What is Ethernet

What is Ethernet

Introduction to Ethernet:

Ethernet refers to the baseband created by Xerox Corporation and jointly developed by Xerox, Intel and DEC Corporation The LAN specification is the most common communication protocol standard used in existing LANs today. Ethernet uses CSMA/CD technology and runs at 10M/S over multiple types of cables. Ethernet is similar to the IEEE802.3 series of standards. Including standard Ethernet, Fast Ethernet and 10G Ethernet. They are all compliant with IEEE802.3.

Standard:

IEEE802.3 specifies the content including physical layer wiring, electrical signals and media access layer protocols. Ethernet is currently the most commonly used LAN technology, and it has largely replaced other LAN standards. Such as Token Ring, FDDI and ARCNET. After the rapid development of 100M Ethernet at the end of the last century, Gigabit Ethernet and even 10G Ethernet are continuously expanding their application scope driven by international organizations and leading companies.

Common 802.3 applications are:

10M: 10base-T,

100M: 100base-TX,

100base-FX,

1000M: 1000base-T

The general characteristics of Ethernet are summarized as follows:

***Shared media: All network devices use the same communication media in turn. ?

Broadcast domain: Frames that need to be transmitted are sent to all nodes, but only the addressed node will receive the frame. ?

CSMA/CD: Carrier sense multiple access/collision detection method is used in Ethernet to prevent twp or more nodes from transmitting at the same time. ?

MAC address: All Ethernet network interface cards in the media access control layer use 48-bit network addresses. This address is unique in the world.

Ethernet basic network composition:

*** Shared media and cables: 10BaseT, 10Base-2, 10Base-5. ?

Repeater or hub: A hub or repeater is a type of device used to receive a large number of Ethernet connections on a network device. The data obtained through the receiving side of a connection is reused and sent to all connected devices on the transmitting side to obtain a transmitting device. ?

Network bridge: The bridge is a second-layer device, responsible for dividing the network into independent conflict domains and segments, so as to maintain broadcast and *** sharing in the same domain/segment. Target. A table covering all segmented and forwarded frames is included in the bridge to ensure proper communication behavior within and around segments. ?

Switch: A switch, like a bridge, is also a layer 2 device and is a multi-port device. The functions supported by a switch are similar to those of a bridge, but its advantage over a bridge is that it can temporarily connect any two ports together. A switch includes a switching matrix through which ports can be quickly connected or disconnected. Unlike a hub, a switch only forwards frames from one port to other ports connected to the destination node and does not contain broadcasts. ?

Ethernet protocol: The Ethernet frame structure is provided in the IEEE802.3 standard. Currently Ethernet supports four transmission rates with fiber optic and twisted pair media support:

10Mbps_?10Base-T?Ethernet?

100Mbps_FastEthernet?

1000Mbps_GigabitEthernet )?

10GigabitEthernet_IEEE?802.3ae

History

The initial advances in Ethernet technology came from many pioneering technology projects at Xerox Palo Alto Research Center one.

Ethernet is generally credited with being invented in 1973, when Robert Metcalfe wrote a memo to his boss at PARC about Ethernet's potential. But Metcalf himself believed that Ethernet only appeared a few years later. In 1976, Metcalf and his assistant David Boggs published an article titled "Ethernet: Distributed Packet Switching Technology for Local Area Computer Networks." In late 1977, Metcalfe and his collaborators received a patent for a "multipoint data communications system with collision detection." The multipoint transmission system was called CSMA/CD, which marked the birth of Ethernet.

In 1979, Metcalf left Xerox and founded 3Com in order to develop personal computers and local area networks. 3com lobbied Digital, Intel, and Xerox, hoping to work with them to standardize and standardize Ethernet. This universal Ethernet standard was introduced on September 30, 1980. At that time, there were two popular non-public network standards in the industry, Token Ring and ARCNET. They quickly shrank and were replaced under the impact of the Ethernet trend. In the process, 3Com has also become a large international company.

