Network Architectures

are needed for operation and maintenance of the mobile network. A wireless telecommunication
device (e.g., a cordless telephone) can connect to the PSTN infrastructure
by replacing the wire attachment with radio transceivers. However, for the wireless
device to change its point of connection, switches in the PSTN must be able to support
mobility. Switches in the PSTN infrastructure were not originally designed to support
mobility. To solve this problem, a cellular telephone service provider adds its own
fixed infrastructure with mobility-aware switches. The fixed infrastructure of the cellular
telephone service provider is an interface between the base stations and the PSTN
infrastructure that implements the functionality to support mobility. Just as a wired
telephone service network needs added infrastructure to allow a mobile telephone to
connect to the PSTN, a wireless data network needs its own added infrastructure to
support wireless Internet access. Consider the next example.
Wireless Internet. Figure 1.3 shows the traditional wired data infrastructure together
with an additional wireless data infrastructure that allows wireless connection to the
Internet. The traditional data network consists of routers, point-to-point connections,
and computers for operation and maintenance. The elements of a wireless network
include mobile terminals, access points, mobility-aware routers, and point-to-point
connections. This new infrastructure has to implement all the functionalities needed to
support mobility.
The difference between the cellular telephone and wireless Internet examples is
that the wireless network in Fig. 1.2 is a connection-based voice-oriented network,
whereas the wireless network in Fig. 1.3 is a connectionless data-oriented network. A
connection-oriented operation needs a setup procedure to connect the communicating
terminals, and after the connection is established, a certain quality of service (QoS) is
guaranteed to the user throughout the communication session. In connectionless operation
there is no setup procedure and terminals are always connected to the network, in
the sense that the communication session remains intact, but the QoS is not guaranteed.
Instead, each protocol data unit (e.g., datagram or packet) is communicated between
network access points on a best-effort basis. Common examples of connectionless protocols
are the Internet Protocol (IP) and the User Datagram Protocol (UDP), both of