What are the network communication interfaces?

Question 1: What are the common network communication devices? Generally, there are the following types of devices: network adapter: also called network interface card (NIC), which is plugged into the bus of a computer to connect the computer with other network devices. Network adapters generally only realize the functions of network physical layer and data link layer. Network transceiver is an interface device between network adapter and transmission medium, which provides signal level conversion and signal isolation. Network media conversion equipment is the conversion equipment between different transmission media in the network, such as twisted pair, optical fiber and so on. Multiplexer is a terminal controller, which is used to improve the utilization of communication channels. Interrupters are also called repeaters. Extend the distance of transmission medium, such as Ethernet interrupter can be used to connect different Ethernet segments to form an Ethernet. Hub: referred to as hub for short, it can be regarded as a multi-port interrupter (one interrupter is dual-port). The above devices are all network devices working in the physical layer. Bridge: Two LANs can be connected into a logical LAN. Network connection equipment working in physical layer and data link layer. Switches: Early switches were equivalent to multi-port bridges. Router: an interconnection device between networks working at the network layer. It can provide the function of path selection between networks. Gateway: it can be regarded as the general name of interconnection equipment between networks, but generally refers to the interconnection of multiple networks above the transport layer. & gt

Question 2: What is a network communication port? 50 points is not, it is to reply to your source port.

When your data is encapsulated, you use a source port (the destination port in our country) of this host, and we will reply according to your port number.

Question 3: What is the serial communication of network port communication? A data line is used to transmit data bit by bit in turn, and each bit of data occupies a fixed length of time. It only needs a few wires to exchange information between systems, especially for long-distance communication between computers and between computers and peripherals.

Serial communication refers to the serial transmission of data between computer host and peripherals and between host system and host system. When using serial communication, each character sent and received is actually transmitted one bit at a time, and each bit is 1 or 0.

Classification of serial communication

Serial communication can be divided into synchronous communication and asynchronous communication. Synchronous communication is to send and receive data according to synchronous characters recognized by software, and asynchronous communication is a communication method using character resynchronization technology.

Synchronous communication Synchronous communication is a communication mode of continuous serial data transmission, which only transmits one frame of information at a time. The information frame here is different from the character frame in asynchronous communication, and usually contains several data characters.

They are all composed of synchronization characters, data characters and check characters (CRC). In which the synchronization character is located at the beginning of the frame to confirm the beginning of the data character. There is no limit to the number of data characters after the synchronization character, which is determined by the length of the data block to be transmitted; There are 1 to 2 check characters, which are used to check the correctness of the received character sequence at the receiving end. The disadvantage of synchronous communication is that the sending clock and receiving clock need to be kept in strict synchronization.

Asynchronous communication

In asynchronous communication, asynchronous traffic has two important indicators: character frame format and baud rate. Data is usually transmitted in character frames in units of characters or bytes. Character frames are sent frame by frame by the sender and received by the receiving device through the transmission line. The transmitter and receiver can control the sending and receiving of data through their own independent and asynchronous clocks.

When the receiver detects a low-level logic 0 (i.e., the start bit of a character frame) transmitted from the transmission line, it determines that the transmitter has started to transmit data. Every time the receiver receives a stop bit in a character frame, it knows that a frame of characters has been sent.

Question 4: What is a communication interface? What communication interfaces does the computer have? In fact, you need to set up an intermediary to make two electronic devices that can't communicate directly. This is the interface. I really can't figure out what communication interface the computer has. . . For example, two chips cannot communicate directly. Think about how many interfaces you have to make. . There are also many types of interfaces. . .

Question What are the underlying functions of Java programming Tcp ip network communication interface? 5-point TCP/IP communication protocol

This part briefly introduces the internal structure of TCP/IP, which lays the foundation for discussing the security issues related to the Internet. TCP/IP protocol family is popular partly because it can be used on various channels and underlying protocols (such as T 1 and X.25, Ethernet and RS-232 serial interface). Specifically, TCP/IP protocol is a set of protocols including TCP protocol and IP protocol, UDP (User Datagram Protocol), ICMP (Internet Control Message Protocol) and so on.

