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Questions about Wi-Fi

Frequently asked questions about wireless local area networks.

What is a wireless local area network (WLAN)?

A WLAN is a type of local area network (LAN) that uses high-frequency radio waves for communication and data transfer between nodes, rather than cable connections. It is a flexible data transmission system that is used as an extension - or alternative - to a cable local area network inside a single building or within a certain area.

What are the benefits of using WLAN instead of wired LAN?

Productivity increase. WLAN provides an unattached network and Internet access. A WLAN network allows users to navigate the enterprise or organization, while remaining connected to the network.
Simple and fast building of a local network. No need to pull and tighten the cables.
Installation flexibility. A wireless network can be built where you can not stretch the cables; WLAN technology facilitates temporary network installation and relocation.
Reduced operating costs. Wireless networks reduce installation costs, since no cable connections are required. As a result, savings are achieved, the more significant the more often the environment changes.
Scalable. Expansion and reconfiguration of a network for a WLAN is not a difficult task: user devices can be integrated into the network by installing wireless network adapters on them.
Compatibility. Different brands of compatible client and network devices will interoperate.

Is the installation and administration of a WLAN difficult?

Not. Wireless LAN is easier to build than cable, the administration of both types of networks is almost the same. The client's WLAN solution is built on the principle of Plug-and-Play, which assumes that computers simply connect to a peer-to-peer network.

What is the communication range of WLAN devices?

The range of radio frequencies, especially in rooms, depends on the characteristics of the product (including the transmitter power), receiver design, noise immunity, and signal path. The interaction of radio waves with ordinary building objects, such as walls, metal structures, and even people, can affect the range of a signal, and thus change the range of a particular system. Wireless networks use radio frequencies because indoor radio waves penetrate walls and floors. The range or coverage of most WLAN systems reaches 160 m, depending on the number and type of obstacles encountered. With the help of additional access points, you can extend the area of ​​coverage, and thereby ensure freedom of movement.

Are WLANs Reliable?

Yes, WLANs are exceptionally reliable. Since wireless technology is rooted in the defense industry, the security of wireless devices has been foreseen from the very beginning. This is why wireless networks are usually more reliable than cable networks. WLANs use the Direct Sequence Spread Spectrum (DSSS) technology, which is highly resistant to data corruption, interference, including intentional, and detection. In addition, all users of the wireless network are authenticated by system identifier, which prevents unauthorized access to data.
To transfer sensitive data, users can use Wired Equivalent Privacy (WEP), in which the signal is encrypted with an additional algorithm, and the data is controlled using an electronic key. Generally speaking, in separate nodes, prior to being included in the network traffic, their own security measures should be taken. For 802.11b WLANs, 40-bit and 128-bit encryption algorithms can be used along with user authentication to provide higher network reliability. Interception of traffic, both intentional and unintentional, is practically impossible.

What is IEEE 802.11b?

IEEE 802.11b is a technical specification released by the Institute of Electrical and Electronic Engineers (IEEE) that defines the operation of wireless local area networks operating in the 2.4 GHz band at 11 Mbps using the Direct Sequence Spread Spectrum protocol.

What is the bandwidth of an 802.11b WLAN?

WLAN 802.11b networks operate at speeds up to 11 Mbps. For users, the speed is comparable to the speed of the cable network. Just like in a regular network, the capacity of a WLAN network depends on its topology, load, distance to the access point, etc. As a rule, there is no noticeable difference in wireless and cable network performance.

What is an access point?

The access point connects the cable and wireless network and allows customers to access the resources of the cable network. Each access point extends the total computing power of the system. Users can move between access points without losing the connection to the network - just like when they connect to the network using a cell phone. In other words, an access point is a hardware and software device that acts as a hub for a wireless client and provides a connection to a cable network.

How many users can a single WLAN system support?

The number of users is almost unlimited. It can be increased simply by installing new access points. With overlapping access points tuned to different frequencies (channels), the wireless network can be expanded by increasing the number of users in one zone. Overlapping channels that will not interfere with each other, no more than three can be installed at the same time; these channels will triple the number of network users. Similarly, you can expand your wireless network by installing access points in different parts of the building. This increases the total number of users and enables them to navigate the building or territory of the organization.

How many users does one access point simultaneously support?

The number of users in this case depends, first of all, on the traffic load. In a WLAN network, bandwidth is shared among users just like in a cable network. Based on the number of users, network performance also depends on the type of tasks performed by users.

Man is a social being. This definition implies first of all communication between different people. With all at once or separately it does not matter. Our distant ancestors were able to realize the opportunities for communication that were laid down by nature. The air exhaled in a special way began to take shape into words, which later received a graphic representation in the form of writing.

However, communication with sound remained and remains the most preferable. For a long time, we used natural ways of transmitting sound waves: shouting as far as possible while gesticulating with all possible limbs, showing that we want something from someone who is far away now; or it was just possible to transfer what was necessary through an intermediary.

In the second half of the XIX century, the voice began to be transmitted by wire. The speed increased by several orders of magnitude - now it was enough to pick up the phone and in a few seconds you could hear a person on another continent 20,000 kilometers away. Technologies of the last century made communication even more accessible and convenient. She became wireless. Today you can "catch" almost anyone wherever he is. Another thing is that not everyone is happy with such "freedom", especially those for whom it has become another way of control, but the story is not about that.

Computers allowed to transmit over distances not only sound (voice in particular), but also text, and recently video transmission has become an increasingly popular service. And if you observe the latest trends, then computer networks become: a) wireless; and b) global. It is in all the diversity of wireless digital network standards that we will try to understand this article.

Cellular communications, the latest generations of which stubbornly become "native" not only for phones, but also for computers, we will not touch. This is done in our other article: "". Here we will touch on those networks that are created at a less "global" level, but at the same time are very common.

Many modern wireless standards support work with almost any PC, but some of them are designed for somewhat less universal, but at the same time very popular devices. For example, cell phones. Indeed, many of them today can transmit and receive data not only from GSM networks (NMT, CDMA and others), but also to exchange data with local devices. It is with short-range wireless networks that we begin.

Bluetooth

The Bluetooth standard (or as it is popularly called “blue tooth”) is one of the most famous and popular today. It was developed in 1994 by two specialists from Ericsson, Sweden, Jaap Haartsen and Sven Mattisson. The main purpose of Bluetooth is to provide data exchange without wires between two or more devices.

Since the origin of the "tooth" was a company engaged in the production of mobile phones, this technology was created for these devices. Is it any wonder that the Ericsson R520 was one of the first phones equipped with the Bluetooth module? By today's standards, it is a very weighty and functionally deprived "brick", which in its time was unclaimed.

Why? Yes, because 6-7 years ago, Bluetooth was literally equipped with a couple of devices. Exactly the same was the situation with Wi-Fi. What was the point of letting Apple buy an iBook with an optional wireless network card if there were only a couple of access points for sale at a fabulous price? But Wi-Fi could easily be paired with a conventional wired network, which is not possible with Bluetooth. After all, for data exchange, not all the standardized TCP / IP protocol is used at all, but its own. But more about that later.

For now let's touch the history of the issue. On May 20, 1998, the creation of the Bluetooth Special Interest Group (SIG) was officially announced, which began to develop and adopt standards for this technology. Initially, it included Ericsson (now Sony Ericsson), IBM, Intel, Toshiba and Nokia). Later they were joined by others. To date, the group has adopted six Bluetooth standards:

Bluetooth 1.0 and 1.0B

The very first versions of the standard had many errors and flaws. When pairing devices, there were various problems, the connection was unstable.

Bluetooth 1.1

The new version of the standard eliminated many errors 1.0B, and was also adopted as the IEEE 802.15.1-2002 standard. This added support for working through channels without data encryption, as well as support for the Signal Strength Indicator (RSSI).

Bluetooth 1.2

Version 1.2 was the peak of the development of the first generation of "blue tooth". You can still find commercially available devices with its support (for example, laptops or phones of three or four years ago). Among its changes are the following:

faster search for devices and connection to them;

increased stability of the compound, especially when driving;

higher data exchange rate (in practice up to 721 Kbps);

improved quality of communication with the sound transmitting headset;

added support for HCI (Host Controller Interface).

This version has been adopted as the IEEE 802.15.1-2005 standard. But, pretty soon it was replaced by the second generation of Bluetooth.

Bluetooth 2.0

Bluetooth 2.0 has become quite a significant event in the digital industry. The new “teeth” could now “chew on” much more data, as the postfix "EDR" clearly indicates, adding to the updated standard name: Bluetooth 2.0 + EDR. EDR means Enhanced Data Rate, which freely can be translated as "Teeth in three rows." Joke. In fact, the translation sounds like "Extended bandwidth". The speed in some cases increased by 10 times, but did not really exceed 2.1 Mbit / s, and the peak value is 3.0 Mbit / s.

