November 18, 2023
ForewordHello everyone, I'm Mr. Lin, maximum transmission distance of network cable, we usually talk about 100 meters, so the question is, how did these 100 meters come about? Text
Maximum network cable transmission distance
Friends who are familiar with network know that twisted pair has an "irresistible" transmission range of "100 meters". Whether it is Category 3 twisted pair with a transmission speed of 10m, Category 5 twisted pair with a transmission speed of 100m, or even Category 6 twisted pair with a transmission speed of 1000m, maximum effective transmission distance is 100 meters.
The integrated wiring specification also explicitly requires that horizontal wiring not exceed 90 meters and total connection length not exceed 100 meters. In other words, 100 meters is limit for wired Ethernet, and that limit is length of link from NIC to hub.
How did maximum distance of 100 meters come about?
What is upper limit of 100m twisted-pair transmission range?
It is necessary to delve into deep physical principle of twisted pair.
Network transmission is actually transmission of a network signal over twisted pair. Like an electronic signal, when it is transmitted over twisted pair, it must be affected by resistance and capacitance, which leads to attenuation of network signal and distortion.
Attenuation or distortion of signal reaches a certain level, which affects efficient and stable transmission of signal.
Therefore, twisted pair has a transmission range limit, so how do you calculate upper limit of 100 meters?
UTP Category 5 and UTP Category 5e mainly serve computer networks. According to 100Base-TX rules for Fast Ethernet, data rate is 100 Mbps, and time it takes 100 Mbps Ethernet to transfer 1 bit of data (also "bit time") can be calculated as follows:
1 bit = 1/100 Mbps = 10 ns
There is a delay in transmitting data across network as it passes through various components. The delay of five types of UTP is 5.56 ns/m. When designing Ethernet, you must follow relay rule, which is also called golden rule or 5-4-3-2-1 rule. This rule applies not only to 10-Mbit Ethernet, but also to Fast Ethernet.
This rule requires collision latency to be no greater than 512 bits and a bit rate of 100 Mbps, that is, 5120 ns. In a ring, network elements include cables, relay units, MAUs, and DTEs. Add their delays and multiply by 2 to get ring delay and calculate ring collision diameter.
According to this theory, it is possible to calculate maximum distance that a signal can be transmitted before minimum frame is sent. That is why length of communication line is limited to 100 meters.
When distance exceeds 100 meters, because collision cannot be detected in time, information packet damaged by collision is completely transmitted and received by recipient. This information packet is forcibly dropped because it cannot pass test. At this time, it will return and resend. The mechanism is not activated, so this will result in packet loss.
When transmission rate is below 100 Mbps, in practical applications, 100 meter length limit can be relaxed accordingly.
It should be noted that while this works, it is not up to standard. During certification test, this must be explained, otherwise some problems may arise, such as product quality assurance.
Maximum cable distance during actual construction
It can be seen from above that when using PoE for power, it is for some reason stipulated that maximum length of network cable should not exceed 100 meters. However, in real construction, 80-90 meters are usually taken to ensure quality of project.
Please note that transmission distance here refers to maximum speed, such as 100m. If speed is reduced to 10m, transmission distance can usually be increased to 150-200m (depending on quality of network cable). . Therefore, range of PoE power transmission is not determined by PoE technology, but by type and quality of network cable.
While in real life a higher quality network cable can break 100-meter limit and equipment can work normally, this approach is not recommended. Because some potential problems do not appear immediately, but slowly, over time, which will cause subsequent service problems. In simplest case, such as increasing throughput, equipment that can work well at a distance of more than 100 meters will not work properly after network speed improves significantly.
Influence of cable type and quality on transmission distance
Category 5:
Currently, it is most common standard network cable on market, but quality of different manufacturers varies greatly, especially in domestic price-oriented environment, many manufacturers use copper-clad iron for copper wires to reduce costs. The replacement of copper-clad steel leads to a reduction in transmission distance of network cable, and even network instability, packet loss and other phenomena, and equipment manufacturers often take blame, which is really wrong. Therefore, if you want PoE to play with maximum effect, you must use a quality network cable, and overall quality of project cannot be affected by small losses.
Category 5e (Cat 5e):
Compared with Category 5 twisted pair, Category 5e twisted pair has lower attenuation and crosstalk, which can provide a stronger network foundation and meet requirements of most applications (especially those that support 1000Base-T Gigabit Ethernet wiring), thus providing convenience of network installation and testing, and has become best solution in current network applications. The transmission characteristics of Category 5e cables are same as conventional Category 5 cables, but Category 5e wiring standard stipulates that all 4 pairs of Category 5e cables can provide full duplex communications.
Directory 6:
The transmission frequency of this type of cable is from 1 MHz to 250 MHz. At 200 MHz, Category 6 cabling must have more PS-ACR margin, which is twice capacity of Category 5e. The transmission characteristics of category 6 wires are much higher than those of category 5e standard and are most suitable for applications with transmission rates above 1 Gbps.
An important difference between Category 6 and Category 5 is this:
Improve performance in terms of crosstalk and return loss. For new generation of full-duplex, high-speed network applications, excellent return loss performance is critical. The basic connection model is canceled in six types of standards, and wiring standard uses star topology. Required wiring distance: length of a permanent connection cannot exceed 90 meters, and length of channel cannot exceed 100 meters.
There is no strict difference in transmission distance between a Category 6 link and a Category 5e link, i.e. maximum transmission distance of one segment is 100 meters. Of course, transmission range of a category 6 line can be extended accordingly. The so-called 100 meters means that after exceeding bandwidth of 1000m and other relevant technical indicators, it will not be able to meet relevant technical indicators, which will cause problems. onexample of a drop in speed.