Overview of TCP/IP overall architecture

TCP/IP protocol does not fully conform to the seven-layer reference model of OSI. Traditional open system interconnect is a seven-layer abstract reference model of communication protocols, in which each layer performs a specific task. The purpose of this model is to make all kinds of hardware communicate with each other at the same level. These seven layers are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer. TCP/IP communication protocol adopts a four-layer hierarchical structure, and each layer calls the network provided by its next layer to fulfill its own requirements. These four layers are:

Application layer: the communication layer between applications, such as Simple Email Transfer (SMTP), File Transfer Protocol (FTP), Network Remote Access Protocol (Telnet), etc.

Transport layer: At this layer, it provides data transmission services between nodes, such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). TCP and UDP add the transmission data to the data packet and transmit it to the next layer, which is responsible for transmitting the data and ensuring that the data has been delivered and received.

Internet layer: responsible for providing basic data packet transmission functions, so that each data packet can reach the destination host (without checking whether it is received correctly), such as Internet Protocol (IP).

Network interface layer: the management of actual network media, which defines how to use the actual network (such as Ethernet, serial line, etc.). ) to transmit data.

TCP/IP protocol

Here is a brief introduction to the functions of the protocols in TCP/IP and how they all work:

1. Internet Protocol

Internet protocol IP is the core of TCP/IP and the most important protocol in the network layer.

The IP layer receives the data packets sent by the lower layer (network interface layer such as Ethernet device driver) and sends the data packets to the higher layer-TCP or UDP layer; Conversely, the IP layer also transmits the packets received from the TCP or UDP layer to the lower layer. IP packets are unreliable because IP didn't do anything to confirm whether the packets were sent in order or not. An IP packet contains the address (source address) of the host that sent it and the address (destination address) of the host that received it.

Advanced TCP and UDP services usually assume that the source address in the packet is valid when receiving the packet. It can also be said that IP addresses form the authentication basis of many services, which believe that data packets are sent from valid hosts. IP confirmation includes an option called IP source routing, which can be used to specify a direct path between the source address and the destination address. For some TCP and UDP services, IP packets using this option seem to be transmitted from the last system on the path, not from its actual location. This option is used for testing, which shows that it can be used to trick the system into making connections that are usually prohibited. Then many services that rely on IP source address for confirmation will have problems and will be illegally invaded.

2. Transmission Control Protocol.

If there are sealed TCP packets in IP packets, IP will send them up to the TCP layer. TCP sorts and detects data packets, and at the same time realizes the connection between virtual circuits. TCP packets contain sequence numbers and acknowledgement information, so you can sort the received out-of-order packets and retransmit the damaged packets.

TCP sends its information to higher-level applications, such as Telnet servers and clients. The application sends the information back to TCP in turn ...>>

Question 6: What are TCP/IP and Internet transport protocols?

The following is a list of various network transmission protocols (the following numbers indicate the default service ports of application layer protocols):

ARP (Address Resolution Protocol)

bgp

Blue Tooth (Bluetooth)

Bootstrap protocol

Dynamic host configuration protocol

Domain name service

DVMRP (Distance Vector Multicast Routing Protocol)

EGP (external gateway protocol)

FTP (File Transfer Protocol) 2 1

HDLC (high-level data link control high-level data link control)

Hello (Routing Protocol)

HTTP hypertext transfer protocol 80

HTTPS secure hypertext transfer protocol

Internet control information protocol

IDRP (inter-domain routing protocol)

IEEE 802

internet group manage protocol

Internal gateway protocol

Internet mail access protocol

IP (internet protocol)

One of the protocols used by Ethernet (Internet Packet eXchange)

Intermediate system to intermediate system protocol

link control protocol

Logical link control protocol

Multicast listening discovery protocol

ordinary

network control protocol

NNTP (network news transfer protocol, network news transfer protocol) 1 19.

Network time protocol

point-to-point protocol

Post office protocol 1 10

rare

inverse address resolution protocol

routing information protocol

Serial link internet protocol

snmp

SMTP (Simple Mail Transfer Protocol) 25

SCTP (stream control transmission protocol Stream Control Transport Publishing Protocol)

Transmission control protocol transmission control protocol

TFTP (Common File Transfer Protocol)

Telnet (Remote Terminal Protocol) 23 > >

Question 7: What functional entities does the mobile communication system consist of? What layers of functions does its wireless interface include? The mobile communication system can be roughly divided into three parts: UE, wireless network subsystem and core network subsystem.

