An ad hoc network, or independent basic service area (IBSS), occurs when individual client devices form a self-supporting network without the use of a separate access point (AP - Access Point). These networks are not designed with any site maps or pre-plans in place, so they are usually small and limited in size to carry shared data when needed.

Since there is no access point in IBSS, timing is not centralized. A client initiating a transmission in IBSS sets a beacon interval to create a set of target beacon transmission time (TBTT). When TBTT ends, each IBSS client does the following:

Suspends all failed backoff timers from the previous TBTT;

Specifies a new random delay;

Basic Service Areas (BSS)

A BSS is a group of 802.11 stations that communicate with one another. BSS technology assumes the presence of a special station called an AP (Access Point). The access point is the central communication point for all BSSs. Client stations do not communicate directly with each other. Instead, they communicate with the access point, and it already sends frames to the destination station. The access point may have an uplink port through which the BSS connects to the wired network (for example, an Ethernet uplink). Therefore, BSS is sometimes referred to as BSS infrastructure. Figure 4 shows a typical BSS infrastructure.

1. bss wireless LAN infrastructure

Extended Service Areas (ESS)

Multiple BSS infrastructures may be connected through their uplink interfaces. Where the 802.11 standard is in effect, the uplink interface connects the BBS to the Distribution System (DS). Several BBSs interconnected through a distribution system form an extended service area (ESS). The uplink to the distribution system does not have to use a wired connection. Figure 5 shows an example of a practical implementation of ESS. The specification of the 802.11 standard leaves the possibility of implementing this channel as a wireless channel. But more commonly, the uplinks to the distribution system are wired Ethernet links.

infrastructure connection

This model is used when it is necessary to connect more than two computers. A server with an access point can act as a router and independently distribute the Internet channel.

Access point using router and modem

The access point is included in the router, the router - in the modem (these devices can be combined into two or even one). Now every computer in the Wi-Fi range that has a Wi-Fi adapter will have Internet access.

1. Extended service area ess wireless network

Client point

In this mode, the access point acts as a client and can connect to an access point operating in infrastructure mode. But only one MAC address can be connected to it. Here the task is to combine only two computers. Two Wi-Fi adapters can work with each other directly without central antennas.

Bridge connection

Computers are connected to a wired network. Access points are connected to each group of networks, which connect to each other via a radio channel. This mode is designed to combine two or more wired networks. Wireless clients cannot connect to an access point in bridge mode.

Equipment designed to work in the 802.11 standard is mainly divided into two classes - these are clients and access points (Access Point). Desktop computers, laptops, PDAs, telephones, printers, game consoles and other portable and stationary household appliances equipped with a Wi-Fi module can play the role of clients. If a PC or PDA initially lacks support for wireless networks, then in most cases this can be easily compensated by purchasing an appropriate adapter, which can be implemented in the form of almost any expansion board. Access points are usually designed as a separate external device that connects directly to a wired Ethernet cable or any other compatible broadband Internet source. Sometimes access points are combined with some other device, for example, ADSL modems combined with a Wi-Fi access point are very common. The access point is responsible for the lion's share of the work of maintaining a wireless network: it must not only maintain radio transmission with all clients and connect the network to the outside world, but also regulate traffic, process data and perform a host of other operations. Also, in some cases, additional equipment may be required: for example, if the signal level is insufficient, antennas are needed, and if it is necessary to connect two networks together, bridges are needed.

Equipment

To build a wireless LAN, you need the following types of equipment:

Access points (Access Point, AP) are used to connect users to the LAN via radio;

Wireless bridges (Wireless Brigde), are used to combine two or more LANs over a radio channel;

External antennas are used to amplify the radio signal and / or to change the direction of signal propagation;

Network radio cards for clients (Wireless Netcard), used to connect the client's computer to the AP;

Wireless LAN Controllers are used to centrally manage the entire enterprise wireless network.

Access points are divided into autonomous (Autonomous) and simplified (Lightweight).

The difference between lightweight access points is the need to use a wireless controller. In this case, all intelligence is concentrated in the controller, and the access point acts only as a radio receiver / transmitter. The controller provides:

Automatic acquisition by access points of the current configuration;

Automatic selection of the channel and power of each transmitter to ensure optimal coverage and prevent interference caused by overlapping coverage areas of transmitters with the same radio channel;

Centralized application of security policies and quality of service (QoS);

Providing roaming for mobile users.

