The Internet has become an inseparable part of people's daily lives. People often use mobile phones, computers and other communication devices for online communication, videos, watching movies, and playing games. . .
But do you know how data is transmitted in this communication process, and what is the network principle?
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The content of this chapter is purely personal understanding, easy to understand, and the overall summary content, because network knowledge is really endless. Good place, please also Haihan, I will improve later.
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To understand how data is communicated, first you have to know what the data is communicating on the network?
In fact, these data are a string of binary codes. People have human languages, and computers have computer languages. This kind of binary (Binary number) code is basically incomprehensible when viewed by humans. If people want to understand it, they need to perform some number system conversion, which can be converted into Octal and Decimal number. , Hexadecimal (Hexaclecimal number).
Communication between communication devices must require an accurate address, that is, an IP address. Just like sending a courier, the courier number, address information, and phone number of the sender and consignee are the same. When it comes to IP addresses, you have to talk about the OSI (Open System Interconnection) seven-layer architecture. What is the OSI seven-layer architecture?
The OSI seven-layer architecture actually divides the process of data communication in the network into seven layers, so that it is convenient for managers to accurately find and troubleshoot problems, and it is also convenient for people to understand the transmission process.
OSI seven-layer architecture:
the layer where the data is located; the function of this layer; the equipment represented by each layer.
Application layer: an interface between network services and end users; computer
presentation layer: data presentation, security, and management
Session layer: data establishment and management , Termination of the session
Transport layer: define the protocol port number for data transmission, as well as flow control and error checking; firewall
network layer: perform logical address addressing, select the best path for
data between different networks; router data link layer: data link Establishment, maintenance, removal, etc.; switch
physical layer: physical connection, disconnection (plugging);
Data is called upper layer data at the application layer; data segment at the transport layer; data packet at the network layer; data frame at the data link layer; bit stream at the physical layer.
Each computer mentioned before has its own IP address, subnet mask and gateway.
The IP address is the precise address of this computer; the
subnet mask is used to determine the network segment where the IP address is located. The
gateway is a checkpoint used by this computer to forward data, and all data to be forwarded between different networks Gateway lost
After the data is sent from this computer, it passes through the application layer, presentation layer, session layer, transport layer, network layer, data link layer and physical layer for a complete package and then transmits it to the target computer's network; The data will go through the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, application layer (layer seven inversion) for data decapsulation (unpacking) and send the data that the sender wants to send to the receiver Transmit to the other party's computer (the other party's computer will reply a prompt or message to the sender's computer a message of information received) This completes a data transmission.
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Introduction to the data link layer:
the role of the data link layer includes the data link The establishment, maintenance and removal of frames, frame packaging, frame transmission, frame synchronization, frame error control and flow control, etc.
Ethernet works at the data link layer.
In communication, the address used to identify the host is a hardware address made on the network card. After each network card is made, it has a globally unique number to identify itself. This address is the MAC address, that is, the physical address of the network card. The first 24 digits are the supplier's identification, and the last 24 digits are the supplier's unique code for the network card. .
When the eighth bit of the MAC address is 0, it indicates that the MAC address is a unicast address; when it is 1, it indicates that the MAC address is a multicast address.
The address of a physical network card must be a unicast address, that is, the eighth bit must be 0; a multicast address is a logical address used to indicate a group of receivers instead of a receiver.
Ethernet has a variety of frame formats. The most common Ethernet II frame format:
frame format: consists of (7 bytes) preamble, (1 byte) frame start delimiter, (6 bytes) destination address, ( 6 bytes) source address, (2 bytes) type, (46-1500 bytes) data, (4 bytes) frame validation sequence.
The Ethernet starts with a preamble and ends with a 32-bit redundancy check code.
The best representative for working in Ethernet is the switch. To understand the switch, you must first know the working principle of the switch:
1. Learning based on the source MAC address;
2. If the target MAC address is not found, the entire network will be displayed for unknown data frames. ;
3, Van Horn response message recipient, the message is discarded and other hosts;
4, switch to learn the destination MAC address, its MAC address in the MAC address table;
5, to achieve both the unicast communication.
