21-03-2012, 04:23 PM
A Glance at Quality of Services in Mobile Ad-Hoc Networks
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Introduction
Ad-Hoc network is a dynamic multihop wireless network that is established by a set of mobile nodes on
a shared wireless channel. Each mobile host performs local broadcasts in order to identify its existence to
the surrounding hosts. Surrounding hosts are nodes that are in close proximity to the transmitting host.
In that way each mobile hosts becomes potentially a router and it is possible to dynamically establish
routes between itself and nodes to which a route exists. Ad-Hoc Networks were initially proposed for
military applications such as battleeld communications and disaster recovery, but the evolution of the
Multimedia Technology and the commercial interest of Companies to reach widely civilian applications
made QoS in MANets an area of great interest. Although much progress has been done in QoS for wire-
based networks, there are still many problems. Moreover the problems that exist for QoS in wire-based
networks, MANets are facing three new constraints. These constrains are: a)the Bandwidth Constrains,
since a MANet has usually poor bandwidth resources, b) the Dynamic Topology of the MANet, since nodes
are continually changing location, connecting and disconnecting from the network making connections
many times unreliable, and c)the Limited processing and Storing capabilities of mobile nodes, in contrast
with routers on the Internet. Due to this constrain we can't design nodes in a complex manner. Although
QoS and complexity are terms that usually go together, we have to keep complexity as low as possible
since this may also lead to excessive power consumption which is another problem that may arise.
The organization of the rest of this report is as follows. In Section 2 we give a denition for QoS. In
Section 3 we will review quickly IP QoS. Section 4 introduces FQMM, the rst QoS Model proposed of Ad-
Hoc Networks. Section 5 makes a comparison between in-band and out-of-band signaling and introduces
INSIGNIA, the rst signaling protocol desinged solely for MANets. In Section 6 we will talk about QoS
Routing and explain various details of QoS for AODV, which is a sucessful routing protocol for MANets.
Finally, we conclude in section 7 with conclusions.
2 What is Quality of Services?
QoS is a term widely used in the last recent years in the area of wire-based networks. QoS stands for
Quality of Services and the truth is that there is much debate on what exactly QoS is supposes to mean.
Most vendors implement QoS protocols having in mind specic scenarios and taking into consideration
dierent parameters, network topologies and variables. The United Nations Consultative Committee for
International Telephony and Telegraphy (CCITT) Recommendation E.800, has dened QoS as: "The
collective eect of service performance which determines the degree of satisfaction of a user of the service".
This is a widely accepted denition since it doesn't makes any reference to any minimum characteristics,
such as Bandwidth or Delay, or mechanisms, such as Admission Control, SLA, Signaling Protocol.