It is advisable to use simplified access points in networks with a large number of access points and a coverage area of ​​complex geometric shape.

Standalone access points are usually used in cases where their number is small, for example, to organize a radio channel between buildings or for wireless networks with a small coverage area, which is sufficient for 1-2 access points.

801.11 - the IEEE standard, which defines the order of access to the transmission medium and provides physical layer specifications for wireless local area networks with speeds up to 2 Mbps. The 802.11 standard applies to DSSS and FHSS high-frequency radio channels, as well as to infrared channels.
802.11a- an edition of the IEEE 802.11 standard, which considers networks operating at speeds up to 54 Mbps using DSSS technology.
802.11b- an edition of the 802.11 IEEE standard, which considers networks operating at speeds up to 11 Mbps using DSSS technology.
802.1lg- a revision of the IEEE 802.11 standard, which considers networks operating at speeds up to 54 Mbps using DSSS technology, backward compatible with the 802.11b standard.
802.1li- IEEE standard related to the security of wireless networks. It combines 802.1x and TKIP/CCMP protocols to provide user authentication, confidentiality and data integrity in wireless LANs.
802.1x- the IEEE standard for authentication and access control at the data link layer. Access point - A type of base station that a wireless LAN uses to allow wireless users to interact with a wired network and roam within a building.

AD HOC MODE

(peer-to-peer network mode) - a wireless network configuration in which users can directly establish connections between their devices without the services of a base station. Wireless personal and local area networks can work in this mode.

The main advantage of this mode is the ease of organization: it does not require additional equipment (access points). The mode can be used to create temporary networks for data transmission. However, it must be borne in mind that ad hoc mode allows you to establish a connection at a speed of no more than 11 Mbps, regardless of the equipment used. The actual data exchange rate will be lower and will not exceed 11/N Mbit/s, where N is the number of devices in the network. The communication range is no more than one hundred meters, and the data transfer rate drops rapidly with increasing distance. To organize long-term wireless networks, infrastructure mode should be used.
Example:
On the client side, we will use a wireless USB adapter. All settings for other types of adapters (PCI, PCMCI, ExpressCard, etc.) are carried out in the same way.
When connecting the adapter, you need to install the driver that comes with all wireless equipment. The Wireless Network Connection icon should appear in the Network Connections window

Wireless network in ad hoc mode first we will build from computer1 and laptop1, and then it will be possible to connect other computers. This can be done in two ways: using the built-in Windows XP or Windows Vista service and the D-Link AirPlus XtremeG Wireless Utility that comes with D-Link equipment.
1) Setting up a connection using the built-in Windows service. When installing the interface, using the built-in Windows utilities, additional programs not required. But for this you need to check the box Use Windows to configure the network on the Wireless networks tab in the properties wireless connection

Before establishing a connection, you must configure static IP addresses. They are configured in the properties of the wireless connection, on the General tab, in the Internet Protocol (TCP/IP) properties.

Let the first computer (Computer1) have an IP address: 192.168.0.1, and the second (Laptop1): 192.168.0.2, and a subnet mask: 255.255.255.0. Now for networking in ad hoc mode, double-click the left mouse button on the wireless interface to launch Windows service. Here, on one of the computers, run Set up a wireless network. In the wizard that appears, you must enter the SSID (for example, AdHocNet) and enter the access key. This completes the configuration of one computer.

On another computer, we also start the Windows service, and in the main window select the network that appears (AdHocNet). If the access keys match, this computer connects to the first one and thus, an Ad Hoc wireless network is created.
If you need to connect more computers, then all the same steps are carried out as with the second one. In this case, the network will already consist of several computers.
2) Setting up a connection using D-Link software AirPlus XtremeG Wireless Utility.
In this case, you need to install this program and uncheck Use Windows to configure the network.
To organize wireless ad hoc Run this program on the first computer and go to the Setup tab.

