A wireless LAN (WLAN) is a wireless Local Area Network that links two or more computers or devices using spread-spectrum or OFDM modulation technology based to enable communication between devices in a limited area. This gives users the mobility to move around within a broad coverage area and still be connected to the network.
For the home user, wireless has become popular due to ease of installation, and location freedom with the gaining popularity of laptops. Public businesses such as coffee shops or malls have begun to offer wireless access to their customers; some are even provided as a free service. Large wireless network projects are being put up in many major cities: New York City, for instance, has begun a pilot program to cover all five boroughs of the city with wireless Internet access.
Some wireless data networks run over wireless voice networks, such as mobile telephone networks. For example CPDP (Cellular Digital Packet Data), HSCSD (High Speed Circuit Switched Data), PDC-P (Packet Data Cellular) and GPRS (General Packet Radio Service). Other wireless networks run on their own physical layer networks, utilizing anything from antennas built into handheld devices to large antennas mounted on towers. 802.11 (Wi-Fi), LMDS (Local Multipoint Distribution Service) and MMDS (Multichannel Multipoint Distribution Service) are examples. A few wireless networks are intended only to connect small devices over short distances. Bluetooth is an example.
Types:
CPDP: CDPD (Cellular Digital Packet Data) is a specification for supporting wireless access the Internet and other public packet-switched networks over cellular telephone networks. CDPD supports TCP/IP and Connectionless Network Protocol (CLNP). CDPD utilizes the RC4 stream cipher with 40 bit keys for encryption.CDPD is defined in the IS-732 standard.
HSCSD: HSCSD (High Speed Circuit Switched Data) is a specification for data transfer over GSM networks. HSCSD utilizes up to four 9.6Kb or 14.4Kb time slots, for a total bandwidth of 38.4Kb or 57.6Kb.
14.4Kb time slots are only available on GSM networks that operate at 1,800MHz. 900 MHz GSM networks are limited to 9.6Kb time slots. Therefore, HSCSD is limited to 38.4Kbps on 900 MHz GSM networks. HSCSD can only achieve 57.6Kbps on 1,800 MHz GSM networks.
PDC-P: PDC-P (Packet Data Cellular) is a packet switching message system utilized by NTT DoCoMo in Japan. PDC-P utilizes up to three 9.6Kb TDMA channels, for a total maximum bandwidth of 28.8Kb.
GPRS: GPRS (General Packet Radio Service) is a specification for data transfer on TDMA and GSM networks.
GPRS utilizes up to eight 9.05Kb or 13.4Kb TDMA timeslots, for a total bandwidth of 72.4Kb or 107.2Kb. GPRS supports both TCP/IP and X.25 communications.
EDGE (Enhanced Data-Rates for GSM Evolution) enabled GSM networks are able to implement EGPRS (Enhanced General Packet Radio Service), an enhanced version of GPRS. EGPRS increases the bandwidth of each timeslot to 60Kb.
After you have the new hard drive installed you might want to leave the case off for a moment and power the computer on and insert your operating system disc into the CD-ROM drive and make sure the computer boots from the disc. After you have everything sorted out you can go ahead and replace the computer case.
Source : http ://www.goarticles.com by Aesha shah
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