GSM Technology

A wireless LAN (WLAN) is a wireless Local Area Network that links two or more computers or devices utilizing spread-spectrum or OFDM modulation technologies based to enable communication between devices in a limited region. 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 turn out to be 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 provide wireless access to their buyers; some are even supplied as a totally free service. Significant wireless network projects are being put up in several 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 significant antennas mounted on towers. 802.11 (Wi-Fi), LMDS (Local Multipoint Distribution Service) and MMDS (Multichannel Multipoint Distribution Service) are examples. A couple of wireless networks are intended only to connect tiny devices over short distances. Bluetooth is an example.

Varieties:

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 obtainable on GSM networks that operate at 1,800MHz. 900 MHz GSM networks are limited to 9.6Kb time slots. For that reason, 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.

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