Wireless Sensor Networks : Technology, Protocols, and Applications

126 WIRELESS TRANSMISSION TECHNOLOGY AND SYSTEMS
3G Release 1999 was the first release of the 3GPP specifications; it was essentially
a consolidation of the underlying GSM specifications and the development of
the new UTRAN radio access network. The foundations were laid for future highspeed
traffic transfer in both circuit- and packet-switched modes. That release was
followed over the years by Releases 4, 5, and 6 [4.23]. Release 1999 was an introductory
specification on the architecture of the UMTS network. According to
Release 1999, UMTS comprises a UTRAN and two core networks [circuitswitched
core network (CS-CN) and packet-switched core network (PS-CN)],
which link up to services networks such as the PSTN and the Internet. Thus, using
both traditional circuit- and modern packet-switched networks, UMTS Release
1999 supports various services, including voice, data (fax, SMS), and Internet
access. Later, Release 4 adapted to the same architecture added more services to
the UMTS network. The coexistence of two core networks, however, signified
many limitations compared to competitive 3G systems, especially in video and multimedia
services. Release 5 was a solution to the limitations that came along to
modernize the UMTS architecture currently employed in 3G networks around
the world. In this final phase, the PS-CN dominates the CS-CN and takes responsibility
for telephony services. Systems based on UMTS Release 5 have much lower
infrastructure and maintenance costs and provide enhanced services. Release
6 added additional capabilities [4.17].
As seen at the macro level in Figure 4.11, a new component is added to the basic
UMTS architecture: the supplementary IP Multimedia Subsystem (IMS). IMS
aims at supporting both telephony and multimedia services. IMS’s role in UMTS
architecture is to interact with both the PSTN and the Internet to provide all types
of multimedia services to users. The CSCF element in the IMS infrastructure is
responsible for signaling messages between all IMS components in order to control
multimedia sessions originated by the user. Consequently, there is a proxy-CSCF
(P-CSCF), an interrogating-CSCF (I-CSCF), and a serving-CSCF (S-CSCF), all
responsible for particular signaling functions using SIP. The P-CSCF’s responsibility
IMS
Telephony
Services
PSTN
VolP
VolP
& multimedia
Services
Radio
Network
(UTRAN)
PS-CN
Internet
Services
Internet
UTRAN = UMTS Terrestrial Access Network
PS-CN = Packet Switched Core Network
IMS = IP Multimedia Subsystem
Figure 4.11
UMTS Release 5 basic architecture.