Maximum distance of network cable data transmission
When doing weak current projects, we all know that industrial Ethernet cables have an "insurmountable" transmission distance of "100 meters". Whether a CAT3 twisted pair with a transmission rate of 10M, a CAT5 twisted pair with a transmission rate of 100M, or even a Category 6 twisted pair with a transmission rate of 1000M, the longest effective transmission distance is 100 meters.
In the comprehensive cabling specifications, it is also clearly required that horizontal cabling cannot exceed 90 meters and the total link length cannot exceed 100 meters. In other words, 100 meters is the limit for wired Ethernet. This limit is the link length from the network card to the hub device.
How is the maximum distance of 100 meters obtained?
What causes the upper limit of the 100-meter transmission distance of twisted-pair cables? Network transmission is the transmission of network signals on twisted-pair wires. As an electronic signal, resistance and capacitance are bound to be affected when transmitted in twisted-pair cables—influence, which leads to attenuation and distortion of network signals. When the signal attenuation or distortion reaches a certain level, it will affect the effective and stable transmission of the signal. Therefore, twisted pair cables have transmission distance limitations.
So, how do you calculate the upper limit of 100 meters?
Cat5 UTP and Category 5e UTP mainly serve computer networks. According to the 100Base-TX regulations of Fast Ethernet, the communication rate is 100mbps. The time it takes for 100mbps Ethernet to transmit 1 bit of data (also known as "bit time" ) can be calculated as follows:
1 bit time=1/100mbps=10ns
Ethernet uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection) and carrier sense multiple access technology with conflict detection to share communication channels. When switching is introduced, it is still separated. Do not use this technology.
When the distance exceeds 100 meters, because the conflict cannot be detected in time, the information packet is damaged due to the conflict and transmitted and received by the receiver. The information packet is forced to be discarded because it fails the verification. At this time, the back-off and re-transmission mechanism is not available. It is activated so that it will be lost. When the transmission rate is lower than 100 Mbps, the 100-meter length limit can be appropriately relaxed in practical applications. It must be stated that although this is actually effective, it does not meet the standards. During the certification test, it must be explained that some problems, such as product warranty, may arise.
Maximum cable distance during actual construction
As seen from the above, during weak current construction, why is it stipulated that the maximum length of the network cable shall not exceed 100 meters? However, during actual construction, to ensure the quality of the project, it is generally 80-90 meters.
Please note that the transmission distance here refers to the maximum rate, such as 100M. If the rate is reduced to 10M, the transmission distance can usually be extended to 150-200 meters (depending on the quality of the network cable). Therefore, the PoE power supply transmission distance is not determined by PoE technology, but by the type and quality of the network cable.
In actual construction, better-quality network cables can break through the 100-meter distance limit and usually allow the equipment to work. However, this approach has potential problems that will not appear immediately but will appear slowly over time. It will cause subsequent maintenance problems. The most straightforward situation is that after the bandwidth is upgraded, the equipment that can usually work at a distance of more than 100 meters cannot work correctly after the network speed is increased.
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