Ethernet plug:

Metcalfe once joked that Jerry Saltzer contributed to 3Com's success. In an influential paper he co-authored, Saltzer argued that Token Ring was theoretically superior to Ethernet. Affected by this conclusion, many computer manufacturers have hesitated or decided not to make Ethernet interfaces a standard configuration of machines, so that 3com can have the opportunity to make a lot of money from selling Ethernet network cards. This situation has also led to another saying that "Ethernet is not suitable for research in theory, but only for practical application." Maybe it's just a joke, but it illustrates a technical point: Often, the actual data flow characteristics in the network are different from what people estimated before the popularity of LANs, and it is precisely because of the simple structure of Ethernet that the popularity of LANs was made . Metcalfe and Saltzer once worked on the same floor of MIT's MAC project while Metcalf was working on his Harvard thesis, during which he laid the theoretical foundation for Ethernet technology.

This standard defines the cable types and signal processing methods used in local area networks. Ethernet transmits information packets between interconnected devices at a rate of 10~100Mbps. Twisted pair cable 10BaseT Ethernet has become the most widely used Ethernet technology due to its low cost, high reliability and 10Mbps rate. The direct expansion wireless Ethernet can reach 11Mbps, and the products provided by many manufacturing suppliers can use common software protocols for communication, with the best openness.

Standard Ethernet:

At first, Ethernet only had a throughput of 10Mbps and used the access control method of carrier sensing multiple access with conflict detection. This early 10Mbps Ethernet is called standard Ethernet. Ethernet can be connected using a variety of transmission media such as thick coaxial cable, thin coaxial cable, unshielded twisted pair, shielded twisted pair and optical fiber. And in the IEEE?802.3 standard, different physical layer standards are formulated for different transmission media. In these standards, the first number indicates the transmission speed, the unit is "Mbps", and the last number indicates the length of a single segment of network cable, which is represented by Base. "Baseband" means "Broadband".

·10Base-5 uses a thick coaxial cable with a diameter of 0.4 inches and an impedance of 50Ω, also called thick cable Ethernet, and the maximum segment length is 500m. Baseband transmission method, the topology is bus type. The main hardware equipment of 10Base-5 networking includes: thick coaxial cable, Ethernet card with AUI socket, repeater, transceiver, transceiver cable, terminator, etc.

·10Base-2 uses a thin coaxial cable with a diameter of 0.2 inches and an impedance of 50Ω, also known as thin cable Ethernet. The maximum segment length is 185m, the baseband transmission method, and the topology is bus type; 10Base -2 The main hardware equipment of the network includes: thin coaxial cable, Ethernet card with BNC socket, repeater, T-shaped connector, terminator, etc.

·10Base-T uses twisted pair cables, and the maximum network segment length is 100m. The topology is star; the main hardware equipment of 10Base-T network includes: Category 3 or Category 5 unshielded twisted pair, Ethernet card with RJ-45 socket, hub, switch, RJ-45 plug, etc.

·1Base-5 uses twisted pair cables, the maximum network segment length is 500m, and the transmission speed is 1Mbps;

·10Broad-36 uses coaxial cables, and the maximum span of the network is 3600m, the maximum network segment length is 1800m, which is a broadband transmission method;

·10Base-F uses optical fiber transmission media, with a transmission rate of 10Mbps

1. The working principle of Ethernet and IEEE802.3

In a broadcast-based Ethernet, all workstations can receive information frames sent to the network. Each workstation must confirm whether the information frame is sent to itself. Once it is confirmed that it is sent to itself, it will be sent to the higher protocol layer.

In Ethernet using CSMA/CD transmission media access, any CSMA/CDLAN workstation can access the network at any time. Before sending data, the workstation needs to listen to see if the network is congested. Only when it detects that the network is idle can the workstation send data.

In contention-based Ethernet, any workstation can send data as long as the network is idle. A conflict occurs when two workstations find that the network is idle and send data at the same time. At this time, both transmission operations are destroyed, and the workstation must retransmit after a certain time. When to retransmit is determined by the delay algorithm.

