Network hub or hub. What is a USB hub: types and features
concentrator(hub) - a multiport device that combines several devices into one segment. In fact, the hub is a multiport repeater, that is, its main functional task is to receive data from computers or other hubs connected to the ports of the hub, reforming the signal simultaneously with its amplification, and its further relaying to other ports.
The principle of operation of the hub is as follows: the computer sends a signal to the hub, which is transmitted to all workstations connected to it. When the computer to which the message is addressed receives such a signal, it sends the requested information back to the hub, which again forwards it to all computers, although only one computer will process it.
The hub is used in networks with a star topology. You can connect network nodes to the hub ports: a computer, a network printer, a storage device, another hub, etc. The hub can have RJ-45 and BNC ports, which allows you to use a coaxial cable as a backbone, connecting several hubs in series in a chain
The constructive device, operation algorithms, functions and characteristics of concentrators depend on their area of application. Therefore, for each network building technology, their own hubs are produced (Ethernet, Token Ring, FDDI), designed to work specifically on this technology (a hub in an Ethernet network repeats a frame for all ports, in a 100VG-AnyLAN network it repeats a frame only to the port to which frame destination is connected).
Concentrates are of two types:
passive - performs only the connection of nodes in the segment of the data transmission medium, without signal regeneration. When using such a hub, each cable segment can be no more than half the length of the maximum possible for the technology used (unshielded twisted pair allows a signal between devices at a distance of up to 300 meters, so each segment from a passive hub to a network device can be no more than 150 m). When using a passive hub, each network device receives the signals sent by all other devices connected to the hub;
active - restores and amplifies the received signals, which allows you to increase the maximum length of cable segments connected to the hub. Also, using an active hub, you can create complex hierarchical network structures. Active hubs are also called switching hubs.
Depending on the application, concentrators can be:
with a fixed number of ports - made in the form of a separate housing with a certain number of ports (5, 8, 16, 24), display and control elements. The two extreme connectors are used to connect to other hubs using special trunk cables, and subscribers are connected to the remaining connectors using adapter cables;
chassis-based modular - has a common chassis with an internal bus to which modules with a fixed number of ports are connected. At the same time, modules can differ in the number of ports and the type of supported physical medium;
stack design - made in the form of a separate case, but has special ports for combining several such cases into a single one. The speed of the internal bus of such a hub is higher than the speed at which it can transfer data, so the speed of communication between stacked hubs will be higher than when connected through a port. At the same time, the number of network segments is limited, so the combination of four stacked hubs is perceived as one.
In addition to the main function (repeating and relaying packets), the concentrator may have additional features:
two speeds when connecting different types of networks. Most hub models are two-speed, but there are also devices with only one speed;
wireless access point - a modern switch has a built-in wireless access point used for a wireless network;
uplink port - allows you to connect the hub to other hubs (you can not replace it if there are not enough connections). One of the RJ-45 connectors of the hub has a wiring that allows you to connect it to other hubs - cascading. This port is labeled In, Uplink, Cascading, Cross-Over. In some cases, there is an MDI/MDI-X switch next to this port, allowing you to turn the port into normal mode or cascading mode. If the port is not equipped with a switch, but another computer needs to be connected to it (all ports are occupied), use a cross-over cable for a point-to-point connection. The uplink port is also used to connect the hub to a router or gateway providing network access to the Internet; when multiple hubs are used, they are all connected directly to the router or gateway, rather than daisy-chained to each other.
In almost all networks, there is definitely one device that has several names − concentrator, hub, repeater. Depending on the type of application, the functions may vary. The unchanging action remains - frame repetition either on some ports or on all, depending on the algorithm. Without knowing all the functions of the device, there may be.
The hub has several ports to which end nodes - computers - are connected using cables. Hubs are used in networks - Ethernet (), Token Ring, etc., to combine individual network segments into a single environment. In Token Rink technology, the hub can perform the function of shutting down misbehaving ports and switching to a backup ring. Ethernet() technology uses repeaters to combine multiple physical cable segments into one medium. In networks for combining coaxial cable are two port repeaters, so the word hub does not apply to them. Figure 1 shows a standard Ethernet hub that has 16 RJ-45 ports and one AUI port for an external transceiver.
