Wired and wireless types of connections for a home network with the Internet. Wireless data transmission technologies ZigBee, BlueTooth, Wi-Fi

Technologieswireless networks

After reading this chapter and completing the practical exercises, you will be able to:

· talk about modern wireless network technologies;

· outline the history of the development of wireless networks and their advantages;

· describe radio network technologies;

· talk about 802.11 radio networks;

· describe alternative radio network technologies (such as Bluetooth, HiperLAN and HomeRF Shared Wireless Access Protocol);

· discuss wireless technologies using infrared radiation;

· talk about microwave networks;

· describe wireless networks using low earth orbit (LEO) satellites.

Wireless networks are an emerging technology that is of great interest for many reasons. The most obvious reason is that such networks provide mobility to portable and handheld computing devices, allowing the user to forget about cables. Another reason is that wireless technology has become more reliable and in some situations cheaper to deploy than cable networks. There are several wireless media alternatives to cable for transmitting network packets: radio waves, infrared (IR) radiation, and microwaves (microwave waves). With all of these technologies, signals are transmitted through the air or atmosphere, making them a good alternative in cases where cable is difficult or impossible to use.

In this chapter, you will become familiar with many types of wireless network communications. First, you will learn what wireless networks are currently in use, and then get a brief history of such networks. T ix advantages. After a general description of networks that use radio waves, we will talk in more detail about the widespread IEEE 802.11 wireless networking standard. You will also learn about alternative radio network technologies: Bluetooth, HiperLAN and HomeRF Shared Wireless Access Protocol, then technologies based on diffuse infrared radiation that provide relatively secure wireless communications will be described, and finally, you will talk about how microwave technologies based on terrestrial networks are used in networks and satellite channels (including networks of widely orbiting Earth satellites).

Modern technologieswireless networks

Currently, the following technologies are used to create wireless networks:

· technologies using radio waves;

· technologies based on IR radiation;

· microwave (microwave) technologies;

· networks based on low-orbit Earth satellites (a special space project using microwave waves).

Technologies using radio waves are very common and represent a rapidly growing sector of wireless network communications. This also includes the 802.11 wireless networking standard, as well as alternative industry standards such as Bluetooth, HiperLAN and NoteShared Wireless Access Protocol (SWAP).

IR-based technologies are not as common as radio networks; however, they have some advantages, since they allow the creation of relatively more secure wireless networks (since the signal is more difficult to intercept unnoticed). Both technologies (radio waves and infrared radiation) are used to organize communications over short distances within an office, building or between buildings.

Microwave (MW) technologies are used for communication over long distances and can provide network communications between continents via satellites).

Networks based on low-orbit satellites are another type of wireless networks, on the basis of which at some point a “worldwide network” can be created, accessible in all parts of the planet.

All of these technologies will be discussed in this chapter. However, first we will look at the history of wireless networks and learn about their advantages.

A Brief History of Wireless Networksand their advantages

The history of wireless networks can be viewed formally and informally. The informal ancestor of wireless networks is amateur radio, whose operators receive licenses from the Federal Communications Commission (FCC) to transmit voice, Morse code, data, satellite and video signals using radio and microwave waves. Although amateur radio is usually considered a hobby, The Federal Communications Commission views it as an important source of ideas and expertise for communications development.

Note

Radio waves and microwave waves are one range of the electromagnetic wave spectrum, which includes visible light, radio waves, infrared radiation, X-rays, microwaves (microwaves), and gamma rays. All of these are types of electromagnetic radiation that propagate in the Earth’s atmosphere and in space. It has both the properties of a wave and the properties of a particle. More information about the electromagnetic wave spectrum can be found at:

http:// imagine. gsfc. nasa. gov/ docs/ science/ knowJ1/ emspectrum. html Andhttp:// imagine. gsfc. nasa. gov/ docs/ science/ knowJ2/ emspectrum. html.

In the 1980s, licensed amateur radio operators received permission from the Federal Communications Commission to transmit data on several radio frequencies in the ranges from 50.1–54.0 MHz (low band) to 1240–1300 MHz (high band). Most people are familiar with these frequencies because they are used to transmit music by AM and FM radio stations. These frequencies represent only a small portion of the possible radio frequencies on which signals can be transmitted. The basic unit of measurement for radio frequency is hertz (Hz)(Hertz (Hz)). In technology, one hertz corresponds to one period of alternating voltage or emitted signal per second.

Note

Radio frequencies represent a range of waves with a frequency above 20 kHz, through which an electromagnetic signal can be radiated into space.

It was a long time since IBM created the personal computer in the early 1980s before radio amateurs linked personal computers into a network using radio waves (usually in the higher bands 902–928 MHz and 1240–1300 MHz). To do this, they created a device called a terminal node controller (TNC). This device was placed between the computer and the transceiver and served to convert the computer's digital signal into an analog signal, amplified by the transceiver and radiated through the antenna. The resulting technology was called packet radio. The discovery by radio amateurs that packet radio works well at frequencies of 902 MHz and above was soon analyzed by companies providing commercial wireless networking services. In 1985, the Federal Communications Commission approved for commercial use in wireless computer networks the Industrial, ScietfJtitle and Medical (ISM) frequency, which can be used for low-power, unlicensed public communications on fixed frequencies" in the range from 902 MHz to 5.825 GHz. In 1996, the Telecommunications Congress prepared the next stage in the development of wireless! communications, establishing the concept of a “wireless communications node (location)” and establishing standards for it, as well as creating incentives for the further development of telecommunications technologies, including wireless communications (additional information can be found at www.fcc.gov/telecom .html). Shortly thereafter, IEEE created the 802.11 Wireless Networking Standards Group, which was responsible for the first 802.11 standard, established in 1997. Currently, wireless networks are being developed and implemented to meet many needs, including the following:

· implementation of communications in areas where it is difficult to deploy a cable network;

· reduction in deployment costs;

· providing “random” access to those users who cannot be tied to a specific cable connection;

· simplification of the procedure for creating networks in small and home offices;

· providing access to the data required in a specific configuration

Why can't cable networks always be used?

In some situations, it is difficult and even impossible to deploy a cable network. Consider this scenario. The two buildings need to be connected by one network, but a federal highway runs between them. In this case, there are several ways to organize a network. First, a trench could be dug under the highway, which would require significant expense and traffic disruption caused by digging the trench, laying the cable, burying the trench, and completely rebuilding the road. Secondly, a regional network can be created linking two buildings. Buildings can be connected to T-1 lines or to a regional Optical Ethernet network through the public network owner or local telephone company. The costs will be less than when laying a new cable, however, renting telecommunication lines will require constant deductions. Thirdly, you can deploy a wireless network, which will require one-time costs for equipment, as well as ongoing costs for managing the network. However, all these costs will most likely be most justified when considering large periods of time.

Let's consider another scenario. A tenant of a large office needs to deploy a network for 77 employees. The owner of the premises prohibits the installation of a permanent cable system. This premises suits the tenant in every sense; in addition, the rent for it is lower than in other alternative options. The solution to the problem is to create a wireless network.

And finally, the third scenario. The public library is located in a historical place. Although the library is owned by the city, strict public and private covenants prevent library management from obtaining the necessary permits to install network cables. The library is many years behind in creating an electronic book catalog because it cannot network the computers of its employees and the reference service for its customers. Therefore, library management can solve their problems by deploying a wireless network that allows them to maintain the integrity of the building and not violate any contracts.

Saving money and timewhen using wireless networks

The cost and time of creating a wireless network may be less than deploying a cable network. For example, older buildings often contain hazardous materials, such as old production shafts containing trace amounts of chlorine released from air ducts and asbestos. Since the shafts are not in use, they can simply be walled up. Or, an expensive hazardous materials removal program could be initiated so that these shafts can be used for network cable installation. In such a situation, it is much cheaper to wall up the mines and deploy a wireless network instead of cable.

You can consider the case where one university needed a working network because large funds were invested in its development. The university invited an expensive consulting company, which allocated

five people for the project and created 18 new jobs. A few days before work began, university officials realized there were no network connections for new employees and consultants. Laying new cables is expensive and also impossible in the next few months since the university's IT department is already overloaded with work. A solution has been found in the form of a wireless network that can be deployed in record time.

Unlimited network access

Some computer users need access to the network from almost anywhere. Consider, for example, a large automotive parts warehouse that needs to be regularly audited using network-connected barcode measures. A wireless network gives users of these scanners unlimited access since users are not tied to cable connections. Another example: A doctor in a hospital might carry a small laptop computer with a wireless adapter that can be used to update patient records, write referrals for tests, or manage patient care.

Simplifying networking for beginners

In the field of computerizing small or home offices with a wireless network, it is head and shoulders above cabling. The networks of such offices can be in very poor condition, since they are usually created by non-professionals. As a result, the wrong type of cable may be selected. The cable may pass through sources of radio interference and electromagnetic radiation, or it may become damaged (for example, by being passed under a chair, table, or in a doorway). Therefore, a user in such an office may waste his time unproductively searching for network inoperability. In this situation, a wireless network may be easier to install and operate. Typically, many online computer stores ask small office and home office users if they would like to purchase wireless devices to network between their purchased computers.

The advantage of wireless networks for this class of users is that currently the cost of wireless devices is quite moderate. A wireless network, combined with the ability to automatically assign IP addresses in Windows 2000 and Windows XP systems, allows you to create a full-fledged home network with minimal or even no experience.

Improving data access

Wireless networks can greatly improve access to certain types of data and applications. Consider, for example, a large university that employs ten full-time auditors who visit several departments (and sites) every day and need access to financial data, reports and other information available in these departments. With a laptop equipped with a wireless network adapter, the auditor can easily move between sites and have constant access to any financial documents. As another example, consider a chemical engineer working in different areas of a chemical plant. At one point, he can observe data during some reaction of the production cycle. At another point, he may need a chemical nomenclature to ensure that the components needed to run another production process are available. At the third point, this engineer can access the company's online research library. Wireless access will allow him to easily cope with all the listed tasks.

