Summary: Android Xiaobai's Growth Path_Knowledge System Summary【Continuously updated...】
Table of contents
internet composition
From the perspective of working methods, the Internet can be divided into two parts:
- Edge part: composed of all hosts connected to the Internet, this part is directly used by users for communication (data transmission, audio and video) and resource sharing
- Core part: Consists of a large number of networks and routers connecting these networks, this part serves the edge part (provides connectivity and switching)
Computer Network Category
- Classified according to the scope of the network:
- Wide area network (WAN): The scope of the wide area network is usually tens to thousands of kilometers, sometimes called the remote network, which is the core part of the Internet, and its task is to transport the data sent by the host through long distances
- Metropolitan Area Network (MAN): The scope of the MAN is generally a city, which can span several blocks or even several cities, and its operating distance is about 5-50km. A metropolitan area network can be owned by one or several units, but it can also be a public facility used to interconnect multiple LANs. At present, many metropolitan area networks use Ethernet technology
- Local area network (LAN): The local area network is generally connected by a microcomputer or a workstation through a high-speed communication line, and the range is small at about 1km
- Personal Area Network (PAN): A personal area network is a network that connects electronic devices used by individuals with wireless technology in the place where individuals work, also known as a wireless personal area network.
- By network users:
- Public network: Refers to the large-scale network funded and built by the telecommunications company, which can be used by all who are willing to pay fees in accordance with the telecommunications company's regulations
- Private network: a network built by a certain department to meet the needs of the special business work of the unit, and this network does not provide services to people outside the unit
computer network performance
Performance indicators measure the performance of computer networks from different aspects. There are seven commonly used performance indicators:
- rate
- Bit: A bit is the unit of information used in information theory, and a bit is a 1 or 0 in a binary number
- Rate: Refers to the data transmission rate, also known as data rate or bit rate, the unit is bit/s or bs/bps
- bandwidth
- In a computer network, bandwidth is used to indicate the ability of a certain channel in the network to transmit data, so the network bandwidth indicates the highest data rate that a certain channel in the network can pass within a unit of time. The unit of bandwidth in this sense is the unit of data rate bit/s
- throughput
- Indicates the actual amount of data passing through a certain network per unit of time. Throughput is often used as a measure of the network in the real world in order to know how much data can actually pass through the network. Bandwidth is the upper limit of throughput. value, generally the throughput is less than the bandwidth
- Latency: Refers to the time it takes for data to travel from one end of the network to the other
- Send delay: the time required for a host or router to send a data frame
Send delay = data frame length (bit) send rate (bit / s) send delay = \frac {data frame length (bit)}{send rate (bit/s)}send delay=Send rate ( b i t / s )Data frame length ( b i t )
- Propagation delay: the time it takes for an electromagnetic wave to travel a certain distance in a channel
Propagation delay = channel length ( m ) propagation rate of electromagnetic waves on the channel ( m / s ) propagation delay = \frac {channel length (m)} {propagation rate of electromagnetic waves on the channel (m/s)}propagation delay=The propagation speed of electromagnetic waves on the channel ( m / s )Channel length ( m ) _
- Processing delay: It takes a certain amount of time for the host or router to process the packet data when it is received
- Queuing delay: When a packet is transmitted through the network, it has to pass through many routers, but after entering the router, the packet needs to be queued in the input queue for processing, and after the router determines the forwarding interface, it needs to be queued in the output queue for forwarding
- Total latency:
Total Delay = Send Delay + Propagation Delay + Processing Delay + Queuing Delay Total Delay = Send Delay + Propagation Delay + Processing Delay + Queuing Delaytotal delay=send delay+propagation delay+processing delay+queuing delay
- Delay Bandwidth Product: link length in bits
Delay-Bandwidth Product = Propagation Delay × Bandwidth Delay-Bandwidth Product = Propagation Delay\times Bandwidthdelay bandwidth product=propagation delay×bandwidth
- Round-trip time RTT: Most of the information on the Internet is two-way interaction, sometimes it is very necessary until the time required for two-way interaction once
- Utilization: There are two types of channel utilization and network utilization
- Channel utilization: refers to the percentage of time that a channel has data passing through
- Network utilization: the weighted average of the channel utilization of the entire network
- Excessive utilization will cause a very large delay, so if the utilization exceeds a certain level, the bandwidth of the line should be increased
computer network architecture
- Application layer: complete specific network applications through the interaction between application processes. Different application layer protocols are required for different network applications, such as domain name system DNS, World Wide Web HTTP protocol, SMTP protocol of email, etc. Usually, the data exchanged by the application layer message
- Transport layer: Responsible for providing general data transmission services for communication between two host processes. There are two main protocols in the transport layer:
- TCP: Transmission Control Protocol, which provides connection-oriented and reliable data transmission services, and its data transmission unit is a segment
- UDP: User Data Protocol, which provides connectionless, best-effort data transmission services, does not guarantee data reliability, and its data transmission unit is user datagram
- Network layer: Responsible for providing communication services for different hosts on the packet switching network. When sending data, the network layer encapsulates the segment or user datagram generated by the transport layer into packets or transmits them. The network layer uses the IP protocol, so the packets are also Called an IP datagram or simply a datagram. The network layer selects an appropriate route so that the data transmitted by the source host's transport layer can find the destination host through the routers in the network
- Data link layer: When data is transmitted between two adjacent nodes, the data link layer assembles the IP datagram called from the network layer into a frame, and transmits the frame on the link between two adjacent nodes. A frame includes data and necessary control information (such as synchronization information, address information, error control, etc.)
- Physical layer: The unit of data transmitted on the physical layer is a bit. The physical layer needs to determine how much voltage represents "1" or "0", and how the receiver recognizes the bit sent by the sender. It is also necessary to determine whether the plug of the connecting cable should be How many pins there are and how each pin should be connected.