OSI Model-physical layer

1. Physical layer

Establish, maintain and disconnect physical connections, define interfaces and media, and realize bit stream transmission.

1 signal

(1) Information

(2) Data:

(3) Signal: the medium of information transmission

(4) Classification of signals:

Analog signal: A continuously changing physical quantity.

Digital signal: discontinuous physical quantity, signal parameters do not change continuously, high and low fixed.

(5) Noise and attenuation

(6) Advantages of digital signals:

strong anti-interference ability

Suitable for long-distance transmission and quality assurance

II. Interface

Ethernet interface: RJ-45 crystal head

Fiber optic interface: FC, ST, SC, LC narrow square fiber connector (current mainstream), MT-RJ

Three, twisted pair

1) Twisted pair classification:

Shielded Twisted Pair (STP)

The wire is coated with a metal film, which is used in industrial environments with very complex electromagnetic environments.

Unshielded twisted pair (UTP)

2) Twisted pair standards and classification:

Cat5 Category 5 twisted pair, 100MHz transmission frequency for 100Mbps networks

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

Cat 6 transmits at 200MHz

Cat 7 transmits at 600MHz

IV. Connection specifications for twisted pairs

1 line sequence

T568A: White green, green, white orange, blue, white blue, orange, white brown, brown

T568B: White orange, orange, white green, blue, white blue, green, white brown, brown

1, 2 send, 3, 6 receive

2 Cable connections:

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

Crossover: Used to connect the same devices (A-B)

Full reverse line: not used for Ethernet connection, mainly used for computer serial port and router or switch console (control port) connection, its line sequence is 1~8 at one end, 8~1 at the other end.

Special case: computers directly connected to routers with cross-wires switches connected to switches with cross-wires or direct wires generally with cross-wires

5. Optical fiber

Single-mode fiber: used for high speed, long distance; high cost; difficult termination; narrow core, requires laser source; low dissipation, high efficiency

multimode fiber: low speed, short distance; low cost; easy termination; wide core, laser or diode light source; high dissipation, low efficiency

VI. Physical layer equipment: network card, repeater, hub