Wireless Networks

A wireless network is a telecommunications network, usually telephonic or computational, which uses radio waves as information carriers. The data is therefore transferred via electromagnetic waves with a frequency depending each time by the data rate that required supporting the network. Wireless communication has as transmission medium the earth’s atmosphere or space, unlike wired communication where the transmission medium is a cable type. In earlier times the telephone networks were analog but today all wireless networks are based on digital technology and thus, in a sense, are essentially computer networks. The evolution of wireless communications in recent years has shown that it is very difficult for a system to be able to satisfy all the needs of user and adapted to the particularities of each environment. Therefore, wireless networks will consist of the consolidation of a set of technologies in next generations, each of which will be specialized in a particular environment.

WiFi

The architecture of the system covers both structured topologies (cellular) and unstructured (ad-hoc). Its main element is the station (Station – STA), which is any device that has an contact compatible with standard IEEE 802.11 and wants to connect and transmit to the system. In structured topologies, transmission is done only from / to the Access Point (Access Point – AP), ie from the station that has a contact with a fixed network (e.g. Ethernet), while in unstructured is done directly to any other station in the coverage area. The stations and access points that constitute a wireless Wi-Fi network are called Basic Service Set (BSS) for the structured topologies and Independent Basic Service Set (IBSS) for the unstructured. The evolution of the pattern followed a step-by-step approach, according to which, at first a simple relatively limited functionality of the system was designed, and then was expanded and continues to expand with additions, which aim to improve the initial weaknesses and omissions. Below briefly we refer to the main developments.

802.11: The first version of the standard, which is supported speed 1 and 2Mbps in the 2,4GHz band using techniques of frequency hopping and direct sequence

802.11a : extension of the physical layer for wireless LANS in the band of 5 GHz, which uses modulation Orthogonal Frequency Division Multiplexing (OFDM). It consists of eight available non-overlapping wireless channels, which have a transmission rate up to 54 Mbps each.

802.11b: : extension of the physical layer for wireless LANS in the band of 2,4 GHz. It is responsible for the upgrade of the physical layer of 802.11 rhythms adding 5.5 Mbps and 11 Mbps via denser modulation. It consists of three available non-overlapping wireless channels, which have a transmission rate of up to 11 Mbps each.

802.11e : This is a supplementary protocol to the level of multiple access 802.11 which provide improved quality of service. It aims at one of the basic weaknesses of the classical 802.11 protocol, namely the lack of capacity to provide differential treatment to different motion classes.

802.11g:: physical layer standard for wireless LANS in the band of 2,4 GHz. It consists of three available non-overlapping wireless channels, which have transmission rate up to 54 Mbps each using OFDM. It is the most widespread physical layer standard today.

802.11i: This is a supplementary standard for improving the security of the system. It provides an alternative mechanism of the classic Wired Equivalent Privacy – WEP with new ones encryption and authentication methods.

What is wireless networking?

Speaking of wireless networks we mean sharing data between computers or devices without using cables. To connect to a hot spot, to send data from our computer to our mobile phone via infrared or Bluetooth are considered as examples of wireless networks. In practice, however, wireless networking between computers or peripherals allows communication via radio frequency. Generally wireless technology is defined by a set of standards named 802.11 although other technologies coexist like a Bluetooth. Wireless network can offer you whatever offers a network cables such as internet access, possibility of shared folders, data sharing, printing to shared printers and more.

What is the WLAN?

WLAN or otherwise wireless local area network is a wireless network that works with other wireless devices. A conventional network of home / small business has two or more computers connected top each other using a network cable and a device such as hub / switch / router. In this already existing network, an upgrade can be done in order to use an access point. However, it there can be a wireless network completely independent from the rest of our network.

What is WiFi;

WiFi Types

Τοπολογίες Ασύρματων Δικτύων

Ad-Hoc: Ad-Hoc: Two or more computers with wireless network card can form a wireless network ad-hoc type. In order to create a network of this topology, using Windows XP or Windows Vista, it is much easier than using older versions of Windows, where in those cases we use the program that accompanies our wireless network card.

Infrastructure: In order to connect one or more computers in a access point, which is connected to a network with cables or not, we have to use necessarily access point. Often these devices combine functions of router / adsl modem which are an ideal solution. The difference between the two topologies is that in one case we use access point while in the other it doesn’t need to connect to the rest of the network.

How does the wireless work?

Wireless technology takes advantage of the free radio frequencies between 2.4GHz and 5GHz. The 802.11b and 802.11g protocols use the 2.4MHz frequency instead of 802.11a, which uses the frequency 5MIz. The advantage is that it uses higher range frequency, although it can be easily get interfered by other wireless devices such as wireless phones.

Why is it useful a wireless network?:

There are two main advantages in using a wireless network: portability and flexibility. If you use a laptop with wireless technology then you can use your computer everywhere in your place. If you travel frequently, you can connect to
the internet via a wireless point (there are many at cafes, conference centers, waiting rooms, airports and other). In case you expand your network, you can place your computers without the cost of installing the cables and materials.