Technology Support Organizationswireless networks

There are several organizations dedicated to promoting wireless networks. One such organization that is a valuable source of information on wireless networks is Wireless LAN Association (WLANA). This association is formed by manufacturers of wireless network devices, as well as interested companies and organizations, including Alvarion, Cisco Systems, ELAN, Intermec, Intersil, Raylink and Wireless Central. Complete Practice 9-1 to become familiar with the situations in which wireless LANs can be used and the information resources offered by the WLANA Association.

WINLAB (Wireless Information Network Laboratory) is a multi-university wireless network research center located at Rutgers University. WINLAB is sponsored by the National Science Foundation and has been in operation since 1989. By completing Practice 9-2, you will learn about the most recent research carried out by the WINLAB laboratory.

Radio network technologies

Network data is transmitted using radio waves, similar to a local radio station, but network applications use radio waves

much higher frequencies. For example, a local AM (medium and long wave) radio station might broadcast on 1290 kHz because the frequency range for amplitude modulation broadcasts is 535–1605 kHz. The frequency range for FM broadcasting (VHF) has boundaries of 88–108 MHz. In the US, network signals are transmitted at higher frequencies in the ranges 902-928 MHz, 2.4-2.4835 GHz, or 5-5.825 GHz.

Note

Each of the frequency intervals mentioned is also called a band: the 902 MHz band, the 2.4 GHz band, and the 5 GHz band. The 902 MHz band is primarily used in older, non-standardized wireless devices and is not discussed further in the book.

In radio networks, the signal is transmitted in one or more directions depending on the type of antenna used. In the example shown in Fig. 9.1, the signal is directional because it is transmitted from an antenna located on one building to an antenna located on another building. The wave has a very short wavelength and low power (unless the carrier has a special license from the Federal Communications Commission for multi-watt communications), i.e. it is best suited for transmissions within line of sight(line-of-sight transmission) with a short range.

With line-of-sight transmission, the signal is transmitted from one point to another, following the curvature of the Earth, rather than bouncing off the atmosphere, crossing countries and continents. The disadvantage of this type of transmission is the presence of obstacles in the form of large elevations on the Earth's surface (for example, hills and mountains). A low-power (1 - 10 W) radio signal can transmit data at speeds from 1 to 54 Mbit/s and even higher.

To transmit packets in wireless radio network equipment, spread spectrum technology is most often used, when one or more adjacent frequencies are used to transmit a signal with greater bandwidth. The spread spectrum frequency range is very high: 902–928 MHz and much higher. Spread spectrum communications typically provide data transmission rates of 1–54 Mbps.

Communications using radio waves can save money in cases where laying cable is difficult or very expensive. Radio networks are especially useful when using laptop computers that are frequently moved. Compared to other wireless technologies, radio networks are relatively inexpensive and easy to install.

The use of radio waves in communications has several disadvantages. Many networks transmit data at speeds of 100 Mbit/s and higher to organize high-speed communications when sending large traffic (including large files). Radio networks cannot yet provide communications at such speeds. Another disadvantage is that some wireless frequencies are shared by amateur radio operators, the military and cellular network operators, resulting in interference from a variety of sources on these frequencies. Natural obstacles (such as hills) may also reduce or distort the transmitted signal.

One of the main radio network technologies is described by the IEEE 802.11 standard. Other technologies also used include Bluetooth, HiperLAN and HomeRF Shared Wireless Access Protocol (SWAP). All these technologies will be discussed in the following sections of this chapter.

IEEE 802.11 radio networks

Various types of radio networks are used to implement wireless communications, but the IEEE 802.11 standard has significant advantages in terms of compatibility and reliability. Many wireless users use devices that comply with this standard because such devices do not involve non-standardized communications (especially in the lower, slow 902-928 MHz band typical of older wireless devices) and 802.11 devices from different manufacturers are interchangeable. These devices follow an open standard, so different models can communicate with each other and can more easily implement new wireless features. Therefore, it is important for wireless network designers to understand the IEEE 802.11 standard and how devices that comply with this standard operate.

The IEEE 802.11 standard is also called the IEEE Standard for Wireless LAN LEDium Access (MAC) and Physical Layer (PHY) Specifications. This standard applies to fixed and mobile wireless communications stations. Stationary is a station that does not move; mobile is a station that can move quickly or slowly, like a walking person.

The 802.11 standard provides two types of communications. The first type is synchronous communications, when data transfer occurs in separate blocks, the beginning of which is marked by a start bit, and the end by a stop bit. The second type includes communications that take place within a certain time frame, when the signal is given a certain time to reach its destination, and if the signal does not fit within that time, then it is considered lost or distorted. Time constraints make the 802.11 standard similar to the 803.11 standard, in which the signal must also reach a given target node within a specified time. The 802.11 standard provides support for network management services (for example, the SNMP protocol). Network authentication is also provided; the 802.11 standard is focused on using the Link and Physical layers of the OSI model. The MAC and LLC sublayers of the Data Link layer define standards for the access method (which will be discussed later in this chapter), addressing, and methods for verifying data using checksums (CRC). At the Physical Layer, the 802.11 standard defined data rates at specified frequencies. Methods (such as spread spectrum technologies) for transmitting digital signals using radio waves and infrared radiation are also provided.

From a work environment perspective, the 802.11 standard distinguishes between indoor (indoor) and outdoor (outdoor) wireless communications. Indoor communications can, for example, be carried out in an office building, an industrial zone, a store or a private home (i.e., wherever they do not extend beyond a separate building). Outdoor communications can be carried out within a university campus, sports field or parking lot (i.e., where information is transferred between buildings). Next, you will become familiar with the following aspects regarding the functioning of 802.11 wireless networks:

· wireless components used in IEEE 802.11 networks;

· access methods in wireless networks;

· methods for detecting errors during data transmission;

· communication speeds used in IEEE 802.11 networks;

· security methods;

· use of authentication when connection is lost;

· IEEE 802.11 network topologies;

· use of multi-cell wireless local networks.

Wireless Network Components

Wireless communications typically involve three main components: a board that acts as a receiver and transmitter (transceiver), an access point, and antennas.

The transceiver board is called wireless network adapter(wireless NIC, WNIC), which operates at the Physical and Link levels of the OSI model. Most of these adapters are compatible with the Network Interface Specification, NDIS (Microsoft) and Open Datalink Interface, ODI (Novell). As you already know from chapter 5, Both of these specifications allow multiple protocols to be transmitted over the network and are used to communicate the computer and its operating system with the WNIC adapter.

Access Thinka(access point) is a device connected to a cable network and providing wireless data transfer between WNIC adapters and this network. As stated in chapter 4, The access point is usually a bridge. It may have one or more network interfaces of the following types, allowing it to be connected to a cable network:

· 100BaseTX, 100BaseT, 100BaseT2 and 100BaseT4;

Advice

Some wireless network providers now offer access points with router capabilities.

Antenna is a device that sends (emit) and receives radio waves. Both WNIC adapters and access points are equipped with antennas. Most wireless network antennas are either directional or omnidirectional.

Advice

When purchasing 802.11 devices, look to see if they are certified by the Wireless Ethernet Compatibility Alliance (WECA), which represents over 150 wireless device companies. More information about this alliance can be found on the website www. wi- fi. com.

Directional antenna

A directional antenna sends radio beams in one main direction can usually amplify the radiated signal to a greater extent than an omnidirectional antenna. The amount of amplification of the emitted signal is called gain(gain). In wireless networks, a directional antenna is typically used to transmit radio waves between antennas located on two buildings and connected to access points (Fig. 9.2). In this configuration, a directional antenna provides transmission over longer distances compared to an omnidirectional antenna, since it is likely to radiate more a strong signal (high gain) in one direction. Looking at Fig. 9.2, please note that in fact the antenna radiates a signal not only in one direction, since part of the signal is scattered to the sides.

Note

To become familiar with the components of wireless networks, complete Practice 9-3. In addition, Practice Exercises 9-4 and 9-5 teach you how to install a WNIC adapter on Windows 2000 and Windows XP Professional. In Practice 9-6, you will learn how to install an adapter on a Red Hat Linux system. 7. x.

Omnidirectional antenna

An omnidirectional antenna emits radio waves in all directions. Since the signal is scattered more than with a directional antenna, it will likely have less gain. In wireless networks, omnidirectional antennas are often used in indoor networks where there is a constant mix of users and signals must be sent and received in all directions. In addition, such networks typically do not require the signal gain to be as high as an outdoor network, since the distances between wireless devices indoors are much shorter. In Fig. Figure 9.3 shows a wireless network using omnidirectional antennas

Rice. 9.3. Omnidirectional antennas

A WNIC adapter for portable devices (such as laptops, pocket computers, and tablet computers) may be equipped with a small omnidirectional antenna circuit. An access point for a local indoor network may have a detachable omnidirectional antenna or an antenna that is connected to the access point via a cable. An access point for an outdoor network connecting two buildings typically has a high-gain antenna that is connected to the access point via a cable.

Access methods in wireless networks

The 802.11 standard provides two access methods: priority-ordered access and carrier-sense multiple access with collision avoidance. Both of these methods work at the Data Link layer.

Using access in priority order(priority-based access access point also functions as a point coordinator, which specifies a conflict-free period during which stations (besides the coordinator itself) cannot transmit without first contacting the coordinator. During this period, the coordinator interrogates the stations one by one. If some station sends a short packet indicating that it needs to be polled because it has a message to transmit, the point coordinator places its poll on that station. If a station is not polled, the coordinator sends it a signaling frame indicating how long to wait before the next period begins without conflicts. In this case, the stations included in the questionnaire alternately receive the right to carry out communications. When all these stations have received the opportunity to transmit data, the next period is immediately set without conflicts, during which the coordinator again polls the station, determining whether the stations waiting for the opportunity to transmit should be included in the questionnaire.

