As early as 2006, Chuandong Cables used rubber-insulated home-applied wires to produce BXF, BLXF, and other cold- and aging-resistant wires, which replaced conventional rubber-insulated BX and BLX wires and stopped the production of BX, BLX, and other products.
At the end of 2008, due to the impact of the global financial crisis, the price of materials was lowered, and Chuandong Cable made reforms on home-improved electric wires again. It formally announced that it would stop the production of wires for ordinary home decorating, and instead fully manufacture environmentally friendly home decorating wires instead of ordinary wires. . At the same time, our company guarantees that prices will remain unchanged when product performance increases. This will not only open up new industry norms and avoid vicious competition, but also allow the technical content of the wire and cable industry to embark on a new level.
The story of Ethernet began in the ALOHA period. The exact time was after a student named Bob Metcalfe received a bachelor's degree from the Massachusetts Institute of Technology and moved to Harvard University across the river to pursue a PhD. During his studies, he came into contact with Abramson's work, and he was very interested in it. After graduating from Harvard, he decided to stay in Hawaii for vacation before going to Xerox Palo Alto Research Center to work in order to help Abramson work. When he arrived at the Palo Alto Research Center, he saw that researchers there had designed and built machines that would later be called personal computers, but these machines were solitary; he used the knowledge he gained to help Abramson work with his colleague David Boggs designed and implemented the first local area network. The local area network uses a long thick coaxial cable and runs at a rate of 3Mbps.
They named this system Ethernet, and people once thought that electromagnetic radiation could be transmitted through it.
Shared medium
The Carrier Sense Multiple Access (CSMA/CD) technology with collision detection specifies a method for multiple computers to share a channel. This technology first appeared in the ALOHAnet developed by the University of Hawaii in the 1960s, which uses radio waves as a carrier. This method is simpler than token ring network or main control network. When a computer wants to send information, it switches between the following actions and states:
Start-If the line is idle, start the transmission, otherwise skip to step 4.
Send-If a conflict is detected, continue to send data until the min echo receive interval is reached to ensure that all other transponders and terminals detect the conflict, and then skip to step 4.
Successful transmission-report to the higher-level network protocol that the transmission was successful, and exit the transmission mode.
Line is busy-keep waiting until the line is free.
Line is idle-before reaching the maximum number of attempts, go to step 1 to try again at random intervals.
Exceeded the maximum number of transmission attempts-report the transmission failure to the higher layer network protocol, and exit the transmission mode.
Because all communication signals are transmitted on the shared line, even if the information is only sent to one of the terminals (destination), it will be sent to all computers on the line in the form of broadcast. Under normal circumstances, the network interface card will filter out the information that is not sent to itself, and will send an interrupt request to the CPU when it receives the information whose destination address is its own, unless the network card is in Promiscuous mode. This "one talk, everyone listen" characteristic is the security weakness of the shared medium Ethernet, because a node on the Ethernet can choose whether to listen to all the information transmitted on the line. Sharing cables also means sharing bandwidth, so in some cases the speed of Ethernet may be very slow, such as after a power failure, when all network terminals are restarted.
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