Then enter the SSID of the network to be created (for example, AdHocNet), select the Ad Hoc mode and set the IP address with the wireless interface mask.
Let's leave authentication and encryption open for now. If you need to do additional settings, they can be made on the Advanced settings tab.
On other computers, we also run this program and open the Browse Networks tab:

In the window that appears, select a network, and to configure the IP address of the second computer, click the Configuration button. Then click the Connect button, and if the access keys match, the wireless adapter will connect to the first computer. Other computers are connected in the same way. Updating available networks is done by clicking the Update button.

infrastructure mode

In this mode, access points provide communication between client computers. The access point can be thought of as a wireless switch. Client stations do not communicate directly with each other, but communicate with the access point, and it already sends packets to the recipients.

The access point has an Ethernet port through which the basic service area is connected to a wired or mixed network - to the network infrastructure. Example:
Set up a wireless access point in infrastructure mode. The setting is made via wired interface, i.e. using an Ethernet connection. Although it is possible to do this through the wireless interface, but we do not recommend it, because. with a sufficiently large number of access points, confusion in the settings can occur.
1. In the Network Connections window, disable network and wireless network adapters. AT context menu select "Disable" for each adapter. As a result, all computers are isolated from each other, network connections no.
2. Set up network adapters to communicate with the access point. Local Area Connections->Properties->TCP/IP Protocol->Properties -Use the following IP address
-Enter the address 192.168.0.xxx, where xxx is your computer number (1, 2, 3, etc.).
-Specify mask 255.255.255.0
-Include cable connection
3. Connect to an access point.
Connecting an access point network cable with a network adapter, supply power.
Reset point settings. To do this, press and hold the reset button for five seconds. Do not turn off the power while pressing reset! Point loading time is about 20 seconds.
When the download is complete, the Power and LAN indicators light up on the point. In browser Internet Explorer type http://192.168.0.50 , You will be prompted to enter a name and password.

4. Let's start the setup. Enter "admin" as the username with a blank password. Let's configure the point's IP address first. This is only necessary if you have many access points. On the Home tab, click the Lan button (on the left).
-Set the address 192.168.0.xxx, where xxx is a unique point number.
-mask 255.255.255.0
-Default Gateway 192.168.0.50
5. Enable hotspot mode.
Wait for the point to load, and enter the new address in the browser http://192.168.0.xxx
On the Home tab, click the Wireless button (on the left)
Install:
Mode: Access Point
SSID: Network
SSID Broadcast: Enable
Channel: 6
Authentication: Open System
Encryption: Disable

Please note that the settings we have chosen are not secure. wireless connection and are used for educational purposes only. If you need to make more subtle settings, go to the Advanced tab. We strongly recommend that you read the setup documentation before setting up your access point, short description all options are on the Help tab.
After completing the settings, click "Apply" to reload the point with the new settings.
Disable dot from network interface. Your point is now configured to connect wireless clients. In the simplest case, to provide customers with the Internet, you need to connect a broadband channel or an ADSL modem to the point. Client computers are connected in the same way as described in the previous example.

wds and wds with ap modes

WDS term(Wireless Distribution System) stands for "Distributed Wireless System". In this mode, access points are connected only to each other, forming a bridge connection. In addition, each point can be connected to several other points. All points in this mode must use the same channel, so the number of points participating in the bridge should not be excessively large. Clients are connected only via a wired network through the uplink ports of the points.

Wireless bridge mode, similar to wired bridges, is used to combine subnets into a common network. With the help of wireless bridges, it is possible to combine wired LANs located both at a short distance in neighboring buildings, and at distances up to several kilometers. This allows you to network branches and the central office, as well as connect customers to the Internet provider's network.

A wireless bridge can be used where cabling between buildings is undesirable or not possible. This solution allows you to achieve significant cost savings and provides ease of setup and configuration flexibility when moving offices.
Wireless clients cannot connect to an access point in bridge mode. Wireless connection is carried out only between a pair of points that implement the bridge.
The term WDS with AP(WDS with Access Point) stands for "distributed wireless system, including access point", i.e. using this mode, you can organize not only bridging between access points, but also simultaneously connect client computers. This allows you to achieve significant savings in equipment and simplify the network topology. This technology supported by most modern access points.