2． Differences between Ethernet and IEEE802.3 services

Although there are many similarities between Ethernet and IEEE802.3 standards, there are also certain differences. The services provided by Ethernet correspond to the first and second layers of the OSI reference model, while the services provided by IEEE802.3 correspond to the channel access portion of the first and second layers of the OSI reference model. IEEE802.3 does not define a logical link control protocol, but defines several different physical layers, while Ethernet only defines one.

Each physical layer protocol of IEEE802.3 can describe its characteristics from three aspects, namely LAN speed, signal transmission method and physical media type.

Ethernet is a baseband LAN technology developed in the 1970s. It uses coaxial cables as network media, adopts carrier multiple access and conflict detection mechanisms, and has a data transmission rate of 10MBPS. But nowadays Ethernet is more often used to refer to various local area networks using CSMA/CD technology. The frame format of Ethernet is consistent with IP and is particularly suitable for transmitting IP data. Ethernet is simple and convenient, low in price, and high in speed.

The name Ethernet originated from a scientific hypothesis: sound travels through the air, but what about light? Light can travel in outer space without air. Therefore, some people say that light spreads through a substance called ether. Later, Einstein proved that the ether did not exist at all.

The difference between Ethernet and the Internet:

Main difference: Ethernet is a local area network that can only connect to nearby devices. The Internet is a wide area network. We can connect to the United States through the Internet. Get the message.

Both are considered networks used to connect computers, but their scopes are different. Ethernet is limited to a certain distance. We can have thousands or hundreds of Ethernets; but the Internet is the largest wide area network. We only have one Internet, so the Internet can be said to be a network within a network.

The Internet is a very large international system that can connect networks in various parts of the world, whether private, public, academic, commercial or government networks. They can all be connected to each other and share resources. To put it figuratively, the Internet is the network we use to open web pages, send emails, listen to music and watch movies online. It includes a very wide range of information, and now we have become accustomed to it.

As for Ethernet, it basically only allows a few local computers to connect to each other. Computers sending messages to each other are supported by a set of technologies. Generally speaking, computers connected to an Ethernet network are in the same building or nearby. But with the development of Ethernet cables, the range of Ethernet can be extended to ten kilometers. But because they are all connected via network cables, it is unrealistic to connect to places far away.

To put it more in daily life, Ethernet is to connect your home computer and laptop to the cat, and then connect to the Internet through the cat, so that you can Skype with friends abroad. Therefore, your computer, laptop and cat form an Ethernet network. As you can imagine, there are thousands of Ethernets in the world. Businesses use Ethernet to connect all their computers to the main server.

An Ethernet network can have one or several administrators. There may be parts of the Internet that are managed by administrators, but there is no one administrator who can control the entire Internet.

Another difference is security. Ethernet is relatively secure because it is a closed internal network and outsiders have no authority. But the Internet is publicly connected and can be browsed by everyone.

The following mainly introduces four different Ethernet frame formats.

There is a 64-bit leading character at the beginning of each format of Ethernet frame, as shown in Figure 1. Among them, the first 7 bytes are called the preamble, the content is the hexadecimal number 0xAA, and the last 1 byte is the frame start identifier 0xAB, which identifies the start of the Ethernet frame. The purpose of the leading character is to synchronize the receiving node and prepare it to receive the data frame.

Figure 1 Ethernet frame leading characters

In addition, the definitions of each field of Ethernet frames in different formats are different and are not compatible with each other. The following introduces their respective frame formats.

EthernetII

That is, DIX2.0: the Ethernet standard frame format developed by Xerox, DEC, and Intel in 1982, as shown in Figure 2.

Figure 2 Ethernet802.3raw frame format

The minimum length of the EthernetII type Ethernet frame is 64 bytes, and the maximum length is 1518 bytes. The first 12 bytes respectively identify the MAC address of the source node that sends the data frame and the MAC address of the destination node that receives the data frame. .

The next 2 bytes identify the upper-layer data type carried by the Ethernet frame. For example, the hexadecimal number 0x0800 represents IP protocol data, the hexadecimal number 0x809B represents AppleTalk protocol data, and the hexadecimal number 0x809B represents AppleTalk protocol data. The number 0x8138 represents Novell type protocol data, etc.