Picture 1
Figure 2 also shows a connection of the type hub station — hub-hub on twisted pair. The choice of connections should be described in .
Figure 2
In most types of repeaters, the ports are connected by one repetition block, and when a signal passes between two ports of the repeater, the block introduces a delay once. It is called rule of 4 hubs(segment delay dependent on two repeaters).
The concentrator also has a function auto-segmentation- it disables incorrectly working ports. One reason for ports being disabled is the lack of a response. The following are also described below when a hub disables a port:
- Frame level errors.If the number of frames with errors exceeds a certain threshold, then the port is closed for a certain time. Such errors can be invalid header fields.
- Multiple collisions. If the hub analyzes that a certain port was the source of collision more than 60 times in a row, it is temporarily disabled.
- Protracted transfer. If the time it takes for a packet to pass through a port exceeds 3 times, that port is disabled.
Port close errors can occur due to:
- wrong;
- unexplored;
- unexplored;
- use is not correct in networks;
- network type - or .
- information security methods
Backup link support. Since the implementation of redundant channels is defined only in FDDI, other standards developers deal with this problem in particular situations. For example, Ethernet hubs can implement hierarchical links without loops. Therefore, backup channels should always connect only disabled ports, so as not to violate the logic of the network. If for some reason the port goes down, auto-segmentation kicks in and the hub makes the backup port active. This is shown in Figure 3. For various back-up communications support, it plays a big role.
Figure 3
Hubs can use a number of methods to protect information transmitted over local networks. Protection against unauthorized access. Local networks allow unauthorized eavesdropping and provide access to broadcast data. To do this, you just need to enable a software protocol analyzer on the end node of the network. The developers have implemented several means of protection in local networks. The simplest remedy is to use resolvable MAC addresses on the hub ports. The remedy lies in the fact that the administrator manually prescribes addresses to the concentrator of the addresses of end nodes. In this case, the fact of unauthorized connection can be fixed. This is shown in Figure 4. This is achieved by the way that the attacker, by disconnecting the end node and connecting his PC, changes the MAC address of the end node. The hub sees this and takes certain actions. For this implementation, the hub must have a control block.
Figure 4
Another means of protection is encryption. However, real-time encryption itself requires a lot of power for the repeater. Therefore, the hub inadvertently mangles the packet sent to all but the destination. This principle is shown in Figure 5. This principle reduces the chance of threats to information security.
A bit about network structuring
To build the simplest one-segment network, it is enough to have network adapters and a cable of the appropriate type. But even in this case, additional devices are often used - signal repeaters, which make it possible to overcome the restrictions on the maximum length of the cable segment.
main function repeater(repeater), as its name implies - repetition of signals arriving at one of its ports, on all other ports (Ethernet) or on the next port in a logical ring (Token Ring, FDDI) synchronously with incoming signals. The repeater improves the electrical characteristics of the signals and their synchronism, and due to this, it becomes possible to increase the total length of the cable between the most remote stations in the network.
A multiport repeater is often referred to as concentrator(hub), which reflects the fact that this device implements not only the signal repetition function, but also concentrates the functions of connecting computers to a network in one central device. In almost all modern networking standards, a hub is a necessary network element that connects individual computers to a network.
Segments of cable connecting two computers or any two other network devices are called physical segments. Thus, hubs and repeaters, which are used to add new physical segments, are a means of physically structuring the network.
Hubs form a common data transmission medium from separate physical cable sections - logical segment. A logical segment is also called a collision domain, because if any two computers in this segment try to transmit data simultaneously, even if they belong to different physical segments, a blocking of the transmission medium occurs. It should be emphasized that no matter how complex the hubs are, for example, by hierarchical connection, all computers connected to them form a single logical segment in which any pair of interacting computers completely blocks the possibility of data exchange for other computers.
What is a concentrator?
hub hub (wheel).
English-Russian dictionary
concentrator is a 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. At the same time, if a fault is detected on any of the ports, then this port is automatically disabled (segmented), and after the fault is eliminated, it becomes active again. Autosegmentation necessary to improve the reliability of the network. Collision processing and current monitoring of the state of communication channels is usually carried out by the concentrator itself. Hubs can be used as stand-alone 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 trunk cable in a bus topology. Since the logic of access to a shared environment essentially depends on the technology, each type of technology has its own models - Ethernet hubs, Token Ring hubs, FDDI hubs, VG-AnyLAN hubs.