However, it must be remembered that all devices in the same WDS with AP operate on the same frequency and create mutual interference, which limits the number of clients to 15-20 nodes. To increase the number of connected clients, you can use several WDS networks configured for different non-overlapping channels and connected by wires through uplink ports.
The topology of organizing wireless networks in WDS mode is similar to conventional wired topologies. Bus topology
The topology of the "bus" type by its very structure assumes the identity of the network equipment of computers, as well as the equality of all subscribers.
There is no central subscriber through which all information is transmitted, which increases its reliability (after all, if any center fails, the entire system controlled by this center ceases to function). Adding new subscribers to the bus is quite simple. It is necessary to enter the parameters of the new access point into the last one, which will only lead to a short reboot of the last point. The bus is not afraid of failures of individual points, since all other computers on the network can normally continue to communicate with each other, but the rest of the computers will not be able to access the Internet. Ring Topology
A "ring" is a topology in which each access point is connected to only two others. clearly defined center in this case no, all points can be the same.
Connecting new subscribers to the "ring" is usually completely painless, although it requires the mandatory shutdown of the two extreme points from the new access point.
At the same time, the main advantage of the ring is that the relaying of signals by each subscriber can significantly increase the size of the entire network as a whole (sometimes up to several tens of kilometers). The ring in this respect is significantly superior to any other topology.
The topology of connections between points in this mode is an acyclic graph of the tree type, that is, data from the Internet from point 4 to point 2 can pass in two directions - through points 1 and 3. To eliminate unnecessary connections that can lead to cycles in the graph, the spanning tree algorithm is implemented. His work leads to the identification and blocking of unnecessary connections. When the network topology changes, for example, due to the disconnection of some points or the impossibility of the channels to work, the Spanning tree algorithm is restarted, and previously blocked extra connections can be used instead of failed ones. Star Topology"Star" is a topology with a clearly defined center, to which all other subscribers are connected. All information exchange goes exclusively through the central access point, which thus bears a very large load.
If we talk about the stability of the star to point failures, then the failure of a conventional access point does not affect the functioning of the rest of the network, but any failure of the central point makes the network completely inoperable. A serious drawback of the star topology is the strict limitation on the number of subscribers. Since all points operate on the same channel, usually the central subscriber can serve no more than 10 peripheral subscribers due to a large drop in speed.
In most cases, for example, to combine several districts in a city, combined topologies are used.

Repeater mode

There may be a situation where it is impossible, or inconvenient, to connect the access point to the wired infrastructure, or some obstacle makes it difficult for the access point to communicate directly with the location of the wireless client stations. In such a situation, you can use the dot in repeater mode.

Similar to a wired repeater, a wireless repeater simply retransmits all packets received on its wireless interface. This retransmission is carried out through the same channel through which they were received. When using a repeater access point, be aware that overlapping broadcast domains can result in a halving of the link throughput, because the original access point also "hears" the relayed signal.
The repeater mode is not included in the 802.11 standard, so for its implementation it is recommended to use the same type of equipment (up to the firmware version) and from the same manufacturer. With the advent of WDS, this mode has lost its relevance, because the WDS functionality replaces it. However, it can be found in older firmware versions and in outdated equipment.

Client Mode

When moving from a wired to a wireless architecture, you may sometimes find that existing network devices support wired Ethernet but do not have interface connectors for wireless network adapters. To connect such devices to a wireless network, you can use an access point - a client

Only one device connects to the wireless network using a client access point. This mode is not included in the 802.11 standard, and is not supported by all manufacturers.

It was originally written for the Chief, who wanted to connect to the Internet through the laptop of my colleague, Tanya. Therefore, I leave proper names in the article.

On the main computer (Tannin) you need to create an ad-hoc network, and then establish the so-called common connection to the Internet (Internet Connection Sharing).

Step 1

We click on the icon with the left mouse button 2 times and get into the window of available wireless networks.

Step 2

Please note that other networks may be detected. Protected have a padlock icon. There are also open ones.

Those. when connecting to them, neither passwords nor keys are required. We will make our network secure.

Click on "Change advanced settings".

Step 3

In the window that opens, select "Internet Protocol TCP / IP" and click the properties button.

Step 4

Check if the "IP address" and "Subnet mask" are set.
By default, the IP address is 192.168.0.1, and the subnet mask is 255.255.255.0 - so we will not change anything.
Click "OK"

This step is generally not required. If you do not specify an IP address, the APIPA automatic addressing service will be used.

