though WAP was quite different in reach, technology, and performance
from the World Wide Web. The WAP Forum has consolidated into the
Open Mobile Alliance (OMA) [1], and no longer exists as an indepen-
dent organization. We don’t count WAP as a successful technology, but
rather as one of the many failed attempts in the telecom industry to
provide data services without adequate bandwidth [2].
■■ Design “next generation” mobile networks that can accommodate both voice and
data—One of the most prominent of such designs is the Third-Generation
Partnership Project (3GPP) initiative. 3GPP is a complex project that has
both a circuit switch legacy and also features the Internet Protocol
Multimedia Subsystem (IMS) that uses SIP for call setup [3] and other
SIP-enabled services, such as presence and IM. Much has been written
about 3G wireless networks and about the IMS, so we will add our
reservations here as well. There are many reasons for prudence or to be
outright skeptical about IMS; see, for example, [4].
■■ Commercial wireless networks for portable devices such as laptops and palm-
sized computers—Such networks extend in variety from IEEE 802.11
wireless LANs to IEEE 802.16 metropolitan networks. Surprising tech-
nology and market developments may make some of these the real
winners in future wireless services.
■■ Proposals for pure Internet-based mobile network designs, such as the proposal
for Internet Technology Supporting Universal Mobile Operation (ITSUMO)
[5]—ITSUMO has not been implemented commercially at present, but
we believe it to be one of the key blueprints for long-term next genera-
tion mobile communications based on SIP application-level mobility.
Various mobile networks have very different approaches to mobility. We
will try to shed some light on the meaning of mobility, so as to provide a
better understanding of the various approaches taken in the design of mobile
networks.Mobility in Different Protocol Layers
Mobility can be implemented in various layers of the protocol stack [6]:
■■ Mobility at the link layer (L2), such as mobility in Wi-Fi networks or mobility
in 2G and 3G mobile networks—L2 mobility works only in the same net-
work and using the same device. Only the point of attachment to the
network can change.
■■ Mobility at the IP network layer (L3)—The protocol for mobile IP (MIP) is
discussed in the following sections. Mobile IP also presumes mobility in
the same network (the Internet) and using the same mobile device.254 Chapter 15