Network Knowledge that Weak Electricity Engineers Should Know

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vedard
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Joined: Wed Dec 05, 2018 12:27 am

Network Knowledge that Weak Electricity Engineers Should Know

Post by vedard » Tue Feb 26, 2019 12:11 pm

Basic Concept of Network
Client: Application C/S (Client/Server) B/S (Browser/Server)
Servers: Machines that provide services, data, and resources to clients
Request: Client requests data from server and clicks to download large quantities of engineering materials free of charge
Response: The server responds to client requests, usually returning data to the client
URL
Uniform Resource Locator
Every resource in the network corresponds to the unique address-URL
IP, Subnet Mask, Router, DNS
IP address:
IP address is a unified address format provided by IP protocol. It assigns a logical address to every network and host on the Internet to shield the difference between physical addresses (each machine has a code, such as something called MAC address on the MAC). It is 32-bit binary data, usually expressed in decimal system and separated by ".". IP address is a logical address that identifies a host in a network and is unique in a local area network.
IP
IP (Protocol of Interconnection between Networks) is a set of rules that enable all computer networks connected to the network to communicate with each other. It stipulates the rules that computers should abide by when communicating on the Internet. Any computer system manufactured by any manufacturer can be interconnected with the Internet as long as it complies with the IP protocol. IP address is Yi-only, that is, the IP address of each machine is Yi-only all over the world. This refers to the real IP on the network, which is calculated through the "and" operation of the local IP address and subnet mask and then through various processing (to comply with the TCP protocol and add messages and ports or something, I did not investigate in detail, now it is not available, anyway, temporarily know what has been processed on the line). By the way, we can teach you how to check their real IP:
Subnet mask
If you want to understand what a subnet mask is, you have to understand the composition of IP addresses. The Internet is made up of many small networks, each network has many hosts, thus constituting a hierarchical structure. In the design of IP address, considering the hierarchical characteristics of address allocation, each IP address is divided into two parts, network number and host number, so as to facilitate the addressing operation of IP address.
How many bits are the network number and the host number of the IP address? If you do not specify, you do not know which bit is the network number and which is the host number, which needs to be achieved through the subnet mask. What is a subnet mask Subnet mask can not exist alone, it must be used together with the IP address. Subnet mask has only one function, that is to divide an IP address into two parts: network address and host address. The setting of subnet mask must follow certain rules. Like IP addresses, the length of subnet mask is 32 bits. On the left is the network bit, which is represented by the binary digit "1". On the right is the host bit, which is represented by the binary digit "0". Suppose the IP address is 192.168.1.1 and the subnet mask is 255.255.255.0. Among them, "1" has 24 bits, 24 bits on the left of the corresponding IP address are the network number; 8 bits on the right of the corresponding IP address are the host number. In this way, the subnet mask determines which of the 32-bit binary digits of an IP address are the network number and which are the host number. This is very important for the network using TCP/IP protocol. Only through the subnet mask, can we show the relationship between the subnet of a host and other subnets, and make the network work normally.
There are hundreds of subnet masks in common use. Here only two of the most commonly used subnet masks are introduced.
Subnet mask is "255.255.255.0" network:
The last digit can vary arbitrarily from 0 to 255, so 256 IP addresses can be provided. But the actual number of IP addresses available is 256-2, or 254, because the host number can not be "0" or "1".
The server
1. Classification of servers
According to the software development stage, servers can be roughly divided into two types
(1) Remote Server
Alias: Extranet Server, Official Server
Use phase: Servers used after the application is online
Users: for all users
Speed: Server Performance, User Speed
(2) Local Server
Alias: Intranet Server, Test Server
Use phase: Application servers in development and testing phase
Users: For internal developers and testers only
Speed: Because it's a LAN, it's very fast, which helps to improve the efficiency of development and testing.
2. Selection of Local Server
Remote servers are local intranet servers that open access to the external network. If they are in the stage of learning and development, they can build a local server themselves.
Port number
Ports include physical and logical ports. Physical ports are used to connect physical devices, and logical ports are used to differentiate services logically. The ports in TCP/IP protocol are logical ports, which differentiate different services by different logical ports.
What's the use of ports? We know that a host with an IP address can provide many services, such as Web services, FTP services, SMTP services, and so on. These services can be fully implemented by an IP address. So, how does the host distinguish different network services? Obviously, we can't rely solely on IP addresses, because the relationship between IP addresses and network services is one-to-many. In fact, different services are distinguished by "IP address + port number".
1. Well-Known Ports
Such ports are also commonly referred to as "common ports". The port numbers of these ports range from 0 to 1023, and they are tightly bound to specific services. Usually the communication between these ports clearly indicates the protocol of a service, which can no longer be redefined as its object of action. Port 80 is actually always used for HTTP communications, while port 23 is dedicated to Telnet services.
2. Registered Ports
Port numbers range from 1025 to 49151. Allocate to user processes or applications. These processes are mainly applications that the user chooses to install, rather than commonly used programs with well-assigned recognized ports.
3. Dynamic and/or Private Ports
It is called dynamic port because it does not allocate a service in a fixed way, but in a dynamic way.
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