What is an ad hoc network. Ad hoc terminal interaction scenarios. Technologies used in building wireless self-organizing networks

Infrastructure mode:

An infrastructure mode wireless network requires an access point. The access point manages the wireless connection and provides several important advantages over an ad-hoc network. For example, an infrastructure mode network supports enhanced levels of security, higher data rates, and wired network integration.

If in the case of a “traditional” wireless network we must deploy an often expensive infrastructure of base stations, then in the case of self-organizing networks one or several 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 “their” traffic through neighboring subscribers.

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

In simple terms, the structure of the simplest self-organizing network consists of 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 subscriber device, depending on its power, has its own range of action. 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 transmitting the packet through nodes located along the path of a pre-defined route occurs. Thus, we can say that each new subscriber, using its resources, increases the range of the network. Therefore, the power of each individual device can be minimal. And this implies both lower costs of subscriber devices and better safety and electromagnetic compatibility indicators.

At the moment, there is a wide range of research and applications of self-organizing networks in the following areas:

Military communications;

Intelligent transport systems;

Local networks;

Sensor networks;

All these areas will be discussed in the following articles.

Currently, there are several “core” 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 master and slave devices with an assigned channel and access time slots. This mode is used in case of time-limited transmissions. Asynchronous mode involves the exchange of data between a master and several slave devices using packet data transfer. Used to organize piconets. One device (both master and slave) can support up to 3 synchronous connections.

In synchronous mode, the maximum data transfer rate is 64 kbit/s. The maximum transmission speed in asynchronous mode is 720 kbit/s.

Advantages of Bluetooth-based networks:

possibility of rapid deployment;

relatively low power consumption of subscriber devices;

a wide range of devices supporting this technology.

Network disadvantages:

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

low data transfer rates (for comparison: in WiFi networks this figure is 11 - 108 Mbit/s);

lack of frequency resource.

Perhaps the latter problem will be solved with the release of Bluetooth 3.0 devices, where it is assumed that it will be possible to use alternative protocols at the MAC and physical levels for the purpose of accelerated transmission of Bluetooth profiles (AMP). In particular, 802.11 standard 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 speeds (up to 108 Mbit/s) make it promising for possible use in those self-organizing networks in which it is necessary to transmit large amounts of information in real time (for example, video signals).

In 2007, a draft version of the 802.11s standard was first released, defining the main characteristics of self-organizing WiFi-based 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 existing 802.11 standards, it is possible to build MANET networks (mobile self-organizing networks), the distinctive feature of which is a large coverage area (several square kilometers).

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

Bandwidth problems;

Network scalability problems.

3.ZigBee

The 802.15.4 (ZigBee) standard describes low-speed, short-range communication networks with low-power transmitting 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 uses DSSS with different sequence lengths for the 868/915 and 2450 MHz bands.

Data rates range from 20 to 250 kbps.

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

There are two types of transceiver devices: 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 can consist of several clusters formed by FFD devices.

ZigBee networks can operate in mesh mode. 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 their routing tables if necessary.

Unlike all previous versions of ad hoc networks, ZigBee is designed for low data transfer rates and there are no problems with the possibility of increasing them.

Initially 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 (Tanin) you need to create an ad-hoc network, and then establish the so-called 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 ones have a padlock icon. There are also open ones.

Those. When connecting to them, no passwords or 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

We check whether 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 won’t change anything.
Click "OK"

In principle, this step is not necessary. If you do not specify an IP address, the APIPA automatic addressing service will be used.

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

Step 5

In this window, check the “Use Windows for configuration” checkbox.

and just below click the “Add” button.

Step 6

Enter the following parameters:

• Network name (SSID) – the name of our network.
• Authentication – choose joint
• Data encryption - WEP
• The key is provided automatically - uncheck this box, otherwise you will not be able to set your key.
• Network key – you must enter a fairly long key consisting of letters and numbers.
• Confirmation - repeat the key.
• Check the box “This is a direct computer-to-computer connection, access points are not used.”

