Shulou(Shulou.com)06/02 Report--

One: RJ45 interface

It is usually used for data transmission, and the most common application is the network card interface. It is a standard interface used on the network card to plug in the network cable. RJ45 is a kind of information socket (communication lead-out) connector in wiring system. The connector is composed of plug (connector, crystal head) and socket (module). The plug has 8 grooves and 8 contacts. RJ is the abbreviation of Registered Jack, which means "registered socket". In FCC (Federal Communications Commission Standards and regulations), RJ is the interface that describes the public telecommunications network, and RJ45 of computer network is the common name of standard 8-bit modular interface.

Second: network card

English name: network adapter (Network Adapter) or Network Interface Card (Network Interface Card). The network card is a network component working in the link layer, and it is the interface between the computer and the transmission medium in the local area network. It can not only realize the physical connection and electrical signal matching with the transmission medium in the local area network, but also involves the sending and receiving of the frame, the encapsulation and unpacking of the frame, the media access control, the encoding and decoding of the data and the function of data cache. The transmission efficiency of different types of network cards varies greatly, including 100Mbps and 10Mbps. Now the network card can be roughly divided into wired network card and wireless network card. The physical address of the network card, that is, the MAC address, is 48 bits, which is the only one in the world.

Wired network card:

Wireless network card:

Three: hub

The hub is called "Hub" in English. "Hub" means "center". The main function of the hub is to regenerate, reshape and amplify the received signal in order to expand the transmission distance of the network, while concentrating all nodes on the nodes centered on it. It works in the first layer of the reference model of OSI (Open Systems Interconnection reference Model), that is, the physical layer. Like network cards, network cables and other transmission media, hubs belong to the basic equipment in the local area network, which adopts CSMA/CD (carrier sensing multiple access technology with collision detection) media access control mechanism. Each interface of the hub simply sends and receives bits. When it receives 1, it forwards 1, and when it receives 0, it forwards 0. There is no collision detection. The hub (hub) belongs to the hardware network underlying equipment, basically does not have the "intelligent memory" ability and "learning" ability similar to the switch. It also does not have the MAC address table that the switch has, so it sends data without pertinence, but by broadcast. In other words, when it wants to send data to a node, it does not send the data directly to the destination node, but sends the packet to all nodes connected to the hub. HUB is a multi-port transponder. When taking HUB as the central device, a line in the network has a fault, which does not affect the work of other lines. So HUB has been widely used in local area network. Most of the time it is used in star and tree network topologies, connecting to hosts with RJ45 interfaces (there are also BNC interfaces). There are many kinds of HUB according to different terms.

Four: switch

The switch is called "Switch" in English. It is an upgraded product of the hub. From the appearance, it is basically no different from the hub. It is a rectangular box with multiple ports. According to the need of transmitting information at both ends of the communication, the switch is a general term for the technology to send the information to be transmitted to the corresponding route that meets the requirements by manual or equipment automatic completion. In a broad sense, the switch is a kind of equipment that completes the function of information exchange in the communication system.

"switch" and "switch" originated from telephone communication system (PSTN). We used to see some old movies in movies or TV. We often saw someone shaking a few times beside the phone (note that it was not a number), and then said, "connect me to XXX, and the operator will plug the corresponding terminal into the terminal when asked to make a call." In fact, this is the most primitive telephone exchange system, but it is a kind of manual telephone exchange system, which is not automatic, nor is it the computer exchange we are going to talk about today. but the computer exchange we are going to talk about now is developed from this telephone exchange technology.

In the computer network system, the concept of switching is an improvement relative to the shared working mode. We know that a hub (HUB) is a network device that shares media, and the HUB itself does not recognize the destination address and is broadcast to all nodes. That is, when the A host in the same local area network transmits data to the B host, the packet is transmitted by broadcast on the network based on HUB, sending the same information to all nodes on the network at the same time, and then each terminal determines whether to receive it by verifying the address information of the packet header. In this way, we know that it is easy to cause network congestion, because in fact, generally speaking, there is only one terminal node that receives data, but now it is sent to all nodes, then most of the data traffic is invalid. as a result, the data transmission efficiency of the whole network is quite low. On the other hand, because the packets sent can be heard by each node, it is obviously not very safe, and it is prone to some unsafe factors.

The switch has a high-bandwidth back bus and an internal fabric. All the ports of the switch are attached to this back bus. After the control circuit receives the data packet, the processing port looks up the MAC address (hardware address of the network card) in memory to determine which port the NIC of the destination MAC (network card) is attached to, and sends the data quickly to the destination node rather than all nodes through the internal fabric, and the destination MAC is broadcast to all ports if it does not exist. In this way, we can clearly see that on the one hand, it is efficient and will not waste network resources, but it is generally not easy to cause network congestion when sending data to the destination address; on the other hand, data transmission is secure. because it is not sent to all nodes at the same time, it is difficult for other nodes to listen to the information sent when sending data. This is one of the important reasons why switches quickly replace hubs.

