Since October, the municipal square opposite the Huiyang District Government has begun to build two LED TVs worth 5 million. At present, LED TVs are in the debugging stage, while some netizens think that these 5 million are worthless, so it is better to use them for infrastructure. The district government responded that the 5 million yuan is paid by the provincial telecommunications company and does not require the government to spend money. The District Telecommunications Bureau said that LED TVs are designed to disseminate information.
Recently, a post titled "5 Million Building LED TVs Is Better Than Building Infrastructure" appeared on the West Lake Forum. Posting netizen "Guangdong Pearl" said in the post that at present, many alleys in Huiyang Danshui City are still silt roads, and there are no street lights, there are security risks, so it is not worth spending 5 million to build LED TVs. In the case of more infrastructure construction, for example, turning the silt roads with the most complaints from the public into cement roads, installing street lights with no street lights in the alleys, and installing black and white surveillance cameras to reduce the incidence of theft and robbery. He believes that this is done well, and the citizens promise to cheer the government in unison.
The post attracted a lot of replies to support, some netizens also questioned the cost of LED TV, that the price is too high.
Yesterday morning, the author came to the Municipal Square to see that two huge LED TVs stood proudly and have not been opened for use. The management of the municipal square said that the two LED TVs are still in the debugging stage and will be used normally in the near future.
Subsequently, the author came to the two committees of the Huiyang District Government responsible for the project. The relevant person in charge told the author that the two LED TVs were invested and built by China Telecom Guangdong Telecom. "They were built according to due process. Because the funds are not issued by the district government, it is not convenient to make any evaluation." The person in charge said.
The relevant person in charge of the Huiyang Telecom Bureau said that in order to shape the image of the modern digital “Huiyang†city and enhance the cultural taste, the electronic display of the municipal square invested by China Telecom Huiyang Branch with an investment of more than 5 million yuan was approved on December 18. Will be fully operational. "We will regularly broadcast Huiyang to relevant government information, economic information, Huiyang news, advertising, broadcast central, city, TV news programs, important events and sports events. We will provide real-time broadcasts of large-scale conferences and large-scale evening events as needed. Said the person in charge.
Classic Ethernet uses a long cable meandering around the building, and this cable connects all the computers. The architecture of classic Ethernet is shown in the following figure "Ethernet":
Physical layer
Each version of Ethernet has a maximum cable length limit (that is, the length that does not need to be amplified). Signals within this range can be transmitted normally, and signals beyond this range will not be transmitted. In order to allow the construction of a larger network, multiple cables can be connected with repeaters. A repeater is a physical layer device that can receive, amplify, and retransmit signals in both directions.
On these cables, the transmission of information uses Manchester encoding.
MAC sublayer
Classic Ethernet uses 1-adhere to the CSMA/CD algorithm, that is, when the station has a frame to send, it must listen to the medium, and send it immediately once the medium becomes free. Monitor whether there are conflicts on the channel while they are being sent. If there is a conflict, immediately terminate the transmission, and send a short conflict enhancement signal, and then wait for a random period of time before resending.
The development of Ethernet is very fast, starting to evolve from the typical Ethernet structure of a single long cable. The problems of a single cable, such as finding out the connection-related problems such as broken or loose locations, have driven people to develop a different type of wiring mode. In this mode, each station has a dedicated wire connected to a central hub. The hub simply connects all the connecting wires electrically, like soldering them together. Hubs cannot increase capacity because they are logically equivalent to classic Ethernet with a single cable. As more and more stations join, the share of fixed capacity shared by each station decreases. Eventually, the LAN will be saturated.
There is another way out to handle the ever-increasing load: switched Ethernet. The core of switched Ethernet is a switch, which contains a high-speed backplane that connects all ports. From the outside, switches look like hubs. They are a box, usually with 4-48 ports, and each port has a standard RJ-45 connector for connecting twisted-pair cables. The switch only outputs the frame to the port where the frame wants to go. A machine can be added or deleted by simply plugging in or unplugging the cable, and since the flaky cable or port usually only affects one machine, most errors are easy to find. This configuration mode still has the problem of a shared component failure, that is, the failure of the switch itself: if all stations lose network connectivity, the IT staff knows how to solve this problem: replace the entire switch.
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