A hub is a generalized name for devices that form a shared environment, regardless of the type of protocol being implemented. For a specific protocol, sometimes its own, narrow name for this device is used, reflecting more accurately its functions, or used due to tradition, for example, as the name of the MAU for Token Ring hubs.
Purpose of hubs- association of separate workplaces in the working group as a part of a local network. The working group is characterized by the following features: a certain territorial concentration; a team of users of the working group solves similar problems, uses the same type of software and common information bases; within the working group there are general requirements for ensuring safety and reliability, there is the same effect of external sources of disturbances (climatic, electromagnetic, etc.); high-performance peripherals are shared; usually contain their own local servers, often geographically located on the territory of the working group.
Hubs and the OSI Model
Hubs work on physical level(Layer 1 of the OSI Core Reference Model). Therefore, they are not sensitive to upper layer protocols. The result 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 these protocols and, accordingly, operational shells at network management stations. But this is not a very serious pressure, because the IP protocol is probably the most popular.
General properties of hubs
Most concentrators have the following characteristic operational features:
- Equipped with LED indicators for Port Status, Collisions, Activity, Fault, and Power for quick monitoring and troubleshooting of the entire hub
- when the power is turned on, perform a self-test procedure, and during operation, perform a self-diagnosis function
- have a standard size in width - 19 inches;
- provide auto-segmentation of ports to isolate faulty ports and improve network integrity
- detect polarity error when using twisted pair cable and automatically reverse polarity to eliminate wiring error
- support configurations using multiple hubs connected to each other either through special cables and stack ports, or a thin coaxial trunk connected between the BNC ports, or via fiber optic or thick coaxial cable connected through appropriate transceivers to the AUI port, or via UTP cables connected between hub ports
- support voice and data communication through the same cable bundle
- transparent to network operating system software
- can be installed and put into operation within minutes
Varieties of concentrators
Entry level hubs- five-, eight-, rarely twelve-, sixteen-port hubs. They often have an additional BNC port, less often an AUI port. It does not provide management 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 working group.
Mid-Range Hubs- twelve-, sixteen-, twenty-four-port concentrators. They have a console port, often additional BNC and AUI ports. This type of hub provides out-of-band management capabilities through the RS-232 console port under the control of some standard terminal program, allowing you to configure other ports and read hub statistics. This type of concentrator is positioned to build networks in the range from small to medium, which will further develop and require the introduction of programmatic control.
SNMP Managed Hubs- Twelve-, sixteen-, twenty-four- and sora-eight-port concentrators. 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), error sources and communication pairs (communications pairs) are identified. It is advisable to use these types of hubs to build local networks in the range from medium to higher, which will certainly develop. These networks always require programmatic network management, including remote.
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, often support SNMP protocols. They, like 10Base-T hubs, segment ports (disconnecting not one station, but subscribers of the entire physical segment) and broadcast incoming packets to all ports. Each BNC port is subject to the same restrictions as a 10Base-2 network fragment: thin coaxial cable segments up to 185 meters per port are supported, up to 30 network connections per segment, including "empty T-connectors" ; if a cable segment is compromised, that segment will be taken out of service, but the rest of the hub will continue to function. The scope of this type of concentrators is the modernization of old 10Base2 networks in order to increase their reliability, the modernization of networks that have reached the limits on the use of repeaters and do not require frequent changes.
10/100Hubs have appeared recently. If you just read ads about them, you can "get ambushed." The fact is that hubs do not know how to buffer packets, and therefore cannot negotiate different speeds. Therefore, if at least one 10Base-T standard station is connected to such a hub, then all ports will operate at its speed. According to rumors, there are already hubs that support two speeds at the same time. Perhaps, in this case, the manufacturer refers to a certain intermediate device (something in between a hub and a switch) as, for example, Cabletron Systems' MicroLAN by the word "hub".
Additional functions
redundant link. Midrange and SNMP-managed hubs support one redundant link per hub to create a back-up link between any two hubs. This provides network fault tolerance at the hardware level. The redundant link is a separate cable mounted between two hubs. Using the console port of a hub, you simply need to configure the primary link and the backup link of one of the hubs. The backup link is automatically unblocked when the primary link of the two hubs fails. Although the hub can control only one redundant link, it can be on the far end of one redundant link and on the controlling end of the redundant link to another hub. Once the fault on the main cable segment is cleared, the main link will not resume automatically. To resume the operation of the main connection, you will have to use the console of the hub or press the Reset button on its body.