Interestingly, Bluetooth 2.0 without EDR is Bluetooth 1.2 with bug fixes. Some devices support exactly this version of it, although most manufacturers have provided increased speed   data transmission. In addition, power consumption was reduced.

Bluetooth 2.1

Recently, Bluetooth 2.1 has been adopted. This happened already during the stay of our project, about which we even wrote the appropriate one. Innovations have been made slightly. Among them - an even greater reduction in power consumption, accelerated pairing, better immunity and others. Until now, not many have attended to the support of this version. So modern laptops (for which the data transfer rate is much more important than for mobile phones) are still equipped with Bluetooth 2.0 + EDR controllers.

Bluetooth 3.0

Of course, the development of Bluetooth has not stopped. Although today there are quite a few alternatives to this standard, which will be discussed later, the development of the Bluetooth 3.0 standard, known under the code name "Seattle", is already underway. That he will be even faster, you can guess so. The Bluetooth SIG organization wants to adapt the UWB technology (a bit lower about it), capable of providing speeds of up to 480 Mbps (here, without undue modesty, we can talk about several hundred “rows of teeth”).

If this concept is implemented, Bluetooth will become a serious competitor to the actively developed and already implemented Wireless USB standard, which, oddly enough, is based on the same UWB specification. But more about that later.

Of course, in addition to significantly increased bandwidth, new features will be added. So it is planned to introduce support for special information points that will contain any information (advertising, weather data, stock prices, currencies, etc.), and it will be possible to read it from them. Simplification of device pairing is also expected, thanks to automated topology management. An alternative to MAC and PHY profiles will be introduced for data transmission, which will reduce energy consumption with low data flow, as well as increase the speed if you need to transfer a large amount of information.

Now consider the principle of Bluetooth. This standard does not work with access points like Wi-Fi — any device equipped with an appropriate controller can act as an access point. Conventionally, it is called a "master" and forms around itself a "piconet" (piconet), into which up to seven other devices can enter. More precisely, seven devices can be active at a given time, while another 255 pieces can be in an inactive state, which is reversed if necessary.

The piconet can be interconnected. Then several devices will act as a bridge for data exchange. But while full support for this functionality has not appeared. However, it is she who should be implemented in future versions of the standard.

At one point in time, data can be exchanged with one device. If you need to give the data to another, then the switch quickly. Parallel transmission is also possible, but it is rarely used. At the same time in the piconet any of the slave devices, if necessary, easily take on the role of master.

Provide Bluetooth support modern computers   Special USB adapters are designed. Many modern laptops of the average price range (from $ 1000) usually have a built-in controller. Controllers come in three classes:

Class 3.   Power 1 mW. The range of about 1 meter;

Class 2.Power 2.5 mW. The range of about 10 meters;

Class 1.Power 100 mW. The range of about 100 meters.

Today Class 1 and 2 are the most common. It is not surprising - despite the very low power consumption of the Class 3, its scope is extremely limited. Even for a headset, it fits very poorly. It is not necessary to keep the phone in a breast pocket - it can easily be in jeans, where the pocket is sewn just above the knee, or even on the table, and the owner will be observed within a radius of 5-7 meters from the device.

But Class 1 and 2 are sold quite actively. If you choose your external USB Bluetooth adapter, it is better to take care of its range. After all, even with a Class 1 adapter, a weaker Class 2 device can work at a greater distance.

Well, a little about the scope. As it has already become clear, these are primarily mobile “gadgets”: the exchange of data between cell phones (pocket computers, cell phones and laptops, etc.), the connection of a wireless headset for a conversation. Recently, Bluetooth has become actively used in computer mice and keyboards. Many GPS navigators "speak" with the help of "blue teeth". Even the joysticks of modern consoles Nintendo Wii and PlayStation 3 work via Bluetooth.

However, not all devices need a high data transfer rate, as well as a large radius of action. This is clearly demonstrated by Apple on its phone communicator. Who does not know, we inform that his Bluetooth-controller can work only with a headset. Data exchange is not available to him.

And really, why should a cell phone (especially an entry level) have the ability to transfer more information? "Teeth" in them are most often used for a headset. And in this case, you need a stable data stream, normally transmitted over a distance of 5-10 meters with a fixed speed, consuming a minimum of energy. This is what prompted some companies to create branched standards.

Wibree

In mid-June 2007, Nokia issued an official press release, which was informed about the development of the standard. Wibree is based on Bluetooth technology and is designed to complement it, but not compete. Most importantly, it differs from the "original" - a significantly lower power consumption. It is assumed that Wibree modules will be used in devices like biometric sensors that monitor human parameters, in a wireless headset, keyboards, and various remote control devices. So do not be surprised if soon a person standing next to you on the bus suddenly presses something in the area of ​​his navel and starts talking to himself.

Wibree will work in the same range as Bluetooth: 2.4 GHz. Maximum bandwidth is up to 1 Mbps. The range is 5-10 meters. Generally reminiscent of Bluetooth 1.2 Class 2 with ultra low power consumption.

Although Wibree is based on blue teeth, there is still no full backward compatibility. Although nothing prevents you from integrating it into modern Bluetooth controllers, you only have to modify them a bit. But in any case, all modern devices will not be able to exchange data with your tennis racket, a bio sensor, stuck to your body or a smart kettle, reporting boiling not with a banal whistle, but through your mobile phone via SMS.

But Wibree is not the only "low-power" standard. There are its analogues, and already ready, and sometimes even the first generation. Wibree final specifications will be ready in the first half of this year, while ZigBee already exists in its third version.

Zigbee

ZigBee is another "ultra mega super maxi low-power" wireless standard with two "ee" at the end. It was first conceived back in 1998, when it became clear that Wi-Fi and Bluetooth are not suitable for all occasions. Like the last ZigBee created to pair devices, but its principle of operation is somewhat different.

There are three types of ZigBee devices: the coordinator (ZigBee Coordinator - ZC), the router (ZigBee Router - ZR) and the "end device" (ZigBee End Device - ZED). The first is the main one in the created wireless network and can serve as both a router and a bridge for data exchange and with other networks. The router receives data from the end device, and can also exchange information with other routers and coordinators. The end device itself can only transfer data.

Thus, ZigBee is excluded as a technology for exchanging data between digital devices such as players, cameras, printers, PDAs, laptops, and so on. But the use of this technology in production or as a security system is much more important. It is in this direction that it is used.

On the official page of the project, you can read successful projects related to the automation of production (at the factory, during construction, etc.), ensuring the safety of the premises, the automation of modern buildings, the integration of home appliances into a single network, and so on. Bluetooth (and Wibree) are more focused on transmitting “computer” data, while ZigBee’s channels mainly circulate bits and bytes from technical information   from sensors, remote controls, etc.

Now a little about the principles of building ZigBee-networks. There are two of them: without and with constant ZED polling. In the first case, the router or coordinator is in constant waiting for a signal from the end device (ZED). Good example   Such a network can serve as a wireless light switch. The lamp acts as a router, usually equipped with a constant power source. ZED is the switch itself. He is in an inactive state. But as soon as you click on it, it will activate and send a signal to the router. The latter will react and give a command to turn on the light. In this case, the energy transfer data will be spent at the very least. Batteries in the switch will last for a year, or even a few years. Of course, if you do not constantly make "light music".

The second option assumes that the router will poll the ZED at regular intervals. At the same time it will consume less energy, so there is no need for a constant power source. But more electricity will be needed for the ZED. We believe that this type of network is more suitable for security systems, or for various sensors. By doing a ZED survey, you can check the status of a particular object, and, if necessary, quickly respond to changes in the situation.

ZigBee devices must comply with the IEEE 802.15.4-2003 standard, which allows operation at 2.4 GHz, 915 and 868 MHz. In the first case, up to 16 channels can be used for data transmission (at frequencies of 2405-2480 MHz in 5 MHz increments). In this case, the speed of information exchange can reach 250 Kbps. At frequencies of 915 and 868 MHz, the speed is 40 and 20 Kbit / s, respectively. The choice of these three frequency ranges is dictated by both technological reasons and geographic ones. So the frequency of 868 MHz is allowed in Europe, 915 in Australia and the USA, and 2.4 GHz almost everywhere. It is worth noting that ZigBee supports 128-bit encryption.

So, ZigBee is a great example of the implementation of an industrial wireless standard that expands and simplifies our life and work. Bluetooth and Wibree would be really bad for this purpose, which is why such specialized technology was created. Today it is supported by a large number of manufacturers. Entering the ZigBee Alliance and starting to use standard specifications for commercial purposes costs only $ 3,500 per year. And if not commercial, it is generally free.

