3G wireless
technology represents the convergence of various 2G wireless telecommunications
systems into a single global system that includes both terrestrial and
satellite components. One of the most important aspects of 3G wireless
technology is its ability to unify existing cellular standards, such as CDMA,
GSM, and TDMA, under one umbrella. The following three air interface modes
accomplish this result: wideband CDMA, CDMA2000 and the Universal Wireless Communication
(UWC-136) interfaces.
3G wireless networks consist of a
Radio Access Network (RAN) and a core network. The core network consists of a
packet-switched domain, which includes 3G SGSNs and GGSNs, which provide the
same functionality that they provide in a GPRS system, and a circuit-switched domain,
which includes 3G MSC for switching of voice calls. Charging for services and
access is done through the Charging Gateway Function (CGF), which is also part
of the core network. RAN functionality is independent from the core network
functionality. The access network provides a core network technology
independent access for mobile terminals to different types of core networks and
network services. Either core network domain can access any appropriate RAN service;
e.g. it should be possible to access a “speech” radio access bearer from the
packet switched domain.
The Radio Access Network consists of
new network elements, known as Node B and Radio Network Controllers (RNCs).
Node B is comparable to the Base Transceiver Station in 2G wireless networks.
RNC replaces the Base Station Controller. It provides the radio resource
management, handover control and support for the connections to circuit-switched
and packet-switched domains. The interconnection of the network elements in RAN
and between RAN and core network is over Iub, Iur and Iu interfaces based on ATM
as a layer 2 switching technology. Data services run from the terminal device
over IP, which in turn uses ATM as a reliable transport with QoS. Voice is
embedded into ATM from the edge of the network (Node B) and is transported over
ATM out of the RNC. The Iu interface is split into 2 parts: circuitswitched and
packet-switched. The Iu interface is based on ATM with voice traffic embedded
on virtual circuits using AAL2 technology and IP-over-ATM for data traffic
using AAL5 technology. These traffic types are switched independently to either
3G SGSN for data or 3G MSC for voice.
References :
www. Wikipedia.com
www.3g.co.uk .com
www.fcc.gov/3G .com