Another important feature of the switch is that it does not share the bandwidth of every port like a hub, and each port of the switch is a part of the total bandwidth of the exclusive switch, which provides a fundamental guarantee for each port in terms of speed. In addition, the network can also be "segmented" by using the switch. by comparing the address table, the switch allows only the necessary network traffic to pass through the switch, which is the VLAN (Virtual Local area Network) that will be introduced later. Through the filtering and forwarding of the switch, we can effectively isolate the broadcast storm, reduce the occurrence of packet errors and packets, and avoid sharing conflicts. In this way, the switch can transmit data between multiple node pairs at the same time, each node can be regarded as an independent network segment, and the network devices connected to it alone enjoy a fixed part of the bandwidth and do not have to compete with other devices for use. For example, when node A sends data to node D, node B can send data to node C at the same time, and both transmissions enjoy bandwidth and have their own virtual connections. For example, if you are using a 10Mbps 8-port Ethernet switch, because each port can work at the same time, when the data traffic is large, its total traffic can reach 8*10Mbps=80Mbps, while when using 10Mbps's shared HUB, because it belongs to shared bandwidth, only one port is allowed to communicate at the same time, and no matter how busy the data traffic is, the total flow of HUB will not exceed 10Mbps. If it is 16-port, 24-port is even more obvious!

Five: router

Router (Router) is a kind of network device responsible for pathfinding, which looks for the network path with the least amount of communication from multiple paths in the interconnection network to provide users with communication. Routers are used to connect multiple logically separate networks. To provide the best communication path for users, the router uses the routing table to select the path for data transmission, and the routing table contains a list of network addresses and the distance between addresses. The router uses the routing table to find the correct path of the packet from the current location to the destination. The router uses the least time algorithm or the optimal path algorithm to adjust the path of information transmission. If a network path fails or is blocked, the router can choose another path to ensure the normal transmission of information. Routers can convert data formats and become necessary equipment for network interconnection between different protocols. Routers use routing protocols to obtain network information, and use routing algorithms and criteria based on "routing matrix" to select the best path. According to OSI reference model, a router is a network layer system. Routers are divided into single-protocol routers and multi-protocol routers.

Now there are two kinds of routers: wired router and wireless router. Wireless router has one more wireless signal transmission module than wired router. Now, of course, software like Cheetah WiFi allows wireless network cards to send wireless signals, thus achieving the function of WiFi.

Six: summary

1.RJ45 interface: the interface that can be plugged into the water crystal head.

two。 Network card: the data in the network is represented as a frame of data, which needs a network card to packet and unpack. Without a network card, it is impossible to recognize these data.

3. Hub: after receiving the data, it is forwarded directly to all the surrounding machines, and it is up to the machine to decide whether to accept the data or not, which is inefficient and unsafe.

4. Switch: the upgraded version of the hub, which stores a table: data and the corresponding MAC address, so sending data is targeted. After receiving the data, it is forwarded to the specified machine. Because the speed is very fast, it makes people feel that they have monopolized a dedicated line. Its basic functions are as follows:

The switch can realize the function of multiplexing a network cable.

Each port status of the switch is equivalent.

A switch can form a subnet, and the serial use of multiple switches can form a larger subnet.

Through the forwarding function of this switch, computers on the same subnet can access each other. Routers are needed for machines inside and outside the subnet to access each other.

5. Router: a router is an important device that connects different networks and contains a routing table. How do two different nodes on the network transmit data, or which one should be chosen if there are multiple paths? This is what routers do. Routing has the function of forwarding and routing. Forwarding (forward) involves only one router, while routing (route) involves multiple routers. The home router generally has a Wlan port and multiple LAN ports, the Wlan port is used to receive signals from the external network, and the lan port is equivalent to the switch port.

The difference between a home router and an enterprise router:

Strictly speaking, the routing function of home routing is optional. Home routers are mainly used to share IP and send WiFi. A subnet can be formed through a home router. The home router has the function of NAT protocol translation, and it also has DHCP protocol, that is, it is used to dynamically assign IP addresses. (the computer can be connected to the home router through the network cable to make relevant settings, pay attention to the LAN port.)

Enterprise router is specially used for data transmission routing function, which can automatically learn the routing table between different networks and realize routing and forwarding.

Note:

The boundaries between the above common devices are becoming less and less obvious. For example, a home router is actually a collection of routers and switches, while the so-called cat (modem) usually has the function of a router. The switch is also divided into different situations: if it is a layer 3 switch, it works in the physical layer, link layer and network layer, and has the functions of general switches and routers. The layer 2 switch only works in the lower two layers and does not have the function of a router.

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