There are several more such developments, for example, MiWi, JenNet, EnOcean, Z-Wave. They compete with both ZigBee and Wibree, and their implementation at some points coincides. We will not dwell on them - although they are digital, they are still used to exchange data between relatively simple and highly specialized devices. And in this material we are primarily interested in what provides for the interaction of computers, cell phones, PDAs and multimedia. household appliances. ZigBee was described only as an example of an alternative use of wireless networks. In the meantime, we are moving on to the next subclass of standards operating at a relatively small radius, but already with tremendous speeds compared to Bluetooth.

Uwb

The volume of information transmitted grows with every second. So 7-8 years ago, the MP3 format seemed like a panacea for the widespread distribution of music over the Internet. Thousands of compressed tracks with an average bit rate of 128 Kbps appeared on the Web, which made the average size of a single composition equal to 3-6 MB. At that time, websites were optimized both in terms of code and graphics, and no one even thought about downloading movies.

Let's see what happens now. Songs are also distributed to MP3, only the average bitrate has grown to 160-320 Kbps. And earlier, if we could look for a smaller version of a song, now it's the other way around - we are looking for a better quality, especially if we like the track very much. Movies in MPEG4 format, which perfectly matched one DVD to one CD, now often take up 1400 MB instead of the more usual 700 MB. But modern speeds allow you to download a full DVD from a P2P network (for example, BitTorrent) in a few hours, which are gradually beginning to be replaced by HDTV. In the latter case, we are talking about tens of gigabytes.

Modern hard drives   easily transfer data at speeds up to 100 MB / s, and the capacity of optical disks has increased to 50 GB, and in two or three years it can double. Do you think modern Bluetooth speed is enough for such volumes? How long does it take to transfer 20 GB through a 3 Mbit / s channel? Even a fairly fast Wi-Fi standard is not good here. It is created rather for wireless internetrather than watching an HDTV movie from a nearby computer. In this case, a technology is needed that can provide a high data transfer rate, and not necessarily at a great distance. This is the main concept of UWB.

UWB is an abbreviation of Ultra-WideBand, which in our free translation sounds like "awesome fast connection". Joke? Nearly. The connection is really very fast, which is ensured thanks to the broadband data transmission. As noted above, this is not really a technology, but rather a concept. This is the basis for various standards, two of which are described below.

At the heart of UWB is still the IEEE 802.15.4a draft standard. Unlike conventional radio transmissions, UWB transmits data using waves generated at specific points in time. It uses a wide frequency range, thus causing time modulation.

For data transmission, frequencies of 500 MHz and higher can be used. But on February 14, 2002, the Federal Communications Commission (FCC - Federal Communications Commission) of the United States recommended a range of 3.1-10.6 GHz for UWB. It is assumed that data transmission will be carried out within the same room, although with increasing transmitter and receiver power, the range of the network will also increase. However, it is prohibited.

Now about the appointment. It is not difficult to guess that UWB will be used to transfer large amounts of data between digital devices. Among the latter, first of all, you can include computers, cell phones (especially top models with large amounts of memory), printers, digital photo and video cameras, audio and video players, and so on. The maximum speed of UWB is unknown to us, but it can reach tens of gigabits. Very impressive value not only by modern standards, but also by the standards of the near future. So there is a stock.

Now directly about the standards based on UWB. First of all, this is a new generation of Bluetooth. It is not yet clear whether this concept will be used in Bluetooth 3.0 or not, but there is definitely something in the plans. There are rumors of an increase in speed of up to 480 Mbps. We believe that they are not far from the truth, only here such opportunities will be available mainly for transferring large amounts of data and after fifty warnings about high power consumption. Yet such speeds will not be available for nothing.

But when the light will see the specifications of Bluetooth 3.0 is still unknown. But now Wireless USB controllers are ready for mass production, and more recently we announced the release of the first version of the standard. Let us dwell on these two technologies in more detail.

Wireless usb

Wireless USB (abbreviated as WUSB) is not entirely new. Intel first spoke about it at its spring 2004 IDF session. The devices themselves then did not provide, as well as not announced the availability of specifications. They simply announced that such a technology exists. There is so there, thought the people who heard it, and continued to live on as they lived before.

In 2005, during the IDF autumn session, Intel had already shown the first prototypes. Prototype i must say inspired. True, it is not clear what exactly: respect or amazement. It was a massive PCI-card on which the PCMCIA-controller was integrated, and an antenna stuck behind the mount. A strange decision, which in the future should have been integrated into motherboards and laptops. However, as it turned out, it was rather the first working sample, rather than the prototype of the series.

To date, it seems that both normal Wireless USB modules and the first devices with its support are available. What are these devices? Yes, exactly the same ones that we connect through a regular USB connector: printers, scanners, cameras, mice, external hard drives, PDA, etc. WUSB allows you to transfer the capabilities of such a popular wired serial bus to wireless rails.

Let's see how it works. Let's start with the topology. For the exchange of data between devices is a special host controller. Each device that is in range, is allocated a separate communication channel. The latter is especially important if you have to transfer data at high speed - channel separation like Wi-Fi can lead to sad consequences (for example, optical disk   when recording, if the data will be too slow). One "normal" WUSB host supports connecting up to 127 devices.

There are also not quite “normal” host controllers — these are the devices themselves. They have a limited list of capabilities, but can also receive and transmit data from other sources. In this way, a kind of cellular network is obtained, when information from a fairly remote source can pass through several devices, and then get to the main host, which will transmit it directly to the computer making the request.

How can this be used in the same apartment or house? Somewhere not very far from the main computer you install a WUSB controller, or connect it directly to motherboard. After that you can use any devices within the room that can work with Wireless USB directly or through a hub. Yes, it is the hub - host controller that can be equipped with the most common USB ports to which the most ordinary devices like a mouse, keyboard, printer can be connected.

At the same time to communicate with other rooms can be used as other host controllers or Wireless USB devices   as well as more convenient Wi-Fi access points, or even ordinary LAN switches.

The huge advantage of Wireless USB is its full compatibility with the original wired standard. An analogy with LAN and WLAN is appropriate: point wi-Fi access   connects to a wired LAN using the most common twisted pair, after which all devices within its radius of operation can safely use the resources of the entire network, not just wireless.

Since WUSB provides USB compatibility, this wireless standard should work just as fast. Actually, the way it is: in a radius of 3 meters, the speed will be 480 Mbit / s, and in a radius of 10 meters - 110 Mbit / s. In subsequent versions of the standard promise to raise the speed to 1 Gbit / s. For data transmission, frequencies from the range of 3.1-10.6 GHz are used, which clearly indicates the origin of this standard from UWB.

As for energy consumption, it should not be very significant. So, modern mobile phones and PDAs with a WUSB controller enabled will work about as much as before (of course, if you do not constantly transfer gigabytes of information), and WUSB-based remotes will be able to hold on for one charge for several months. Although in the latter case it is much more relevant to use technologies like Wibree or ZigBee - it’s more economical, and the range is more.

Does Wireless USB have any future prospects? Judging by the data of the agency iSuppli has. So in 2007, the market for compatible devices amounted to only $ 15 million, but by 2011 it will increase to $ 2.6 billion. The number of devices sold will increase from 1 million to 500 million in the same 2011. Well, let's hope that everything will be .

Wirelesshd

Wirelessly connect computers and peripheralsworking with them is far from the limit for modern technology. Yes, and put up with a short USB cable from the printer to system block   big work will not be. But if you have an expensive home theater system installed, from which and to which a cloud of wires stretches, then it may be thought to get rid of them and her. Nevertheless, it is not always so easy to hide such "charms of life", even if there are only a few of them.

If we consider that modern home theaters are original semi-computers, then equipping them with the support of wireless communications is not so difficult. Is it any wonder that Sony LocationFree-like consoles began to appear capable of transmitting video and audio from a computer to LCD TVs and acoustics? However, they work via Wi-Fi, and this type of network bandwidth will not always be enough, especially if you transmit video in 1080i / p format.

So the WirelessHD standard was invented. Most recently, we are on the adoption of the first version of its specifications. This is a special wireless standard designed to combine consumer electronics. Its frequency range goes far beyond UWB and operates at 60 GHz (± 5 GHz depending on the country). Its radius of action is small - only 10 meters. This is quite enough to customize the interaction of home theater devices.

The use of such frequencies is necessary to achieve high data transfer rates. It is about 2-5 Gbit / s in the first versions of the standard. But the theoretical limit is 20-25 Gbit / s. For comparison, the peak for HDMI 1.3 is 10.2 Gbps. So there is a reserve for the future, and very good one at that.

At the head wireless networkHD is the coordinator - a device that controls the transmission of audio and video streams, as well as sets their priorities. All other devices are stations that can be both a source and a receiver of data, as well as the coordinator himself.

