- Computer Network Overview
Computer network definition : A collection of autonomous computer interconnections
Basic functions of computer network
Resource Sharing
Comprehensive information services
Distributed processing and load balancing
Types of computer networks
local area network
LAN（Local Area Network)
A network built by users themselves and using private addresses
metropolitan area network
MAN(Metropolitan Area Network)
Built by operators or large-scale enterprises to connect city-wide networks
Wan
WAN(wide Area Network)
A network built by operators to connect various metropolitan area networks across the country
Also known as backbone network (metropolitan area network connected to various cities), core network, and transmission network
The central office (the operator's router) interconnects all current users of the same operator. The metropolitan area network is generally a ring network buried with underground optical cables.
Network topology
definition
How network device connections are arranged
Classification
bus topology
All devices share a common line
A line outage will cause all devices to interrupt communication
ring topology
All devices share a ring bus
There is some redundancy
star topology
Failure of the central node will cause the entire network to be disrupted
All other nodes are directly connected to the central node
The interruption of a certain line will not affect other nodes
tree topology
Further divergence of star topology
• advantage
Simple structure and low networking cost
Easy maintenance and management
• shortcoming
The central node is under great pressure: there is only one line between any two points. Once there is a problem with the line, the two cannot communicate, there is no backup, and there is no effective way to deal with physical network failures.
Poor reliability
mesh topology
There are multiple lines between nodes that can be reached
• advantage
High reliability. If one of the lines hangs up, it will not affect network transmission. There is line backup.
• shortcoming
High networking cost
Complex maintenance and management
Metrics for measuring network performance
bandwidth
definition
The total amount of data that can be transmitted per unit time
Unit: bps (bit per second)
The greater the bandwidth, the better the network quality
Delay
definition
The time it takes for data to travel from one node to another
Unit: ms
The lower the latency, the better the network quality
data unit
1Kb=1024b
1Mb=1024Kb
1Gb=1024Mb
Byte
Bytes, a number or letter occupies 1 byte, a Chinese character occupies 2 bytes
bit
Bit, 1Byte=8bit
protocols and standards
protocol
Communication rules observed by both parties in data communication
standard
Recognized, agreement rules that all manufacturers abide by
standardization organization
A group of organizations that defines internationally recognized reference standards.
Common International Standards Organizations
I SO • International Organization for Standardization
IEEE •Institute of Electrical and Electronic Engineers