However, after going through steps 9-21, the address will be replaced by the master with the one in the figure.

Step 5

In this window, check the box "Use Windows for configuration",

and just below, click the "Add" button.

Step 6

Enter the following parameters:

• Network Name (SSID) - The name of our network.
• Authentication - select joint
• Data Encryption - WEP
• The key is provided automatically - uncheck the box, otherwise you will not be able to set your key.
• Network key - you must enter a sufficiently long key consisting of letters and numbers.
• Confirmation - repeat the key.
• Check the box "This is a direct computer-to-computer connection, no access points are used."

Go to the "Connection" tab.

Step 7

Check the "Connect when the network is in range" checkbox.

We press "OK".

Step 8

We again click on the icon of the wireless connection in the tray and see that our connection has appeared in the list of available networks.

Now, we can say that the network is ready, only for this moment, it will be of little use, because our goal is to access
to the Internet using your laptop. To do this, in the same window, click "Change advanced settings" again.

Step 9

In the window that opens, go to the "Advanced" tab. Select "Home Network Wizard".

Step 12

Check the "Ignore disabled network equipment" checkbox.
It's disabled because we haven't connected our laptop to it yet. Click next.

Step 13

Here, select the option that suits you.
In your case, this is the 2nd point - through the gateway.

Step 14

The setup wizard prompts you to select an Internet connection.

We select the adapter with which Tanya's computer is connected to the network, click "Next".

Step 15

Check the "Wireless Network Connection" checkbox and click "Next".

Step 16

Here you are free to enter whatever you want or the parameters of your locale. In short, just click "Next".

Step 17

Enter the name of the working group (any, you can use the default) and click "Next".

Step 18

We select "Turn off sharing", because if you need it,

Step 20

Select "Just complete the wizard" and click "Next".

Step 21

Click the "Finish" button. After that, the computer will prompt you to reboot. We agree.

Then your computer must be connected to this ad — hoc networks

You must follow step 1 and 2 from the previous part of the instructions.

You should then see the network (as in step 8) whose name you specified in step 6.

This is where you need to connect.

You may need to take additional steps to set up your laptop to use Internet Connection Sharing:

Click the Start button on the taskbar and select Control Panel.

In Control Panel, click the Network and Internet Connections button under Select a category.

In this section or in the Control Panel, click the Internet Options icon.

In the Internet Options dialog box, click the Connections tab.

Click the Install button.

The New Connection Wizard will start.

On the New Connection Wizard page, click Next.

Select the Internet connection option and click Next.

Select the Set up my connection manually option, and then click Next.

Select the Connect through always-on broadband connection option, and then click Next.

On the Completing the New Connection Wizard page, click Finish.

Close the control panel.

It seems like everything. Hope it works.

Wireless ad hoc networks.

The IEEE 802.11 standard defines two wireless local area network (WLAN) operating modes: Ad hoc mode and Infrastructure mode.

Infrastructure mode is used to connect wireless clients to an existing wired network using a special device called a wireless access point.

Figure 1. Infrastructure mode

Peer-to-peer mode (Ad hoc mode) is used to build peer-to-peer wireless networks without using an access point. An ad hoc wireless network can contain up to 9 computers, each of which communicates directly with other computers.

Figure 2. Ad hoc mode

In Ad Hoc mode, subscriber stations communicate directly with each other without using an access point or WiFi router. This mode is also called IBSS (Independent Basic Service Set) or Peer to Peer mode. With this configuration, no network infrastructure is required. This creates only one service area that does not have an interface for connecting to a wired LAN. Any devices equipped with a wireless network adapter or a Bluetooth interface that are within range of a radio signal can be connected to each other via an Ad hoc network. It is ideal for fast data exchange between multiple computers, cell phones, PDAs or laptops that need to be connected locally and only for a while to each other.

The Ad hoc network is a dynamically changing network with an arbitrary structure. Each network node forwards data destined for other nodes. In this case, the determination of which node to transmit data to is made dynamically, based on the connectivity of the network. This is their main difference from wired networks and managed wireless networks, in which routers or access points perform the task of managing data flows.