Whether the support for WirelessHD will be provided for the computer is still unknown, but we believe that it will. This is just like the HDMI outputs on many modern video cards and laptops. Thus, video and audio can be played with ordinary computerthat will significantly expand the functionality. After all, domestic players do not always support the latest codecs, not to mention the formats of disks. I must say that the implementation of this technology is really very useful and relevant. It is much more convenient than what is used now. And now, as we said, Wi-Fi is used. We proceed to the description of this standard.

Wi-Fi

Of all the Wi-Fi standards discussed in this article, paired with Bluetooth is the most famous and popular. Wi-Fi gained its popularity thanks to laptops. Today, even the cheapest models are equipped with a wireless network card. But, as always, this technology did not become popular right away as it was presented.

The first work on Wi-Fi began in the 80s of the last century. However, the final specifications were ready only in 1997. The IEEE organization assigned them the label 802.11 (or rather 802.11-1997). In 1999, they were adopted as a standard. New and promising technology immediately picked up Apple. As an option to the new iBook laptops, a Wi-Fi network card was offered. But Apple even now does not occupy a dominant position in the market, and then it only began to emerge from a protracted crisis. So the "fruit company" was not able to walk around the planet as a pioneer, sowing Wi-Fi grain everywhere. This honor was reserved for Intel.

We believe many have heard about the mobile platform Intel Centrino. Her first generation was introduced in 2003. The laptop, to get a new and trendy logo, must be based on an Intel processor (now Core Duo or Core 2 Duo, and then on a Pentium M), an Intel chipset, and also inside it must be installed Wi-Fi network   Intel production card. This was the impetus for the widespread distribution of wireless local area networks.

However, it cannot be said that this is the sole merit of Intel alone. Just the market was already ready for this technology. The initiative of Apple at one time was too innovative, that it was accepted by no means all. Four years later, Wi-Fi equipment was also quite expensive, but not so much. Yes, and the range has expanded significantly. Intel simply provided everyone with the most convenient form for adopting the next technology, designed to bring a bright future closer.

Now let's see how the Wi-Fi works. As has already become clear, the corresponding network card must be installed in the computer. It can be either a PCI (or PCI Express) expansion card, or a relatively small USB stick. For laptops there are versions in PCMCIA (PC Card) and ExpressCard.

Using wireless network card   You can establish a connection with another one the same. That is, it is not difficult to establish network connection   between two laptops or between a laptop and a desktop PC. Only here, despite the apparent freedom to connect to them another participant will not succeed. The third, as they say, is superfluous. To get around this restriction, one has to resort to access points.

A Wi-Fi access point is an analogue of a regular local area network router. Only connections to it are made via radio transmission, and not by wire. Theoretically, their number is unlimited, although for greater speed and stability it is better to distribute the connected computers between several points. In this case, the analogy with cellular communication is relevant. One base station can serve several subscribers at the same time, but if there are a lot of them it is overloaded and someone can not get through, and someone will disconnect.

In general, the principle of deployment of Wi-Fi is quite similar to a cellular network. In the role base stations   Access points protrude. If set up accordingly, they will communicate with each other, making it possible to exchange information between computers connected to any of them. If you do not do this, the Wi-Fi card management program will provide the ability to connect to one of the available networks.

But to connect to Wi-Fi network   sometimes you need to know the password, or the key to access it. Still, very important data can be transmitted via the network, such as passwords for accessing money accounts of various services, and it is much easier to intercept a radio program than the usual information exchange over wires. To this end, several encryption standards have been implemented.

The first of these, WEP (Wired Equivalent Privacy), adopted in 2001, did not last long. It is considered a rather weak protection against unauthorized entry. Today, you can easily find a program that can hack a key in a short time, after which it will be possible to track all packets on the network.

In mid-2003, WEP was proposed to replace new algorithm   WPA encryption (Wi-Fi Protected Access). It was based on the 802.11i draft standard. The latter was later adopted in June 2004. At the same time, as the main method of protection, he proposed a more advanced WPA2 algorithm. Hacking it is much more difficult, so its use is strongly recommended. Of course, progress does not stand still, and even more advanced protection features have been proposed, which will be adopted as standards in the future. One of these is 802.11w.

A little about the need to protect data. Today, quite often the access point is installed in the apartment to network all local computers (Yes, and PDAs with cell phones, if they support Wi-Fi). Moreover, if you exchange only movies, music and similar information, then your network is of no great value. However, nothing will prevent a neighbor behind the wall from connecting his laptop to your network, especially if it is not protected. In addition, in such a network there is no need to fear everyone and everything, so you can open certain sections in full free access. hard drives. Of course, nothing but the latest comedy and action movie may not lie there, but there will always be those who want to spoil it. It's still not nice if the movie just copied is deleted before viewing.

But the situation is different. At your home, the Internet is connected via an ADSL modem. If you have several computers, or one laptop for convenience, the modem can be equipped Wi-Fi point   access. Agree to sit comfortably from anywhere in the apartment on the web. If Wi-Fi is not properly secured, then anyone can access your Internet. Theoretically, even from the street, you can sit on the bench under the window. Well, if you have an unlimited channel - you just feel a decrease in speed. And if the traffic? You can fly into the entire amount that lies on the account. So protection of a local wireless network is of paramount importance. And it is not necessary to be limited only to WPA (2) encryption. If computers are always a static number, each can create a separate account, and at the same time make identification by the MAC address of the network card.

Well, about the standards of Wi-Fi. In total, we managed to learn about 28 standards. But only six of them directly describe the speed of data exchange, the range of action and the operating frequency:

The very first version of Wi-Fi to put it mildly is not impressive. Although it was adopted before Bluetooth, it does not even reach modern Bluetooth 2.0 + EDR. But the standard was originally developed as a wireless analogue of wired LANs where huge amounts of data can be transmitted. 802.11a / b provided far better options, especially 802.11a. But the frequency of 5.0 GHz is not allowed everywhere, so it was not widespread. That is why 802.11g was developed, which provides the same speed as well as the ability to work at 2.4 GHz.

Since last year, access points and network cards with 802.11n support began to appear on the market. As can be seen from the table, it works several times faster than 802.11g. However, this standard is still designated as draft. Judging by the available data, it will be adopted no earlier than next year. But most likely all modern devices based on 802.11n draft will be compatible with the final specification after updating the firmware.

The 802.11y standard is an analogue of 802.11g capable of operating at a much greater distance (up to 5 km in open space). It was for this purpose that he was created. To achieve these indicators, we had to use higher-frequency waves from the 3.7 GHz range.

Now we will list all other standards from the 802.11 family. All Latin characters were reserved for it:

As you can see, Wi-Fi is still growing. It is possible that the speed of this technology will increase even more in the future. In addition, today not a small attention is paid to the implementation of support for this standard in all devices. Communicators and mobile phones with Wi-Fi are not rare. It is not surprising, there are access points in many modern cities. And the Internet through them can be much faster than through the WWAN (EDGE / GPRS, UMTS / WCDMA, HSDPA). However, another very promising technology was invented for the Internet: WiMAX.

WiMAX

Completes our list of standard WiMAX. Its main difference from all previous ones is in the range. Depending on the transmitters used, the signal can be received at a distance of up to 50 km from the source. Here we are talking about analog cellular communication, and not just about "another wireless LAN".

WiMAX is not entirely designed for deploying a network within an apartment, house or area, although it can be used for this. One of its main goals is to provide high-speed access to the Internet both for particularly remote communities, and for individual areas of the city.

This is not exactly an alternative to cellular communication, since it provides several other possibilities and it is no longer computer oriented. Rather, it is an intermediate option between the standards of cellular communication. last generations   (UMTS, HSDPA) and wireless local area networks. WiMAX provides a larger radius than Wi-Fi, but the average data transfer rate will be lower. At the same time, cellular communication is deployed for much greater distance and is more noise-resistant, but the data transfer rate in it is lower.

However, WiMAX is called a competitor to fourth-generation cellular networks. We tend to believe that this is not far from the truth, but only in part. Yet WiMAX is designed primarily for computers, and only then for communicators and mobile phones. But we are starting to delve into the specifics of the work of this standard. First, a little history.

The WiMAX Forum organization, formed in 2001, is responsible for the development of WiMAX specifications. The WiMAX name itself is an abbreviation of Worldwide Interoperability for Microwave Access or "Worldwide Networking for Microwave Access." In December 2001, the final WiMAX specifications, ratified as the 802.16-2001 standard, were presented. In 2004, the 802.16-2004 standard, also known as 802.16d, was adopted, describing the possibility of organizing WiMAX indoors. Finally the latest version   The standard was adopted in 2005 and received the 802.16-2005 index, but also informally referred to as 802.16e.