Priority-based access is intended for communications that require low delays in transmitting information. These types of communications typically include voice, video, and video conferencing—applications that work best when running continuously. According to the 802.11 standard, access in the priority order is also called point coordination function

Most often used in wireless networks multiple access with controlcarrier lem and conflict avoidance(Carrier Sense Multiple Access with Collision Avoidance, CSMA/CA), which is also called distributed coordination functions(distributed coordination function). In this case, the station waiting to transmit listens to the communications frequency and determines its occupancy by checking the level of the receiver signal strength indicator (RSSI). At the 14th moment, when the transmitting frequency is free, conflicts are most likely between two stations that simultaneously want to start transmitting. As soon as the transmitting frequency is released! each station waits a few seconds (the number of which is determined by the DIPS parameter) to ensure that the frequency remains idle. DIFS is an abbreviation for the term Distributed coordination function's In-tra-Frame Space, which defines a predetermined mandatory waiting time (delay).

If stations wait for the time specified by the DIFS interval, the likelihood of conflict between stations is reduced because each station requiring transmission has a different delay time (delay time) calculated before the station again checks the occupancy of the transmitting frequency. If the frequency remains unoccupied, then the station with the minimum delay time begins transmission. If the frequency is busy, then the station requiring transmission waits until the frequency is free, after which it remains idle for the already calculated delay time.

When determining the delay time, the duration of a predetermined time interval is multiplied by a random number. A time interval is a value stored in the Management Information Base (MIB) available at each station. The random number value ranges from zero to the maximum conflict window size, which is also stored in the station control information database. Thus, a unique backoff time is defined for each station waiting to transmit, allowing stations to avoid collisions.

Handling transmission errors

Wireless communications are subject to weather conditions, solar glare, other wireless communications, natural obstacles, and other sources of interference. All of these interferences can interfere with successful data reception. The 802.11 standard provides automatic request forrepetition(automatic repeat-request, ARQ), which allows you to take into account the possibility of transmission errors.

When using ARQ requests, if the station that sent the packet does not receive an acknowledgment (ACK) from the target station, then it automatically retransmits the packet. The number of retries made by the transmitting station before it determines that the packet cannot be delivered depends on the size of the packet. Each station stores two values: the maximum short packet size and the long packet size. In addition, there are two additional parameters: the number of repetitions for sending a Short packet and the number of repetitions for a long packet. Analysis of all these values ​​allows the station to decide whether to stop retransmitting a certain packet.

As an example of error handling using ARQ requests, consider a station for which a short packet has a maximum length of 776 bytes, and the number of retries for a short packet is 10. Let's say that the station transmits a packet with a length of 608 bytes, but does not receive an acknowledgment from the receiving station. In this case, the transmitting station will retransmit this packet 10 times in the absence of acknowledgment. After 10 unsuccessful attempts (i.e., without receiving an acknowledgment), the station will stop transmitting this packet.

Transfer rates

The transmission speeds and corresponding frequencies of 802.11 networks are determined by two standards: 802.11a and 802.1111b. The communication speeds specified in these standards refer to the Physical Layer of the OSI model.

For wireless networks operating in the 5 GHz band, the 802.11 standard provides the following data rates:

· 6 Mbit/s;

· 24 Mbit/s;

· 9 Mbit/s;

· 36 Mbit/s; "

· 12 Mbit/s;

· 48 Mbit/s;

· 18Mbit/s;

· 54 Mbit/s.

Note

All devices that comply with the 802.11a standard must support speeds of 6, 12, and 24 Mbps. Standard 802. PA is implemented at the Physical layer of the OSI model and for the transmission of information signals using radio waves provides for the use orthogonal multiplexing of channels separatedfrequency(Orthogonal Frequency Division Multiplexing, OFDM). Using this multiplexing method, the 5 GHz frequency range is divided into 52 subcarriers (52 subchannels). The data is split between these subcarriers and transmitted simultaneously across all 52 subcarriers. Such transmissions are called parallel. Four subcarriers are used to control communications, and 48 carry data. The 802.11b standard is used in the 2.4 GHz frequency range and provides the following communication speeds: "

· 1 Mbit/s;

· 10Mbit/s;

· 2 Mbit/s;

· 11Mbps.

Note

At the time of writing, an extension of the 802.11b standard, called 802.11d, was expected to be approved. The 802.11d standard allows data transmission in the 2.4 GHz band at speeds of up to 54 Mbit/s.

The 802.11b standard uses direct sequence modulationand extended spectrum(Direct sequence spread spectrum modulation, DSSS), which is a method of transmitting information signals using radio waves and belongs to the Physical layer. With DSSS modulation, data is distributed among several channels (up to 14 in total), each of which occupies a 22 MHz band. The exact number of channels and their frequencies depend on the country in which communications are carried out. In Canada and the USA, 11 channels are used in the 2.4 GHz band. In Europe, the number of channels is 13, with the exception of France, where only 4 channels are used. The information signal is transmitted one by one to the channels and amplified to values ​​sufficient to exceed the interference level.

At the time of writing, 802.11a offers faster speeds than 802.11b. However, the increase in speed is achieved by reducing the working distances. Currently, 802.11a devices can transmit data over distances of up to 18 m, while 802.11b devices are capable of operating at distances of up to 90 m. This means that if you use 802.Na devices, then to increase the overall working area of ​​the communicating devices, you will need to purchase more access points.

In addition to speed, the advantage of the 802.Pa standard is that the total range of frequencies available for it in the 0.825 GHz range is almost twice as large as the frequency range in the 0.4835 GHz range for the 802.11b standard. This means that much more data can be transmitted during broadcasting, since the wider the frequency range, the more information channels over which binary data is transmitted.

For applications that require more bandwidth (such as voice and video), plan to use 802 devices. Additionally, consider using such devices in situations where there are a large number of users within a small area (such as a computer lab). Higher bandwidth will allow all clients on the network to perform better and faster.

The scope of 802.11b devices covers those configurations where high bandwidth is not so important (for example, for communications intended primarily for data transfers). Additionally, 802.11b is well suited for low-budget projects because it requires fewer access points than 802.11a. This is because the 802.11a standard provides a wider working area (up to 90 m versus 18 m allowed by the 802.11a standard). Currently, the 802.11b standard is used more often than 802.11a, since networks based on it are cheaper to implement, and the range of devices intended for it is more widely represented on the market (the production of which, moreover, was started earlier). The characteristics of the 802.11a and 802.11b standards are presented in table. 9.1.

Table 9.1. Characteristics of 802.11a and 802.11 standardsb

	802.11a	802.11b
Operating frequency
Working speeds (band skipKaniya)	6, 9, 12, 18, 24, 36, 48, 54 Mbit/s	1, 2, 10, 11 Mbit/s
Communi methodcation	Orthogonal Frequency Division spread spectrum Multiplexing (OFDM)	Direct sequence modulation DSSS
Current maximum working distance
Real costtions	Relatively high due to the need for additional access points	Relatively low due to the use of a small number of access points

Security methods

Security is just as important in wireless networks as it is in cable networks. The 802.11 standard provides two security mechanisms: open systems authentication and shared key authentication. When using open system authentication, any two stations can authenticate each other. The transmitting station simply sends an authentication request to the target station or access point. If the target station accepts the request, authentication is complete. This authentication method does not provide sufficient security, and you should be aware that many manufacturers' devices use it as the default.

Provides much better protection shared key authentication(shared key authentication), since it implements Wired Equivalent Privacy (WEP). With this security mechanism, two stations (for example, a WNIC adapter and an access point) operate with the same encryption key generated by WEP services. The WEP encryption key is a 40- or 104-bit key with the addition of a checksum and trigger information, resulting in a total key length of 64 or 104 bits.

When using shared key authentication and WEP, one station contacts another with an authentication request. The second station sends back some special text request. The first station encrypts it using the WEP encryption key and sends the ciphertext to the second station, which decrypts it using the same WEP key and compares the resulting text with the text request originally sent. If both texts match, the second station authenticates the first and communications continue.

Using authentication when connection is lost

Another function of authentication is to disconnect the connection after the communication session ends. The connection failure authentication process is important because two communicating stations cannot be accidentally disconnected by another unauthenticated station. The connection between two stations is broken if one of them sends an authentication failure notification. In this case, communications immediately stop.

Network topologiesIEEE 802.11

The 802.11 standard provides two main topologies. The simplest one is topology with a set of independent basic services(Independent Basic Service Set (IBSS) topology), formed by two or more wireless communication stations that can communicate with each other. This type of network is somewhat unpredictable as new stations often appear unexpectedly. The IBSS topology is formed by arbitrary peer-to-peer (equal) communications between WNIC adapters of individual computers (Fig. 9.4).

Compared to IBSS topology, superset topology(Extended service set (ESS) topology) has a large service area because it has one or more access points. Based on the ESS topology, you can create a small, medium or large network and significant! expand the wireless communications area. The ESS topology is shown in Fig. 9.5.

If you are using 802.11 compliant devices, the network and IBSS topology can be easily converted to a network based on the ESS topology. However, networks with different topologies should not be located nearby, since peer-to-peer IBSS communications behave unstable in the presence of access points used in the ESS network. Communications in the ESS network may also be disrupted. "

Advice

For more information about the IEEE 802.11 standard, visit the IEEE website at www. ieee. org. A complete copy of this standard can be ordered from this website.

Multi-mesh wireless LANs

When a network based on an ESS topology uses two or more access points, the network becomes multi-cell wireless localenew network(multiple-cell wireless LAN). The broadcast area around a certain point in such a topology is called cell(cell). If, for example, an indoor network inside a building has five access points, then there are five cells in this network. Additionally, if all five cells are configured identically (same operating frequency, same baud rate, and common security settings), then a personal computer or hand-held device equipped with a WNIC adapter can be moved from one cell to another. This process is called roaming(roaming).