(The switch will not always store the learned MAC address in the MAC address table, and there will be an aging time of 300s.) The
switch has an Ethernet interface divided into working modes:
simplex: only a single line between two secretary stations Direction of data transmission
Half duplex: Two data stations can transmit data in both directions, but not at the same time.
Full duplex: Two data stations can transmit data in both directions and simultaneously
Ethernet interface rate: negotiated; if two interfaces that follow different rate standards are connected, the communication rate of the two parties is determined by the lower rate of the two parties.
Port aggregation (implemented at the data link layer)
Port aggregation aggregates multiple ports together to form an aggregation group, so as to realize the sharing of outbound/inbound load among various members.
The advantages of port aggregation:
increase link bandwidth; traffic load sharing; improve reliability.
Restrictions on
port aggregation : The physical parameters at both ends of the port aggregation must be consistent:
the number of links being aggregated; the link rate for aggregation; the duplex mode of the link being
aggregated. The logical parameters at both ends of the port aggregation must be consistent:
The basic configuration of the ports in the same aggregation group must be consistent. The basic configuration mainly includes STP, Qos, VLAN, port and other related configurations.
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Introduction to the network layer: The
network layer is responsible for defining the path through which data flows through the network. Its main functions are summarized as follows:
define the logical address based on the IP protocol;
select the best path for data to pass through the network;
connect different media types;
ICMP protocol:
As a network administrator, you must know the connection status between network devices. Therefore, a mechanism is needed to detect or notify the various sub-conditions that may occur between network devices. This is the function of ICMP.
The full name of the ICMP protocol is the Internet Control Message Protocol.
It is an "error detection and feedback mechanism"
encapsulated by ip data packets
to send error and control messages.
Protocol port number: No. 1; consists of two protocols, ping and traceroute.
The main function of the IP protocol is the
ip data packet format realized by the encapsulation and decapsulation of ip data packets:
version (4 bits) header length (4 bits) priority and service type (8 bits) total length (16 bits)
identifier (16 bits) mark (3 bits) segment offset (13 bits)
TTL (8 bits) protocol number (8 bits) header verification number (16 bits)
source address (32 bits)
destination address (32 bits)
Optional: Variable length
data according to actual situation
ARP protocol:
ARP: Address Resolution Protocol; resolve a known IP address into a MAC address
. The working principle of ARP: The
sender sends data to the receiver, and it will check whether the cache has the receiver's MAC address; if there is no MAC address, it will The entire network sends ARP broadcasts; all hosts receive the ARP request message, the receiver replies with the ARP response, and other hosts discard the message; the sender stores the receiver's MAC address in the cache table for communication.
RARP protocol is the opposite of ARP protocol, which resolves a known MAC address into an IP address
Representative routers working at the network layer:
What is routing: the forwarding process from the source host to the destination host
What is a router: a device that can forward data packets to the correct destination and select the best path in the forwarding process.
The formation of the routing table:
Directly connected network segment: Configure IP address, port up state, form a directly connected route
Non-directly connected network segment: For non-directly connected network segments, static routing or dynamic routing is required to add the network segment to the routing table .
Static routing: manually configured by the administrator, which is one-way; lacks flexibility.
Default route: When the router cannot find the route entry of the target network in the routing table, the router forwards the request to the default route interface. (The default route is a special method of static routing)
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Introduction to the transmission layer:
transmission The layer defines the protocol port number for data transmission, as well as flow control and error validation. The
transport layer protocols include: TCP protocol, UDP protocol
TCP protocol number and function:
protocol number: 21; FTP protocol; FTP server open control port
protocol number: 23 ;TELNET protocol; remote login, remote control pipeline target computer
Protocol number: 25; SMTP protocol; SMTP server open port, sending mail
Protocol number: 80; HTTP protocol; Hypertext transfer protocol
protocol number: 110; pop3 protocol; use
The characteristics of the TCP protocol for receiving mail : reliable, connection-oriented transmission protocol; providing full-duplex service, that is, data can be transmitted in both directions at the same time.
