Return to zero code RZ: high is 1, low is 0, and the intermediate jump returns to zero.

Non-return-to-zero encoding NRZ: high is 1, low is 0, and there is no return to zero in the middle

Inverse non-return to zero encoding NRZI: the signal does not change to 1 and changes to 0

Manchester encoding: high in front and low in back is 1, vice versa is 0

Differential Manchester coding: the symbol set interval does not change to 1, but changes to 0

ASK: change amplitude

FSK: change frequency

PSK: change phase

QAM: Combining ASK and PSK

Preamble: used for clock synchronization, 8 bytes, generally not included in the Ethernet MAC frame

Destination address: 6B, a MAC address

Source address: 6B, a MAC address

Type: 2B, protocol type number

Data: 46~1500B

FCS: Check code 4B, the check range is the destination address, source address, type field, data, no preamble

802.1Q frame: VLAN tag inserted between source address and type, used for virtual LAN

Frame control: 2B, where the going to AP bit, the coming from AP bit, MF (more fragments) are set to 1 if they are, otherwise they are set to 0

Duration: 2B channel reservation time

Address 1: 6B, receiving MAC address

Address 2: 6B, sending MAC address

Address 3: 6B, source address/destination address

Sequence number control: 2B, used for frame fragmentation

Address 4: 6B, used for ad hoc networks

Frame body: 0~2312B

FCS: 4B, the check range is similar to the 802.3 frame

Version: 4b, IP version

Header length: 4b, unit is 4B, usually 20B

Total length: 2B, unit is B, sum of header data lengths

Identification: uniquely identifies a group

Flag: 3b, the first digit is not used, the second digit DF (do not fragment) = 0 can only be fragmented, the third digit MF (more fragment) indicates that there will be fragments later

Fragment offset: 13b, the unit is 8B, indicating the relative position of the fragment in the original group

Time to live (TTL): 1B, literally, the router forwards the packet once, TTL-1; discarded when TTL=0

Protocol: 1B, the transport layer protocol corresponding to the packet

Header checksum: 2B, only the header is checked, regardless of the data part

Source address: 4B, an IP address

Destination address: 4B, an IP address

Source port: 2B, port number

Destination port: 2B, port number

UDP length: 2B, including header and data length, minimum 8B (header only)

UDP checksum: 2B, check the entire UDP datagram

Source port number and destination port number: 2B, one port number

Serial number: The number of the first byte of data sent this time

Confirmation number: Valid when ACK=1, the sequence number we hope the other party will send next time

Data offset: the header length, the unit is 4B, the same as the IP header length unit

Reserve: Reserve for later use

Urgent bit URG: high-priority transmission data, starting the emergency pointer (urgent data: from the first byte to the emergency pointer)

Confirmation bit ACK: startup confirmation number, used for the second and third handshake of TCP connection establishment, and the second, third and fourth handshake of releasing the connection

Push bit PSH: The message segment with PSH=1 is delivered directly instead of waiting for the cache to be full. It can be used to establish the third handshake of TCP.

Reset bit RST: Release connection in case of error

Synchronization bit SYN: establishing a connection, used for TCP to establish the first and second handshake

Abort bit FIN: Release the connection, used for TCP to release the first and third handshake

Window: receiving window size, unit is B

Checksum: The check range includes header, data, and pseudo header

Urgent pointer: Urgent data length

Options: can be MSS (maximum segment data length)

Padding: Make the header length an integral multiple of 4B