Now about the principles of work. Inside WiMAX, the IP protocol is implemented, allowing it to simply integrate with modern networks. So this technology can be a great addition to Wi-Fi. But unlike the latest WiMAX provides a more stable connection. For example, a connection to a Wi-Fi access point with a significant distance may be unstable if there is another point nearby. In the case of WiMAX, a single slot is allocated to one connection, which no one else can use. And when you move, various WiMAX base stations will be responsible for its activity.

Yes, WiMAX is also based on base stations. Depending on the tasks, they can be quite small (for example, for premises), or installed on separate towers in order to transmit data over a long distance. Initially, WiMAX was assigned a frequency range of 10-66 GHz, but later added support for lower frequencies 2-11 GHz.

Why does everyone need this? The range of 10-66 GHz is good for constant transmission at high speeds. So the peak transfer rate can reach 120 Mbps and this is at a distance of tens of kilometers. A great option for connecting a small settlement. But since ultra-high frequencies require direct visibility for an ordinary city, they are not as good. So from a laptop or mobile phone to connect to the network will be somewhat problematic. For them, the range of 2-11 GHz is much better suited.

In this regard, there are four modes of WiMAX:

Fixed WiMAX.Uses the high-frequency range of 10-66 GHz, designed to combine distant objects that are within the line of sight;

Nomadic WiMAX.   Essentially the same Fixed WiMAX, but with session support. So having connected to one tower session is created. If you go beyond its reach, but you find yourself in a different area, your session can be transferred. In this case, the connection will not suffer;

Portable WiMAX.Allows you to automatically switch sessions from one base station to another. Uses a lower frequency range, allowing you to move at speeds of up to 40 km / h;

Mobile WiMAX.This version of the standard was adopted as the latest version of the 802.16-2005 supplement. Allows you to receive a signal at speeds up to 120 km / h. Great for mobile devices.

As you can see, all categories are covered: from sleeping areas of large cities, as well as their offices, to remote settlements and people moving between them with laptops, PDAs, mobile phones. If it is widely distributed, it can really become a serious competitor of fourth-generation cellular networks being developed today. Of course, the latter meanwhile promise speeds of up to several gigabits, but the second version of WiMAX standards will also raise the bar to 100 Mbps in the case of mobile mode and to 1 Gbps in fixed mode.

However, WiMAX has not really been introduced anywhere. Dozens of test networks are deployed worldwide, including Russia and Ukraine. And in the majority while it is Fixed WiMAX. However, South Korea in a test mode deployed a WiBro network, which is essentially renamed Mobile WiMAX. It provides a connection at speeds up to 30-50 Mbit / s in a radius of up to 5 km. The speed can be up to 120 km / h. For comparison - the usual cellular communication operates at speeds up to 250 km / h.

Also for the time being there are few devices on sale both for deployment and for using WiMAX. The latter should be presented with the fifth generation of the mobile platform Intel Centrino in mid-2008. We hope that this can serve as a similar impetus for the market, which at one time was the first Intel Centrino for Wi-Fi.

Will end

Total what we see? Wireless networks surround the whole world with their invisible "threads". They do not interfere with any boundaries, without drying water, or buildings, and even better there would be more energy and more open space. And the more this will be, the closer our bright future is with you. The future, where everything will be united into a single network between not only all possible phones, computers, coffee makers, kettles, stoves, refrigerators and irons, but also all the planets of the solar system, the galaxy, and the small planet K-PAX.

Seriously, the future prospects are clear. Miniature devices will gradually gain the ability to exchange data using the Bluetooth standard (or its similar replacement). The range of the wireless headset will expand with the assistance of Wibree, and the ZigBee will turn on the light in the room from the remote.

Unite the periphery within the room called Wireless USB. By the way, not so long ago he was called to help him. It provides the same speeds, except that the distance from the source can be no more than a few centimeters. Freedom of placing devices is not much, but there is no need for wires. For home theater is designed WirelessHD. An interesting and promising technology that may eventually push out the modern wired connection.

At the level of an apartment or even several apartments, or for the interconnection of wired LANs between houses, Wi-Fi will be used. It is for this purpose created and it is more convenient. It is much cheaper to install a small access point for $ 50-70 in an apartment or in a cafe (for visitors) than expensive WiMAX equipment. But it will also have to be installed and configured correctly.

As for WiMAX, this standard is well suited primarily for Internet providers. With it, they will be able to bring the light beam of the World Wide Web into the darkest backwaters of our planet. However, it is not yet known what the fourth generation of cellular communication will offer us. In any case, we will win - the ordinary inhabitants of the small planet Earth, already girdled with wires, from which everyone is now rapidly getting rid of.

The material used information from the following resources:

Wireless Technologies - Wireless Network Classification

  First of all, let's define the names and standards so that we can speak the same language.
So, the interaction of wireless devices is regulated by a number of standards. They indicate the spectrum of the radio frequency range, data transfer rate, method of data transmission and other information. The main developer of technical standards for wireless communications is the IEEE organization.
  The IEEE 802.11 standard regulates the operation of wireless devices on WLAN networks (Wireless LAN). Today the following amendments are in effect - 802.11a, 802.11b, 802.11g and 802.11n. All these technologies are classified as Wi-Fi (Wireless Fidelity).

The Wi-Fi Alliance is responsible for testing devices for wireless LANs manufactured by different manufacturers. The Wi-Fi logo on the case of the device means that this equipment can interact with other devices of the same standard.
  For those who are curious, I provide some technical data from existing IEEE 802.11 revisions:
802.11a:

• uses 5 GHz radio spectrum;
• incompatible with 2.4 GHz spectrum, i.e. 802.11 b / g / n devices;
• range is approximately 33% of 802.11 b / g;
• relatively expensive to implement compared to other technologies;
• 802.11a compliant equipment is becoming increasingly rare.

802.11b:

• the first technology 2.4 GHz;
• maximum data transfer rate of 11 Mbps;
• the range is approximately 46 meters indoors and 96 meters outdoors.

802.11g:

• 2.4 GHz technology family;
• maximum data transfer rate increased to 54 Mbps;
• the range is the same as the 802.11b;
• backward compatible with 802.11b.

  802.11n:

• newest standard;
• 2.4 GHz technology (the draft standard provides support for 5 GHz);
• increased range and throughput;
• backward compatibility with existing 802.11g and 802.11b hardware.

  Most of the existing devices work with 802.11g and 802.11n standards. It is noteworthy that due to the mass advantages, the widespread use of the 802.11n standard began long before its ratification.
  Each wireless access point has its own service set identifier (SSID) - for us, users, this identifier is represented as a network name:

  The SSID tells wireless devices what wireless network they belong to and what devices they communicate with. Accordingly, if several wireless devices (computers) are connected to one access point - they form a local wireless network.
The SSID is an alphanumeric string, case-sensitive, of up to 32 characters. This identifier is sent in the header of all data packets transmitted over the local wireless network.

There are two types of wireless networks: ad-hoc and infrastructure network.

  As mentioned, the access point has a limited coverage area. To increase coverage, you can set up multiple access points with a common SSID. In this case, it should be remembered that in order for the transition between cells to be possible without losing the signal, the coverage areas of neighboring access points must intersect each other by about 10%. This allows the client to connect to the second access point before disconnecting from the first access point.

Basic access point setup

  Let's try setting up an access point. I will give an example of setting up an integrated router (this is the name of the box that combines the router, switch and wireless access point) D-Link DGL-4500. Since the web interface of interaction with the router is very similar for different models of different manufacturers, you can easily perform the same operations with your device.
  In my case, the wireless settings are as follows:

Let us examine the most significant points:

• Enable Wireless   - turns the access point on and off. We are, of course, interested in the state of "on".
• Wireless Network Name (Also called SSID)   - ID of the wireless network, or in other words, its name. The SSID is the hallmark of each wireless LAN, and all devices participating in the same network must use the same SSID.
• 802.11 band   - this setting is not present in most routers and corresponds to the frequency of the used radio frequency spectrum. Leave the default value - 2.4 GHz.
• 802.11 mode - It is worth to focus attention. Most home access points support different standards. These are mainly 802.11b, 802.11g and 802.11n standards. Although they all use the 2.4 GHz frequency band, each of them uses its own technology to achieve maximum throughput. Therefore, the choice of 802.11 Mode at the access point depends on the type of connected wireless device. If only one type of device is connected to the access point, select 802.11 Mode that supports this device. If several types of wireless devices are connected, you should select mixed mode, but remember that network performance will decrease due to the increased load on support for multiple 802.11 Mode. The type of wireless standard in each device can be found in the user manual.
• Wireless channel   - if all access points worked at a single frequency, they would be in a single coverage area, they would become a serious obstacle to each other, just as I interfere with two radio stations on neighboring frequencies. To solve this problem, 11 wireless communication channels were created - each channel has its own frequency (all of them are close to 2.4 GHz or 5 GHz, depending on the type of connection used). The channel for the access point is selected taking into account the adjacent wireless networks. In order to achieve optimal operation of neighboring access points, bandwidth should be chosen in each channel with a difference of at least 6 channels (for example, in one 1st channel, in the second 7th and above). All access points provide the ability to manually configure the channel. My access point also provides the ability to automatically search for the least loaded channels (setting Enable Auto Channel Scan).
• Transmission Rate   and Channel width   - these settings are also not present in most routers and are responsible for the speed of data transfer. Leave them as default values.
• Visibility Status - To quickly detect a wireless network by clients, an access point sends a network identifier SSID every few seconds. The SSID distribution feature can be disabled by setting the Visibility Status to “invisible”. In this case, the SSID will not be broadcast, it will need to be manually configured on wireless clients, so network invisibility can be an additional security measure to prevent unwanted connections. This can be useful if you need to hide the network (it simply will not appear in the search results of available networks on client devices).

