Shulou(Shulou.com)06/01 Report--

The network uses transmission media to connect isolated hosts together so that they can communicate with each other and complete the function of data transmission.

2.1 Cable transmission media

2.1.1 Cable signal

There are three kinds of electrical signals transmitted on the cable: analog signal, sine wave signal and digital signal.

. An analog signal is a continuously changing signal.

. Sine wave signal is a special analog signal.

. Digital signal is a kind of discrete signal with 0 and 1 variation.

The relationship between three kinds of signals: both analog signals and digital signals can be synthesized by a large number of sine waves of different frequencies.

The three kinds of signal relationships described in the above words can be described numerically as follows:

Y (t) = A0 + A1Sinw1t + A2Sinw2t + A3Sinw3t +... + AiSinwit +...

The meaning of the formula is that any signal y (t) is composed of harmonic wi of different frequencies.

2.1.2 Cable signal frequency

The frequency of harmonics: the harmonics of a signal y (t) are not infinite. When the frequency of harmonics increases to wi, the signal strength Ai of harmonics will be too small to ignore.

Not counting, the harmonic frequency wi and the maximum frequency of the harmonic is the harmonic frequency.

Band width (bandwidth, bandwidth): that is, the frequency range of signal harmonics [Wmin, Wmax], such as the bandwidth of sound is [20Hz, 20KHz].

The transmission of the cable is also limited by its own bandwidth, for example, the bandwidth of the ordinary telephone line cable is 2MHz, so if you want to transmit dozens of MHz

Word, it needs to be modulated into an analog signal and then transmitted.

Ordinary twisted pair cables have a bandwidth as high as 100MHz and can transmit digital signals directly.

Whether a signal can use a certain type of cable without distortion depends on whether the broadband of the cable is greater than the bandwidth of the signal.

The term bandwidth is used to describe not only the frequency characteristics of network cables, but also the communication speed of the network. Describe the cable frequency with KHz and MHz

Characteristics, using Kbps, Mbps to describe the communication speed.

2.1.3 unshielded twisted pair (UTP: Unshielded twisted-pair cable)

The transmission speed can reach 1000Mbps.

2.1.4 shielded twisted pair (STP: Shielded twisted-pair cable)

2.1.5 Frequency characteristics of twisted pair

Category 5 twisted pair (CAT 5): 100MHz

Super Category 5 twisted pair (CAT 5e): 100MHz

Category 6 twisted pair (CAT 6): 250MHz

Category 7 twisted pair (CAT 7): 600MHz

2.1.6 twisted pair termination

TD+

TD-

RD+

NC

NC

RD-

NC

NC

2.1.7 Test of twisted pair termination

At present, there are three popular international standards: ANSI/TIA/EIA-568 and ISO/IEC 11801 in the United States and EN 50173 in Europe.

Main test parameters of twisted pair cable and twisted pair cable placement and termination:

Linear sequence Wire map

Connect Connection

Cable length Cable length

DC resistance DC resistance

Impedance Impedance

Attenuated Attenuation

Near-end crosstalk Near-end crosstalk (NEXT)

Power and near-end crosstalk Power sum near-end crosstalk (PSNEXT)

Equivalent remote crosstalk Equal-level far-end crosstalk (ELFEXT)

Power and remote crosstalk Power sum equal-level near-end crosstalk (PSELFEXT)

Return loss Return loss

Conduction delay Propagation delay

Delay Delay skew

Portable cable testing instrument Fluke DSP-LIA013, which can test more than category 5 twisted pair cables.

2.2 Optical fiber transmission media

2.2.1

When using optical cable to transmit data, a photoelectric converter is used at the transmitting end to convert the electrical signal into an optical signal, which is transmitted to the optical cable, and is connected at the receiving end.

The receiver then restores the optical signal into an electrical signal.

The optical cable has two kinds of plastic cladding design: loose package and tight package.

2.2.2 the principle of optical fiber data transmission

Optical fiber transmission is based on the law of total reflection of optics.

Optical fibers include single-mode fiber (small diameter, almost no scattering, tens of kilometers) and multimode fiber (large diameter, scattering, 2 km).

2.3 Wireless transmission media

2.3.1 Frequency band used for wireless transmission

Radio waves and microwaves have a wide range of frequency choices. 2.4G microwave is dominant.

2.3.2 composition and equipment of wireless network

Wireless Local area Network (WLAN).

Wireless network card + wireless hub (wireless Hub).

At present, the average speed of popular WLAN is 10Mbps.

2.4 International Organization for Standardization

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.