25-07-2012, 01:33 PM
A Practical View on Quality-of-Service Support in Wireless Ad Hoc Networks
[attachment=28883]
Introduction
Substantial progress has been achieved in solving the
routing challenge in mobile wireless ad hoc networks. The
Ad hoc On demand Distance Vector protocol (AODV)
and the Dynamic Source Routing protocol (DSR) [23] are
among the most prominent ad hoc routing protocols. These
protocols provide a basic routing functionality that is sufficient
for conventional applications such as file transfer or
e-mail download. However, ad hoc networks are also an interesting
platform for more demanding applications such as
Voice over IP (VoIP), which are very susceptible to larger
delays, jitter, and packet losses. In order to support such
applications, it is not sufficient to provide a basic routing
functionality alone.
Bandwidth Reservation in Wired Networks
Guaranteeing a certain amount of bandwidth for a certain
flow or service class requires that the station providing that
guarantee is in control of that bandwidth. This is certainly
the case in a wired network with full-duplex point-to-point
links (e.g. a switched Ethernet).
It is also possible to agree on a determined share of bandwidth
in a shared wired medium. All stations within this domain
are able to communicate with each other directly and
whenever one station transmits data to another station, all
the other stations on the medium are aware of that.
Bandwidth Reservation in Wireless Networks
The situation is completely different for wireless ad hoc
networks consisting of devices with a single network interface.
Networks consisting of devices with multiple network
interfaces (such that each interface handles one link exclusively)
could possibly overcome the drawbacks we discuss
in the following, but also, new challenges would have to
be solved. Discussing such ad hoc networks is beyond the
scope of this article, since ad hoc networks in the near future
will most certainly consist of devices with a single network
interface (or perhaps a few interfaces for different radio
technologies).
Service Differentiation
Apart from the general difficulties outlined in section 2,
there is no chance to integrate classical QoS (based on bandwidth
reservations) in wireless ad hoc networks which are
to be deployed with off-the-shelf hardware in the near future.
And in the face of the complications elaborated above,
it can be seriously doubted that it will ever be worthwhile
to implement bandwidth reservation mechanisms in mobile
wireless ad hoc networks as long as a single network interface
is used to communicate on several links. As a consequence,
IntServ [9] based approaches are not applicable in
wireless ad hoc networks.
Priority Queueing
An important factor in service differentiation is the
queueing strategy. Several approaches have been proposed
in the literature.
In [30], two prioritisation schemes for FQMM are proposed.
Firstly, a simple priority queue ensures that highpriority
packets are given unconditional preference over
low-priority packets. Secondly, they consider a FIFO queue
which they enhance with a RIO buffer management (Random
Early Discard with IN/OUT).
[attachment=28883]
Introduction
Substantial progress has been achieved in solving the
routing challenge in mobile wireless ad hoc networks. The
Ad hoc On demand Distance Vector protocol (AODV)
and the Dynamic Source Routing protocol (DSR) [23] are
among the most prominent ad hoc routing protocols. These
protocols provide a basic routing functionality that is sufficient
for conventional applications such as file transfer or
e-mail download. However, ad hoc networks are also an interesting
platform for more demanding applications such as
Voice over IP (VoIP), which are very susceptible to larger
delays, jitter, and packet losses. In order to support such
applications, it is not sufficient to provide a basic routing
functionality alone.
Bandwidth Reservation in Wired Networks
Guaranteeing a certain amount of bandwidth for a certain
flow or service class requires that the station providing that
guarantee is in control of that bandwidth. This is certainly
the case in a wired network with full-duplex point-to-point
links (e.g. a switched Ethernet).
It is also possible to agree on a determined share of bandwidth
in a shared wired medium. All stations within this domain
are able to communicate with each other directly and
whenever one station transmits data to another station, all
the other stations on the medium are aware of that.
Bandwidth Reservation in Wireless Networks
The situation is completely different for wireless ad hoc
networks consisting of devices with a single network interface.
Networks consisting of devices with multiple network
interfaces (such that each interface handles one link exclusively)
could possibly overcome the drawbacks we discuss
in the following, but also, new challenges would have to
be solved. Discussing such ad hoc networks is beyond the
scope of this article, since ad hoc networks in the near future
will most certainly consist of devices with a single network
interface (or perhaps a few interfaces for different radio
technologies).
Service Differentiation
Apart from the general difficulties outlined in section 2,
there is no chance to integrate classical QoS (based on bandwidth
reservations) in wireless ad hoc networks which are
to be deployed with off-the-shelf hardware in the near future.
And in the face of the complications elaborated above,
it can be seriously doubted that it will ever be worthwhile
to implement bandwidth reservation mechanisms in mobile
wireless ad hoc networks as long as a single network interface
is used to communicate on several links. As a consequence,
IntServ [9] based approaches are not applicable in
wireless ad hoc networks.
Priority Queueing
An important factor in service differentiation is the
queueing strategy. Several approaches have been proposed
in the literature.
In [30], two prioritisation schemes for FQMM are proposed.
Firstly, a simple priority queue ensures that highpriority
packets are given unconditional preference over
low-priority packets. Secondly, they consider a FIFO queue
which they enhance with a RIO buffer management (Random
Early Discard with IN/OUT).