As an example of roaming in a wireless ESS topology, consider a university department that has deployed a wireless network with five access points associated with cells numbered I through V.1 Cell I may belong to a library. Cells II and III may cover the faculty office area. Cell IV may be located in the administration office, and Cell V may be located in the teaching laboratory. If all cells are configured identically, any student, faculty, or office employee can move a laptop computer equipped with a WNIC adapter from one cell to another while maintaining access to the department network. Although the 802.11 standard does not provide a specification for a roaming protocol, wireless device manufacturers have developed one such protocol called Inter- Access Point Protocol (IAPP), which in its main points meets this standard. The IAPP protocol allows a mobile station to move between cells without losing connection to the network. To ensure communications with IAPP roaming, we encapsulate the UDP and IP protocols.

Note

As you already know from chapter 6, User Datagram Protocol (UDP) is a connectionless protocol that can be used in conjunction with IP instead of TCP, which is a connection-oriented protocol.

The IAPP protocol allows you to notify existing access points that a new device is connecting to the network, and also allows adjacent access points to exchange configuration information with each other. In addition, the protocol allows some access point communicating with a mobile station to automatically transmit information about the original connection (including any data waiting to be sent to another access point in cases where the mobile station moves from a cell served by the first access point to a cell served by the first access point). associated with the second access point.

Alternative radio network technologies

Some of the most common communication technologies using radio waves include the following alternative technologies to the IEEE 802.11 standard:

· HomeRF Shared Wireless Access Protocol (SWAP).

Each technology listed represents a wireless networking specification and is supported by specific manufacturers. All these technologies are discussed in the following sections.

Bluetooth

Bluetooth – is a wireless communication technology described by the Bluetooth Special Interest Group. This technology has attracted the attention of manufacturers such as 3Com, Agere, IBM, Intel, Lucent, Microsoft, Motorola, Nokia and Toshiba. It uses frequency hopping in the 2.4 GHz band (2.4-2.4835 GHz) designated by the Federal Communications Commission for unlicensed ISM communications2. The frequency hopping method involves changing the carrier frequency (one of 79 frequencies is selected) for each transmitted packet. The advantage of this method is that it reduces the likelihood of mutual interference in cases of simultaneous operation of several devices.

When using multi-watt communications, Bluetooth technology allows data transmission over distances of up to 100 m, but in practice most Bluetooth devices operate at a distance of up to 9 m. Typically, asynchronous communications are used at a speed of 57.6 or 721 Kbps. Bluetooth devices that provide synchronous communications operate at a speed of 432.6 Kbps, but such devices are less common.

Bluetooth technology uses duplex transmission with time divisionchannel alignment(time division duplexing, TDD), in which packets are transmitted in opposite directions using time slots. One transmission cycle can use up to five different time slots, so packets can be sent and received simultaneously. This process is reminiscent of duplex communications. Up to seven Bluetooth devices can communicate simultaneously (some manufacturers claim that their technologies can connect eight devices, but this does not meet the specifications). When devices exchange information, one of them is automatically selected as the master. This device defines control functions (for example, time slot synchronization and forwarding control). In all other aspects of Bluetooth communication, it resembles a peer-to-peer network.

Advice

To learn more about Bluetooth technology, visit the official website at www. bluetooth. com. Complete Practice 9-7, which introduces you to the Bluetooth website, which describes the applications of Blue-tooth for universal access wireless communications.

HiperLAN

Technology HiperLAN was developed in Europe and there is currently a second version called HiperLAN2. This technology uses the 5 GHz band and provides data transfer rates of up to 54 Mbps. In addition to speed, the advantage of HiperLAN2 is its compatibility with Ethernet and ATM communications.

HiperLAN2 technology supports Data Encryption Standard (DES) – a data encryption standard developed by the National Institute on Standards and Technology (NIST) and ANSI. It uses a public encryption key, viewable by all network stations, as well as a private one. (private) a key allocated only to transmitting and receiving stations. Both keys are needed to decrypt the data.

HiperLAN2 technology ensures quality of service (QoS), providing a guaranteed level of communications for different classes of service (for example, voice or video). This is possible due to the fact that access points centrally manage wireless! communications, and plan all information transfer sessions.

The HiperLAN2 network operates in two modes. Direct mode (directlmode) is a peer-to-peer network topology (similar to the 1B58 topology in 802.11 networks), which is formed only by communicating stations. The other mode is called centralized mode because it is implemented in large networks where there are access points that concentrate and manage network traffic. The communication method for both modes is Time Division Duplex (TDD), the same technology used in Bluetooth.

Advice

For a closer look at HiperLAN2, visit the website www. hiperian2. com.

HomeRF Shared Wireless Access Protocol (SWAP)(HomeRF) is a technology supported by companies such as Motorola, National Semiconductor, Proxim and Siemens. This

the technology operates in the 2.4 GHz band and provides network speeds of up to 10 Mbit/s. It uses CSMA/CA as an access method (like the 802.11 standard) and is intended for home networks where data, voice, video, multimedia streams and other information are transmitted.

An example of a typical use of HomeRF SWAP technology is a wireless network that connects several personal computers and provides them with Internet access. Another area of ​​application is the implementation of wireless connections for entertainment centers (for example, for connecting several televisions and stereo systems with each other). The HomeRF SWAP network can link several phones together. It can also be used to provide communication between home control devices (lighting, air conditioners, kitchen units, etc.). To ensure security, HomeRF SWAP networks use 128-bit data encryption and 24-bit network identifiers.

At the time of writing, HomeRF SWAPS technology was under development, providing communications at a speed of 25 Mbit/s. The creators of this technology are striving to integrate it into televisions and multimedia servers in order to expand the capabilities of complex video systems.

(Advice)

You can get acquainted with HomeRF SWAP in more detail on the website www. homerf. org.

Network technologies usinginfrared radiation

Infrared (IR) radiation can be used as a transmission medium for network communications. You're very familiar with this technology thanks to TV and stereo remote controls. Infrared radiation is an electromagnetic signal, similar to radio waves, but its frequency is closer to the range of visible electromagnetic waves called visible light.

IR radiation can propagate in either one direction or in all directions, with a light emitting diode (LED) used for transmission and a photodiode for reception. IR radiation belongs to the Physical level, its frequency is 100 GHz - 1000 THz (terahertz), and the electromagnetic wavelength ranges from 700 to 1000 nanometers (nm, 10~9).

Like radio waves, IR can be a low-cost solution when cabling is unavailable or when users are mobile. Its advantage is that the PC signal is difficult to intercept without being noticed. Another advantage is the resistance of the ICC signal to radio and electromagnetic interference. However, this communication environment also has a number of significant disadvantages. Firstly, with directional communications the data transfer rate does not exceed 16 Mbit/s, and with omnidirectional communications this value is less than 1 Mbit/s. Secondly, IR radiation does not pass through walls, which is easy to verify by trying to control the TV with a remote control from another room. On the other hand, this disadvantage turns into an advantage, because due to the limited distribution area, communications using IR signals are made more secure. Third, infrared communications may be subject to interference from strong .

Advice

Infrared technologies can use access points to expand the work area and create large networks.

When transmitting information using diffused infrared radiation, the sent IR signal is reflected from the ceiling, as shown in Fig. 9.6. For such communications, there is an IEEE 802 standard, which provides for operation at a distance of 9 to 18 m, depending on the ceiling height (the higher the ceiling, the smaller the network coverage area). For scattered infrared radiation, this standard defines data rates of 1 and 2 Mbit/s. The wavelengths of the diffuse IR signal used in the 802.11R standard are in the range of 850–950 nm (out of the entire range of IR rays, which is 700–1000 nm). By comparison, visible light has a wavelength range of approximately 400–700 Megahertz. The maximum optical emitted signal power according to the 802.11R standard is 2 W.

Advice

Although scattered IR signals are not subject to radio and electromagnetic interference, windows in buildings can cause interference because these signals are sensitive to strong light sources. Consider windows when designing a wireless network using diffuse IR radiation.

The signal transmission method used by the IEEE 802.11R standard is called pulse phase modulation(Pulse position modulation, PPM). According to this method, the binary value of the signal is associated with the location of the pulse in a set of possible positions in the spectrum of electromagnetic radiation. For 1 Mbps communications, the 802.11R standard provides sixteen possible pulse positions (16-PPM), with each position representing four binary bits. With communications at 2 Mbit/s, each pulse represents two bits, and there are only four possible pulse positions (4-PPM). A pulse at a certain position indicates that some value is present, and the absence of a pulse means that the value is not present. PPM is a character encoding method that is similar to binary encoding in that it uses only ones and zeros.

Microwave network technologies

Microwave systems operate in two modes. Terrestrial microwave channels transmit signals between two directional parabolic antennas, which are shaped like a dish (Fig. 9.7). Such communications occur in the 4-6 GHz and 21-23 GHz frequency bands and require the carrier to obtain a license from the Federal Communications Commission (FCC).

Satellite microwave systems transmit a signal between three antennas, one of which is located on the Earth's satellite (Fig. 9.8). Satellites in such systems are in geosynchronous orbits at an altitude of 35,000 km above the Earth. In order for an organization to use such communication technology, it must either launch a satellite or lease a channel from a company that provides such services. Due to long distances, delays during transmission range from 0.5 to 5 seconds. Communications are carried out in the frequency range 11–14 GHz, which require licensing.

Like other wireless communication media, microwave technologies are used when cable systems are too expensive or when cable installation is not possible. Terrestrial microwave channels can be a good solution when laying communications between two large buildings in the city. Satellite communication systems are the only possible way to connect networks located in different countries or on different continents, but this solution is very expensive.

Microwave communications have theoretical bandwidths of up to 720 Mbit/s and higher, but in practice, current speeds are typically in the range of 1–10 Mbit/s. Microwave communication systems have some limitations. They are expensive and difficult to deploy and operate. The quality of microwave communications may be degraded by atmospheric conditions, rain, snow, fog and radio interference. Moreover, the microwave signal can be intercepted, so authentication and encryption are of particular importance when using this transmission medium.

Wireless networks basedlow earth orbit satellites

Communications satellites orbit at a distance of approximately 30,000 km above the Earth. Due to the large distance of these satellites and disturbances in the upper atmosphere, delays in signal transmission may occur that are unacceptable for communications with high requirements for this communication parameter (including the transmission of binary data and multimedia).