"Connected Bit" for hubs, it is a periodic pulse with a duration of 100 nanoseconds, sent every 16 milliseconds. It does not affect network traffic. The link bit is sent during the period when the network is not transmitting data. This function monitors the integrity of the UTP channel. This feature should be used whenever possible and disabled only when a device that does not support it, such as HP StarLAN 10 type equipment, is connected to the hub port.
Ensuring secrecy in networks built using hubs, this is a rather thankless task, since a hub, by definition, is a broadcast device. But if necessary, the network administrator may have access to the following tools: blocking unused ports (by distorting the data field in frames repeated on ports that do not contain a computer with the destination address), setting a password on the console port, setting information encryption on each of the ports (some models have this option).
Multifunctional Modular Hubs
When building a complex network, all types of communication devices can be useful: hubs, bridges, switches, and routers (network adapters are excluded from this list because they are always needed). Most often, a single communication device performs only one main function, representing either a repeater, or a bridge, or a switch, or a router. But this is not always convenient, since in some cases it is more rational to have a multifunctional device in one housing that can combine these basic functions and thus allows the network designer to use it more flexibly.
Ideally, one can imagine a universal communication device that has a sufficient number of ports for connecting network adapters, which are combined into groups with programmable relationship functions between themselves (according to the algorithm of a repeater, switch or router). However, it is known that any universalization always harms the quality of performing narrow special functions and, perhaps, therefore, such a completely universal device has not yet appeared at the current level of technological development, although a separate combination of functions in one device is sometimes performed.
So routers can often act as bridges as well, depending on how their software is configured by the administrator. But the functions of the repeater require high performance, which can only be achieved at a purely hardware level. Therefore, repeater functions are not combined with bridge or router functions.
A different approach can be used to combine functions. In special devices modular hubs- individual components that perform one of the three main functions described are implemented as modules installed in a common housing. In this case, inter-module communications are organized not externally, as is done when the modules are separate devices, but through the internal buses of a single device.
Modular multifunction devices are often referred to as hubs, emphasizing their centralizing role in the network. At the same time, the term "hub" is used not as a kind of synonym for the term "repeater", but in a broader sense. It is necessary to understand well in each case the functional purpose of the individual modules of such a hub. Depending on the configuration, a modular multifunctional hub can combine the functions of a repeater (of different technologies), a bridge, a switch, and a router, or it can perform only one of them.
Switch or hub?
When building small networks that make up the lower level of the corporate network hierarchy, the question of using one or another communication device is reduced to the question of choosing between a hub or a switch.
In answering this question, several factors must be taken into account. Undoubtedly, it is of great importance cost per port, which you need to pay when choosing a device. From technical considerations, first of all, it is necessary to take into account the existing traffic distribution between network nodes. In addition, it is necessary to take into account the prospects for the development of the network: whether multimedia applications will be used in the near future, whether the computer base will be modernized. If yes, then today it is necessary to provide reserves for the bandwidth of the communication equipment used. The use of Intranet technology also leads to an increase in the amount of traffic circulating in the network, and this must also be taken into account when choosing a device.
When choosing a device type - hub or switch - you also need to determine and protocol type, which will support its ports (or protocols, if we are talking about a switch, since each port can support a separate protocol).
It is quite difficult to choose a communication device for a network with a dedicated server. In order to make a final decision, one must take into account network development prospects in relation to movement towards balanced traffic. If the network may soon have interaction between workstations, or a second server, then the choice must be made in favor of a switch that can support additional traffic without prejudice to the main one.
The factor can also play in favor of the switch distances- the use of switches does not limit the maximum network diameter to 2500 m or 210 m, which determine the size of the collision domain when using Ethernet and Fast Ethernet hubs.
