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

Physical layer

1. Signal

1) Information

2) data

3) signal: the medium of information transmission

4) signal classification:

Analog signal: a continuously changing physical quantity.

Digital signal: discontinuous physical quantity, signal parameters are not continuous change, high and low fixed.

5) noise and attenuation

6) advantages of digital signals:

Strong anti-interference ability

Suitable for long-distance transmission and guarantee quality

2. Interface

Ethernet interface:

RJ-45 crystal head

Fiber interface:

FC 、 ST 、 SC

LC narrow-body square fiber connector (mainstream at present)

MT-RJ

3. Twisted pair

1) twisted pair classification:

Shielded twisted pair

Unshielded twisted pair

2) Standard and classification of twisted pair:

Cat5 category 5 twisted pair, transmission frequency is 100MHz, suitable for 100Mbps network

Cat 5e has less attenuation, less crosstalk and better performance than Category 5 lines (over Category 5)

4. Connection specification of twisted pair

1) Line order

T568A:

White green, green, white orange, blue, white blue, orange, white brown, brown (operation and maintenance will be)

T568B:

White orange, orange, white green, blue, white blue, green, white brown, brown (necessary for operation and maintenance)

1-line, 2-line transmission, 3-line, 6-line reception

2) connection of cables:

Standard network cable (straight-through or straight-through): used to connect different devices (A-mai A-mai B)

Crossover cable: used to connect the same device (Amurb An is T568A B is T568B)

Reverse line: the serial port of a computer is mainly connected to the console (control port) of a router or switch. its line sequence is 1: 8 at one end and 8: 1 at the other (that is, the opposite).

Special case

5. Physical layer equipment

Network cards, hubs, repeaters (the latter two are rarely used in enterprises, because most enterprises can use switches)

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