160,000 pieces of express mail, up 25.68% year-on-year, reaching a record high. Among them, only Tmall's "double 1 1" logistics orders exceeded 1 100 million pieces. 65.438 billion logistics orders, roughly equivalent to 20 days of parcels in the United States and 4 months of parcels in the United Kingdom. But in China, it only takes one day to create this number: Tmall Double 1 1.
65.438+00 billion logistics orders are also equivalent to the express delivery business in China in 2006. In the ten years of Tmall's "double 1 1", logistics orders started from 260,000, increasing by more than 4,000 times. Together, these packages are long enough to circle the equator of the earth for more than 7 times.
If these data were placed 10 years ago, it would undoubtedly be an astronomical figure. At that time, private express delivery was still in the stage of extensive growth. Buyers, sellers and courier companies communicate with each other through SMS. The access network has just established a national prototype, but it has not really developed.
20 10 express delivery capacity can't keep up with the development speed of e-commerce, and "empty positions" sometimes occur. In the process of "barbaric development" of the industry, this festival, which ushered in the wave of development of the express delivery industry, has mercilessly magnified the shortcomings of express delivery companies.
In May of 20 13, Alibaba, together with other express delivery companies such as Sitong Yida, established Cainiao Network, a smart logistics platform company, which brought new development ideas for the development of express delivery industry with its scientific and technological advantages and synergistic advantages. In the same year, Tmall double 1 1 logistics orders exceeded 1 billion, reaching 654.38+52 million.
Since the beginning of this year, although the number of double 1 1 parcels has increased, the express delivery has become more and more stable, the arrival speed is faster every year, and the service quality is also improving year by year.
The reason is, first of all, because the whole industry has formed a real synergy. Now before every double 1 1, the courier company will make a plan in advance according to the rookie's algorithm prediction, and increase the investment in venues, equipment and personnel. In addition, real-time distribution has become the new main force. It is understood that the full participation of crowdsourcing capabilities such as point size makes the minute-level distribution of rookie networks gradually become the norm.
On the other hand, the investment in technology has greatly improved the efficiency of the industry. Automatic sorting system has become a standard, and robots, mechanical arms and assembly lines have become very common in the warehouse of rookie network. Coupled with the standardization of electronic bills, the whole express delivery industry is rapidly upgrading digitally, which makes it possible to coordinate the whole network and realize intelligent billing, intelligent routing and early prediction.
In the past 10 year, when the express logistics industry started the era of automation and robot warehouse with the help of rookie network platform and intelligent technology, Tmall Double 1 1 reached a new height at this key node. In the future, the circulation of 654.38 billion parcels will become the daily norm, and it is more urgent to build a smart logistics backbone network.
As we all know, the logistics industry is called the "artery" of the economy and is the main channel to maintain the stable operation of the economy. According to the data, at present, there are nearly 300,000 legal entities in China's logistics enterprises, which have become important enterprise groups. 20 16 the main business income of the top 50 logistics enterprises in China is 840 billion yuan, accounting for 1 1.5% of the total income of the logistics industry. However, the growth rate of China's logistics industry is gradually slowing down, the traditional industrial development mode is difficult to meet the requirements of rapid growth of consumer demand, and the existing resource conditions are not enough to support the sustained and rapid growth of industrial scale. In this case, smart logistics has ushered in a major opportunity.
If we build an intelligent platform reasonably, promote the development of intelligent logistics in an all-round way, and use information technology to release offline information, it will further promote the development of China's logistics industry.
Based on this, China has also strengthened its policy support. Last year, China's logistics industry focused on six strategic priorities: high efficiency, connectivity, wisdom, coordination, coordination and reform. In the same year, leaders at the the State Council executive meeting also stressed the need to promote logistics in internet plus. In the same period, it was also made clear that "promoting the deep integration of information technologies such as Internet, big data and cloud computing with logistics, and promoting the transformation and upgrading of the logistics industry and even China's economy is the' supply-side reform' of the logistics industry".
What measures did Japan take to deal with the earthquake? 1. Estimate the magnitude of the earthquake and its harm, such as its intensity distribution, death toll and economic loss.
2. Formulate a policy framework and master plan, including a series of actions, such as preventive actions, post-disaster response and reconstruction.
3. Formulate a strategy for earthquake relief and disaster reduction, formulate a series of quantitative indicators, such as halving the number of people affected and economic losses within ten years, and formulate some specific measures to achieve these goals.
4. Formulate some guiding principles for earthquake emergency activities taken by relevant institutions. According to these guiding principles, a series of detailed plans have been made.
In addition, Japan has also developed an earthquake early warning information system. Although this early warning information system can only provide a few seconds or dozens of seconds of early warning, it is very useful. "For example, if you receive such an early warning, the new train in Japan will stop. There are more than 1000 seismic stations in Japan. When an earthquake occurs, the station closest to the earthquake center can receive the Ranbo, and the time when the shear wave arrives at each station can be analyzed.
What measures have the head teacher and the school taken to deal with (1) the epidemic situation of infectious diseases? The three basic links are the source of infection, the route of transmission and the susceptible population. The source of infection refers to people and animals whose pathogens grow and reproduce in the body and can spread pathogens. Transmission route refers to the route or various biological vectors by which pathogens leave the source of infection to reach others; Susceptible population refers to people who lack specific immunity to an infectious disease, so patients with infectious diseases belong to the source of infection
(2) Influenza is caused by influenza virus, which is mainly spread by droplets and air, and belongs to respiratory infectious diseases.
(3) In view of the three basic links in the epidemic of infectious diseases, the general measures to prevent infectious diseases can be divided into: controlling the source of infection, cutting off the route of transmission, and protecting susceptible people. Early detection, early diagnosis, early reporting, early isolation and early treatment should be done for patients with infectious diseases to prevent the spread of infectious diseases, which belongs to controlling the source of infection.
(4) After the vaccine enters the human body, lymphocytes will produce a special protein called antibody, which can help phagocytes destroy specific pathogens. This type of immunity only works on specific pathogens and belongs to specific immunity.
So the answer is: (1) the source of infection.
(2) Water drops and air
(3) control the source of infection
(4) antibodies; Specific immunity
What measures can be taken for the Double Eleven Online Shopping Festival? Because there are too many people buying goods at the time of double 1 1, many express delivery companies have exploded! So it affects the delivery speed of express delivery! You can appropriately increase the personnel of the courier company to help handle the express mail quickly!
I wish you a happy shopping!
Please accept it if you are satisfied!
thank you