Go to the “Connection” tab.

Step 7

Check the “Connect if the network is within range” checkbox.

Click “Ok”.

Step 8

Click on the wireless connection icon in the tray again and see that our connection appears in the list of available networks.

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

Step 9

In the window that opens, go to the “Advanced” tab. Select the “Home Network Wizard” item.

Step 12

Check the “Ignore disabled network equipment” checkbox.
It is disabled because we have not yet connected our laptop to it. 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.

Select the adapter with which Tanya’s computer is connected to the network, click “Next”.

Step 15

Check the box next to “Wireless network connection” and click “Next”.

Step 16

Here you are free to enter whatever you want or the parameters of your local area. In short, just click “Next”.

Step 17

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

Step 18

We select “Disable sharing”, because if you need it,

Step 20

Select “Just complete the wizard” and click “Next”.

Step 21

Click the “Done” button. After this, the computer will prompt you to reboot. We agree.

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

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

In this case, you should see the network (as in step 8), the name of which you specified in step 6.

This is where you need to connect.

You may need to do additional steps to configure your laptop to use a shared Internet connection:

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

In Control Panel, click Network and Internet Connections under Select a Category.

In this section or in 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 launch.

On the New Connection Wizard page, click Next.

Select the Internet connection option and click Next.

Select the Set up a connection manually option and click Next.

Select the Connect via persistent broadband connection option and click Next.

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

Close the control panel.

It seems like everything. I hope it works.

An ad hoc network, or independent basic service area (IBSS), occurs when individual client devices form a self-sustaining network without the use of a separate access point (AP). When such networks are created, no maps of their deployment location or preliminary plans are developed, so they are usually small and have a limited extent sufficient to transmit shared data when the need arises.

Since IBSS does not have an access point, timing is distributed non-centrally. A client initiating transmission in IBSS sets a beacon interval to create a set of target beacon transmission time (TBTT). When TTTT completes, each IBSS client does the following:

Suspends all untried backoff timers from the previous TVTT;

Defines a new random delay;

Basic Service Areas (BSS)

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

1. BSS local wireless network infrastructure

Extended Service Areas (ESS)

Multiple BSS infrastructures can be connected via their uplink interfaces. Where the 802.11 standard is in effect, the uplink interface connects the BBS to the Distribution System (DS). Multiple BBSs interconnected through a distribution system form an Extended Service Area (ESS). The uplink to the distribution system does not necessarily have to use a wired connection. Figure 5 shows an example of a practical implementation of ESS. The 802.11 standard specification leaves the possibility of implementing this channel as a wireless channel. But more often, 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 a router and modem

The access point is connected to the router, the router is connected to the modem (these devices can be combined into two or even one). Now the Internet will work on every computer within the Wi-Fi coverage area that has a Wi-Fi adapter.

1. Extended ess wireless service area

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 connect 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. Each group of networks is connected to access points that 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 operating in bridge mode.

Equipment designed to work in the 802.11 standard is mainly divided into two classes - clients and access points. The role of clients can be played by desktop computers, laptops, PDAs, phones, printers, game consoles and other portable and stationary household appliances equipped with a Wi-Fi module. If a PC or PDA initially lacks support for wireless networks, then in most cases this can be easily compensated for by purchasing the appropriate adapter, which can be implemented in the form of almost any expansion card. Access points are usually designed as a separate external device that connects directly to a wired Ethernet cable or any other compatible source of broadband Internet access. 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 bears the lion's share of the work in maintaining a wireless network: it must not only support radio transmission with all clients and connect the network with 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, 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 a LAN via a radio channel;

Wireless bridges (Wireless Brigde) are used to connect 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 simplified access points is the need to use a wireless network 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 receipt of the current configuration by access points;

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

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

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.

Autonomous 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, for which 1-2 points are enough.