The first physical layer in the layer 7 of the third phase OSI

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)

Thank you