24-07-2012, 02:59 PM
Two-way Admission Control and Resource Allocation for
Quality of Service Support in Location-Aided Mobile Ad
Hoc Networks
Two-way Admission Control and Resource.pdf (Size: 488.63 KB / Downloads: 18)
Introduction
There is a growing need to support Quality of Service
(QoS) in mobile ad hoc networks (MANETs), however,
this is challenging. This task often requires acceptable
channel conditions, QoS-aware mechanisms
for channel access, identification of proper forwarding
(transit) nodes, as well as measures for congestion
prevention and management in those nodes. The absence
of fixed infrastructure in MANETs means that
there is no dedicated agency to manage and regulate
the scarce channel resources. This problem gets exacerbated
when the network grows in size, and additional
problems such as increasing node-density and
large number of nodes have to be faced and tackled
[3].
Related Work and Our Motivation
It is difficult to compare different MAC protocols, as
each has been developed with a different architecture
and application in mind. A scheme termed soft
reservation multiple access with priority assignment
(SRMA-PA), is presented in [8]. It is a time division
multiple access (TDMA) based MAC protocol that allocates
stations to different time-slots. This scheme
does not take asynchronous data traffic into consideration,
as all data transmissions are required to reserve
slots irrespective of whether they are real-time or besteffort
traffic. Also there is a possibility for higher priority
traffic to starve lower priority traffic by “confiscating”
the slots already reserved by it.
Proposed MAC Mechanism
The proposed protocols are targeted for an unslotted
multihop system, which is typical for mobile ad hoc
wireless networks. In our scheme, both the DCF and
PCF of IEEE 802.11 are used for the first time in multihop
MANETs after being modified to accommodate
MAC-level service differentiation. Although the PCF
does require a centralized node, we describe next how
this can be achieved in multihop MANETs using a
novel strategy. The motivation for this work comes
from the observation that the PCF-based operation offers
a “packet-switched connection-oriented” service
which is well suited for voice as well as multimedia
traffic. The “connection-oriented” aspect of the PCF
would allow the network to provide throughput, delay,
and possibly jitter guarantees [6].
Need for the Creation of Multiple Parallel Channels
Although relatively simple, as explained in sections
I and II, the use of single radio based on 802.11
DCF is not suitable for multimedia traffic in multihop
MANETs [1][2]. On the other hand, supporting
real-time applications in any network necessitates
the availability of predictable resources. This is simply
possible – especially in wireless networks where
bandwidth is not abundant – with a central agency,
which can have a control over the scarce channel resources
for efficient and fair sharing. On the other
hand, the very basic requirement of an ad hoc network
is that it should not rely on any central node. However,
some form of an agency to manage the channel
resources is still required for QoS support.
Protocol Description
Our QoS-aware MAC protocol is based on a hierarchical
approach consisting of two sub-layers on each
unique channel (i.e., this is not the case for the common
channel) [1]. Like in the IEEE 802.11 standard,
the lower sub-layer of the MAC protocol is called
the DCF. This is to provide the fundamental access
method in order to support asynchronous data traffic.
The upper sub-layer (called PCF) is implemented
on top of DCF to support real-time traffic through the
“association process” [6][7]. Once a node A becomes
“associated” with its forwarding-node B, the node A
would not need to contend the unique medium (channel)
of B any more during the whole session as long
as B is within the transmission range of A.