Each of the subscriber devices, depending on its power, has its own range. If a subscriber, being "on the periphery" sends a packet to a subscriber located in the center of the network, the so-called multihop process of packet transmission through nodes located on the path of a pre-laid route takes place. Thus, each new subscriber at the expense of their resources increases the range of the network. Therefore, the power of each separate device may be minimal. And this implies both lower cost of subscriber devices, and better safety and electromagnetic compatibility.

Figure 3. Approximate view of the Ad hoc network

Features of wireless ad hoc networks:

General data transmission medium;

All network nodes are initially equal;

The network is self-organizing;

Each node acts as a router;

The network topology is free to change;

New nodes can freely enter the network and old nodes can leave.

Consider the conditions for successfully building a wireless network in Ad-Hoc mode:

Line of sight between connected computers.

When connecting in Ad-Hoc mode, a very important factor affecting the speed of the network is the location of computers within the line of sight. This is due to the fact that the power of the transmitters of the wireless adapters is slightly lower than the power of the access points. Accordingly, the range of such a network is about half that of a network built using the infrastructure mode (using an access point).

You can increase the range of the Ad-Hoc network by using more powerful antennas. If there are barriers between computers, such as office walls, then the radius of the network and the speed will be drastically reduced.

Wireless adapter standard.

As you know, the speed of data transfer in the network depends on the standard in which network adapters work. If a device is installed on one computer, the standard of which supports a lower data transfer rate, then the speed of the entire network will be equal to the speed of this adapter. Therefore, it is recommended to use adapters of the same standard.

The number of connected computers.

This is primarily due to the peculiarities of the process of information exchange between computers. For wireless networks, especially when using the Ad-Hoc mode, this factor is especially important. Therefore, for the successful functioning of the network in Ad-Hoc mode, you should limit the number of connections (from two to nine). If their number exceeds the recommended one, then a more profitable solution in this situation would be to use an access point and infrastructure mode.

Currently, there are several "basic" technologies for building ad hoc networks:

The maximum data transfer rate is 2.1 Mbps, the range of one subscriber device is 1 - 100 m.

Bluetooth-based networks are applicable only in a small area (eg city centers, small offices, shops). So, such a network can serve to organize video surveillance at a small facility.

In areas where power consumption and cost are the main criteria, ZigBee technology can be applied. This is an inexpensive way to organize communication in industrial systems that do not need high data transfer rates. Data rates vary from 20 to 250 kbps.

It is the main technology for self-organizing networks. In WiFi networks, the transmission speed is 11 - 108 Mbps, which allows you to transfer large amounts of information in real time (for example, a video signal).

To build an ad hoc network, adapters are used that are connected via the PCI, PCMCI, CompactFlash expansion slot. There are also USB 2.0 adapters available. Wi-Fi adapter performs the same function as Network Card on a wired network. It is used to connect the user's computer to a wireless network. Thanks to the Centrino platform, all modern laptops have built-in wifi adapters, which are compatible with many modern standards. Wi-Fi adapters, as a rule, are also equipped with PDAs (pocket personal computers), which also allows you to connect them to wireless networks.

Figure 4. Wi-Fi adapters.

The main advantages of Ad hoc mode are fast network deployment and ease of organization (no access point required).

The disadvantages of this variant of building a network include a small radius of action and low noise immunity.

Ad hoc mode is mainly used to create temporary data networks, such as transport, office networks, military communications.

Materials used:

http://www.acorn.net.au/telecoms/adhocnetworks/adhocnetworks.cfm

http://ntrg.cs.tcd.ie/undergrad/4ba2.05/group11/index.html

http://wireless09.livejournal.com/334.html

Proletarsky A. V., Baskakov I. V., Chirkov D. N. "Wireless Wi-Fi Networks"

Whereas in the case of a "traditional" wireless network we have to deploy an often expensive infrastructure of base stations, in the case of self-organizing networks one or more access points are sufficient.

The essence of self-organizing networks is to provide the subscriber with the opportunity to access various network services by transmitting and receiving “own” traffic through neighboring subscribers.

Self-organizing communication networks are networks with a changeable decentralized infrastructure. In general, these networks have such advantages as wide coverage and theoretically wide subscriber base without a large number of expensive base stations and increase in the power of the radiated signal.