Several companies are currently developing low-orbitsatellites(Low Earth Orbiting (LEO) satellite), whose orbits should be at a distance of 700 to 1600 km from the Earth's surface, which should speed up the two-way transmission of signals. Due to their lower orbit, LEO satellites cover smaller areas, and therefore about thirty LEO satellites are needed to completely cover the surface of the planet. Currently, Teledesic, Motorola and Boeing are developing a network of such satellites with the help of which the Internet and other global network services will become available anywhere on Earth. Users interact with LEO satellites using special antennas and signal decoding equipment. Starting in 2005, LEO satellites can be used in the following areas:

Broadcast Internet communications; conducting planetary video conferences;

· distance learning;

· other communications (speech, video and data transmission).

Communication speeds based on LEO satellites are expected to range from 128 Kbps to 100 Mbps for upstream flows (to the satellite) and up to

720 Mbit/s for downstream streams (from satellite). LEO satellites use ultra-high frequencies approved by the Federal Communications Commission in the United States and similar organizations in different parts of the world. The electromagnetic spectrum of communications using LEO satellites is also approved by the ITU. Operating frequencies are in the range of 28.6–29.1 GHz for uplink channels and 18.8–19.3 GHz for. downstream channels. Once this network is operational (the network architecture is shown in Figure 9.9), a project manager in Boston, for example, will be able to videoconference or exchange important binary files with a researcher living in a mountain hut in Wyoming, and a cattle farm owner in Argentina will be able to contact agricultural data from the University of North Carolina (Colorado) network. (Complete Practice 9-8 for more information on using LEO satellites to build networks.)

Summary

1 Modern wireless network technologies use radio waves, infrared radiation, microwave waves and low-orbit satellites.

2 The basis for wireless networks was experiments with packet radio communications, which were carried out long ago by amateur radio operators.

3 Currently, wireless networks are used in many areas (for example, when it is difficult to deploy cable networks). In addition, such networks reduce network installation costs and provide connectivity to mobile computers.

4 Radio communications technologies typically use line-of-sight communications that travel from one point to another along the Earth's surface (rather than having the radio signal bounce off the Earth's atmosphere). Such technologies also use spread spectrum communications, where radio waves are transmitted over several adjacent frequencies.

5 The IEEE 802.11 standard is currently used in various types of radio networks. This standard has three main components: a wireless network adapter (WNIC), an access point, and an antenna. There are two standards (802.11a and 802.11b) that define the speeds of communications that comply with the 802.11 standard. A new standard is being introduced - 802.11g, which is an extension of the 802.11b standard.

6 Common alternatives to 802.11 include Bluetooth, HiperLAN, and HomeFR Shared Wireless Access Protocol.

7 The 802.11R standard uses diffuse infrared (IR) radiation to build small, relatively secure networks located in fairly confined offices or work areas.

8 Microwave networks exist in two types: networks based on terrestrial microwave channels and satellite networks. Satellite networks, of course, can be very expensive due to the high costs of launching a satellite into space.

9 Low Earth Orbit (LEO) satellite networks use a constellation of satellites in very low orbits above the Earth, resulting in significantly lower signal transmission delays than conventional satellite communications. Once networks based on LEO satellites are deployed, networking capabilities will become available anywhere on the planet.

10 In table. 9.2 lists the advantages and disadvantages of network communications using radio waves, infrared radiation and microwave waves.

Table 9.2. Advantages and disadvantages of wireless communication technologies

	Radio waves	IR radiation	Microwave waves	Low-orbit satellites
Advantages	An inexpensive alternative for cases where it is difficult to implement cable communications. One of the means of implementing mobile telecommunications Usually does not require licensing.	The signal is difficult to intercept unnoticed.	An inexpensive alternative for cases where it is difficult to implement cable communications, especially over long distances. A terrestrial microwave channel over long distances may be cheaper than leased telecommunication lines	Can be located above the Earth when creating a global network. They do not create such delays in signal transmission as geosynchronous satellites.
Flaws	May not meet high-speed network requirements. Subject to interference from cellular networks, military, conventional and other sources of radio signals. Subject to naturally occurring interference.	May not be suitable for high-speed communications. Subject to interference from extraneous light sources. Not transmitted through walls. The range of devices offered is smaller than for other types of wireless networks	May not be suitable for high-speed communications Roads in installation and operation. Subject to natural disturbances (rain, snow, fog) and radio interference, and also dependent on atmospheric conditions.	Will only be available in 2005

The article discusses three wireless data transmission technologies, the names of which, as they say, are familiar to everyone: ZigBee, BlueTooth and Wi-Fi, and also provides possible areas of their use and recommendations for choosing technology for a specific task.

BlueTooth wireless data technology

BlueTooth technology (IEEE 802.15 standard) was the first technology that allows organizing a wireless personal network (WPAN - Wireless Personal Network). It allows data and voice transmission over short distances (10–100 m) in the unlicensed 2.4 GHz frequency range and connects PCs, mobile phones and other devices in the absence of line of sight.

BlueTooth owes its birth to Ericsson, which in 1994 began developing a new communication technology. Initially, the main goal was to develop a low-power, low-cost radio interface that would allow communication between cell phones and wireless headsets. However, subsequently, work on the development of the radio interface smoothly grew into the creation of a new technology.

In the telecommunications market, as well as in the computer market, the success of new technology is ensured by leading manufacturing companies who decide on the feasibility and economic benefits of integrating new technology into their new developments. Therefore, in order to ensure a decent future and further development for its brainchild, in 1998 Ericsson organized the BlueTooth SIG (Special Interest Group) consortium, which was given the following tasks:

• further development of BlueTooth technology;
• promotion of new technology in the telecommunications market.

The BlueTooth SIG consortium includes companies such as Ericsson, Nokia, 3COM, Intel, National Semiconductor.

It would be logical to assume that the first steps taken by the BlueTooth SIG consortium would be to standardize the new technology with the goal of compatibility between BlueTooth devices developed by different companies. This was implemented. For this purpose, specifications were developed that describe in detail the methods of using the new standard and the characteristics of data transfer protocols.

As a result, the BlueTooth wireless data transmission protocol stack was developed (Fig. 1).

Rice. 1. Bluetooth protocol stack

BlueTooth technology supports both point-to-point and point-to-multipoint connections. Two or more devices using the same channel form a piconet. One of the devices operates as the main one (master), and the rest - as subordinates (slave). A single piconet can have up to seven active slaves, with the remaining slaves in a "parked" state, remaining synchronized with the master. Interacting piconets form a “distributed network” (scatternet).

There is only one master device in each piconet, but slave devices can be part of different piconets. In addition, the master device of one piconet can be a slave device in another (Fig. 2).

Rice. 2. Piconet with slave devices. a) with one slave device. b) several. c) distributed network

Since the first BlueTooth modules hit the market, their widespread use in new applications has been hampered by the complex software implementation of the BlueTooth protocol stack. The developer had to independently implement control of the BlueTooth module and develop profiles that determine the interaction of the module with other BlueTooth devices using host controller interface commands (HCI - Host Controller Interface). Interest in BlueTooth technology was growing every day, more and more companies were appearing to develop components for it, but there was no solution that would significantly simplify the management of BlueTooth modules. And such a solution was found. The Finnish company, having studied the market situation, was one of the first to offer developers the following solution.

In most cases, BlueTooth technology is used by developers to replace a wired serial connection between two devices with a wireless one. To organize a connection and perform data transfer, the developer needs to programmatically, using host controller interface commands, implement the upper levels of the BlueTooth protocol stack, which include: L2CAP, RFCOMM, SDP, as well as the serial port interaction profile - SPP (Serial Port Profile) and Service Discovery Profile (SDP). The Finnish company decided to play on this by developing a firmware version for BlueTooth modules, which represents a complete software implementation of the entire BlueTooth protocol stack (Fig. 1), as well as SPP and SDP profiles. This solution allows the developer to control the module, establish a wireless serial connection and perform data transfer using special character commands, just as is done when working with conventional modems through standard AT commands.

At first glance, the solution discussed above can significantly reduce the time for integrating BlueTooth technology into newly developed products. However, this imposes certain restrictions on the use of BlueTooth technology. This mainly affects the reduction in maximum throughput and the number of simultaneous asynchronous connections supported by the BlueTooth module.

In mid-2004, the BlueTooth specification version 1.2, which was published in 2001, was replaced by the BlueTooth specification version 1.2. The main differences between specification 1.2 and 1.1 include:

1. Implementation of adaptive frequency hopping (AFH) technology.
2. Improved voice connectivity.
3. Reduce the time it takes to establish a connection between two BlueTooth modules.

BlueTooth and Wi-Fi are known to use the same unlicensed 2.4 GHz band. Therefore, in cases where BlueTooth devices are in range of Wi-Fi devices and communicate with each other, this may lead to collisions and affect the performance of the devices. AFH technology allows you to avoid collisions: during the exchange of information, to combat interference, BlueTooth technology uses channel frequency hopping, the selection of which does not take into account the frequency channels on which Wi-Fi devices exchange data. In Fig. Figure 3 illustrates the operating principle of AFH technology.

Rice. 3. Operating principle of AFH technology. a) collisions b) avoiding collisions using adaptive channel frequency tuning

The development of BlueTooth technology does not stand still. The SIG consortium has developed a concept for technology development until 2008 (Fig. 4).

Rice. 4. Stages of development of Bluetooth technology

Currently, there are a large number of companies on the market offering BlueTooth modules, as well as components for independent implementation of the hardware of a BlueTooth device. Almost all manufacturers offer modules that support BlueTooth specifications version 1.1 and 1.2 and correspond to class 2 (range 10 m) and class 1 (range 100 m). However, while version 1.1 is fully compatible with version 1.2, all of the improvements discussed above that are included in version 1.2 can only be obtained if both devices are compliant with version 1.2.