UDP protocol features: unreliable, connectionless transmission protocol
UDP protocol number and function:
protocol number: 69; TFTP protocol; simple file transfer protocol
protocol number: 111; RPC protocol; remote procedure call
protocol number: 123; NTP protocol ; Network Time Protocol
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What is a signal?
Signal is the medium of information transmission. The signal is transmitted in the network, so that the information can be transmitted.
The signal can be divided into: analog signal and digital signal
In the process of signal transmission, due to external interference or the impedance of the transmission medium itself, a certain degree of distortion will occur:
Noise: When the signal is transmitted in the channel, it is often interfered by noise. A simple definition of "noise": additional signals generated due to the equipment itself and environmental interference during signal transmission and processing. These signals have nothing to do with the input signal and are harmful.
Attenuation: As the signal spreads, the energy gradually decreases. Both analog signals and digital signals have attenuation during propagation. In order to compensate for the attenuation, digital and analog signals must be frequently amplified during transmission. The problem with the analog signal is that when it is amplified, the accompanying accumulated noise will also be amplified, which makes the deformation of the analog signal more serious.
Advantages of digital signal: strong anti-interference ability, long-distance transmission can still guarantee its quality
Twisted pair is the most commonly used transmission medium in wiring engineering.
Twisted pair wire is a pair of mutually insulated metal wires twisted together in a counterclockwise direction to resist a part of electromagnetic interference. The denser the twisted wire, the stronger its anti-interference ability. Therefore, the "twisted pair" name.
Optical fiber: With the rapid development of optical communication technology, people can now use optical fiber to transmit data.
The advantages of optical fiber: high transmission bandwidth; long transmission distance; strong anti-interference ability.
Optical fiber can be divided into single-mode fiber and multi-
mode fiber. The characteristics of single-mode fiber: used for high speed and long distance; high cost; difficult port installation; narrow core wire and laser source; low dissipation and high efficiency.
Multimode fiber: used for low speed and short distance; low cost; easy port installation; wide core wire, good light concentration, light source can be laser or light-emitting diode; large dissipation and low efficiency.
Optical fiber interface classification:
FC round threaded optical fiber connector
ST snap-on round optical fiber connector
SC square fiber connector
LC narrow-body square fiber connector
MT-RJ transceiver integrated square fiber connector
Wireless propagation medium (the most common radio wave)
its propagation mode: direct, reflection, refraction, penetration, diffraction and scattering
Integrated wiring system
building cabling system (PDS) is the transmission of voice, data, video, and other standard structured cabling system information
is within the transmission network building or building complex
physical structure of modular design and general star topology
makes Voice and data communication equipment, switching equipment and other information management systems are connected to each other
Six major subsystems of integrated wiring:
Work area subsystem: from information sockets to equipment RJ-45 jumpers and information sockets.
Horizontal subsystem: From information sockets in the work area to the distribution frame
key subsystems of the management room subsystem: Cross-connections, interconnections and 1/0 floor wiring closets, cabinets, distribution frames, network equipment, etc.
Vertical subsystems: the backbone cables of the building and the front is mostly optical fibers; the connection equipment room and management room
building group subsystem: Cables connecting different buildings are generally composed of optical cables and corresponding equipment.
Equipment room subsystem: located in the host room, consisting of cable connectors and related supporting hardware to connect various groups of public systems
The advantages of integrated wiring include: easy expansion, easy management, etc.
The materials used in integrated wiring include: trunking, bridge frame, patch panel, etc. The
integrated wiring implementation process includes: punching, slotting, wiring, racking, testing, etc.
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This is the end of the introduction to the network... I hope it can be helpful to you. The
network is infinitely mysterious, come on!