General Packet Radio Service or GPRS
The General Packet Radio Service or GPRS is a telecommunications technology that is presently transforming the present shape of mobile communications. GPRS is a packet oriented Mobile Data Service providing data rates from 56 up to 114 kbit/s. Users of IS-36 mobile phones and Global System for Mobile Communications (GSM) can readily avail of this service.
How does a GPRS work? A GPRS connection is linked by orientation to its Access Point Name (APN). The APN then identifies the appropriate services like Wireless Application Protocol (WAP) access, Multimedia Messaging Service (MMS), Short Message Service (SMS), and for Internet communication services such as World Wide Web access and email. The charge for GPRS data transfer is per megabyte of traffic transferred as compared to data communication via traditional circuit switching that is charged per minute of connection time, whether or not the capacity is used or is in an idle state. Thus, as compared to circuit switching, GPRS is a best-effort packet switched service providing a certain Quality of Service (QoS) that is guaranteed in the link for non-mobile clients.
What are the basic features of GPRS? Frequency division duplex of FDD and TDMA provide multiple access methods used in GSM and GPRS. When a session is ongoing, a user is assigned to a pair of down-link and up-link frequency channels that is combined with time domain statistical multiplexing. This is done through packet mode communication making it feasible for more users to use the same frequency channel. To correspond to the GSM time slot, the packets have constant length. The down-link follows a first-come-first served packet scheduling and on the other hand, the up-link uses a mechanism close to reservation ALOHA. Meaning, the slotted Aloha (S-ALOHA) during a contention phase is used for reservation inquiries while a dynamic TDMA is used to transfer the actual data with first-come first-served scheduling.
What are the different types of connections to GPRS? Today there are various types with distinct features that exist in the market:
Class A can be linked to GPRS and GSM services (voice, SMS), where both can be used at the same time. Class B can also be linked to GPRS and GSM service (voice, SMS), however only one can be used at a given time thus, suspending the GPRS service during GSM service (voice call or SMS), and only then will it automatically resume after the GSM service has concluded. This class covers most GPRS mobile devices. Class C must be switched manually between GPRS service or GSM service since it is connected to either.
How does GPRS upgrade GSM data services? The GPRS supports GSM data with Multimedia Messaging Service (MMS), push to talk over Cellular PoC/PTT, in the wireless village an instant messaging and presence feature, access of Wireless Application Protocol (WAP) in Internet Applications for Smart devices, Short Message Services or SMS, and further enhances new functions such as higher capacity, new protocols, new accesses and new radio networks.
The channel encoding used will dictate the GPRS speed transfer. The fastest however least robust coding scheme (CS-4) is accessible when in proximity to a base transceiver station (BTS). Going further away from the BTS though gives the most robust coding scheme (CS-1).
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