Day04 functional characteristics of computer network
The basic method of learning computer networks is to fully and deeply understand the functional characteristics of computer networks. That is, computer networks are How to provide an access path between two end users?
Here I simply draw a diagram for better understanding:
First, computer networks should be divided into source and target nodes. A transmission line is provided between them, and this transmission line may pass through some intermediate forwarding nodes.
In the case of long-distance networking, public communication lines provided by leased telecommunications companies are required, which may be tangible links on the ground or invisible satellite links in the atmosphere.
In addition, if the communication line provided by the telecommunications company is analog, the modem (cat) must also be used for signal changes, so the network should provide physical and electrical interfaces with the modem.
If the communication line is analog, then we need to use a modem to convert digital signals into analog signals for transmission.
An example: a phone call is transmitted through sound, and sound is an analog signal, but it can only be transmitted through digital signals in network communication. A modem is required to convert digital signals into analog signals for transmission over the telephone line.
Features of computer networks
When people are on the phone, information flows smoothly and continuously, and the rate is not too high. Communication between computers is not like this. When the user is still thinking about the content using the terminal, no information flows through the line at this time. When the user starts to issue a file transfer command, the data that comes in suddenly needs to be sent quickly, and then it starts to wait for a new transfer command.
Therefore, the communication link between the computers should have a higher bandwidth, and at the same time, the high-speed lines should be shared by the nodes that need them, so as to obtain a reasonable and economical use efficiency.
computer network features.
Designers of computer networks have invented some new switching technologies to meet these special switching communication requirements, such as “message switching” and “packet switching” technologies. Therefore, one of the functions of the computer network is to group the transmitted information flow, add control information, and deliver the packets correctly to the destination.
The role of control information
Control information is used for “error control” and is used by the receiving end to verify whether the information stream has been received correctly;
The control information is also “address information,” which refers to the address information of the sender and receiver of the data packet.
Therefore, the computer network must have error control and addressing functions.
Grouping and Multiplexing
Messages transmitted over a computer network can be large or small. For example, high-quality photos may have a large number of messages and consume a lot of network resources. Delivering a large photo in a continuous stream may mean that if a device loses an important update, it will need to be resent, also using more bandwidth.
Information into small pieces (packets) that can be more easily transmitted together across the medium.
It enhances the communication efficiency of the network.
What is multiplexing?
Multiplexing refers to when multiple packets can merge with each other and share a shared medium.
As shown in the figure:
The diagram above shows how a message can be split into small pieces and multiplexed on a single medium.
What happens when multiple end nodes want to send packets at the same time?
Therefore, our network must also include some “arbitration process” to decide which end node sends first and who sends last. The arbitration process here is equivalent to the multiplexing process. The function of all these data packets with control information being correctly forwarded from node to node in the network is the “Data Link Control (DLC) function.”
computer network architecture.
Use the way of writing to help you understand the characteristics of computer network architecture:
The whole communication process is carried out in layers. The
The postal letter communication process can be divided into three layers: user, post office, and transshipment. Each layer only knows what it should do, regardless of what other layers do.
The communication protocol is the protocol between the corresponding layers. The
The communication protocol (rules, conventions—the format of writing letters can be understood here) in the whole communication process is also layered, and each layer has its own communication protocol.
There are only simple interface relationships between layers. There are only simple interface relationships between the layers.
in the postal letter communication process.
From this, we can draw the characteristics of computer network architecture:
Divide a computer network system into several functional levels.
used within each layer-up communication protocol. Complete intra-layer communication
by means of the layersinterfacerelationship service
Each layer can use the most appropriate technology to achieve changes within each layer. It does not affect other layers.
With this chapter’s understanding, we can move on to the next chapter and learn about layered models and computer network protocols. on!