  After saving the settings, wireless network   will become available for connection. It's time to get familiar with the security settings.

Securing Wireless LAN

  One of the main advantages of wireless networks is the convenience of connecting devices. The flip side of the coin is a network vulnerability to intercept information and attacks from malicious users — a hacker does not need to physically connect to your computer or any other device to gain access to your network; it can tune into your wireless, network signals just like a radio station wave.
  A hacker can access your network from anywhere within the wireless range. Having access to your network, attackers will be able to use your Internet services for free, as well as gain access to computers on the network and damage files, or steal personal or confidential information. Of course, this does not apply to cafes, airports and other establishments, where the access point devoid of any protection is specifically set up so that everyone can use it.
  To protect against these wireless vulnerabilities, special security features and methods to protect against external attacks are needed. To do this, it is enough to perform several simple operations during the initial setup of the access point.
  As mentioned, one of the easiest ways to restrict access to a wireless network is to disable the SSID distribution.
  As an additional security measure, it is strongly recommended to change the default settings, as the integrated routers come with pre-configured SSIDs, passwords and IP addresses. Using the default settings, an attacker can easily identify the network and gain access.
Even if the SSID broadcast is disabled, there is a possibility of network penetration if the attacker becomes aware of the default SSID. If you do not change other default settings, namely passwords and IP addresses, hackers can penetrate the access point and make changes to its configuration. The default settings should be changed to more secure and unique.
  These changes alone do not guarantee the security of your network. For example, the SSID is transmitted in clear text, without data encryption. But today there are devices for intercepting wireless signals and reading messages in plain text. Even if the SSID broadcast function is disabled and defaults are changed, hackers can find out the name of the wireless network using such devices, since the identifier is sent in the header of all data packets transmitted over the local wireless network. Using this information, they will be able to connect to the network. To ensure wireless LAN security, a combination of several security methods should be used.
  One way to restrict access to a wireless network is to filter by MAC address:

  When using filtering by MAC address, the decision on the admission of a specific device to the wireless network is made based on the MAC address. Every time a wireless client attempts to establish a connection or associates with an access point, it must transmit its MAC address. If the filtering function is enabled by MAC address, the access point will search for the MAC address of this device in its predefined list. Connection to the network will be allowed only to those devices whose MAC addresses are entered into the database of the router. If the MAC address is not in the database, the device will be refused to connect or exchange data over the wireless network.
  You can find out the MAC address of a computer network card by running the getmac command in command line. MAC addresses of other network devices are available in the settings of the devices themselves or in the user manual.
  This security method has some drawbacks. For example, he assumes that the MAC addresses of all devices that must be granted access to the network are included in the database before the connection attempt is made. A device not recognized by the database cannot complete the connection. In addition, an attacker can create a clone of the MAC address of a device that has access to the network.
Another way to administer access is authentication. Authentication is the granting of permission to enter the network based on the results of authentication of a set of credentials (a password and in some cases a user name).
  There are three groups of authentication methods in wireless networks: open authentication, PSK and EAP.

• Open authentication   - This is the default authentication setting, in which all devices are allowed to establish connections regardless of their type and membership. Open authentication should only be used in publicly available wireless networks, such as schools and Internet cafes (restaurants).
• Pre-shared Key (PSK)   - in this mode, the access point and the client must use a common key or a code word. The access point sends a random byte string to the client. The client accepts this string, encrypts it using the key, and sends it back to the access point. The access point receives an encrypted string and uses its key to decrypt it. If the decoded string received from the client matches the source string sent to the client, the client is given permission to establish a connection. As you can see, one-way authentication is performed in this technology, i.e. access point checks the details of the connected node. PSK does not imply that the device authenticates the access point, nor does it authenticate the user connecting to the access point.
• Extensible Authentication Protocol (EAP)- provides mutual or two-way authentication, as well as authentication of each specific user. If EAP software is installed on the client side, the client interacts with an internal authentication server, such as the Remote Authentication Dial-In User Service (RADIUS). This internal server operates independently of the access point and maintains a database of users who have permission to access the network. When using EAP, the user must present the name and password, which are then checked against the RADIUS server database. If the presented credentials are valid, the user is considered authenticated.

If the authentication function is enabled, then regardless of the method used, the client must successfully authenticate before being granted permission to connect to the access point. If the authentication and MAC filtering functions are enabled, then authentication is performed first.
  Authentication and MAC filtering can block a hacker from accessing a wireless network, but cannot prevent the interception of transmitted data. Since there are no clear boundaries of wireless networks and all traffic is transmitted without wires, a hacker can easily intercept or read data frames of a wireless network. Encryption is the process of transforming data in such a way that even intercepting information is useless. There are several ways to encrypt data in wireless networks:

• Wired Network (WEP) Compatible Privacy Protocol   - It is an advanced security mechanism that allows you to encrypt network traffic during transmission. WEP uses pre-configured keys to encrypt and decrypt data. The WEP key is entered as a string of numbers and letters 64 or 128 bits long (in some cases, WEP also supports 256-bit keys). To simplify the creation and entry of these keys, many devices use passphrases. A passphrase is a simple means of memorizing a word or phrase used in automatic key generation.
• For effective operation of the WEP protocol, the access point, as well as each wireless device that has permission to access the network, must use a common WEP key. Without this key, devices will not be able to recognize data transmitted over the wireless network.
• WEP is an effective means of protecting data from interception. However, WEP also has its weaknesses, one of which is the use of a static key for all devices with WEP support. There are programs that allow an attacker to determine the WEP key. These programs can be found on the Internet. After the burglar gets the key, he gets full access   to all information transmitted.
• One of the means of protecting against such a vulnerability is frequent key changes. There is an advanced and secure encryption tool - Wi-Fi Protected Access Protocol (WPA).
• Wi-Fi Protected Access Protocol (WPA) - this protocol uses encryption keys of length from 64 to 256 bits. At the same time, WPA, in contrast to WEP, generates new dynamic keys each time a client attempts to establish a connection with an access point. For this reason, WPA is considered to be more secure than WEP, since it is much harder to crack.

  The most preferred type of connection in a home or small office environment is to use the WPA-Personal mode:

With such a connection, all users wishing to connect to the network will have to enter a single password predefined in the settings of the access point (Pre-Shared Key), and the data sent will be encrypted with the WPA protocol.
  In a large-scale wireless network, it may be worth switching to using WPA-Enterprise, where access control to the network will be controlled by the RADIUS authentication server, and the data being sent will be encrypted with WPA.

Customer setup

  In the case of the included SSID mailing, setting up clients with modern softwarecomes down to simple input   Password (in case of non-open network authentication):

In the case of disabled SSID distribution, the network will have to be manually determined once. In Windows 7, to do this, go to the Network and Sharing Center, select Manage Wireless Networks and click the Add button. In the window that appears, select Manually create a network profile and in the window that appears, enter all the network data:

  After saving the settings, you can connect to this hidden network at any time by selecting it from the list of available.

Tags: wlan, wireless networks, authentication

Detailed description

Wireless LAN (WLAN)   represents wireless computer networkthat connects two or more devices using a wireless distribution method (often with spread spectrum or OFDM) within a limited area, such as at home, school, computer lab, or office building. This gives users the ability to move within local coverage   and still be connected to the networkand can also provide internet connection. Most modern wireless lan   based on the IEEE 802.11 standards sold under the brand name Wi-Fi .

Wireless local networks   have become popular in everyday life, due to ease of installation and use, as well as in commercial complexes offering wireless access   to their customers, often for free.

Do you know that ... New York, for example, has launched a pilot program to provide urban workers in all parts of the city with wireless Internet access.

Initially hardware WLAN (Wireless Local Area Network)   used only as cable network alternatives where the use of cables was difficult or impossible at all.