After the variable-length data field is a 4-byte frame check sequence, a 32-bit CRC cyclic redundancy check is used to perform data from the "target MAC address" field to the "data" field. check.

Ethernet802.3raw

The dedicated Ethernet standard frame format announced by Novell in 1983, as shown in Figure 3.

Figure 3 Ethernet802.3raw frame format

In the Ethernet802.3raw type Ethernet frame, the type field in the original EthernetII type Ethernet frame is replaced by the "total length" field, which Specify the length of the following data field, its value range is: 46~1500.

The next 2 bytes are the fixed hexadecimal number 0xFFFF, which identifies this frame as a Novell Ethernet type data frame.

Ethernet802.3SAP

The Ethernet frame format of the SAP version of Ethernet802.3 announced by IEEE in 1985, as shown in Figure 4.

Figure 4 Ethernet802.3SAP frame format

As can be seen from Figure 4, in the Ethernet802.3SAP frame, the 2 bytes of 0xFFFF in the original Ethernet802.3raw frame are changed to DSAP and SSAP of 1 byte each, and a 1-byte "control" field are added, forming the header of 802.2 logical link control. LLC provides connectionless and connection-oriented network services. LLC1 is used in Ethernet, while LLC2 is used in IBMSNA network environment.

The new 802.2LLC header includes two service access points: source service access point and target service access point. They are used to identify the upper-layer data type carried by the Ethernet frame. For example, the hexadecimal number 0x06 represents IP protocol data, the hexadecimal number 0xE0 represents Novell type protocol data, and the hexadecimal number 0xF0 represents IBMNetBIOS type protocol data, etc.

As for the 1-byte "control" field, it is basically not used.

Ethernet802.3SNAP

The SNAP version of the Ethernet frame format of Ethernet802.3 announced by IEEE in 1985, as shown in Figure 5.

Figure 5 Ethernet802.3SNAP frame format

The main difference between the Ethernet802.3SNAP type Ethernet frame format and the Ethernet802.3SAP type Ethernet frame format is:

2 The contents of the DSAP and SSAP fields of bytes are fixed, and their value is the hexadecimal number 0xAA.

The content of the 1-byte "control" field is fixed, and its value is the hexadecimal number 0x03.

The SNAP field is added, consisting of the following two items:

A new 3-byte organization unique identifier field is added, whose value is usually equal to the first 3 bytes of the MAC address. , which is the network adapter manufacturer code.

The 2-byte "type" field is used to identify the upper layer data type carried by the Ethernet frame.

Ethernet can use a variety of connection media, including coaxial cables, twisted pairs, and optical fibers. Among them, twisted pairs are mostly used for connections from hosts to hubs or switches, while optical fibers are mainly used for cascading between switches and point-to-point links between switches and routers. Coaxial cable, as the main connection medium in the early days, has gradually been phased out.

Pay attention to distinguishing between straight-through cables and crossover cables in twisted pairs.

Straight-through cables should be used for the following connections:

Switch to router Ethernet Network Port

Computer to Switch

Computer to Hub

Crossover cables are used to directly connect the following devices in a LAN:

Switch to Switch

Switch to Hub

Hub to Hub

Router to Router Ethernet Port Connection

Computer to Computer

Computer to Router Ethernet Port

CSMA/CD*** Shared Media Ethernet

Carrier Sense Multiple Access with Collision Detection [2] Technology Specifies the method for multiple computers to share a channel. This technology first appeared in the ALOHAnet, developed by the University of Hawaii in the 1960s, which uses radio waves as a carrier. This method is simpler than Token Ring or Master Control Network. When a computer wants to send information, it must abide by the following rules:

Start: If the line is idle, start the transmission, otherwise go to step 4.

Send: If a conflict is detected, continue sending data until the minimum message time is reached, and then go to step 4.

Successful transmission: Report successful transmission to the higher-layer network protocol and exit transmission mode.

Line Busy: Wait until line is idle Line goes idle - wait a random amount of time, go to step 1, unless max attempts are exceeded.

Exceeded the maximum number of transmission attempts:? Report the transmission failure to the higher-layer network protocol and exit the transmission mode.

