The most precisely currently available technology can be defined as use of radio waves for granting broadband network services to the individual users. In addition, this technology is not only advantageous in those regions, where the telephone cable network is insufficient, but also where the level of telephone or cable networks is rather high. In this case, operators using technologies of broadband wireless access are already direct competitors of the local telecommunication providers.
Comparable with the organization of television translation, the wireless lines are organized by a principle of direct visibility. The signal transfers via aerial, usually located on a height or on a high building, to special reception aerials established on the users buildings. Reception the pure spectrum of frequencies can be a rather difficult task; other problem is the requirement of direct visibility for the majority of organized lines. As well as in a case with television broadcasting, any obstacles (for example, dense top of trees, height, high buildings and even the strong atmospheric precipitation) can in the certain measure complicate reception. It is necessary to take into account and distance, as the signals of wireless communication can be accepted only within the limits of certain distance from the transmitter. The solution of this problem can be the installation of a network relays on all zone of service (by a principle of cellular communication).
Because the radio system provides already coverage of the certain zone, it means much easier planning of a network in comparison with cable systems. The wireless systems allow much more operatively adaptation to changes of requirements and amount of the users.
The standard IEEE 802.11 was the first standard for WLAN products from independent international organization developing the majority of the standards for wire circuit networks.202
IEEE ratified expansion of the previous standard. Named IEEE 802.11b, it defines the standard for products of wireless networks, which work on speed 11 Mbps that allows successfully applying these devices in large organizations. The compatibility of products of the various manufacturers is guaranteed by an independent organization, which refers to as Wireless Ethernet Compatibility Alliance (WECA). Now there are more than 80 companies as members of WECA, including such known manufacturers, as Cisco, Lucent, 3Com, IBM, Intel, Apple, Compaq, Dell, Fujitsu, Siemens, Sony, AMD and others. 203
802.11 defines two types of equipment - client, which represents the computer completed with wireless network interface card (NIC), and Access point, which carries out a role of the bridge between wireless and wire circuit networks. The point of access comprises the transceiver, wire interface (802.3), and software engaged in data processing. ISA, PCI or PC Card network card can act as wireless station in the standard 802.11, or built-in decisions, for example, telephone set 802.11.
The standard IEEE 802.11 determines two modes of operations of a network - mode "Ad-hoc" and client/server (or mode of an infrastructure - infrastructure mode). In a client/server mode, the wireless network consists of a minimum of one access point connected to the wire network, and some set of wireless terminal stations. Such configuration is called a Basic Service Set (BSS). Two or more of BSS, forming uniform subnet, form the Extended Service Set (ESS). As the majority of wireless stations need to receive access to file servers, printers, Internet, accessible in wire local network, they will work in a client / server mode.
The mode "Ad-hoc" (also named a point - point, or Independent Base Set of Services, IBSS) is a simple network, in which the connection between numerous stations is established directly, without the use of a special point of access. Such mode is helpful in the event that the infrastructure of a wireless network is not generated (for example, hotel, exhibition hall, airport), or for any reasons where required infrastructure cannot be generated.
802.11b provides the access control on MAC level (second level in OSI model), and mechanisms of encoding known as Wired Equivalent Privacy (WEP), which purpose is the maintenance of a wireless network security equivalent to wire networks security. When WEP is turning on, it protects only packets, but does not protect headers, so other stations in a network can look through the data necessary for network management. For the access control in each access point is placed so-called ESSID (or WLAN Service Area ID), without knowledge of which the mobile station cannot be connected to an access point. In addition, point of access can store the list of competent MAC addresses, named as the Access Control List (ACL), permitting access only to those clients, whose MAC addresses are in the list.
For enciphering the data, the standard gives opportunities of enciphering with use of RC4 algorithm with a 40-bit shared key. After the station connects to an access point, all transmitted data is ciphered with use of this key. When the enciphering is used, the access point will send the ciphered packets to any station trying to be connected to it. The client should use his key for enciphering the correct answer for authenticate itself and to receive access in a network. Above the second level of a network 802.11b supports the same standards for the access control and enciphering (for example, IPSec), as other networks like 802.
At present, development of the standard of the following generation - standard IEEE 802.11a, using a strip of frequencies in area 5 GHz takes place. The speed of transfer in the given networks runs up to 54 Mbps.
Speaking about wireless technology it is impossible not to tell about hot spots. This is probably the most hot topic in the world of telecommunications. The reason is the increase of interest to mobile data transfer, when there is depression in cellular 3G businesses. Hot spot is a small zone outside of the office or home, where mobile users could have access to the Internet or to their corporate network. A typical example of mobile user is corporate executive been on official business trip or even vacation, she/he needs to access to emails and attachments, web-servers and other corporate network resources. Hot spots are in places, where mobile users stay: in airport lounges and railway stations, in hotels and business centers, exhibitions, Internet-cafes and even parks. Another common areas of hot spots installations can be within corporate networks (for high-speed Internet access for clients, customers and visitors to increasing of business quality and service) and at universities, schools, libraries.
202. 802.11 workgroup: http:// www.manta.ieee.org/groups/802/11/
203. With products that are meeting the Wi-Fi requirements (the term WECA for IEEE 802.11b), it is possible to familiarize on WECA web site http://www.wi-fi.com
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