STATIONS
  All components that can be connected to a wireless network environment are called by stations. All stations are equipped wireless network interface controllers (WNICs). Wireless stations   fall into one of two categories: wireless access points   and customers . Access points , usually, wireless routers   are base stations for wireless network. They transmit and receive radio frequencies for wireless devices with support   to communicate with others. Wireless customers   can be mobile devicessuch as laptops, pocket personal computers, IP phones and other smartphones or stationary devices, such as desktop computers and workstations, which are equipped wireless network interface.

BASE SET
Basic Service Kit   is a set of all stations that can interact with each other at the physical level. Each set has an identification number and is called Bssid   which is MAC address of the access pointserving the basic service.

There are two types basic service set: Independent bss (IBSS)   and bSS infrastructure . Independent BSS (IBSS)   represents special network that does not contain access points , which means that they cannot connect to any other basic services.

EXTENDED SERVICE SET
Extended Service Set (ESS)   represents set of connected bss, access points in which are connected by a distribution system. Each Ess   has an id called sSID, which is a 32-byte character string.

DISTRIBUTION SYSTEM
Distribution System (DS) connects all access points to Extended set of services. DS    can be used to increase network coverage through roaming between cells.

Also, DS   may be   wiredor   wireless. Modern wireless distribution systems   mainly based on WDS   or mesh protocols, however other systems are used.

Problems and areas of application of wireless LAN

Wireless local area networks (WLAN) in some cases are preferable to the wired network solution, and sometimes just the only possible one. In WLAN, the signal is propagated by high frequency electromagnetic waves.

The advantage of wireless LANs is obvious - they are easier and cheaper to deploy and modify, since the entire bulky cable infrastructure is redundant. Another advantage is the mobility of users. However, the main problem is an unstable and unpredictable wireless environment, for example, interference from various household appliances   and other telecommunications systems, atmospheric noise and signal reflections.

Local networks are, first of all, a network of buildings, and the propagation of a radio signal inside a building is even more complicated than outside it.

Spread spectrum techniques help to reduce the effect of interference on the wanted signal, in addition, forward error correction (FEC) and protocols with retransmission of lost frames are widely used in wireless networks.

Uneven distribution of signal intensity leads not only to bit errors of the transmitted information, but also to the uncertainty of the coverage area of ​​a wireless local area network. There is no such problem on wired LANs. Wireless LAN does not have a precise coverage area. In fact, the signal can be so weakened that devices that are within the intended limits of the coverage area cannot receive and transmit information at all.

In fig. 12.14a shows a fragmented local network. The incomplete wireless network raises the problem of accessing a shared environment, known as a hidden terminal. The problem occurs when two nodes are out of reach of each other (nodes A and C in Fig. 12.14, a), and there is a third node B that receives signals from both A and C. Suppose that The radio network uses a traditional access method based on listening to the carrier, for example CSMA / CD. In this case, collisions will occur much more frequently than in wired networks. Suppose, for example, node B is busy exchanging with node A. It is difficult for node C to determine that the medium is busy, it can consider it free and start sending its frame. As a result, the signals in the vicinity of the node B will be distorted, that is, a collision will occur, the probability of occurrence of which in a wired network would be immeasurably lower.

The recognition of collisions is difficult in the radio network also because the signal of the own transmitter substantially suppresses the signal of the remote transmitter, and it is often impossible to recognize the distortion of the signal.

In access methods used in wireless networks, they refuse not only to listen to the carrier, but also to recognize collisions. Instead, they use collision avoidance techniques, including polling methods.

The use of a base station can improve network connectivity (Fig. 12.14, b). The base station usually has more power, and its antenna is installed so as to cover the necessary territory more evenly and smoothly. As a result, all nodes of a wireless local area network are able to communicate with the base station, which transits data between nodes.

Fig. 12.14. Wireless LAN connectivity: a - a specialized wireless network, b - a wireless network with a base station

Wireless LANs are considered promising for applications in which it is difficult or impossible to use wired networks. Applications of wireless local area networks.

Home LANs. When several computers appear in the house, the organization of a home local network becomes an urgent problem.

Resident access by alternative telecom operators who do not have a wired one, access to clients living in apartment buildings,

The so-called "nomadic" access at airports, railway stations, etc.

The organization of local networks in buildings, where there is no possibility to install a modern cable system, for example, in historic buildings with an original interior.

The organization of temporary local networks, for example, during conferences.

LAN extensions. Sometimes one building of an enterprise, such as a testing laboratory or workshop, may be located separately from others. A small number of jobs in such a building makes it extremely disadvantageous to lay a separate cable to it, so wireless communication turns out to be a more rational option.

Mobile local networks. If a user wants to receive network services, moving from room to room or from building to building, then there is simply no competitor for a wireless LAN. A classic example of such a user is a crawler who uses his laptop to communicate with a hospital database.

802.11 LAN Topologies

The 802.11 standard supports two types of local network topologies: with basic and with extended service sets.

A network with a basic set of services (Basic Service Set, BSS) is formed by individual stations, the base station is not present, and the nodes interact with each other directly, Figure 12.15. in order to enter the BSS network, the station must perform the join procedure.

BSS networks are not traditional cells in terms of coverage areas, they can be located at a considerable distance from each other, but can partially or completely overlap - the 802.11 standard leaves freedom here for the network designer.

Stations can use a shared environment to transmit data:

directly to each other within the same BSS network;

within the same BSS network through the access point;

between different BSS networks via two access points and a distributed system;

between the BSS network and the wired LAN through the access point, distributed system and portal

Fig. 12.15. Networks with basic services

In networks with infrastructure, some network stations are basic, or, in 802.11 terminology, access points (Access Point, AP). A station that performs the functions of an AP is a member of some BSS network (Fig. 12.16). All network base stations are interconnected using a distributed system (Distribution System, DS), which can use the same medium (i.e. radio or infrared waves) as the medium of interaction between stations, or a different one, for example wired. Access points along with the distributed system support the Distributed System Service (DSS). The task of DSS is to transfer packets between stations that for some reason cannot or do not want to interact with each other directly. The most obvious reason for using DSS is that stations belong to different BSS networks. In this case, they transmit 1 frame to their access wheelbarrow, which through DS transmits it to an access point serving the BSS network with the destination station.

Fig. 12.16. Extended Service Network

An Extended Service Set (ESS) network consists of several BSS networks interconnected in a distributed environment.

The ESS network provides stations with mobility - they can move from one BSS network to another. These movements are provided by functions of the MAC level of working and base stations, because they are completely transparent for the LLC level. An ESS network may also interface with a wired LAN. For this, a portal must be present in the distributed system.

Bridge as a predecessor and functional analog of the switch

Logical Networking and Bridges

Bridgelocal network(LAN bridge), or just bridge,appeared as a means of building large local networks on a shared environment, since it is impossible to build a fairly large network on a single shared environment

Using a single shared environment on an Ethernet network leads to several very strict limitations:

the total diameter of the network can not be more than 2500 m;

the number of nodes cannot exceed 1024 (for Ethernet networks on coax, this restriction is even stricter).

Figure 13.1 shows the dependence of the access delay to the transmission medium on the network load, obtained for Ethernet, Token Ring and FDDI by means of simulation modeling.

Fig. 13.1. Ethernet Access Delay for Ethernet, Token Ring and FDDI

As can be seen from the figure, all technologies are characterized by a qualitatively identical picture of the exponential growth of the value of access delays with increasing network utilization. However, they are distinguished by a threshold at which a sharp change occurs in the behavior of the network, when an almost straight-line relationship turns into a steep exponential one. For the whole family of Ethernet technologies - this is 30-50% (the effect of collisions has an effect), for the Token Ring technology - 60%, and for the FDDI technology - 70-80%.

Restrictions arising from the use of a single shared environment can be overcome by performing a logical network structuring, that is, by segmented a single shared environment into several and connecting the resulting network segments with some communication device that does not transmit data bit by bit as a repeater, but bases frames and then sends them to one or another segment depending on the destination address of the frame (Figure 13.2)

It is necessary to distinguish logical structuring from physical. Hubs of the 10Base-T standard allow building a network consisting of several cable segments on a twisted pair, but this is physical structuring, since all these segments logically represent a single shared environment.

The bridge has long been the main type of devices that were used for the logical structuring of local networks. Now, bridges have replaced switches, but since the algorithm of their work repeats the algorithm of operation of the bridge, the results of their application are of the same nature, they are only enhanced due to the much higher performance of the switches.

In addition to bridges / switches, routers can be used to structure local area networks, but they are more complex and expensive devices, and, moreover, always require manual configuration, so their use in local area networks is limited.

The logical structuring of the local network allows you to solve several problems, the main of which is to increase productivity, flexibility and security, as well as improving network manageability.

Fig. 13.2. Logical network structuring

When building a network as a set of segments, each of them can be adapted to the specific needs of the working group or department. This means increased network flexibility. The process of splitting the network into logical segments can be viewed in the opposite direction, as the process of creating a large network from existing small networks.

