Gigabit optical transceivers (also known as optoelectronic converters) are Fast Ethernet, with data transmission rates of up to 1 Gbps. They still use CSMA/CD access control mechanisms and are compatible with existing Ethernet networks with the support of cabling systems. , Can make the original fast Ethernet smooth upgrade and can fully protect the user's original investment. Gigabit network technology has become the technology of choice for new networks and retrofits, and the performance requirements for integrated cabling systems have also increased.
According to the Shannon Theorem, the relationship between channel bandwidth and channel capacity is:
C=Wlog2(1+S/N)(bps)................................(1)
Where C is the channel capacity, W is the channel width, N is the noise power, S is the signal power, and S/N is the signal-to-noise ratio.
From (1), it can be seen that the channel capacity can be increased by increasing the channel bandwidth and the SNR. The types of twisted pairs available to support high-speed network applications are Category 5, Category 5, and Category 6, with maximum bandwidths of 100 MHz, 100 MHz, and 200 MHz, respectively. Since Gigabit twisted pair cabling standard 802.3ab is based on the use of 4 to 5 UTP, the 5 UTP bandwidth is 1/100 MHz. Therefore, only from the bandwidth point of view, select Category 5 twisted pair to meet the requirements of Gigabit network applications.
Then consider from the perspective of signal to noise ratio. Gigabit networks need to use UTP's four pairs of cables for high-speed parallel data transmission. Signals and noise are related to the following characteristic parameters of the cables. These parameters are:
Attenuation: The attenuation of transmission along a link.
Return Loss (RL): The reflection of transmitted signal power due to the characteristic impedance of the cable and the link connector impedance deviating from the standard value.
Near End Crosstalk Loss (NEXT): Similar to noise, an interference signal that is transmitted from an adjacent pair of lines. This crosstalk signal is due to the proximity of pairs in the UTP coupled through capacitive or inductive coupling.
Adjacent line pair synthesis crosstalk (Powersum): Refers to the sum of the crosstalk between the working signal of the other three pairs of lines and the other pair of lines under the environment of using UTP four pairs of lines to transmit data simultaneously. Let the transmission signal be T. The above four characteristic parameters are denoted by A, R, NE, and P, respectively:
Singal(f)=f1(T,A).....................(2)
Noise(f)=f2(R,NE,P)........(3)
Equations (2) and (3) represent the received signal and noise, respectively, and the parameters A, R, NE, and P in both equations are functions of the frequency f. Therefore, the following two formulas for calculating SNR are obtained:
From these two formulas, it is known that to improve the signal-to-noise ratio, we must choose A, R, N, P and other parameters of good UTP to improve S, reduce N. The higher the category of UTP, the greater the margin of the above parameters from the standard limit values, and the better the performance. Since some of the parameters of Category 5 UTP are greatly influenced by the construction quality or the environment, the requirements of the wiring standards are often not met. The Category 5 UTP improves the above-mentioned defects of Type 5 UTP. Therefore, Ultra-Five and Six UTP can meet the requirements of SNR. Because the performance of Category 6 UTP is better than Super Category 5, and Category 6 UTP can also meet the needs of higher-speed network applications in the future, therefore, Category 6 UTP and its supporting plug-ins and plug-ins should be preferred in the current situation.
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