In simple terms, the structure of the simplest self-organizing network is a large number of subscribers in a certain area, which can be simply called the network coverage area, and one or more access points to external networks. Each of the subscriber devices, depending on its power, has its own range. If a subscriber, being "on the periphery" sends a packet to a subscriber located in the center of the network or to an access point, the so-called multi-hop process of packet transmission through nodes located on the path of a pre-laid route takes place. Thus, we can say that each new subscriber, at the expense of his resources, increases the range of the network. Therefore, the power of each individual device can be minimal. And this implies both lower cost of subscriber devices, and better safety and electromagnetic compatibility.

At the moment, research and application of self-organizing networks in the following areas are on a wide front:

military communications;

Intelligent transport systems;

Local networks;

Sensor networks;

About all these directions - in the following articles.

Currently, there are several "basic" technologies for self-organizing networks:

1.Bluetooth

Self-organizing devices based on Bluetooth consist of master and slave devices (these roles can be combined), capable of transmitting data in both synchronous and asynchronous modes. Synchronous transmission mode involves direct communication between the master and slave devices with a dedicated channel and access time slots. This mode is used in case of time-limited transmissions. Asynchronous mode involves the exchange of data between the master and several slave devices using packet data. Used to organize piconets. One device (both master and slave) can support up to 3 synchronous connections.

In synchronous mode, the maximum data rate is 64 kbps. The maximum transfer rate in asynchronous mode is 720 kbps.

Advantages of Bluetooth-based networks:

the ability to quickly deploy;

relatively low power consumption of subscriber devices;

a wide range of devices supporting this technology.

Network Disadvantages:

small radius of action (radius of action of one subscriber device is 0.1 - 100 m);

low data transfer rates (for comparison: in WiFi networks, this figure is 11 - 108 Mbps);

lack of frequency resource.

Perhaps the last problem will be solved with the release of Bluetooth 3.0 devices, where it is supposed to use alternative protocols of the MAC and physical layers in order to accelerate the transfer of Bluetooth profiles (AMP). In particular, 802.11 protocols can be used.

Based on the above, we can conclude that Bluetooth-based networks are applicable only in crowded places (for example, in city centers, small offices, shops). For example, such a network can be used to organize video surveillance at a small facility.

802.11 networks were originally conceived as a way to replace wired networks. However, relatively high transmission rates (up to 108 Mbps) make promising possible application in those self-organizing networks in which it is necessary to transmit large amounts of information in real time (for example, a video signal).

In 2007, a draft version of the 802.11s standard was first released, defining the main characteristics of WiFi-based self-organizing networks.

Unlike traditional WiFi networks, in which there are only two types of devices - "access point" and "terminal", the 802.11s standard assumes the presence of so-called "network nodes" and "network portals". Nodes can communicate with each other and support various services. Nodes can be combined with access points, while portals serve to connect to external networks.

Based on already existing standards 802.11, you can build MANET networks (mobile self-organizing networks), the hallmark of which can be called a large coverage area (several square kilometers).

Problems that require special attention in the further development of self-organizing networks in WiFi base can be divided into the following classes:

Bandwidth issues;

Problems of network scalability.

3. ZigBee

The 802.15.4 (ZigBee) standard describes low-speed, short-range communication networks with low-power transmission devices. The use of three frequency ranges is provided: 868-868.6 MHz, 902-928 MHz, 2.4-2.4835 GHz.

The channel access method used is DSSS with different sequence lengths for the 868/915 and 2450 MHz bands.

Data rates vary from 20 to 250 kbps.

According to the standard, the ZigBee network supports star and each with each topologies.

There are two types of transceivers: full-featured (FFD) and non-full-featured (RFD). The fundamental difference between these devices is that FFDs can communicate directly with any device, while RFDs can only communicate with FFDs.

A ZigBee network may consist of several clusters formed by FFD devices.

ZigBee networks can operate in mesh mode. In this case, it is assumed that each network node (the network node forms an FFD device, RFDs work as so-called sensors) constantly monitors the state of neighboring nodes, updating its routing tables if necessary.

Unlike all previous versions of ad hoc networks, ZigBee is designed for low data transfer rates and there is no problem of increasing them.