Features of national governance
How do they manage to steal in Russia when there is no money anywhere, there is nothing to steal? Everything is very simple: in the West they steal from profits, while in our country they steal from expenses.
sad anecdote
Russian network administrators have especially warm feelings about hubs, and here's why. I will list once again the main criteria that should be followed when choosing a communication device:
· Price
traffic distribution
protocol type
Prospects for the development of the network
distance factor
And here is how (I'm exaggerating, of course) the same list looks like in the eyes of a typical Russian executive who makes a decision to purchase equipment for a small network:
· Price
They turn a blind eye to the distribution of traffic, the type of protocol and the geometric configuration of the network are chosen based on which equipment costs less, and it is generally not customary to think about development prospects. As a result, equipment is purchased that is cheaper "here and now", "if only it worked." Naturally, the most popular network technology is Thin Ethernet, the most popular server software (until recently) is Novell NetWare, and they try to do without any additional devices because of all their efforts, as long as the entire network fits in one physical segment.
And how does a typical manager answer the question “hub or switch”? What is cheaper! Of course, a hub, and often with such a number of ports, which is only enough "back to back".
This is such a glorious national tradition.
No, it's time to change traditions. It's time for the system administrator to explain to his boss that the savings now will turn into even greater expenses in a couple of years.
In no way did I mean to offend any of the leaders. It is nice to know that there are exceptions to the rules, and, fortunately, there are more and more such exceptions over time.
A bus is the simplest and most widely used topology. It has a line configuration, where all computers are connected by one cable. When computers are connected along the same cable [segment], the topology is called a bus. Signals are sent to all computers on the network. To prevent the effect of signal reflection, terminators are connected to the ends of the cable.
Basic topologies To share resources or perform other network tasks, computers must be connected to each other. Most networks use cable for this purpose.
The concept of network topology. Basic topologies The most important characteristic of a local area network is its topology, or, in other words, its configuration.
Topic 3. Network layout. Network topology
1. The concept of network topology. Basic topologies
2. Concepts of a hub and a switch .
3. Network with "bus" topology.
4. Network with "Star" topology
5. Network with "Ring" topology.
6. Combined topologies.
Topology or network topology, refers to the specific physical location of computers, cables, and other components on a network. Topology is a standard term used by professionals when describing the basic layout of a network. In addition to the term “topology”, the following are also used to describe the physical layout:
physical location;
layout;
Diagram;
The topology of a network determines its characteristics. In particular, the choice of a particular topology affects:
Network management method.
To share resources or perform other network tasks, computers must be connected to each other. Most networks use cable for this purpose.
Each network topology imposes a number of conditions. For example, it can dictate not only the type of cable, but also the way it is laid. Topology can also define the way computers on a network interact. Different types of topologies correspond to different methods of interaction, and these methods have a great impact on the network.
However, simply connecting a computer to a cable connecting other computers is not enough. Different types of cables, combined with different network cards, network operating systems, and other components, require different relative positions of computers.
Each network topology imposes a number of conditions. For example, it can dictate not only the type of cable, but also the way it is laid.
Topology can also define the way computers on a network interact. Different types of topologies correspond to different methods of interaction, and these methods have a great impact on the network.
Exists three basic types topologies: tire(bus);star(star);ring(ring). Based on these topologies, various combinations are built, such as star-bus and star-ring.
Only one computer can transfer data at a time. Therefore, the more computers in the network, the less its bandwidth.
When computers are connected to cable segments originating from a single point, or hub, the topology is called star. in topology "star" each computer is directly connected to a central component called concentrator.
concentrator used to centralize LAN traffic at one point. If a cable break occurs in the network where the hub is located, then this will only affect the operation of this segment, and not the entire network. Hubs allow you to easily expand the network and use different types of cables. If the central component fails, the entire network ceases to function.
concentrator- This is a device that allows you to connect computers to a network according to the star scheme. In the schematic diagram, the hub is located in the center of the star, and all computers are connected to it, computers seem to be concentrated in this device - hence the name.
Each computer can be connected to the hub with a cable up to 200 m long. If the distance at which the computer is located from the hub is more than 200 m, then an additional hub must be connected. Hubs can be connected to each other by a direct cable or through another device - a switch.
Switch is a device for connecting hubs in order to create an extensive network with many segments. Using a switch, you can create a network consisting of several simple "stars".
Using a combination of a switch and hubs, you can build networks of any complexity and configuration.
