Wireless Sensor Networks : Technology, Protocols, and Applications

128 WIRELESS TRANSMISSION TECHNOLOGY AND SYSTEMS
essentially uses address translation to provide mobility, it cannot do fast handoff,
due to the latency of address updates from distant agents [4.18].
Comparison of Services The 3GPP and 3GPP2 architectures are different because
of the underlying base networks and evolution strategies. In 3GPP, GPRS-based
mobility was already defined, so the IP network enhancements were considered
on top of GPRS. On the other hand, 3GPP2 needed to develop a mobility mechanism
for packet data since one did not exist previously. As noted, 3GPP2 has decided
to use MIP as the basis for packet data mobility [4.18].
To illustrate the similarities and differences of the two approaches, mobility
needs to be addressed at three levels: air-interface mobility, link-level mobility,
and network-level mobility. Air-interface mobility supports cell-to-cell handoff
within a radio access network. Link-level mobility maintains a point-to-point
protocol (PPP) context across multiple radio access networks. Network-level mobility
provides mobility across networks. In both approaches, air-interface mobility is
handled in the radio access network. Air-interface mobility is specific to the radio
technology, therefore harmonization of the two depends on the harmonization
efforts under way for global CDMA. In 3GPP, link-level mobility is handled by
GTP; this protocol is used to provide mobility to other 3GPP-defined networks.
The 3GPP architecture also provides an option in which an FA may be located in
the GGSN. This allows roaming from GPRS-based networks to other IP access networks.
In 3GPP2, link-level mobility is provided by defining a tunneling protocol as
an extension of MIP. The MIP architecture allows the mobile device to have a point
of presence and to roam across any IP network. Registration and authentication in
the 3GPP architecture for access and data networks are integrated and utilize the
schemes used for wireless. In the 3GPP2 architecture, the registration and authentication
for access and data networks are performed separately. For a data network,
authentication and registration as defined in MIP are used; hence, the data architecture
is access-independent [4.18].
3G Operators After many delays, 3G networks are now being rolled out. 3G wireless
networks offer all the normal mobile telephony services plus high-speed data
access. 3G operators may initially limit data access to their own branded data services
or at least price open Internet access significantly higher than access to their
own traditional data services. The mobile market, however, is competitive, and
there are consumer and business requirements for access to the open Internet. In
fact, flat-rate bundles for data access services are already available in some markets.
This data-channel access can be used to support VoIP services [4.24]. Wireless
operators that are looking to continue to displace wireline voice revenues as their
business posture need to reduce their overall delivery costs as users move from 2G
TDM to 3G VoIP [4.25]. Below we look briefly at the VoIP possibilities because a
successful commercial ‘‘play’’ in this space would accelerate the deployment (and
ubiquity) of 3G services, thereby indirectly opening up an opportunity for WSN
applications.