Question

The Question: A communication technology appeared that was not classified as the second or third generation, and some have known it as the 2.5 generation, and it has become widely known and used widely in cellular communications.

- What is the 2.5G?

- What are the technologies used in 2.5G?

Answer 1

What is the 2.5G?

In the world of cellphones, 2.5G wireless technology was a stepping stone that bridged second-generation (2G) wireless technology and third-generation (3G) wireless technology. While 2G and 3G are formally defined as wireless standards, 2.5G is not.

2.5G is used to describe 2G-systems that have implemented a packet-switched domain in addition to the circuit-switched domain. In simpler words, 2.5G is actually a 2G cellular technology combined with GPRS, a technology between the second (2G) and third (3G) generations of mobile telephony. It provides moderate-speed data transfer, by using unused time division multiple access (TDMA) channels in, for example, the GSM system. General Packet Radio Service (GPRS), is a wireless data standard used on GSM networks and was the first step in the evolution of 3G technology. GPRS networks eventually morphed to Enhanced Data Rates for GSM Evolution (EDGE).

Interim 2.5G technology introduced a packet-switching technique that was more efficient than its predecessor. Its infrastructure could be used on an as-needed basis rather than on a per-minute basis, which made it more efficient than 2G technology. The 2.5G improved the available data rates supported by the air interface, thereby permitting the introduction of new, data-oriented services and applications. The increased data rates rise to a theoretical maximum of 384 Kbps, although in the field available data rates may often be as low as 20 Kbps.

What are the technologies used in 2.5G?

GSM was capable of providing a data rate of 9.6 kbps on a single time slot. With the advent of High Speed Circuit Switched Data (HSCSD), the capability of the network was increased multi-fold to 115.2 kbps. In practice, however, it was only 64 kbps, owing to the limitation of the A-interface and the core network. The main benefit of the implementation of the HSCSD was that with limited upgrading, the capacity for data transfer was increased upto four TS on the receiving side and two TS on the transmitting side. But the traffic was still circuit switched, which meant a long access time to the network. As charging is proportional to the logging time, the subscriber ends up paying more. This led to the evolution of the packet switched network. In this technology, the accesss time to the network is reduced and charging is done solely on the usage of the network, that is, even when a connection is there but is not being used, the subscriber is not charged. Usage of the network resources, hence, becomes more dynamic and efficient. They are no longer reserved for a user logged to the network. It can be accessed even when he is not using the resources. This system is known as General Radio Packet System (GPRS) , which was implemented into the 2G technology, to give birth to the 2.5G.

GPRS is an addition to the already existing GSM system, enabling packet-switched transmission in the network whilst keeping the existing value added services like SMS. Because of this, data rates increase substantially. The user can now log into the GPRS network, and can make use of all eight TS dynamically and be charged only when using the resources. The packet data can be sent during idle times also, between speech calls, thus making effective use of the network resources and saving money on the subscriber's end.