What is a USB hub: types and features. Network hub
This is a multiport information repeater in a network with auto-segmentation.
All ports are equal. Having received a signal from one connected station, hab transforms the information into all active ports. If a fault is detected on one of the ports, that port is automatically disabled or segmented. After the error is resolved, it becomes active again. Collision processing and channel status monitoring are carried out by the concentrator itself. It is possible to create a union of hubs to increase the size of the subnet, or to create trunk communication channels between hubs.
Autosegmentation is used to improve network reliability.
The purpose of hubs is to unite individual workstations into a workgroup within a local network. This working group should have the following characteristics:
certain territorial concentration;
the working group team solves similar problems;
the same type of software and common information databases are used;
within the working group there are general requirements to ensure safety and reliability;
peripheral devices are shared.
All hubs are designed according to the IEEE 802.3 standard.
The operation of concentrators is carried out at the 1st level of the OSI model, so they are not sensitive to the protocols of upper levels. It is not important for the concentrator to work on local computers.
Characteristics of concentrators.
All hubs have the following characteristics:
Equipped with an LED indicator indicating the status of the ports, the presence of collisions, the activity of the transmission channel, and the presence of faults;
When the power is turned on, the concentrator performs a self-test procedure, and during operation, self-diagnosis;
Provides auto-port segmentation to isolate faulty ports;
They have a standard size for mounting;
Detects polarity error when using twisted pair cable and automatically switches polarities.
RJ 45 connector for twisted pair operation. A twisted pair cable consists of wires of the following colors:
White-orange;
White-blue;
White-brown;
White-green.
When implemented, connections A and B are used. These types of connections depend on the sequence of wires inside the connector. All equipment is marked A and B.
Connection via A:
Connection via B:
A-B polarity is only possible in switch.
By changing polarity we mean changing the first with the eighth, the second with the seventh, the third with the sixth, the fourth with the fifth.
The pairs b/s, s, b/k, k are not used in a standard Ethernet network. Therefore, in modern networks you can use four wires.
Pairs b/s, s, b/k, k are used to transmit power to the device over an Ethernet network.
Types of concentrators.
The entry-level ones are five- to eight-port capacitors. They do not have the ability to manage through the console port and do not allow management of subnet hubs. The cost of the devices is low.
Middle class - 12.16-24 port. They have a console port, a port for connecting a BNC to a coaxial cable, and allow you to manage the network and configure security levels.
CNMP managed hubs. 12, 16, 24, 48 – ports, console port, and there is also the ability to collect statistics on the network. It also allows you to detect errors and fix them.
BNC hubs are multiport repeaters for thin coaxial cables for use in a 10BASE 2 network, that is, they consist of BNC connectors that allow segmentation of ports; operation is supported for a segment length of 185 meters per port. Each port can support 30 nodes.
10/100 Mbps hubs allow you to connect devices at either 10 or 100 Mbps speeds.
Hubs are broadcast devices so ensuring privacy is challenging, but the following privacy tools are available if needed:
blocking unused ports;
setting a password for the console port;
setting information encryption on each port.
A modern hub is usually integrated into other devices. For example, in routers, a device for organizing a tunnel.
USB technology, which was invented to connect computer and telecommunication devices, is now the main means of connecting many gadgets. Their number is simply surprising - these are keyboards, mice, modems, coolers, external hard drives, printers, flash drives, even coffee makers and lamps. And since all these devices need to be connected to a computer, there are currently simply not enough USB ports.
There are two ways to solve this problem. The easiest way is to connect only those devices that are needed at the moment, and disconnect unused devices, thereby freeing up USB ports. And the second way is to purchase an original device called a USB concentrate (USB hub).
A USB hub is a small device that has several USB ports. It connects to one of the computer's USB ports (thus taking up only one USB connector), and makes it possible to use several USB devices. Thus, a USB hub increases the number of USB connectors on a computer, reduces their wear, and also makes it easier to use numerous devices.
Types of USB hubs
There are four types of USB hubs. The first is a USB PCI card that plugs into the PCI slot on the motherboard. To do this, you will have to open the system unit, and if you do not understand this, then it is better not to use this type of USB hub.
The second type is a non-powered USB hub. This simple device connects to one of your computer's external USB ports. After this, you can connect any other devices to it. These USB hubs are very compact and are great for both computers and laptops. But they have a small disadvantage. Some USB devices (printer, digital camera, scanner, etc.) require power, and this type of hub will not be able to provide them with the required amount of electricity, especially if you connect several devices at once.
The third type is a powered USB hub. It is also very compact and plugs into an external USB port on your computer. In addition, such a USB hub can be plugged directly into an outlet. This makes it possible to connect any types of USB devices to it.
And the fourth type is a USB computer card. If you use a laptop for work and also need to constantly move with it, then this USB card would be an excellent alternative to a USB hub. It connects to the USB connector on the side of the laptop and allows you to connect two additional devices.
