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Wi-Fi
 
Wi-Fi (or Wi-fi, WiFi, Wifi, wifi) is a standard for local wireless networks (Wireless LAN, WLAN) and results from the specification IEEE 802.11. The name Wi-Fi is a word play with Hi-Fi (i.e. analogically to the high fidelity we could understand it as “wireless fidelity”), however, the name is not an abbreviation in fact..

The former aim of Wi-Fi networks was to provide mutual wireless connection of portable devices and their connection to (e.g. office) LAN networks. However, the strong potential of this technology has started to be used for connection to the internet. The initially slow spreading of the Wi-Fi technology was rapidly accelerated by its integration into the mobile platform Centrino by Intel. Not only thanks to it Wi-Fi has become a standard part of portable computers. It has spread mainly due to using the non-license band which has negative effects in strong interference within that frequency spectrum and common security incidents.

A partially evolutionary result and successor of Wi-Fi is the currently-constructed wireless technology called WiMAX which should provide wireless access to the internet within large areas in the city.

Wifi


Network construction

Wi-Fi networks may be constructed in several basic ways:

  • AP – These networks are using a central network element, the so-called Access Point that controls the network communication within the particular Wi-Fi cell. If the AP stops working, the other devices cannot communicate with one another.
  • • Ad-hoc – By connecting the network elements in this mode a peer-to-peer network is created where the given Wi-Fi devices (such as notebooks) communicate directly and it is not necessary to provide the access point. Since no control element is used in such network, other devices are able to communicate normally after the connection with one of them is lost.
  • • WDS or Repeater – This is the architecture that is used slightly less often. All the devices are equal and communicate with one another. They transmit the information via the closest devices in the network.

In literature you can also meet the following terms that describe the network architecture:

  • Point-to-point – interconnection of two places.
  • Point-to-multipoint – common WiFi network when one of the devices is the control one (Master) and serves to client devices (Slave).
  • Bridge – can mean the same as Point-to-point but can also designate a feature of the physical layer of the communication device (Access Point)

Network security

An important problem of security arises. Even though most of the commonly used devices supports the basic ways of encryption – WEP, WEP2, WPA and WPA2 – a large amount of APs is unprotected or only protected by the ARP filter (MAC address filtering). That allows the attacker to connect to the network and possibly impersonate other network members. Many security problems have been discovered in the WEP encryption protocol that make it possible to gain the necessary key for accessing the network. The corresponding howto-s have been published on the web and made accessible to wide public together with required program equipment.

Compatibility

Compatibility is ensured by the certification process. The device that has been stated as compatible is usually marked with Wi-Fi alliance logo.

IEEE 802.11 Standard Overview
Standard
Band [GHz]
Maximum speed [Mbit/s]
Physical layer
IEEE 802.11 original
2,4
2
DSSS
IEEE 802.11a
5
55
OFDM
IEEE 802.11b
2,4
11
DSSS
IEEE 802.11g
2,4
54
OFDM
IEEE 802.11n
2,4 nebo 5
540
OFDM, MIMO

Ronja

RONJA is a word composed of the first letters of the following words Reasonable Optical Near Joint Access. It is an optical link for wireless connection of two computers that works over large distances with constant transfer speed of 10 Mb/s. It can be used with the Ethernet card or switch with RJ45 connector.

 

Ronja

How it works

RONJA works with the beam of light. So that the transfer is possible over the biggest possible distances, the light must be rectified into a cone with minimal dispersion – RONJA uses a set of lenses. Both the transmitting and the receiving LED diode must be in the focus point of the lens. The transmitter lens reduces this light into a single point, thus increasing the efficiency of the transfer.

RONJA vs. Wi-fi
  Advantages Disadvantages
RONJA Its biggest advantage is the always-constant transfer speed of 10 Mb/s. The transfer has a very low latency. It is highly resistant to interference and fully compatible with the Ethernet cards with RJ45 connector which are the cheapest and most common right now. The optical data transfer may be interrupted by many things as fog, heavy snow or rain. RONJA has to have a direct visibility between the devices, without any obstacles, and its development is complicated.
Wi-Fi Easy installation, almost no maintenance is required and the connection is very reliable. The 11b standard states that the maximum transfer speed is 11Mb/s, however, practically it is 3 to 4 Mb/s, by the most because the technology is very vulnerable for interference. The bandwidth is already very crowded which causes problems especially in the big cities.