Hubs - what is it? Device Hubs
Many people are interested in the question of what hubs andthan they are used. Now we will understand this question. Under the hub in the general case is understood the node of any network. This term has different meanings in different branches.
Using a hub in different industries
For example, in transport, hubs are the transplant nodesor overload, hub airports. In the energy industry, it is a kind of special center in which one route is divided into several. On off-road vehicles this word refers to a freewheel clutch mounted on the front axle. In various Internet networks, hubs are also used. What is it in the network "Fidonet"? Here the hub is a node that serves for mail transfer. In a file exchange network, Direct Connect is a network server.
But the most widely used concept is used incomputer technology and the Internet. A specific set of network equipment is based on the tasks that are put before the projected network and the costs of implementing a specific solution. An important element of such tasks is the selection of devices, among which the main role is played by routers, switches and hubs. We will try to understand what this is.
Hubs in computer networks
Technologies of building computer networksare constantly evolving. Devices that are based on them and are used to organize communication between computers are called differently: a hub, a switch and a router. What this is, we will consider in more detail.
Each of the above devices performs its ownrole in the organization of communication between network computers. Externally, they can look the same: boxes of small metal, having a number of ports or connectors, where the Ethernet cable is connected. As for concepts such as a switch, hub, hub, router, they are often used as synonyms, but this is a mistake. All these are different devices.
One of the first network devices are hubs. What are these devices? The term is of English origin. The word hub means the center of activity. A hub, or network hub, is designed to combine computers into a simple peer-to-peer network. The device provides a number of ports to which all personal computers of the network can be connected. Most often, a twisted pair is used for this purpose, which is compressed in a special way.
The principle of the hub
Consider the principle of network operationconcentrator. At the moment of attempting to access any of the computers of the network equipped with the hub to another PC, the first device sends a special block of information called a packet to the address of the network hub.
Let's try to understand the example of the scheme with threecomputers. Let's say computers PC1, PC2 and PC3 are connected to the device. The role of the hub is to multiply the data packet from PC1 by transferring it to other devices connected to the local network, that is, PC2 and PC3. At the time of receipt of the signal on the PC3 computer, for which it was intended, the latter sends the reply packet to the hub. The network hub again sends this packet to all network computers until the response from PC3 returns to the PC-sender PC1.
This is an approximate scheme of the interface of computers,connected to a local network, with a hub. The main drawback of such networks is that too much information is being sent. The network hub continuously sends data packets to all devices on the computer network, even if the destination is one particular PC. At the same time, computers receive blocks of information, which are often completely unnecessary to them. The technology is proving to be very expensive. That's why now the network hubs are almost out of use. In return, more intelligent devices were developed - network switches, which in everyday use are called switches.
The term "switch" is of English natureand means a switch, or network switch. Like a hub, a switch is required to connect computers on the same local network. The scheme for connecting it to computers does not differ from the scheme with a network hub. Just instead of the hub, the PCs are connected to the switch.
Being outwardly very similar to a network hub, the switch has principal differences from it, consisting in the method by which information is transferred between the computers of the local network.
After receiving a packet of information from the computer,the network switch, unlike the hub, does not forward it to all PCs participating in the network, but organizes the direction of the packet to the address of the computer for which the premise is intended. For example, when PK1 sends a packet of information to the PK3 computer, the switch arranges transmission to him, bypassing PK2. The return packet from PK3 also returns the network switch to the sender of the information packet - PK1.
Switch has the ability to memorize addressesall computers that are connected to its ports, and because of this can work as a regulator, transferring information only to the destination PC and ignoring the others.
The work of the network switch is based ontable of special MAC-addresses of network equipment users in the external and internal network. As a result, the packet of information that falls on each of the ports goes through a comparison with the routing table and is sent to the port address where the corresponding equipment is located.
The name "router" spawned an English router. This is a router that can organize the transfer of information between two or more different local networks. In addition, the router provides ports that are required to connect some other devices to it using a cable.
How does the router work?
Like a network switch that storestable of registered MAC addresses, the router stores the IP address table as a routing table. The main task of the router is to store this data and to ensure that other routers know about the changes in the network configuration. It is solved by applying routing protocols to coordinate with other routers. When packets arrive at the router, the latter uses different protocols and criteria to determine the best way to forward the information packet to the destination.
The router can be programmed to activatemulti-level rules, which are determined by the content of the information packets that arrive at it. The router is programmed to activate the network equipment protection system, translate network NAT addresses and represent DHCP network services.
Having intelligent stuffing, routersare among the most complex network devices. In addition to the ability to redirect traffic to the information packet, routers can be used to monitor traffic on the network. In addition, they have the ability to respond to changes in the network, dynamically detecting them, protecting it with packet filtering, computing packets for blocking or skipping.
In addition to Ethernet network hubs,The term "hub" is used in connection with USB technologies. The development of new equipment places high demands on the level of development of user interfaces for computer equipment. A lot of various computer peripherals connected through a USB connection, needs a special device that allows you to connect several devices simultaneously via USB. It is called a USB hub. What is the principle of its operation?
USB hub (USB hub) is a deviceA small size that has several ports. Connect it through the computer socket. It allows you to connect several USB devices to one PC USB port.
USB Hub Device
The design and construction of hubs do not differgreat complexity. They are designed to switch signals and provide power supply voltage. In addition, they control the status of the periphery connected to them, setting the host aware of the changes.
The hub consists of two modules - a controller andrepeater. A repeater is a managed key that connects the input and output ports. It has the ability to reset and suspend signal transmission. Registers are included in the controller, allowing to interact with the host. Registers are controlled by special commands that allow you to configure the hub, monitor the status and change the parameters of the downstream ports. It is possible to use the hub of the contract, when the devices are switched in series.
Types of USB Hubs
One such type is the internal map onsystem bus. It serves to connect USB devices to the motherboard. This is done using a USB PCI card, installed on the free space of the PCI bus, located directly on the motherboard. This kind of USB hub is best used by those who are familiar with the computer device. Those who do not have experience, it is better to dwell on a different form.
Another view is an external USB hub without power. Such a device is simple and relatively inexpensive. This kind of USB hub connects to the USB port of your computer. This device is great for laptop owners. For users of home computers, it is also possible to use such a USB hub, but one must take into account that a number of devices connected to the computer require power supplied via the USB port. This type of hub is not able to power several such devices at once. In this situation, it is best to use the powered hubs. What are these devices and how do they differ from devices without power?
On the powered USB hub, the principle of operationexactly the same as the hub without power. The difference is that it can be plugged into the outlet. This allows you to provide full power to all devices that are connected through the USB. The biggest USB hubs are seven-port.
Another kind of such device is a computerUSB board. This device is suitable for laptop users. It connects to a special USB port located on the laptop and allows you to use two ports instead of one.