Hub or hub- multiport network repeater with auto-segmentation. All hub ports are equal. Having received a signal from one of the stations connected to it, the hub broadcasts it to all its active ports. In this case, if a fault is detected on any of the ports, then this port is automatically disabled (segmented), and after it is eliminated, it becomes active again. Collision processing and ongoing monitoring of the state of communication channels is usually carried out by the concentrator itself. Hubs can be used as standalone devices or connected to each other, thereby increasing the size of the network and creating more complex topologies. In addition, it is possible to connect them with a backbone cable into a bus topology. Auto segmentation necessary to improve network reliability. After all, the Hub, which forces the use of a star cable topology in practice, is within the framework of the IEEE 802.3 standard and is thus required to provide a MONO CHANNEL connection.
Purpose of hubs- combining individual workstations into a work group within a local network. A working group is characterized by the following characteristics: a certain territorial concentration; a team of users in a working group solves similar problems, uses the same type of software and common information databases; within the working group there are general requirements for ensuring safety and reliability, the same impact of external sources of disturbances occurs (climatic, electromagnetic, etc.); high-performance peripherals are shared; usually maintain their own local servers, often geographically located on the territory of the work group.
OSI. Hubs operate at the physical layer (Layer 1 of the OSI reference model). Therefore, they are not sensitive to upper-layer protocols. The result of this is the ability to share different operating systems (Novell NetWare, SCO UNIX, EtherTalk, LAN Manager, etc., compatible with Ethernet or IEEE 802.3 networks). There is, however, a certain “pressure” on the network owner when using network management programs: management programs, as a rule, use the IP protocol to communicate with SNMP equipment. Therefore, in terms of network management, it is necessary to use only this protocol and, accordingly, operating shells at network management stations. But this is not a very serious pressure, because the IP protocol is probably the most popular. All concentrators have the following characteristic operational features:
equipped with LED indicators indicating the status of the ports (Port Status), the presence of collisions (Collisions), the activity of the transmission channel (Activity), the presence of a fault (Fault) and the presence of power (Power), which provides quick monitoring of the status of the entire hub and diagnostics of faults;
when the power supply is turned on, they perform a self-test procedure, and during operation - a self-diagnosis function;
have a standard width size - 19"";
provide auto-segmentation of ports to isolate faulty ports and improve network integrity;
Detects polarity error when using twisted pair cable and automatically switches polarity to correct installation error;
support configurations using multiple hubs connected to each other either through special cables and stack ports, or a thin coaxial backbone connected between the BNC ports, or through a fiber optic or thick coaxial cable connected through appropriate transceivers to the AUI port, or through UTP cables, hubs connected between ports;
support voice and data communications through the same cable harness;
transparent to network operating system software;
can be installed and put into operation within a few minutes.
Entry-level hubs- 8, 5, less often 12...16 port hubs. They often have an additional BNC, less often an AUI port. It does not provide management capabilities either through the console port (due to its absence) or over the network (due to the absence of an SNMP module). They are a simple and cheap solution for organizing a small work group.
Mid-range hubs- 12, 16, 24 port hubs. They have a console port, often additional BNC and AUI ports. This type of hub provides out-of-band network management capabilities through an RS232 console port under the control of some standard terminal program, which makes it possible to configure other ports and read hub statistics. This type of hubs is positioned for building networks in the small to medium range, which will further develop and require the introduction of software control.
SNMP-managed concentrators- 12, 16, 24 and 48 port hubs. They are distinguished not only by the presence of an RS-232 console port for management, but also by the ability to manage and collect statistics over the network using the SNMP/IP or IPX protocols. The owner of such a hub has access to the following collection of statistics on network nodes (hubs), its primary processing and analysis: the main sources of messages /top talkers/, the most active users /heavy users/, sources of errors and communication pairs /communications pairs/ are identified. It is advisable to use these types of hubs for building LAN networks in the range of medium and higher, which will certainly develop. These networks always require software network management, including remote control.
BNC hubs or ThinLAN hubs - multiport repeaters for thin coaxial cables used in 10Base2 networks. They include BNC ports and, as a rule, one AUI port, and often support SNMP protocols. They, like 10Base-T hubs, segment ports (disabling not just one station, but subscribers of the entire beam) and broadcast incoming packets to all ports. Each BNC port is subject to the same restrictions as a fragment of a 10Base-2 standard network: it supports the operation of thin coaxial cable segments up to 185 meters long per port, up to 30 network connections per segment are provided, including “empty T-connectors”, If a cable segment fails, that segment will be disabled, but the rest of the hub will continue to function. The scope of application of this type of concentrators is the modernization of old 10Base2 standard networks in order to increase their reliability, the modernization of networks that have reached restrictions on the use of repeaters and do not require frequent changes.
10/100Hubs replaced 10 MB of device. If you just read the advertisements on them, you can be ambushed. The fact is that Hub does not know how to buffer packets, and therefore does not know how to coordinate different speeds. Therefore, if at least one 10Base-T station is connected to such a hub, then all ports will operate at speed 10. According to rumors, there are already hubs that support two speeds simultaneously. I have not seen such devices, but I believe that in this case the word “hub” is used by the manufacturer to refer to some intermediate device (something between a hub and a switch), such as MicroLAN from Cabletron Systems.
