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5.1 INTRODUCTION
Diverse wireless networks are becoming an integral part of the ubiquitous computing and commu-
nication environment, providing new infrastructure for multiple applications such as video phone,
multimedia-on-demand and others. In order to access multimedia information, certain level of
Quality of Sertvice (QoS) needs to be considered such as high success ratio to access multimedia
data, bounded end-to-end delay, low energy usage, high bandwidth rate, and others. We have dis-
cussed some of the QoS and resource enforcement and adaptation techniques in Chapters 3 and 4,
especially at the end-nodes to enable efficient multimedia data delivery. One function that remains
to be discussed is the routing function that connects sources and destinations of information when it
moves information/packets through the mobile or static multi-hop/ad hoc wireless network.
Before we discuss the various routing aspects in more details, we present the routing function
with its ties to higher layer functions via cross-layer design. Routing functions, similar to schedul-
ing and rate allocation functions in Chapters 3 and 4, benefit from the interaction between the
middleware and routing layers. We will briefly show the cross-layer interactions and benefits on an
example.
Let us consider the cross-layer system architecture between application, middleware and
routing layers in Figure 5.1 [54]. The cross-layer architecture includes (1) group-based applica-
tion that produces and shares multimedia data with other users within a group in the network;
(2) middleware that runs the data accessibility service to assist applications in locating, accessing and
replicating data; and (3) routing that computes feasible routes and forwards packets to other mobile
nodes within a group in the network. The sharing between routing and middleware layers is done
in the form of system profiles. For example, system profiles may include contextual information useful
such as nodes’ location and motion pattern, known at the routing layer, and data priority informa-
tion, known at the middleware layer. Middleware utilizes nodes’ location and movement pattern to
predict future connectivity of a group for data replication purpose. Routing utilizes data priority to
differentiate network packets for routing purposes.
C H A P T E R 5
Routing
110 QUALITY OF SERVICE IN WIRELESS NETWORKS OVER UNLICENSED SPECTRUM
The benefit for routing function from the cross-layer design is manifold. The routing func-
tion yields (a) better routing results in terms of route discovery, selection and maintenance, and (b) less
computational and communication overhead due to access to higher level information such as nodes’
location and mobility patterns.
There is a huge body of wireless routing work, hence what we present here is only an exemplary
cut through possible routing designs and solutions which might provide guiding directions to the
reader, i.e., where to start when facing certain wireless computing and communication environments.
Overall, the wireless routing space can be characterized and classified along many dimensions:
(a) routing over
mobile vs static multi-hop ad hoc networks [e.g., 42, 47, 52, 53, 54];
(b) routing with
QoS support vs best effort [e.g., 47, 48, 57, 58];
(c)
point-to-point routing vs multicast routing [e.g., 42, 47, 54, 59, 60];
(d) network layer routing vs overlay routing [e.g., 42, 54, 59, 60];
(e) source routing vs distributed routing [e.g., 42, 47, 54];
(f ) proactive vs hybrid vs reactive mobile ad hoc routing [e.g., 48, 50, 51, 74, 102, 123];
(g) routing for networks with
persistant wireless connectivity vs routing for delay-tolerant net-
works with intermittent wireless connectivity [e.g., 42, 47, 54, 61];
(h) routing considering
user-based optimization with their social structure vs routing considering
system-based optimization [e.g., 43, 44, 45, 46];
FIGURE 5.1: Cross-layer system framework between middleware and routing layers [54].

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