In November 2004, the BlueTooth specification version 2.0 was adopted, supporting Enhanced Data Rate (EDR) technology. Specification 2.0 with EDR support allows data exchange at speeds of up to 3 Mbit/s. The first mass-produced samples of modules corresponding to version 2.0 and supporting EDR advanced data transfer technology were offered by manufacturers at the end of 2005. The range of such modules is 10 m in the absence of line of sight, which corresponds to class 2, and in the presence of line of sight it can reach 30 m.

As noted earlier, the main purpose of BlueTooth technology is to replace a wired serial connection. However, the SPP profile used to organize the connection is, of course, not the only profile that developers can use in their products. BlueTooth technology defines the following profiles: Generic Access Profile, Service Discovery Profile, Cordless Telephony Profile, Intercom Profile, Headset Profile Profile), Dial-up Networking Profile, Fax Profile, Lan Access Profile, Generic Object Exchange Profile, Object Push Profile, File Transfer Profile, Synchronization Profile.

Wi-Fi wireless data technology

The situation with Wi-Fi is somewhat confusing, so first let’s define the terminology used.

The IEEE 802.11 standard is the basic standard for building wireless local networks (Wireless Local Network - WLAN). The IEEE 802.11 standard has been constantly improved, and currently there is a whole family, which includes the IEEE 802.11 specifications with the letter indices a, b, c, d, e, g, h, i, j, k, l, m, n, o , p, q, r, s, u, v, w. However, only four of them (a, b, g and i) are the main ones and are most popular among equipment manufacturers, while the rest (c-f, h-n) are additions, improvements or corrections to the accepted specifications.

In turn, the Institute of Electronics and Electrical Engineers (IEEE) only develops and adopts specifications for the above standards. His responsibilities do not include testing equipment from different manufacturers for compatibility.

To promote wireless local area network (WLAN) equipment on the market, a group was created called the Wi-Fi Alliance. This alliance manages the certification of equipment from various manufacturers and grants permission for members of the Wi-Fi Alliance to use the Wi-Fi trademark logo. The presence of the Wi-Fi logo on the equipment guarantees reliable operation and compatibility of the equipment when building a wireless local network (WLAN) on equipment from different manufacturers. Currently, Wi-Fi compatible equipment is equipment built according to the IEEE 802.11a, b and g standard (may also use the IEEE 802.11i standard to provide a secure connection). In addition, the presence of a Wi-Fi logo on the equipment means that the equipment operates in the 2.4 GHz or 5 GHz band. Consequently, Wi-Fi should be understood as the compatibility of equipment from different manufacturers intended for building wireless local networks, taking into account the limitations stated above.

The original IEEE 802.11 specification, adopted in 1997, established data transmission at 1 and 2 Mbps in the unlicensed 2.4 GHz frequency range, as well as a method of controlling access to the physical medium (radio channel) that uses authentication multiple access. carrier and collision elimination (Carrier Sense Multiple Access with Collision Avoidance, CSMA-CA). The CSMA-CA method is as follows. To determine the state of the channel (busy or free), an algorithm is used to estimate the signal level in the channel, according to which the signal power at the receiver input and signal quality are measured. If the power of the received signals at the receiver input is below the threshold value, then the channel is considered free, but if their power is above the threshold value, then the channel is considered busy.

Since the adoption of the IEEE 802.11 standard specification, several manufacturers have introduced their equipment to the market. However, IEEE 802.11 equipment has not become widespread due to the fact that the standard specification did not clearly define the rules for the interaction of protocol stack layers. Therefore, each manufacturer presented its own version of the IEEE 802.11 standard, which is incompatible with the others.

To correct this situation, in 1999, IEEE adopted the first addition to the IEEE 802.11 standard specification, called IEEE 802.11b. The IEEE 802.11b standard was the first wireless local area network standard to become widespread. The maximum data transfer speed in it is 11 Mbit/s. The developers of the standard were able to achieve this speed by using the coding method using a sequence of complementary codes (Complementary Code Keying). To control access to the radio channel, the same method is used as in the original specification of the IEEE 802.11 standard - CSMA-CA. The above value of the maximum data transfer rate is, of course, a theoretical value, since the CSMACA method is used to access the radio channel, which does not guarantee the availability of a free channel at any time. Therefore, in practice, when transmitting data via the TCP/IP protocol, the maximum throughput will be about 5.9 Mbit/s, and when using the UDP protocol - about 7.1 Mbit/s.

If the electromagnetic environment deteriorates, the equipment automatically reduces the transmission speed initially to 5.5 Mbit/s, then to 2 Mbit/s, using the Adaptive Rate Selection (ARS) method. Reducing the rate allows the use of simpler and less redundant encoding methods, making transmitted signals less susceptible to attenuation and distortion due to interference. Thanks to the adaptive rate selection method, IEEE 802.11b equipment can communicate in different electromagnetic environments.

The next standard to join the IEEE 802.11 family is IEEE 802.11a, a specification adopted by IEEE in 1999. The main differences between the IEEE 802.11a standard specification and the original IEEE 802.11 standard specification are as follows:

• data transmission is carried out in the unlicensed 5 GHz frequency range;
• orthogonal frequency modulation (OFDM) is used;
• the maximum data transfer speed is 54 Mbit/s (real speed is about 20 Mbit/s).

Just like 802.11b, 802.11a implements an adaptive rate selection (ARS) technique that reduces the data rate in the following order: 48, 36, 24, 18, 12, 9, and 6 Mbps. Information is transmitted via one of 12 channels allocated in the 5 GHz band.

The use of the 5 GHz band in the development of the 802.11a specification is primarily due to the fact that this band is less congested than the 2.4 GHz band, and therefore the signals transmitted in it are less susceptible to interference. Undoubtedly, this fact is an advantage, but at the same time, the use of the 5 GHz band leads to the fact that reliable operation of IEEE 802.11a equipment is ensured only in line of sight. Therefore, when building a wireless network, it is necessary to install more access points, which, in turn, affects the cost of deploying a wireless network. In addition, signals transmitted in the 5 GHz band are more susceptible to absorption (the emitted power of IEEE 802.11b and 802.11a equipment is the same).

The first samples of IEEE 802.11a equipment were introduced to the market in 2001. It should be noted that equipment that only supports the IEEE 802.11a standard has not been in great demand in the market for several reasons. Firstly, at that time, IEEE 802.11b equipment had already proven itself in the market, secondly, everyone noted the disadvantages of using the 5 GHz band, and thirdly, IEEE 802.11a equipment was not compatible with IEEE 802.11b. However, subsequently, to promote IEEE 802.11a, manufacturers offered devices that support both standards, as well as equipment that allows adaptation to networks built on equipment of the IEEE 802.11b, 802.11a, 802.11g standard.

In 2003, the IEEE 802.11g standard specification was adopted, establishing data transmission in the 2.4 GHz band at a speed of 54 Mbit/s (the actual speed is about 24.7 Mbit/s). Radio access control uses the same method as the original IEEE 802.11 specification - CSMACA, as well as orthogonal frequency modulation (OFDM).

IEEE 802.11g equipment is fully compatible with 802.11b, however, due to interference, in most cases the actual data transfer rate of 802.11g is comparable to the speed provided by 802.11b equipment. Therefore, the only correct solution for potential users of wireless local area networks is to purchase equipment that supports three standards at once: 802.11a, b and g.

Most developers associate Wi-Fi-compatible equipment primarily with the organization of access points for Internet access and with subscriber equipment. It should be noted that the embedded systems industry has not ignored the IEEE 802.11a, b and g standards. There are already offers in this market segment that make it possible to make any device Wi-Fi compatible. We are talking about OEM modules of the IEEE 802.11b standard, which include: a transceiver, an application processing processor and software execution. Thus, these modules represent a completely complete solution that can significantly reduce the time and cost of implementing Wi-Fi compatibility of the product under development. Basically, OEM modules of the IEEE 802.11b standard are integrated into products for remote monitoring and control via the Internet. To connect an OEM module of the IEEE 802.11b standard to the product, an RS-232 serial interface is used, and the module is controlled by AT commands. The maximum distance between an OEM module of the IEEE 802.11b standard and an access point when using a special remote antenna can be up to 500 m. Indoors, the maximum distance does not exceed 100 m, and in the presence of line of sight increases to 300 m. A significant disadvantage of such OEM modules is their high price.

Table 1 shows the main technical characteristics of the IEEE 802.11a, b and g standards.

Table 1. Main technical characteristics of IEEE 802.11a, b and g standards

ZigBee wireless data technology

ZigBee wireless data transmission technology was introduced to the market after the advent of BlueTooth and Wi-Fi wireless data transmission technologies. The emergence of ZigBee technology is primarily due to the fact that for some applications (for example, for remote control of lighting or garage doors, or reading information from sensors), the main criteria when choosing wireless transmission technology are low power consumption of the hardware and its low cost. This results in low throughput, since in most cases the sensors are powered by a built-in battery, the operating time of which must exceed several months or even years. Otherwise, monthly replacement of the battery for the garage door opening/closing sensor will radically change the user’s attitude towards wireless technologies. The existing BlueTooth and Wi-Fi wireless data transmission technologies at that time did not meet these criteria, providing data transmission at high speeds, with high levels of power consumption and hardware costs. In 2001, IEEE 802.15 Working Group No. 4 began work on creating a new standard that would meet the following requirements:

• very low power consumption of hardware that implements wireless data transmission technology (battery life should range from several months to several years);
• information transfer should be carried out at low speed;
• low cost of hardware.

The result was the development of the IEEE 802.15.4 standard. In many publications, the IEEE 802.15.4 standard is understood as ZigBee technology, and vice versa, ZigBee is the IEEE 802.15.4 standard. However, it is not. In Fig. Figure 5 shows a model of interaction between the IEEE 802.15.4 standard, ZigBee wireless data transmission technology and the end user.

