Gprs

From iA wiki

Acronym : General Packet Radio Service

GPRS is different from the older Circuit Switched Data (or CSD) connection included in GSM standards. In CSD, a data connection establishes a circuit, and reserves the full bandwidth of that circuit during the lifetime of the connection. GPRS is packet-switched which means that multiple users share the same transmission channel, only transmitting when they have data to send. This means that the total available bandwidth can be immediately dedicated to those users who are actually sending at any given moment, providing higher utilisation where users only send or receive data intermittently. Web browsing, receiving e-mails as they arrive and instant messaging are examples of uses that require intermittent data transfers, which benefit from sharing the available bandwidth.

Usually, GPRS data are billed per kilobytes of information transceived while circuit-switched data connections are billed per second. The latter is to reflect the fact that even during times when no data are being transferred, the bandwidth is unavailable to other potential users.

The multiple access methods used in GSM with GPRS is based on frequency division duplex (FDD) and FDMA. During a session, a user is assigned to one pair of uplink and downlink frequency channels. This is combined with time domain statistical multiplexing, i.e. packet mode communication, which makes it possible for several users to share the same frequency channel. The packets have constant length, corresponding to a GSM time slot. In the downlink, first-come first-served packet scheduling is used. In the uplink, a scheme that is very similar to reservation ALOHA is used. This means that slotted Aloha (S-ALOHA) is used for reservation inquiries during a contention phase, and then the actual data is transferred using first-come first-served scheduling.

GPRS originally supported (in theory) IP, PPP and X.25 connections. The last has been typically used for applications like wireless payment terminals although it has been removed as a requirement from the standard. X.25 can still be supported over PPP, or even over IP, but doing this requires either a router to do encapsulation or intelligence built into the end terminal. In practice, mainly IPv4 is used. PPP is often not supported by the operator, while IPv6 is not yet popular.

Edited copy from wikipedia