1. Local area network
Local area network, abbreviated as LAN, refers to a group of computers interconnected by multiple computers in a certain area, using broadcast channels.
The local area network has the following four topological structures:
Transmission medium:
Wired LAN commonly used: twisted pair, coaxial cable, optical fiber
Commonly used in wireless LAN: electromagnetic waves
Local area network classification:
2. MAC sublayer and LLC sublayer
The IEEE 802 standard divides the data link layer into logical link layer LLC and medium access control layer MAC.
Three, Ethernet
Ethernet is a baseband bus local area network specification, which uses the CSMA/CD protocol.
Features:
Provide connectionless and unreliable services.
No connection: There is no "handshake process" between the sender and the receiver.
Unreliable: The sender’s data is not numbered, and the receiver does not confirm to the sender. Error frames are directly discarded, and the higher layer is responsible for error correction.
Ethernet only realizes error-free reception and does not realize reliable transmission.
The topological structure of Ethernet is: logically bus type, physically star type.
Use: twisted pair + hub.
Fourth, the network adapter
Also known as network card, network interface board.
The connection between the computer and the external LAN is realized through a network interface board inserted in the main box.
There are:
Memory, processor.
Each network card has a unique code, called MAC address, also called physical address. (Media access control address)
This address is used to control the data communication of the host on the network.
There is a 48-bit binary address: the first 24 bits represent the manufacturer and are specified by IEEE;
The last 24 bits are specified by the manufacturer.
It is usually represented by 6 two-digit hexadecimal numbers, such as 02-60-8c-e4-b1-21.
One hexadecimal number occupies four digits,
6*2*4 = 48.
There are two standards for Ethernet MAC frames:
DIX Ethernet V2 standard and IEEE 802.3 standard.
Strictly speaking, Ethernet should be a local area network conforming to the DIX Ethernet V2 standard.
However, due to the small difference between the DIX Ethernet V2 standard and the IEEE 802.3 standard,
Therefore, the IEEE 802.3 local area network is usually called Ethernet.
Frames in V2 format:
64B is the minimum frame length of the Ethernet.
Five, high-speed Ethernet
Ethernet with a rate greater than 100MB/s.
6. Wireless LAN and IEEE 802.11
IEEE 802.11 is a universal standard for wireless local area networks.
WLAN has a much wider range than WiFi,
Among them, WiFi is an application of WLAN.
Because the medium is electromagnetic waves, the CSMA/CA protocol is adopted.
This is why the wireless network is slower than the wired network.
802.11 MAC frame header:
Wireless LAN is divided into:
Wireless local area network with fixed infrastructure
Contains service access point AP,
Can be connected to a backbone distribution system through an access point,
Then access another basic service set,
Form an extended service set.
Self-organizing network of wireless local area network without fixed infrastructure
No service access point,
Each node has its own router function, and each is an intermediate node (forwarding node).