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CONVERGENCE OFIPANDCELLULARSYSTEMS—TOWARD THEMOBILEINTERNET 845BS RNC SGS GGSHLRIP
NetworkBackbone
Network
IPM
SFigure 4: Architecture of a UMTS network.chip rates, synchronization approach, pilot channels, and
frame duration, and are incompatible with each other.
Both WCDMA and CDMA2000 provide the user with
channels, either shared with other users or dedicated,
with different maximum data rates, depending on the
spreading factor used. It provides a wide range of chan-
nel bit rates, and is very well suited for bursty packet-
based traffic. These radio standards offer quite some
room for further improvement. New modulation tech-
niques, more advanced scheduling, dynamic link adap-
tation, and multiple-input-multiple-output antenna tech-
niques are some of the improvements currently under
study (Honkasalo, Pehkonen, Niemi, & Leino, 2002). The
high-speed downlink packet access channel (HSDPA) in
WCDMA, with data rates up to 10 Mbps, has been stan-
dardized as a first step in this direction.
2.5G systems are widely available now throughout the
world, although the use of these systems is not (yet) over-
whelming. 3G systems are currently starting service in
limited areas, especially in Japan (WCDMA), and are be-
ing expanded in functionality, performance, and coverage.
Availability of terminals is still very limited.CONVERGENCE OF IP AND
CELLULAR SYSTEMS—TOWARD
THE MOBILE INTERNET
It is expected that the future will show a convergence be-
tween the Internet and cellular systems. They will con-
verge both in the services provided and in the technology
used. The converged system will combine the wide range
of horizontal services offered by the Internet with mobil-
ity and highly integrated services and devices offered by
the cellular networks. As for the technology, it is expected
that future systems will combine radio technology from
cellular systems with switching and routing technology
based on the IP protocol suite. Looking at a possible net-work architecture of a UMTS network (Figure 4), we see
two distinct IP networks. One is the external IP network,
the other an IP-based transport network. The external IP
network is a network providing services and connectiv-
ity from remote end-users to the user of the MS. For the
MS, the GGSN is a gateway to the external IP network,
and provides the MS with an IP address valid on that net-
work. IP headers of packets on their way from the MS to
the external IP network (or vice versa) are only processed
by the GGSN, not by all the intermediate nodes. From
the point of view of the external IP network, the UMTS
network is a single subnetwork.
The IP-based transport network is typically owned by
the cellular operator, and provides connectivity between
the various nodes in the UMTS network. These are, for the
packet-switched core network, the SGSN and the GGSN,
and for the RAN, the BSs and Radio Network Controllers
(RNCs). The BS provides the main radio (physical layer)
functions, whereas the RNC provides the higher layer
functions, including radio resource management, and soft
handover.
For the packet-switched core network, it has been spec-
ified that the SGSNs and GGSNs should be interconnected
by an IP-based transport network. User-level IP packets
are encapsulated and tunneled using the so-called GPRS
tunneling protocol (GTP) on top of the transport level IP.
GTP provides for the routing of the user level IP pack-
ets to the appropriate SGSN, using the database of the
HLR, for mobility management functions. As such, GTP
provides an alternative to MIP.
In the first release of UMTS, ATM is used as transport
technology for the RAN. However, it is foreseen that IP
will also be introduced in this part of the cellular network
in the near future. The use of IP as transport technol-
ogy in a RAN, besides enabling the operators to provide
new packet-based services, is especially beneficial since
it provides the means for statistical aggregation of traf-
fic, which leads to increased transmission efficiency and