If the cable to which computers are connected is shorted in the ring such a topology is called a ring. Online token ring (with token passing) computers form a logical ring. The signal, or marker, circulates around the ring (in a clockwise direction) as it passes through each computer. The computer receives a free token and transmits data over the network. The receiving computer copies the data and marks it as received. The data then continues to circulate through the network to the transmitting computer, which removes it from the network and returns a free token.
For a real network to work, each computer must have network fee. The network card plugs into a free expansion slot on the computer's system board. A cable is connected to the network board through a special connector. In addition to network cards, other network equipment is also used - hubs, switches, print servers and other devices.
The topology of the network determines it characteristics. In particular, the choice of a particular topology affects:
On the composition of the necessary network equipment;
Characteristics of network equipment;
Network expansion options;
Network management method.
If you learn how to use different topologies, you can understand what capabilities different types of networks have.
Although the basic topologies themselves are not complex, in reality there are often quite complex combinations that combine the properties of several topologies. Let's take a closer look at each of the topologies.
3. Bus topology network
topology "tire" often call "line bus"(linear bus). This topology is one of the simplest and most widely used topologies. It uses a single cable, called a backbone or segment, along which all the computers on the network are connected.
The networks with the so-called tree structure and with a topology called "common bus". Any of the machines included in such a network can become a server, in addition, the network can expand almost unlimitedly - connecting new users does not entail configuration changes.
In a bus network, computers address data to a specific computer by transmitting it over a cable in the form of electrical signals. To understand the process of interaction of computers on the bus, you need to know the following concepts: signal transmission; signal reflection; Terminator.
signal transmission lies in the fact that data in the form of electrical signals is transmitted to all computers in the network; however, information is received only by the one whose address corresponds to the address of the recipient encrypted in these signals. Moreover, only one computer can transmit at a time.
Since data is transmitted to the network by only one computer, its performance depends on the number of computers connected to the bus. The more of them, i.e. the more computers waiting to transfer data, the slower the network.
However, it is impossible to derive a direct relationship between network bandwidth and the number of computers in it. For, apart from the number of computers, Network performance is influenced by many factors, including:
Characteristics of the hardware of computers in the network;
The frequency with which computers transmit data;
Type of running network applications;
Network cable type;
Distance between computers on the network.
Tire - passive topology. This means that computers only “listen” to data transmitted over the network, but do not move it from sender to recipient. Therefore, if one of the computers fails, it will not affect the operation of the others. AT active topologies, computers regenerate the signals and transmit them over the network.
Reflection signal is , that data, or electrical signals, propagate throughout the network - from one end of the cable to the other. If no special action is taken, the signal will be reflected when it reaches the end of the cable and prevent other computers from transmitting. Therefore, after the data reaches the destination, the electrical signals must be extinguished.
To prevent the reflection of electrical signals, at each end of the cable is installed terminators(terminators), absorbing these signals.
All ends of the network cable must be connected to something, such as a computer or to barrel connector- to increase the length of the cable. A terminator must be connected to any free - unconnected - end of the cable to prevent reflection of electrical signals.
At network integrity breach A network cable break occurs when it is physically broken or one of its ends is disconnected. It is also possible that there are no terminators at one or more ends of the cable, which leads to the reflection of electrical signals in the cable and the termination of the network. The network is down. By themselves, the computers on the network remain fully functional, but as long as the segment is broken, they cannot communicate with each other.
An increase in the area covered by the network necessitates its extensions. In a network with a bus topology, the cable is usually extended two ways. To connect two pieces of cable, you can use barrel connector(barrel connector). But you should not abuse them, as the signal weakens in this case.
It is better to buy one long cable than to connect several short lengths. With a large number of “connections”, signal distortion often occurs.
Used to connect two pieces of cable repeater(repeater). Unlike the connector it enhances signal before passing it on to the next segment. Therefore, it is preferable to use a repeater than a barrel connector or even one long cable: signals over long distances will go without distortion.
4. Network with "Star" topology
In a star topology, all computers are connected using cable segments to central component, called concentrator(hub). Signals from the transmitting computer go through the hub to everyone else. This topology originated in the early days of computing, when computers were connected to a central, main computer.
In star networks, cabling and network configuration management are centralized. But there is also flaw: since all computers are connected to a central point, cable consumption increases significantly for large networks. In addition, if the central component fails, the operation of the entire network will be disrupted. And if only one computer (or the cable connecting it to the hub) fails, then only that computer will not be able to transmit or receive data over the network. Other computers on the network will not be affected.
