GPRS

Sony Ericsson T39m cell phone was the first GPRS enabled phone in world. General Packet Radio Service (GPRS) allows information to be sent and received across a mobile telephone network.

It supplements Circuit Switched Data and Short Message Service. Please note that GPRS is a 2.5G technology that supports data transmissions up to 56-114k bit/ sec, though theoretically can provide speed up to 171.2 kbps.  So, it is basically a link between GSM and GPRS and many GSM service providers adopted it before jumping to the full 3G technology.

What are packets?

GPRS (general packet radio service) is a packet-based data bearer service for wireless communication services that is delivered as a network overlay for GSM, CDMA and TDMA networks. Packet switching means that data is split into packets that are transmitted separately and then reassembled at the receiving end. GPRS supports the world’s leading packet-based Internet communication protocols, Internet protocol (IP) and X.25, a protocol that is used mainly in Europe. This was one of the reasons that made it popular instantly.

Since, cellular networks with GPRS capabilities are wireless extensions of the Internet and X.25 networks, it gives almost instantaneous connection set-up and continuous connection to the Internet.

Difference between GPRS and GSM:

• GPRS is different to GSM because it offers higher bandwidth and, therefore, data speeds.
• GPRS is seamless, immediate and continuous connection to the Internet – ‘always on-line’.
• Due to high speed, the new text and visual data and content services such as email, chat, still and moving images, information services (stock prices, weather reports, train times), video conferencing, e-commerce transactions (buying flight and cinema tickets) and Internet-based remote access to corporate intranets and public networks was made possible via GPRS.
• The major technical difference is that GPRS uses packet-switching rather than circuit-switching, which means that there is higher radio spectrum efficiency because network resources and bandwidth are only used when data is actually transmitted even though it is always connected.
• GPRS supports leading Internet communications protocols – Internet protocol (IP) and X. 25.

Please note that from upgrade from GSM to GPRS needs additional components and protocols to the GSM network – the key elements are SGSN (serving GPRS support node), GGSN (gateway GPRS support node) and a charging gateway. The devices are different devices (not GSM phones). In summary GPRS served as first important step on the path to 3G.

Serving GPRS Support Node

SGSN is the most important element in a GPRS network. It is the service access point for the mobile station. Its main functions include mobility management and registration and authentication. It also interacts with a mobile with packet data flow and functions related to it like compression and ciphering. These are handled by protocols such as the SNDCP (sub-network dependent convergence protocol) and LLC (logical link control). SGSN is also responsible for GTP (gate tunneling protocol) tunneling to the other support nodes.

Gateway GPRS Support Node (GGSN)

The GGSN is connected to the SGSN on the network side and to the outside world external networks such as the Internet and X.25. As it is a gateway to the external networks, its main function is to act as a ‘walt’ for these external networks in order to protect the GPRS network. When data come from the external network, after verification of the address, the data are forwarded to the SGSN. If the address is found to be invalid, the data are discarded. On the other hand, the SGSN also routes the packets it receives from the mobile to the correct network. Thus, for the outside networks the SGSN acts as a rooter.

High Speed Circuit Switched Data (HSCSD)

Please note that HSCSD (High Speed Circuit Switched Data) comes in between GSM and GPRS. It was the first step towards faster data speeds on GSM circuit switched networks. HSCSD concentrated up to four GSM timeslots and allowed data speeds of up to 64 kbit/s. Today mobiles supporting HSCSD are not  available.

Enhanced Data for GSM Evolution (EDGE)

GPRS was followed by EDGE (Enhanced Data for GSM Evolution), which was the second step towards 3G for GSM/GPRS networks. EDGE was able to increase data rates on GSM to 384 kbit/s by bundling up to eight channels or 48 Kbit/s per channel. EDGE was deployed on GSM networks beginning in 2003.

Difference between EDGE and GPRS:

GPRS is based on a modulation technique known as Gaussian minimum-shift keying (GMSK). EDGE is based on a new modulation scheme that allows a much higher bit rate across the air interface – this is called eight-phase-shift keying (8 PSK) modulation. This was the major difference between the two.