How many meters does the network cable transmit at most? Several common categories of network cable and network cable transmission

Source: Internet
Author: User

How many meters does the network cable transmit at most? Several common categories of network cable and network cable transmission

Maximum network cable data transmission distance

If you know more about the network, you know that the twisted pair wires have an insurmountable "100 meters" transmission distance. The maximum transmission distance is 100 meters, regardless of the three types of twisted pair wires with 10 m transmission rate, the five types of twisted pair wires with M transmission rate, or even the six types of twisted pair wires with M transmission rate. In the Generic Cabling specification, horizontal cabling cannot exceed 90 meters and the total link length cannot exceed 100 meters. That is to say, 100 meters is a limit for wired Ethernet, which is the link length from the NIC to the Collector line.

How is the maximum distance of 100 meters obtained? 

What causes the maximum transmission distance of twisted pair wires to 100 meters? This requires a deep understanding of the deep physical principle of twisted pair wires. Network Transmission is actually the transmission of network signals over twisted pair wires. As an electronic signal, when transmitted over twisted pair wires, it must be affected by the resistance and capacitance, this leads to network signal attenuation and distortion. Signal Attenuation or distortion to a certain extent will affect the effective and stable transmission of the signal. Therefore, twisted pair wires have transmission distance restrictions. How can we calculate the upper limit of 100 meters?

UTP category 5 and UTP Category 5 are mainly used for computer networks. According to the 100 BASE-TX specification of fast Ethernet, the communication rate is mbps, the time (also known as "bit time") used to transmit 1-bit data over 1/100 mbps Ethernet is calculated as follows: 1-bit time = mbps = 10ns

The Ethernet adopts CSMA/CD (CarrierSenseMultipleAccesswithCollisionDetection), that is, the Multi-Channel Access Technology (Multi-Point Access/collision detection for carrier monitoring) with conflict detection. After switching is introduced, this technology is still indispensable. A device is connected to both ends of a link. The two devices may send data at the same time, causing a conflict. In this case, the conflict domain is 2. If a conflict occurs, data packets are lost. To avoid packet loss caused by conflicts, the Ethernet adopts the conflict detection and rewind technologies. In order to back and resend, ensure that one end can detect a conflict before transmitting a packet. The minimum frame length of the Ethernet is 64 bytes, that is, 512 bits. Based on the 512 Mbps rate, it takes 512 bits * 10ns = 5120ns to transmit bits.

Data Information is transmitted over the network. When different components are used, the latency is 5.56ns/m. When designing Ethernet, a relay rule is required. This rule is also known as the gold rule or the 5-4-3-2-1 rule. This rule applies not only to 10 Mbps Ethernet, but also to Fast Ethernet. This rule requires that when the cycle conflict delay cannot exceed 512 bits, the transmission rate of Mbps is 5120ns. In the loop, the network components include cables, relay units, MAU and DTE, and their latencies are added up and multiplied by 2 to get the loop latency. At the same time, the diameter of the loop conflict can be calculated. Based on this theory, we can calculate the maximum distance that a signal can transmit before a minimum frame is sent. This is why the link span is limited to 100 meters.

When the length exceeds 100 meters, the information packet that is damaged due to the conflict cannot be detected in a timely manner is transmitted and received by the recipient. The packet is forced to be discarded because it cannot pass the verification, in this case, the mechanism for sending the resend is not activated, which may cause packet loss. When the transmission rate is lower than 100 Mbps, the limit of meters can be relaxed in practical applications. It must be declared that, although it is effective, it does not conform to the standards. During the certification test, it must be described. Otherwise, some problems may occur, such as product quality assurance.

Maximum cable distance during actual construction 

As can be seen above, why does the maximum length of the network cable not exceed 100 meters when PoE is used for power supply. But in actual construction, to ensure the quality of the project, generally take 80-90 meters.

Please note that the transmission distance here refers to the maximum rate, for example, 100 M. If the speed is reduced to 10 M, generally, the transmission distance can be extended to-meters (depending on the quality of the video network ). Therefore, the PoE power transmission distance is not determined by the PoE technology, but by the network cable category and quality.

Although in actual construction, the network cable with good quality can break the limit of 100 meters, and the equipment can work normally, this method is not recommended. Some potential problems do not appear immediately, but gradually occur over time, which may cause subsequent maintenance problems. In the simplest case, for example, bandwidth upgrade, the device that can work normally at a distance of more than 100 meters cannot work after the network speed is greatly improved.

Influence of cable category and quality on transmission distance

Cat5 is the most common standard network cable on the market, but the quality of production varies greatly from manufacturer to manufacturer, especially in the domestic price-oriented environment, in order to reduce costs, many manufacturers use copper clad iron and copper clad steel instead, resulting in a decline in the network cable transmission distance, and even the network instability, packet loss, and other phenomena, and equipment manufacturers often back to the black pot, it's really embarrassing.

Therefore, if you want to make PoE play the best effect, you must use a good quality network cable. This will not affect the overall quality of the project.

  • Cat5e: Compared with Cat5e, Cat5e has lower attenuation and Crosstalk, providing a more solid network foundation, to meet the requirements of most applications (especially supporting Gigabit Ethernet BASE-T cabling), it facilitates network installation and testing and has become a good solution for network applications. The transmission characteristics of cat5e cables are the same as those of common cat5e cables. However, according to the cat5e cabling standard, all the four pairs of cat5e cables can implement full-duplex communication.
  • Cat6: the transmission frequency of this type of cable is 1 MHz ~ 250 MHz, cat6 cabling system at MHz integrated attenuation crosstalk ratio (PS-ACR) should have a large margin, it provides 2 times the bandwidth of cat5e. The transmission performance of cat6 cabling is much higher than that of cat5e, which is most suitable for applications with a transmission rate higher than 1 Gbps.

An important difference between Category 6 and Category 5 is that it improves the performance in crosstalk and return loss. for a new generation of full-duplex high-speed network applications, the excellent return loss performance is very important. The basic link model is removed from Category 6 standards. The cabling standard adopts a star-shaped topology. The required cabling distance is: the permanent link length cannot exceed 90 meters, and the channel length cannot exceed 100 meters.

There is no strict difference between cat6 and cat5e, that is, the maximum transmission distance of a single segment is 100 meters. Of course, cat6 lines can be appropriately increased in terms of transmission distance. The so-called 100 m means that the system will not be able to meet technical indicators such as M bandwidth after exceeding the limit, resulting in problems such as speed reduction.

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