By installing various logical filters on bridges / switches, you can control user access to resources in other segments, which repeaters do not allow. This is achieved by improving data security.

A side effect of reducing traffic and improving data security is to simplify network management, that is, improve network manageability. Problems are very often localized within a segment. The segments form logical network management domains.

IEEE 802.1D transparent bridge algorithm

In the local networks of the 80s and 90s, bridges of several types were used:

transparent bridges (for Ethernet technology);

bridges with source routing (for Token Ring technology);

broadcast bridges (for Ethernet and Token Ring technology connections).

The word “transparent” in the name of the transparent bridge algorithm reflects the fact that bridges and switches in their work do not take into account the existence of network adapters for end nodes, hubs and repeaters. At the same time, the listed network devices function without “noticing” the presence of bridges and switches in the network.

The bridge builds its promotion table (address table) on the basis of passive observation of the traffic circulating in the segments connected to its ports. In this case, the bridge takes into account the addresses of the sources of data frames arriving at its ports. At the source address of the frame, the bridge concludes that the source node belongs to one or another network segment,

Consider the process of automatically creating a table of bridge promotion and its use on the example of a simple network shown in Fig. 13.4.

Fig. 13.4. The principle of the transparent bridge / switch

The bridge connects two network segments. Segment 1 consists of computers connected with one coaxial cable to port 1 of the bridge, and segment 2 - computers connected with another coaxial cable to port 2 of the bridge. In the initial state, the bridge does not know about the computers with which MAC addresses are connected to each of its ports. In this situation, the bridge simply transmits any captured and buffered frame to all its ports, except for the port from which this frame is received. In our example, the bridge has only two ports, so it sends frames from port 1 to port 2, and vice versa. The difference in the operation of the bridge in this mode from the repeater is that it transmits a frame, pre-buffering it, and not bit by bit, as the repeater does. Buffering breaks the logic of all segments as a single shared environment.

Simultaneously with the transfer of the frame to all ports, the bridge studies the source address of the frame and records its belonging to a particular segment in its address table. This table is also called the filter table, or promotion. For example, having received a frame from computer 1 on port 1, the bridge makes the first entry in its address table:

MAC-address 1 - port 1.

This entry means that the computer with the MAC address 1 belongs to the segment connected to port 1 of the switch. If all four computers of this network are active and send frames to each other, then the bridge will soon build a complete network address table consisting of 4 entries - one entry per node (see. Fig. 13.4).

With each arrival of the frame in the port of the bridge, it first of all tries to find the destination address of the frame in the address table. We continue the consideration of the actions of the bridge for example (see Fig. 13.4).

When receiving a frame sent from computer 1 to computer 3, the bridge scans the address table for matching address in any of the records with the destination address - MAC address 3. The record with the desired address is in the address table.

The bridge performs the second stage of the table analysis - it checks whether the computers with source and destination addresses are in the same segment. In the example, computer 1 (MAC address 1) and computer 3 (MAC address 3) are in different segments. Consequently, the bridge performs a frame forwarding operation — it forwards the frame to port 2, which leads to the recipient segment, gets access to the segment and sends the frame there.

If it turned out that the computers belonged to the same segment, the frame would simply be removed from the buffer. Such an operation is called fikering.

If the MAC address 3 entry was missing from the address table, that is, different and words, destination address was unknownto the bridge, it would transmit the frame to all its ports, except the port - the source of the frame, as well as at the initial stage of the learning process.

The process of learning the bridge never ends and occurs simultaneously with the promotion and filtering of personnel. The bridge constantly monitors the source addresses of the buffered frames in order to automatically adapt to changes occurring in the network, such as the movement of computers from one network segment to another, the disconnection and the appearance of new computers.

The entries of the address table can be dynamic, created during the self-learning process of the bridge, and static, manually created by the network administrator. Static entries, but have a lifetime, which gives the administrator the ability to influence the operation of the bridge, for example, by limiting the transfer of frames with specific addresses from one segment to another.

Dynamic records have a lifetime — when you create or update an entry in the address table, a time stamp is associated with it. After a certain time-out, the entry is marked as invalid if during this time the bridge has not received a single frame with the given address in the source address field. This allows the bridge to automatically respond to moving the computer from segment to segment — when it is disconnected from the old segment, the record that the computer belongs to that segment is deleted from the address table over time. After the computer is connected to another segment, its frames will start to get into the bridge buffer through another port, and the address table will appear new recordcorresponding to the current state of the network.

Frames with broadcast MAC addresses, like frames with unknown destination addresses, are transmitted by the bridge to all of its ports. This frame propagation mode is called flooding. The presence of bridges in the network does not prevent the spread of broadcast frames in all network segments. However, this is an advantage only when the broadcast address is generated by a correctly working node.

Often, as a result of any software or hardware failures, the top-level protocol or network adapter   It starts to work incorrectly, namely, to generate frames with a broadcast address constantly with high intensity. The bridge, in accordance with its algorithm, transmits erroneous traffic to all segments. This situation is called a broadcast storm (broadcast, storm).

In fig. 13.5 shows a typical bridge structure. The media access functions for receiving and transmitting frames are performed by MAC chips, which are identical to the network adapter chips.

Fig. 13.5. Bridge / Switch Structure

The protocol that implements the switch algorithm is located between the levels of the MAC HLLC.

In fig. Figure 13.6 shows a copy of the terminal screen with the bridge address table.

Fig. 13.6. Switch Address Table

The address table displayed on the screen shows that the network consists of two segments - LAN A and LAN B. There are at least 3 stations in the LAN A segment, and 2 stations in the LAN B segment. The four addresses marked with asterisks are static, that is, manually assigned by the administrator. An address marked with a plus is a dynamic, expired address.

The table has the field Dispn - “disposition” (this is an “order” for the bridge about what operation to do with the frame having the given destination address). Usually, when a table is automatically compiled in this field, the symbol of the destination port is set, but if you manually set the address, you can enter a non-standard frame processing operation in this field. For example, the Flood operation (flooding) causes the bridge to distribute the frame in a broadcast mode, despite the fact that its destination address is not broadcast. The Discard operation (discard) tells the bridge that the frame with this address does not need to be transmitted to the destination port. Generally speaking, the operations specified in the Dispn field define special conditions for filtering frames that complement the standard conditions for their distribution. Such conditions are usually called custom filters.

Topological limitations when using bridges in local networks

Consider this limitation on the example of the network shown in Fig. 13.7.

Fig. 13.7. Influence of closed routes on switch operation

Two Ethernet segments are connected in parallel by two bridges, so that a loop is formed. Let the new station with MAC address 123 for the first time start working on this network. Usually, the start of operation of any operating system is accompanied by broadcasting frames in which the station declares its existence and simultaneously searches for network servers.

In step 1, the station sends the first frame with the broadcast destination address and source address 123 to its segment. The frame falls into both bridge 1 and bridge 2. In both bridges, the new source address 123 is entered into the address table with a note about its belonging to segment 1, that is, a new record is created:

MAC address 123 - Port 1.

Since the destination address is broadcast, each bridge must transmit a frame to segment 2. This transmission takes place alternately in accordance with the random access method of Ethernet technology. Let bridge 1 gain access to segment 2 first (stage 2 in Fig. 13.7). When a frame appears on segment 2, bridge 2 receives it into its buffer and processes it. He sees that address 123 is already in his address table, but the incoming frame is more recent, and he decides that address 123 belongs to segment 2, but not 1. Therefore, bridge 2 corrects the contents of the database and records that address 123 belongs to segment 2:

MAC address 123 - Port 2.

Similarly, Bridge 1 enters when Bridge 2 transmits its copy of the frame to segment 2. The consequences of the presence of a loop in the network are listed below.

The “duplication” of a frame, that is, the appearance of several copies of it (in this case, two, but if the segments were connected by three bridges, then three bridges, etc.).

The endless circulation of both copies of the frame around the loop in opposite directions, which means that the network is clogged with unnecessary traffic.

Permanent rebuilding of address tables by bridges, since the frame with source address 123 will appear on one port, then on another.

In order to eliminate all these undesirable effects, bridges / switches should be used in such a way that there are no loops between logical segments, that is, building only tree structures using switches to ensure that there is only one path between any two segments. Then the frames from each station will always arrive at the bridge / switchboard from the same port, and the switchboard will be able to correctly solve the problem of choosing a rational route in the network.

There is another possible cause of loops. So, to improve reliability, it is desirable to have back-up links between bridges / switches that do not participate in the normal operation of the main links for transferring information frames of stations, but if any primary link fails, they form a new coherent working configuration without loops.

Redundant communication must be blocked, that is, put them in an inactive state. In networks with a simple topology, this problem is solved manually by blocking the corresponding ports of bridges / switches. In large networks with complex connections, algorithms are used that allow solving the loop detection problem automatically.