Digital transmission using twisted pair cable applications and performance analysis

1. Overview   With the development of information society, Network Technologies become more complex, and as the cornerstone of the network, the keel?? Network cable is even more important. Currently used network, there are three main Cable Media: Cable , Coaxial cable And the number of twisted pair cables. This paper analyzes the largest number of applications of the twisted cable.

Data cable is a pair Integrated wiring The most commonly used engineering transmission medium. It consists of two layers with insulation Copper Wire form. The two insulated copper wires twisted together with each other by a certain density, which reduces signal interference level, every wire in the transmission of radiation of radio waves will be another online radio waves off the root. If one or more pairs of twisted pair on an insulating sleeve has become twisted pair cables. The current twisted pair cable into two categories: non-shielded twisted pair (UTP: UnshieldedTwisted Pair) and shielded twisted pair (STP: Shielded Twisted Pair).

LAN using twisted pair cables used bandwidth depends on the quality of wire, length and transmission technology. As long as carefully selected and installed, it can be achieved within a limited distance of a few million bits per second transfer rate and reliable. When the distance is short, and the use of appropriate transmission equipment and transmission protocol, transmission rate up to 100Mbit / s ~ 155Mbit / s, or even gigabit. Shielded twisted-pair cable of outer-foil package, to reduce the twisted pair transmission information generated by the surrounding radiation. Unshielded twisted pair cables become the mainstream, mainly because it is cost-effective, easy to install, and has the independence and flexibility for structured cabling.

2. Digital cable pair Main performance In ANSI and EIA/TIA568 standard and application-level physical characteristics according to the cable is divided into several categories. LAN applications, the current practice mainly five categories, over five and six as a data transmission on twisted pair cable. At present three types of cable is mainly used as a voice line.

Three types of cable transmission frequency is 16MHz, for voice transmission and a maximum transmission rate of 10Mbit / s data transmission, mainly for 10base-T; five cable routing density increases, a quality jacket insulating materials, transmission frequency of 100MHz, for voice transmission and data transmission, mainly for 100base-T Ethernet cable; super five and six cables to meet the emerging Gigabit Ethernet applications, the performance There are no perfect indicators of the final.

From the perspective of the actual network application, as the underlying network link, its electrical performance is very important. Performance analysis on the cable in two ways: one is Laboratory Test The method, which according to international standards and China’s relevant performance test on the cable applied normalized and environmental performance testing; the other is field-based performance testing, completion of construction in the premises cabling system to measure Assessment After laying cable routing performance overall.

Practice we are most concerned about is the characterization of the performance of several indicators:

(1) attenuation Attenuation (Attenuation) is a measure of signal loss along the link. Cable attenuation and length of relationship, with the increase in the length of the signal attenuation is also increased. Attenuation with the “db” for units that source the signal transmitter to the receiver signal strength ratio. Since attenuation varies with frequency, so the application should be measured within the entire frequency attenuation.

(2) crosstalk Crosstalk, near-end crosstalk and far-end crosstalk points (FEXT). NEXT loss is a measure of a UTP link from a pair of lines to another signal on the line coupling. The UTP link, NEXT is a key performance indicator, is also the most difficult to accurately measure a target. As signal frequency increases, the measure will increase the difficulty.

NEXT not imply that the crosstalk produced by the proximal point value, it simply means that the measuring point in the proximal to the crosstalk value. This value will change with different cable lengths, the longer the cable, and its value becomes smaller. While the transmitter signal will decay, on the other line on the crosstalk is relatively smaller.

(3) DC resistance DC loop resistance will consume part of the signal, and transform it into heat, which is a pair of wire resistance and the. ISO11801 specifications for twisted pair shall not be greater than the 19.2 ohm DC resistance. Differences between each pair can not be too large (less than 0.1 ohm), or that poor contact, you must check the connection point.

(4) characteristic impedance The characteristic impedance, including resistance and frequency 1 ~ 100MHz inductive impedance and capacitive impedance, with the distance between a pair of wires, and electrical properties of the insulator. All kinds of cables have different characteristic impedance, while the twisted-pair cable is 100 ohms, 120 ohms and 150 ohms are several.

(5) ACR (ACR) In some frequency range, the ratio of crosstalk and attenuation performance relationship is reflected in another important parameter cable. ACR sometimes signal to noise ratio (SNR: Signal-NoiceRatio) said it from the worst value of attenuation and NEXT margin calculation. ACR value is greater, indicating a stronger anti-interference ability. General system requires at least greater than 10 dB.

(6) Cable properties Communication channel cable quality is by its characterization. SNR is the signal interference, taking into account the circumstances, a measure of signal strength data. If the SNR is too low, will lead to the data signal is received, the receiver can not distinguish between data signal and noise signal, eventually causing data errors. Therefore, in order to limit data errors within a certain range, you must define a minimum to receive the SNR.

On these indicators tested in several different ways, the index slightly different requirements.

Performance index above are required according to the physical characteristics of cables, in real network applications, more people want to know what their transfer bandwidth should meet the requirements of what. In the cable analysis, the physical bandwidth of (0 ~ 100MHz) and Data Transfer bandwidth (0 ~ 100Mbit / s) are two totally different concepts. Shannon can be seen from the theorem of physical bandwidth and data transfer bandwidth
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