It should be noted that in networks with a star topology, the central node is concentrator.
There are three types of concentrators: active(active) concentrators, passive(passive) concentrators, hybrid(hybrid) concentrators.
Active Hubs regenerate and transmit signals in the same way as repeaters do. Sometimes they are called multiport repeaters- they have 8 to 12 ports for connecting computers.
Passive hubs- this is most often mounting panels or switching blocks. They simply pass the signal through themselves like switching nodes, without amplifying or restoring it. Passive hubs do not need to be connected to a power source.
hybrid hubs called hubs, to which you can connect cables of various types.
Networks built on hubs can easily be expanded by connecting additional hubs.
Advantages hubs are as follows:
1. A cable break in a network with a conventional “linear bus” topology will cause the entire network to “fall”. Meanwhile, breaking the cable connected to the hub will disrupt the operation of only this segment. The remaining segments will remain operational.
2. Easy to change or expand the network: just connect another computer or hub;
3. Using various ports to connect different types of cables, centralized monitoring of network operation and network traffic: in many networks, active hubs are endowed with diagnostic capabilities to determine the health of the connection.
5. Network with "Ring" topology. In a ring topology, computers are connected to the cable, closed in a ring. Therefore, the cable simply cannot have a free end to which the terminator must be connected. Signals travel around the ring in one direction and pass through each computer. In contrast to the passive bus topology, here every computer acts as a repeater, amplifying the signals and transmitting them to the next computer.
One of the principles of data transmission in a ring network is called passing the token. Its essence is this. The token is sequentially transmitted from one computer to another until it is received by the one that “wants” to transmit data. The transmitting computer changes the token, puts the email address in the data, and sends it around the ring.
The data passes through each computer until it reaches the one whose address matches the recipient address specified in the data.
After that, the receiving computer sends a message to the transmitting computer, where it confirms the fact of receiving data. After receiving the confirmation, the transmitting computer creates a new token and returns it to the network.
It seems like it takes a long time to send a marker, but in reality the marker moves at almost the speed of light. In a ring with a diameter of 200 m, the marker can circulate at a frequency of 10,000 revolutions per second.
Main disadvantage networks with a ring topology, when all computers are connected in series in a ring and any of them can become a server, is the difficulty of incorporating new users into the network.
6. Combined topologies. Topologies that combine bus, star, and ring network layouts are often used today. Let's consider some of them.
Star-tire(star bus) is a combination of bus and star topologies. Most often it looks like this: several networks with a star topology are combined using a backbone linear bus.
In this case, the failure of one computer has no effect on the network - the rest of the computers still communicate with each other. And the failure of the hub will cause the computers and hubs connected to it to stop.
ring star(star ring) seems somewhat similar to a star-tire. In both topologies, computers are connected to a hub, which actually forms a ring or bus. The difference is that the hubs in the star-bus are connected by a main linear bus, while in the star-ring they form a star based on the main hub.
Topology selection occurs when taking into account many factors for each specific situation.
USB technology, which was invented to connect computer and telecommunications devices, is now the main means for connecting many gadgets. Their number is simply amazing - 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 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 devices that are not in use, 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 multiple USB ports. It connects to one of the computer's USB ports (thus taking up one USB port in total), and allows you to use multiple USB devices. Thus, the USB hub increases the number of USB connectors on the computer, reduces wear and tear, and also facilitates the process of using multiple devices.
Types of USB hubs
There are four types of USB hubs. The first is a USB PCI card that plugs into a 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 plugs into one of your computer's external USB ports. After that, it will be possible to 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 downside. Some USB devices (printer, digital camera, scanner, etc.) require power, and this type of hub will not be able to provide the required amount of power, especially if you connect several devices at once.
The third type is a powered USB hub. It is also very compact and plugs into your computer's external USB port. In addition, such a USB hub can be plugged directly into a power outlet. This makes it possible to connect any kind of USB devices to it.
And the fourth type is a USB computer card. If you use a laptop at work, and you also need to constantly move with it, then just such a USB card would be an excellent alternative to a USB hub. It connects to the USB port on the side of the laptop and allows you to connect two additional devices.