Redundant link. Mid-range and SNMP-managed hubs support one redundant link per hub to create a back up link between any two hubs. This ensures network fault tolerance at the hardware level. The redundant link is a separate cable mounted between two hubs. Using the hub's console port, you simply need to configure the primary link and backup link for one of the hubs. The backup communication channel is automatically released if the main communication channel of two concentrators fails. Although a hub can only control one backup link, it can be at the remote end of one backup link and at the controlling end of a backup link to another hub! Once the fault on the primary cable segment is corrected, the primary link will not automatically resume operation. You will need to use the hub's console or press the Reset button on the hub to restore host communications.
Communication bit for hubs it is a periodic pulse with a duration of 100 ns, sent every 16 ms. It does not affect network traffic. The communication bit is sent during periods when the network is not transmitting data. This function monitors the safety of the UTP channel. This function should be used in all possible cases and disabled only when a device that does not support it is connected to the hub port, for example, equipment such as HP StarLAN 10.
Ensuring secrecy in networks built using hubs, this is a rather thankless task, because... The Hub is by definition a broadcast device. But, if necessary, the following tools may be available to you: blocking unused ports, setting a password for the console port, setting information encryption on each port (some models have this feature).
At present, the use of hubs in local computer networks has practically ceased. In their place came faster and “smarter” devices - switches.
Designed to combine network devices into segments. The basic principle of its operation is to broadcast packets arriving on one of its ports to all other ports. Thus, a packet arriving on the network will be sent to all other devices on the network, i.e. will be broadcast. The hub operates on the open systems interoperability model (). The hub is used in various technologies: , xDSL, Token Ring, but it is most widespread in .
A hub can be thought of as having multiple outputs. In contrast, it does not analyze the contents of packets or their headers, but simply copies them. Hub does not allow you to increase the number of devices in one segment or relieve it by reducing the number of collisions. Its main task is to connect new devices to the network and organize its topology. In addition, the hub can be used to organize backup channels.
An example of network operation with a hub
The main advantage of the concentrator is its ease of implementation and, accordingly, low cost. However, due to the fact that it simply copies packets to all its ports, the likelihood of collisions on the network increases. This may result in reduced transmission speeds and packet delivery times. That is why, instead of hubs, they usually try to use ones that transmit packets only to the port to which the recipient computer is connected.
Depending on the tasks performed, you can find hubs of different capacities from 4 to 64 ports. However, this is not the limit. They can be combined into more capacious devices. The maximum possible number of devices operating in paired mode is limited only by the characteristics of the technology used (for - 1024 ports in one segment). Hubs also differ in the type of conductors used (twisted pair, coaxial cable) and the transmission medium used (electrical or ).
Using cable infrastructure like twisted pair. Currently replaced by network switches.
Network hubs could also have connectors for connecting to existing networks based on thick or thin coaxial cable.
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Operating principle
The hub operates at the first (physical) layer of the OSI network model, relaying the incoming signal from one of the ports to a signal to all other (connected) ports, thus implementing the typical Ethernet topology common bus, with division of network bandwidth between all devices and operation in half-duplex mode. Collisions (that is, an attempt by two or more devices to start transmitting at the same time) are processed similarly to the Ethernet network on other media - the devices independently stop transmitting and resume the attempt after a random period of time; in modern terms, a hub unites devices in one collision domain.
A network hub also ensures uninterrupted operation of the network when a device is disconnected from one of the ports or the cable is damaged, unlike, for example, a network on a coaxial cable, which in this case stops working entirely.
Advantages and Disadvantages
Compared to a repeater
The hub is a logical continuation of the repeater. Various manufacturers implement some of the following features:
- Ability to combine network segments with different physical media (for example, coaxial cable and twisted pair)
- Automatic shutdown of ports when errors occur on them
- Support for redundant links
Compared to a switch
The only advantage of the hub - low cost - was relevant only in the early years of the development of Ethernet networks. As electronic microprocessor components have improved and become cheaper, this advantage of the hub has completely disappeared, since the cost of the computing part of switches and routers is only a small fraction compared to the cost of connectors, isolation transformers, housing and power supply, common to the hub and switch.
The disadvantages of a hub are a logical continuation of the disadvantages of a shared bus topology, namely, a decrease in network throughput as the number of nodes increases. In addition, since the nodes are not isolated from each other at the physical layer, they will all operate at the data rate of the worst node. For example, if there are nodes in the network with a speed of 100 Mbit/s and only one node with a speed of 10 Mbit/s, then all nodes will operate at a speed of 10 Mbit/s, even if the 10 Mbit/s node does not show any information activity at all. Another disadvantage is that network traffic is broadcast to all ports, which reduces the level of network security and makes it possible to connect sniffers.
Switches
Intelligent devices that appeared later, operating at the second (link) level according to the OSI model (as opposed to hubs operating only at the first (physical) level) - switches capable of providing independent and selective transmission of Ethernet frames between ports by opening frame headers and forwarding them to the required ports in accordance with
