Computer Network Overview Part One
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1. Rate-related performance indicators
1.1 Rate
Definition: The rate at which the host connected to the computer transmits the number of data bits on the digital channel.
Units: b/s, Kb/s, Mb/s, Tb/s. If it is expressed in bytes, it is B/s, KB/s, MB/s, TB/s. Note that 1Byte=1bit
1.2 Bandwidth
In computer networks, it refers to the highest speed supported by the network equipment. The unit is the same speed, which is the highest speed under ideal conditions.
1.3 Throughput
Refers to the total amount of data** passing through a network in a unit time.
2. Latency related indicators
2.1 What is delay
The delay includes four major types of delay, as shown in the figure:
| name | description | Calculation formula |
|---|---|---|
| Send delay | The time it takes for data to go from the host to the channel | Data length sent/send rate |
| Propagation delay | The time it takes for the data to travel on the channel | Channel length/speed of electromagnetic wave propagation on the channel |
| Queuing delay | The time the data waits for the previous data processing before the router | No calculation method |
| Processing delay | The data is in the router to deal with the demand time | No calculation method |
2.2 Delay bandwidth product
Formula: Delay Bandwidth Product = Propagation Delay * Bandwidth, which
means how many bits of data are on the link
2.3 Round-trip delay RTT
From the start of the sender sending the data, to the sender receiving the confirmation sent by the receiver
RTT = propagation delay * 2 + processing time (sometimes directly ignored)
2.4 Utilization rate
2.4.1 Channel utilization
Channel utilization = data passing time/(yes+no) data passing time
2.4.2 Network utilization
Network utilization = weighted average of all channel utilization
2.4.3 The relationship between delay and utilization
The higher the utilization, the greater the delay
3. Hierarchical structure
3.1 Why stratification and what to do with stratification
(1) The computer that initiates the communication must activate the data communication path.
(2) Tell the network how to identify the destination host.
(3) The computer that initiates the communication should find out whether the destination host is turned on and whether it is properly connected to the network.
(4) The computer that initiates the communication must figure out whether the file management program in the other party's computer has been prepared.
(5) Ensure that errors and accidents can be resolved.
3.2 Formally understand the hierarchy
4. Reference Model
| name | English | effect |
|---|---|---|
| Application layer | ApplicationLayer | Provide services directly for users' application processes (such as email, file transfer, and terminal emulation). Such as HTTP, SMTP, FTP, DNS |
| Presentation layer | PresentationLayer | Convert the data into a format compatible with the recipient's system and suitable for transmission, that is, the two systems can exchange information |
| Session layer | SeesionLayer | Responsible for setting up and maintaining the communication connection between two computers in the computer network during data transmission |
| Transport layer | TranssportLayer | Responsible for end-to-end communication, categories: reliable transmission, unreliable transmission, flow control, and sharing |
| Network layer | NetworkLayer | Responsible for selecting the best route for routing, planning IP addresses (ipv4 and ipv6 changes will only affect the network layer), congestion control |
| data link layer | Data Link Layer | The beginning and end of the frame, as well as transparent transmission and error checking (error correction is solved by the transport layer) |
| Physical layer | PhysicalLayer | Define the interface standard of network equipment, electrical standard (voltage), how to transmit faster on the physical link |
4.1 Introduction to OSI Process
At the network layer and above, each layer has to process the data sent by the previous layer (add a header). The
data link layer not only needs to add the header, but also the tail. The
physical layer does not add anything, and only the data occurs ( Bitstream)
4.2 TCP/IP Reference Model
4.3 Introduction to the five-layer reference model and its transmission process
Reference materials
2019 Wangdao Postgraduate Entrance Examination Computer Network .
Reference blog original address : https://blog.csdn.net/weixin_45067603/article/details/106974036