Why is the network cable interface RJ45 specification, but not USB type?

Author: The country's pregnant

Link: https://www.zhihu.com/question/23071966/answer/24638177

If it is said that the cable is not as light as USB? 

The network cable is very good, the transmission distance is 100 meters (USB is 5 meters), it is also considered plug and play, 8 lines (USB is 4) size and volume are basically the same, I think the design is very good. If the card slot on the network cable is inconvenient, the cable is not a device that is frequently plugged and unplugged. Who can change the cable? Mobile devices? Mobile devices have wifi. 8 lines, 100 meters transmission distance, 100Mbps-1000Mbps bandwidth, it is really not easy to do a little fine. 

If it is said that the USB protocol does not replace the network protocol? 

USB transmission distance is short, bandwidth is low, how long do you look at the 1Gbps network earlier than USB3.0? Seven types of lines can reach 10Gbps, and USB3.0 is only 5Gbps, so the speed is still not reached. Ethernet has fiber, USB does not. USB is a host-device mode, which is a non-peer-to-peer architecture. When the host is down, the devices cannot communicate with each other. Ethernet is a bus structure, and any node hanging does not affect the entire network. Such a good thing, how can USB be replaced? USB has an OTG, but I haven't seen a productized device that can automatically switch host-device locations without relinking. So USB wants to replace the network, and the road to go is still very long.

If it is a problem with the connector?

Regarding the quality of the crystal head, I added the contents of the comment. First of all, the appearance of the USB interface is very late. The earliest USB interface appeared in 1995. At this time, the standard of 100M Ethernet has already come out, USB The speed is only a little more than 1Mbps. Therefore, the crystal head as a relatively mature equipment at that time, generally will not easily change, we must know that changing the interface involves countless manufacturers, the resistance is very big. Moreover, changing the connector is not only a matter of the PC side, but also involves the entire Internet from access to the core, a line card like a core switch, a price of tens of thousands or even hundreds of thousands, and the cost of changing the mold is too large, so The needs of only PC users cannot completely change the status quo. USB is 4 wires (3.0 is 5), the transmission distance is 5 meters, the twisted pair (network cable) is 8 and the transmission distance is 100 meters. The electrical performance difference between the two is very large, and the twisted pair is Better shielding. This means that the cable itself can't be made too thin, so the crystal head can't be too small. Compare the ratio of the micro-A connector size to the USB cable size. Then look at the crystal head and the network cable. The difference in ratio is not Big, so it is difficult to make the crystal head smaller, and it will also affect the shielding. As far as ease of use is concerned, USB is really good, but have you ever wondered if the cable itself is a device that is frequently plugged and unplugged? I believe that many people have encountered accidents when the mobile phone being charged is accidentally unplugged. I believe that most people who plug in the network cable do not want their network cable to be accidentally pulled out, so the cable has the design of the bayonet. Moreover, wired devices are not designed for mobile design. Under the premise that wifi can meet the mobility, the transformation of the crystal head is not an urgent need. For the above reasons, the crystal head has remained.