Wireless Telecommunication Networks
We use the term Wireless Networks in the case we want to transfer information between computers or other devices that are interconnected, as a natural way of transmitting radio waves. For wireless connection of devices there are many technologies and prototypes such as GSM/GPRS that are used for the communication between mobile phones, the standard being 802.11, Bluetooth technology e.t.c.

Bluetooth technology (specifically named in honour of Harald Bluetooth, the king that lived in Denmark from 910 a.c. until 940 a.c.) allows the interconnection of computers, mobile phones, and many more other digital devices that are within a small distance in relation to each other (about 10 metres) and works within the frequency band of 2,4 GHz.

All previous technologies using the traditional way of transmitting data, use wiring that allows users with the suitable infrastructure to connect to the network and send and receive data via wireless networks. The various transmission speeds achieved depend on the technology used, in many cases, hence they are very high and therefore allow users to use broadband services.

Wireless/Lan Standards
The first standard that was developed for Wireless Lans (WLANs) is the IEEE 802.11 which was published in 1997 and predicted transmittion rates between 1 - 2 Mbps. Comparing the transmittion rates that were achieved with those of the traditional networks were considered from many insufficient and forbidden for the use of many broadband services. Initially as a result of that the particular standard did not achieve a great success. The need for improving and developing the above standard led to the creation of working groups and according to the research results sub-standards of 802.11. They are determined by the letters a to i (table 3)

Πίνακας 3

In this family of protocols only the first two of the seven OSI are described and specifically the physical level (PHY, Physical Layer) is described as well as data links (MAC, Medium Access Control), resulting to any application being able to work on the device 802.11 as it would work with ethernet. The increase in the transmission rate, the compatibility that was achieved and the satisfacroty for most applications scope of the networks are only a few of the reasons that enable the users to use widely wireless networks.

The Bandwith zone of 2.4GHz that is used in most cases of wireless local networks, which is suitable for transmitting data within satisfactory distances, while it is free for use in all the countries that only place a few regulatory conditions. On the contrary, the use the bandwidth zone of 5GHz in other countries is totally forbidden and in others there are significant conditions. This happens, because in a lot of cases this spectrum is used either from the army or other public services, and interjections on their systems must be avoided. However, the past few years European countries, such as Greece have expanded on the specific range of frequencies to be used.

The scope and speed of transmission on the network depends on a lot of factors such as: the standard that will be used, the presence or not of visible between the the transmitter and the receiver, the presence of interference and noise, the power of the transmitter and the sensitivity of the receiver, the correct choice of equipment, the number of users, and the distance between the aerials, the exact allignment of the aerials e.t.c. 

• ΙΕΕΕ 802.11 a: It was published in 1999 and constitutes of a standard for the operation of local networks that use the bandwidth zone of 5 GHz and the configuration of OFDM . Tha rates of transmission of data can reach up to 54Μbps, as with the use of technical OFDM the use of the available scope becomes more effective.
• IEEE 802.11b: It was published in 1999 and is the most widely used standard. It constitutes of a standard for the operation of wireless local networks that uses the zone of 2.4 GHz and the technical physical format of DSSS. It is also used in Greece and the rates of transmission of data can reach up to 11Μbps.
• IEEE 802.11c:  It provides documentation for concrete processes of level MAC of 802.11 in the ISO/ IEC (International Standards Organisation/ International Electronical Commission) 10038 standard (ΙΕΕΕ 802.1D). 
• IEEE 802.11d:  It constitutes of definitions and demands that intend in the standard 802.11 being used in other bandwidth zones so that it can be used from countries that are accommodated with the specific standard. 
• IEEE 802.11e:  Is trying to enrich the MAC format of 802.11 to increase the quality of the provided service. The Improvement of the faculties and the efficiency are designed in such a way that they allow applications such as voice, video, or the transmission of sound over the 802.11 wireless networks.
• IEEE 802.11f: It deals with the με την mobility of των stations within an IP network ( Intra - network Handover ) aiming to increase the compatibility between the devices of the login point of different suppliers. 
• IEEE 802.11g: extends the 802.11b such that it ώστε να provides the high rate of transmission of data of 802.11a, therefore sustaining the backwards compatibility with the 802.11b products. It is used in greece and the rates of transmission can reach up to 54 Μbps.
• IEEE 802.11h: It strengthens the formats MAC of 802.11 and PHY of 802.11a to provide the extensions of manageming and controlling networks, for the scope and power of transmitting within the bandwidth zone of 5GHz. This will allow the regulatory acceptance of the standards in some european countries.
• IEEE 802.11i: It studies subjects relevant to security of the local wireless networks with the aim to strentgthen security mechanisms and id verification of 802.11.

the wireless networks that are compatible with the standard ΙΕΕΕ 802.11 are also known as Wi Fi (Wireless Fidelity). One of the many advantages that such a network has is the ease with which we can add to it new devices.

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