Just like in a symposium without a moderator, all participants are connected through a

Is Ethernet a broadband connection?

Ethernet uses CSMA/ CD technology and runs on multiple types of cables at 10M/S. Ethernet is similar to the IEEE802.3 series of standards.

Broadband connections in basic electronics and electronic communications describe extensions or electronic circuits that contain or are capable of processing a wide frequency range at the same time. It is a relative description. The larger the frequency range, the greater the frequency range. That is to say, the higher the bandwidth, the more data is transmitted.

Repeater:

Due to signal attenuation and delay, there are distance restrictions for Ethernet segments based on different media. For example, the maximum distance of 10BASE5 coaxial cable is 500 meters. The maximum distance can be achieved through Ethernet repeaters, which amplify the signal in the cable and transmit it to the next segment. The repeater can connect up to 5 network segments.

But there can only be 4 devices. This can alleviate problems caused by cable breaks: when a section of coaxial cable is disconnected, all devices on this section cannot communicate, and the repeater can ensure that other network segments work normally.

The difference between Ethernet and WiFi

The difference between Ethernet and wireless network

1. Wi-Fi is a wireless network that can connect personal computers to , handheld devices and other terminals are connected to each other wirelessly. In fact, it is a high-frequency radio signal. WIFI can be synonymous with small wireless LAN and can be regarded as a short-distance wireless extension of wired LAN.

2. Ethernet is a wired network and requires a network cable to be plugged into the computer to access the Internet. It is a kind of local area network, which is a kind of network divided according to geographical distribution range. A local area network is generally small in scope and is connected by at least two computers.

Wifi only specifies the frequency and speed of the wireless network. Ethernet is a local area network standard. It includes transmission frequency, speed, etc., and also stipulates that data companies outsource IT services, server maintenance in computer rooms, and weak current integrated wiring

link layer. The coverage of Ethernet is much wider than that of WiFi, and the two cannot be compared.

How to change the WIFI password via Ethernet

Connect the computer to any LAN port of the router, enter the settings page, and set and modify the router WIFI name and password.

The method is as follows:

1. Open the browser, enter the router gateway IP address in the address bar, enter the login username and password;

2. After successful login The running status will be displayed, click "Wireless Settings";

3. Then click "Wireless Security Settings", the wireless network name is just a name, you can fill it in casually, usually alphanumeric;

4. Then set the password, generally choose WPA-PSK/WPA2-PSK encryption method;

5. After setting the password, click Save and prompt to restart;

6. Click Click "Restart Router" in "System Tools" to restart routing.

How to change Ethernet to wireless network on a computer

1. Click the network icon in the lower right corner of Win10, and click "View Connection Settings" in the network panel that appears

2. In the computer settings interface, it will automatically jump to the network item, click "Network" in the left window

3. In the search device and content interface, we can set the network type. If you find Dots, devices, and Rongrong on this network, and then automatically connect to devices such as printers and TVs, in the "on" state, the computer network type is "private network."

4. If it is in the "off" state, the computer network type is "public network". Of course, in addition to having to make manual settings when we need to change, we can also set the default network type to a public network or a private network, depending on the occasions when you usually use the network.

How to change Ethernet to WiFi

Taking Windows 10 system as an example, the method of changing Ethernet to WiFi is as follows:

1. First open the control panel. Open in the start menu.

2. After opening the control panel, find the option Network and Sharing Center, and then open it.

3. After opening the Network and Sharing Center, here are the details

4. Select the option according to the situation, and then click Next.

5. On the page of selecting the connection method, if there is a wireless network, a wireless connection option will be displayed in the list below. Click this option with your mouse and click OK.

Wi-Fi is a technology that allows electronic devices to connect to a wireless local area network, usually using the 2.4GUHF or 5GSHFISM radio frequency bands. Connections to a wireless LAN are usually password protected, but can also be open, allowing any device within range of the WLAN to connect.

Broadband has become Ethernet

Ethernet is generally used by plugging in a network cable. Win10 is called Ethernet.

XP is called local connection, but if it is wireless, it is not called Ethernet.