UE is a mobile station, and mobile phone users usually belong to UE, and the analog signals generated by UE are transmitted to the base station by wireless;

The wireless network subsystem includes a base station (2G refers to BTS, 3G refers to Nodeb, and LTE refers to Enodeb) and a base station controller (2G refers to BSC, 3G refers to RNC, and LTE refers to ERNC), wherein UE is transmitted to the base station through wireless, and the base station is transmitted to the controller through optical fiber;

The core network subsystem (CN) can control and detect the broadcast information sent by the controller to the base station and UE, and the transmission from the controller to the core network is mainly based on optical fiber (also coaxial cable).

Abstract: As shown in the figure

Question 8: What are the common network port numbers? Confessions are pasted words, but I think they are comprehensive. Tell me!

2 1/tcp FTP file transfer protocol

22/tcp SSH secure login, file transfer (SCP) and port redirection

23/tcp Telnet Unsafe Text Transmission

25/tcp SMTP Simple Mail Transfer Protocol (E-mail)

69/udp TFTP common file transfer protocol

79/tcp Finger Finger

80/tcp HTTP Hypertext Transfer Protocol (WWW)

88/tcp Kerberos authentication agent

1 10/tcp POP3 post office protocol (e-mail)

1 13/tcp identifies the old identification server system.

1 19/ tcp NNTP for newsgroups

220/tcp IMAP3

443/tcp HTTPS for secure transmission of web pages

Port: 0

Service: reserved

Description: Usually used to analyze the operating system. This method is effective because "0" is an invalid port in some systems, and when you try to connect it to a port that is usually closed, it will produce different results. A typical scan uses the IP address 0.0.0.0, sets the ACK bit and broadcasts it in the Ethernet layer.

Port: 1

Service: tcpmux

Description: This means that someone is looking for SGI Irix machine. Irix is the main provider of tcpmux, which is turned on by default in this system. Irix machine contains several default password-free accounts when it is released, such as: IP, guest UUCP, NUUCP, DEMOS, TUTOR, DIAG, OUTOFBOX, etc. Many administrators forget to delete these accounts after installation. So hackers searched for tcpmux online and used these accounts.

Port: 7

Service: echo

Description: When searching for Fraggle amplifier, you can see many messages sent by people to X.X.X.0 and X.X.X.255.

Port: 19

Service: Character Generator

Description: This is a service that only sends characters. The UDP version will respond to packets containing junk characters after receiving UDP packets. When TCP connects, it sends a data stream containing junk characters until the connection is closed. Hackers can use IP spoofing to launch DoS attacks. Forge UDP packets between two chargen servers. Similarly, the Fraggle DoS attack will broadcast a packet with a forged victim IP to this port of the target address, and the victim will be overloaded in response to the data.

Port: 2 1

Service: FTP

Description: FTP server opens ports for uploading and downloading. The most common attacker is to find a way to open anonymous's FTP server. These servers have read-write directories. Trojan Doly Trojan, Fore, Stealth FTP, WebEx, WinCrash and blade runner open ports.

Port: 22

Service: Ssh

Description: The connection between TCP established by PcAnywhere and this port may be to find ssh. This service has many weaknesses. If configured in a specific mode, many versions that use the RSAREF library will have many loopholes.

Port: 23

Service: Telnet

Description: Remote login, the intruder is searching for the service of remote login UNIX. In most cases, scanning this port is to find the operating system running on the machine. Using other technologies, intruders can also find passwords ... >>

Question 9: What is the use of communication interface? Communication Interface Simply put, devices need to exchange data with external devices. Everyone has developed a communication interface. The network port is a communication interface, so is RS-232/485, and there are many others, just as the mobile phone is a communication tool, so is the telephone, and in fact, so is the mouth. Hehe, the function of communication interface is similar to those things.

Question 10: What are the common port numbers that are too lazy to write, copy and paste? . .

But very comprehensive.

Please adopt it if it is useful.

Actually, just read the first paragraph.