Rice. 5. Model of interaction between the IEEE 802.15.4 standard, ZigBee wireless data transmission technology and the end user

The IEEE 802.15.4 standard defines the interaction of only the lowest two layers of the interworking model: the physical layer (PHY) and the radio access control layer for three unlicensed frequency bands: 2.4 GHz, 868 MHz and 915 MHz. Table 2 shows the main characteristics of equipment operating in these frequency ranges.

Table 2. Main characteristics of the equipment

The MAC layer is responsible for controlling access to the radio channel using the Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA) method, as well as for managing connection and disconnection from the data network and ensuring the protection of transmitted information by symmetric key (AES-128).

In turn, the ZigBee wireless data transmission technology proposed by the ZigBee Alliance determines the remaining levels of the interaction model, which include the network level, security level, application structure level and application profile level. The network layer, ZigBee wireless data technology, is responsible for device discovery and network configuration and supports three network topologies shown in Fig. 6.

Rice. 6. Three network topology options

To ensure low cost integration of ZigBee wireless technology into various applications, the physical hardware implementation of the IEEE 802.15.4 standard comes in two forms: reduced function devices (RFDs) and fully functional devices (FFDs). When implementing one of the network topologies shown in Fig. 6, at least one FFD device is required to act as a network coordinator. Table 3 lists the functions performed by FFD and RFD devices.

Table 3. List of functions performed by FFD and RFD devices

The low cost of the hardware of RFD devices is ensured by limiting the set of functions when organizing interaction with a network coordinator or FFD device. This, in turn, is reflected in the incomplete implementation of the interaction model shown in Fig. 5, and also imposes minimal requirements on memory resources.

In addition to dividing devices into RFD and FFD, the ZigBee Alliance defines three types of logical devices: ZigBee coordinator (coordinator), ZigBee router and ZigBee terminal device. The coordinator initializes the network, manages nodes, and also stores information about the settings of each node connected to the network. A ZigBee router is responsible for routing messages transmitted over the network from one node to another. An endpoint device refers to any endpoint device connected to a network. The RFD and FFD devices discussed above are precisely the end devices. The type of logical device when building a network is determined by the end user by selecting a specific profile (Fig. 5) proposed by the ZigBee alliance. When building a network with an “everyone to everyone” topology, the transmission of messages from one network node to another can be carried out along different routes, which makes it possible to build distributed networks (combining several small networks into one large one - a cluster tree) with the installation of one node from another on a sufficiently large distance and ensure reliable delivery of messages.

Traffic transmitted over the ZigBee network is usually divided into periodic, intermittent and repeating (characterized by a short time interval between sending information messages).

Periodic traffic is typical for applications that require information to be received remotely, such as from wireless sensors or meters. In such applications, obtaining information from sensors or meters is carried out as follows. As mentioned earlier, any end device, which in this example is a wireless sensor, should be in “sleep” mode for the vast majority of its operating time, thereby ensuring very low power consumption. To transmit information, the terminal device at certain times wakes up from the “sleep” mode and searches the radio for a special signal (beacon) transmitted by the network management device (ZigBee coordinator or ZigBee router) to which the wireless meter is connected. If there is a special signal (beacon) on the radio, the terminal device transmits information to the network management device and immediately goes into “sleep” mode until the next communication session.

Intermittent traffic is common, for example, with remote lighting control devices. Let's imagine a situation where, when a motion sensor installed at the front door is triggered, it is necessary to transmit a command to turn on the lighting in the hallway. The command transmission in this case is carried out as follows. When the network management device receives a motion sensor signal, it instructs the end device (wireless switch) to connect to the ZigBee wireless network. Then a connection is established with the terminal device (wireless switch) and an information message is transmitted containing a command to turn on the lighting. After receiving the command, the connection is terminated and the wireless switch is disconnected from the ZigBee network.

Connecting and disconnecting an end device to the ZigBee network only at the necessary moments allows you to significantly increase the time the end device stays in the “sleep” mode, thereby ensuring minimal power consumption. The method of using a special signal (beacon) is much more energy-intensive.

In some applications, such as security systems, the transmission of information about sensor activation must be carried out almost instantly and without delay. But we must take into account the fact that at a certain point in time several sensors can “work” at once, generating so-called repeating traffic in the network. The probability of this event is low, but it is unacceptable not to take it into account in security systems. In the ZigBee wireless network, for messages transmitted to the wireless network when several security sensors (end devices) are triggered at once, data transmission from each sensor is provided in a specially allocated time slot. In ZigBee technology, a specially allocated time slot is called a Guaranteed Time Slot (GTS). The presence in ZigBee technology of the ability to provide a guaranteed time slot for the transmission of urgent messages allows us to talk about the implementation of the QoS (quality of service) method in ZigBee. The allocation of a guaranteed time slot for the transmission of urgent messages is carried out by the network coordinator (Fig. 6, PAN Coordinator).

When developing hardware for ZigBee wireless data transmission technology that implements the interaction model, almost all manufacturers adhere to the concept according to which all the hardware is placed on a single chip. In Fig. Figure 7 shows the concept of the hardware implementation of ZigBee wireless data transmission technology.

Rice. 7. Concept of hardware implementation of ZigBee wireless data transmission technology

To build a wireless network (for example, a network with a star topology) based on ZigBee technology, the developer must purchase at least one network coordinator and the required number of end devices. When planning a network, it should be taken into account that the maximum number of active end devices connected to the network coordinator should not exceed 240. In addition, it is necessary to purchase software tools for developing, configuring the network and creating user applications and profiles from the ZigBee chip manufacturer. Almost all manufacturers of ZigBee chips offer a whole line of products on the market, differing, as a rule, only in the amount of ROM and RAM memory. For example, a chip with 128 KB of ROM and 8 KB of RAM can be programmed to act as a coordinator, router, and end device.

The high cost of the debugging kit, which includes a set of software and hardware for building ZigBee wireless networks of any complexity, is one of the limiting factors for the mass distribution of ZigBee technology on the Russian market. It should be noted that the emergence of ZigBee wireless transmission technology has become a definite response to the needs of the market for the creation of intelligent control systems for private homes and buildings, the demand for which is increasing every year. In the near future, private homes and buildings will be equipped with a huge number of wireless network nodes that monitor and control the life support systems of the home. Installation of these systems can be done at any time and in a short time, since they do not require cabling in the building.

We list the applications into which ZigBee technology can be integrated:

• Life support automation systems for houses and buildings (remote control of network sockets, switches, rheostats, etc.).
• Consumer electronics control systems.
• Systems for automatically taking readings from various meters (gas, water, electricity, etc.).
• Security systems (smoke sensors, access and security sensors, gas and water leakage sensors, motion sensors, etc.).
• Environmental monitoring systems (temperature, pressure, humidity, vibration sensors, etc.).
• Industrial automation systems.

Conclusion

The brief overview of BlueTooth, Wi-Fi and ZigBee wireless data transmission technologies given in the article shows that even for experienced developers it can be difficult to clearly give preference to one or another technology only on the basis of technical documentation.

Therefore, the selection approach should be based on a comprehensive analysis of several parameters. Comparative characteristics of BlueTooth, Wi-Fi and ZigBee technologies are shown in Table 4. This information will help you make the right decision when choosing a wireless data transmission technology.

Table 4. Comparative characteristics of BlueTooth, Wi-Fi and ZigBee technologies

Literature

1. V.A. Grigoriev, O.I. Lagutenko, Yu.A. Raspaev. “Systems and networks of radio access”, M.,: EcoTrends, 2005.
2. www.ieee.com
3. www.chipcon.com
4. www.ember.com
5. www.BlueTooth.org

Modern science is experiencing a boom in its development. At the moment, computer technology has begun to play a major role. This is due, first of all, to the advent of tablets, smartphones, laptops and computers in people’s lives, the normal operation of which requires access to the Internet.

In agriculture, industry and, of course, in the military sphere, there is a need for reliable control systems and their unification in a special global network. Such trends are occurring all over the world and are driving the development of wireless technologies. This article provides a list of the main types of wireless technologies, as well as a description of each type.

All wireless technologies can be divided into the following main types according to the number of objects:

• personal wireless technologies;
• wireless network;
• local wireless networks;
• global wireless networks.

Personal wireless technologies (networks)

This type includes technologies such as:

Bluetooth is a short range radio technology. Usually this distance is about 300 meters. This type of communication is based on the FHSS algorithm.

IrDA is an infrared port that describes the protocols of the logical and physical layers. This technology is commonly known as infrared. This technology has been replaced by the Wi-Fi and Bluetooth technologies we know. Infrared ports, like Bluetooth, are short-range technologies. One of the features of the infrared port is that data is transmitted only when the receiver is fully visible.

USB technology is a wireless technology with a range of almost 9-10 meters. This is by far the widest range used by commercial communications devices. Wireless USB is a type of wireless USB technology that is designed to replace wired USB. The main function of this technology is to ensure fast exchange over short distances and ensure the process of interaction between PCs and peripheral devices.

Wireless HD is a wireless technology whose main function is the transmission of HD quality videos. WiGig is a broadband wireless technology that operates in the frequency range from 60 GHz and provides data transmission up to 7-8 Gbit per second, at approximately a distance of 9-10 meters. LibertyLink is a wireless network technology that uses magnetic induction to transmit data.

Wireless networks RuBee is a local wireless network, which is a network for sensors. To transmit data, the network uses magnetic waves. The network is used for unusual purposes that do not require high speed, but require long operation and good secure communication.

Such networks are used to operate high-risk facilities. Wavenis is a wireless network using frequencies of 433, 868 and 915 MHz, and provides data transmission over a distance of almost 1000 m in an open area and up to 200 meters in a building at speeds of up to 100 Kbps.

This technology is used to organize a personal network or a network for sensors. One-Net is a protocol for creating wireless sensor networks, as well as networks for automation of buildings and objects.

Data is transmitted over a distance of up to 100 m, in open space, at a data transmission speed of approximately 28 – 230 Kbps. DASH7 is a standard for organizing wireless sensor networks. A sensor network is a network of computing devices that are equipped with special touch sensors. The propagation distance is directly dependent on the strength of the signal that is transmitted.

Local wireless Wi-Fi networks are a family of IEEE standards. Used to transmit data in the range from 2 to 5 GHz and provide transmission speeds from 1 Mbit per second, at a distance of up to 150 meters. Wi-Fi is used to organize both local networks and to connect to the global Internet. Wi-Fi is the most popular technology for organizing both home and office networks and Internet access. HiperLAN is a wireless networking standard. There are two families of standards: HiperLAN1 and HiperLAN2. This standard is used to transmit data over a distance of up to 50 meters and transmission speeds of up to 10 Mbit per second.

Global wireless networks

Such networks include: - 1G generation mobile communications; — 2G generation mobile communications; — 2.5G generation mobile communications; — 3G generation mobile communications; — mobile communications 3.5 G generation; — 4G generation mobile communications;

This article provides the main classification of wireless technologies. This is not a list of all wireless technologies, but only a small part of them. Wireless technologies appear as science and technology develop, so their number is huge.

Well, if you are a web developer or the owner of a highly loaded web resource, then it is currently relevant for you dedicated server rental to suit the needs of the web resource. You can get detailed advice on all the advantages of a dedicated server on the hosting provider’s website.

high-speed wireless communication technologies- - [L.G. Sumenko. English-Russian dictionary of information technologies. M.: State Enterprise TsNIIS, 2003.] Topics information technologies in general EN high speed wireless technologies ...

It is proposed to rename this page to Wireless Computer Network. Explanation of the reasons and discussion on the Wikipedia page: To rename / December 1, 2012. Perhaps its current name does not correspond to the standards of modern ... ... Wikipedia

A wireless sensor network is a distributed, self-organizing network of multiple sensors (sensors) and actuators interconnected via a radio channel. Moreover, the coverage area of ​​such a network can range from... ... Wikipedia

- (other names: wireless ad hoc networks, wireless dynamic networks) decentralized wireless networks that do not have a permanent structure. Client devices connect on the fly, forming a network. Each network node tries to forward... ... Wikipedia

Wireless computer networks are a technology that allows you to create computer networks that fully comply with the standards for conventional wired networks (for example, Contents 1 Application 2 Security 3 ... Wikipedia

Wireless ad hoc networks are decentralized wireless networks that do not have a permanent structure. Client devices connect on the fly, forming a network. Each network node tries to forward data intended for other nodes. At the same time... ... Wikipedia

wireless local lines- The most commonly used designation for subscriber access technology. Topics information technology in general EN Wireless Local LoopWLL ...

Technical Translator's Guide wireless digital subscriber lines Topics information technology in general EN Wireless Local LoopWLL ...

- Application of high-speed data transmission technology over xDSL cable lines to build digital wireless access networks. Equivalent terms AirDSL and skyDSL. [L.M. Nevdyaev. Telecommunication technologies. English-Russian intelligent... ... wireless multimedia and messaging services Topics information technology in general EN Wireless Local LoopWLL ...

- - [L.G. Sumenko. English-Russian dictionary of information technologies. M.: State Enterprise TsNIIS, 2003.] Topics information technology in general EN wireless multimedia and messaging servicesWIMS ...

It is proposed to rename this page to Wireless Self-Organizing Network. Explanation of the reasons and discussion on the Wikipedia page: To rename / December 1, 2012. Perhaps its current name does not correspond to the standards of modern ... ... Wikipedia

• Books
• , V. M. Vlasov, B. Ya. Maktas, V. N. Bogumil, I. V. Konin. The training manual describes in detail the technology of satellite navigation as applied to the tasks of monitoring and controlling the movement of road transport. The technology for determining...

Wireless technologies in automobile transport. Global navigation and vehicle location. Tutorial. Grif Ministry of Defense of the Russian Federation, V.M. Vlasov. The textbook describes in detail the technology of satellite navigation as applied to the tasks of monitoring and controlling the movement of road transport. The technology for determining... assist | . cafe| . KSM KovaliovM. .P., st.grKSM-06-1

Vaulin D.K.

Krivorizky Technical University, Ukraine

This article is devoted to an overview of modern standards in wireless network technologies. The article describes all the positive and negative qualities of this option for solving problems of transmitting packet data over a distance. We will also find out the groups of modern wireless network technologies and identify the best standards in their group, which are best suited for transmitting packet data over the “air” path.

Wireless network technologies

The choice of wireless network technology depends on your business's needs, budget, and future plans. Let's say that connecting your enterprise directly with copper or fiber optic cable is not possible (for example, due to lack of appropriate permission), or is too expensive, or the load on your network has increased to such an extent that its bandwidth usage has reached critical levels, or the manager Marketing offers you to connect the network of the central office with networks of stores scattered over a large area. No matter how difficult your business's communications situation may be, wireless networking technologies can help you find the solution you need.

Wireless network technologies can be divided into three main types: mobile communications, wireless communications between buildings and communications within them . We'll analyze the advantages and disadvantages of each type of technology, provide pricing information for related communications equipment, and explore potential wireless communications applications.

mobile connection

Wireless network technologies for mobile users are widespread and inexpensive to implement. Examples of such technologies are packet radio, Cellular Digital Packet Data (CDPD), and circuit switched cellular communications. Although these technologies provide the lowest data transfer rates (compared to other wireless network technologies), the systems that implement them operate throughout the world. A number of technologies, such as Enhanced Specialized Mobile Radio (ESMR), Personal Communications Services (PCS), and two-way satellite communications, are just beginning to come to market.

Cellular circuit switching

Like CDPD, circuit switched cellular uses existing analog cellular networks. The difference is that in this case, instead of switching data packets, regular cellular network circuit switching is used. To transfer data, the user connects a cellular modem to their PC and a data-enabled cell phone and establishes a dial-up connection just like with a good old analog modem.

If you need to transfer long files, circuit switched cellular is your best choice; packet radio and CDPD are more suitable for sending short messages. Circuit switched cellular communications are a fairly slow form of communication. Data is transmitted at speeds of up to 14.4 Kbps, and only in certain service areas the speed increases to 20 Kbps. In large cities and when moving away from the base station, the transmission speed may decrease. The technology under consideration is the most accessible, because more than 95% of the US territory is covered by cellular networks.

Wireless communication between buildings

Sometimes, for short-distance communications, a network administrator may consider wireless communications systems as an alternative to direct cable connections or leased lines. This alternative is attractive for several reasons: such systems provide fairly high data transfer rates, are highly scalable, and are cheaper to operate. Wireless communication technologies - such as infrared, laser, narrowband microwave (microwave) and broadband (using spectral modulation) - provide data transmission at speeds up to 155 Mbit/s. The cost of purchasing wireless line equipment is typically lower than the cost of using a leased line and much lower than the cost of installing fiber optic or coaxial cable.

Classification of technologies

Let's divide the standards of wireless network technologies into 2 groups:

· Mobile communication technologies

·

Mobile communication technologies

These are technologies that are actively used in cellular and other mobile communications.

3 G - digital packet technology that is used to describe the third generation of mobile telephony, providing access to video content and broadband Internet services for mobile devices. The first generation was represented by analog cellular phones, the second by digital cellular networks.

Uses standardsW-CDMA(UMTS), CDMA2000, TD-CDMA/TD-SCDMA, DECT, UWC-136.

.Bluetooth– mobile communication technology operating at frequencies 2400-2483.5 MHz. These frequencies were not chosen by chance; they are open and free of any licensing in most countries of the world. . The frequencies used determine Bluetooth's data transfer capabilities. The channel width for Bluetooth devices is 723.2 kb/s in asynchronous mode (however, even in this mode there is still up to 57.6 kb/s for simultaneous transmission in the opposite direction), or 433.9 kb/s in fully synchronous mode.

The distance over which a Bluetooth connection can be established is small, ranging from 10 to 30 meters. Currently, work is underway to increase this distance, at least to 100 meters.

The main feature of Bluetooth is that various Bluetooth devices connect to each other automatically as soon as they are within range. The user does not have a headache about cables, drivers, or anything else, all that is required of him is to make sure that the Bluetooth devices are close enough to each other, the Bluetooth devices and software themselves should take care of the rest.

Wireless communication technologies between and within objects

These are technologies that are actively used to organize communication between different buildings and also within them.

WiMAX- short for worldwide interoperability for microwave access - is a technology for providing wireless broadband Internet access. WiMAX is based on the IEEE 802.16 standard.

WiMAX networks can operate in two access options: fixed And mobile

Mobile WIMAX allows the user to receive both fixed access (similar to the usual xDSL, only without wires) and access to the Network from anywhere within the coverage area or even on the move (something very roughly speaking, like the existing GPRS cellular standard, only much faster).

The 802.16 standard defines several modes of operation of WiMAX networks:

· Fixed WiMAX - fixed access;

· Nomadic WiMAX - session access;

· Portable WiMAX - access while moving;

· Mobile WiMAX - mobile access.

WiFiis a shorter-range system, typically covering hundreds of meters, that uses unlicensed frequency bands to provide network access. Typically, Wi-Fi is used by users to access their own local network, which may not be connected to the Internet. If WiMAX can be compared to mobile communications, then Wi-Fi is more like a landline cordless phone.

In Wi-Fi networks, all user stations that want to transmit information through an access point (AP) compete for the latter’s “attention”. This approach can cause a situation in which communications for more distant stations are constantly interrupted in favor of closer stations. This state of affairs makes it difficult to use services such as Voice over IP (VoIP), which rely heavily on an uninterrupted connection. Wi-Fi uses 802.11 - e family of specifications developed by EEE for wireless local networks (wireless LAN) There are the following types of specifications:

Conclusion.

This article examined the types of modern wireless network technologies. Their description was given, characteristics, operating features and the environment of use were considered. To summarize this article, we can say that today wireless network technologies have very good potential for development and also have many advantages compared to other network technologies. Let us note that due to the rapid development of electronic technologies, wireless technologies may very soon become the best, highest quality and most importantly effective solution in network technologies.

Literature