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OPNET Technologies |
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University: University
of Central Florida |
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A Scheduler Based Architecture for QoS Provisioning
in IEEE 802.11 MAC Protocol ABSTRACT The
existing IEEE 802.11 MAC protocol lacks inherent built-in features to support
multimedia and QoS sensitive traffic. Extensions to the MAC protocol to
include QoS support have been proposed in the literature. Most of the schemes
address either fairness in bandwidth allocation or provide service
differentiation in terms of throughput, without maximizing the total channel
utilization. In this paper, we extend a p-persistent CSMA based MAC protocol
for single queue to multiple queues by adding scheduler based architecture to
provide service differentiation in terms of throughput while providing
maximum system capacity. KEYWORDS IEEE
802.11, QoS, Scheduler, Service Differentiation, P-Persistent MAC,
Throughput, Performance Analysis Scheduler Architecture In this paper, we propose
a scheduler based architecture to provide throughput service differentiation
among the multiple traffic queues within a node. Most of QoS enhancements
suggested for the EDCF in 802.11 MAC protocol involves using different AIFS,
CWmin, CWmax, and MF values
at each traffic queue in the MAC layer. This increases the complexity of the
EDCF MAC functionality. In our Scheme, we separate the QoS functionality from
the channel access functionality of the EDCF by means of a scheduler. The scheduler is built
above the core MAC layer and deals only with providing QoS for the traffic
queues. The core MAC layer consists of a p-persistent 802.11 CSMA based MAC
protocol and considers only channel access mechanism. As a result, each
component can be changed, improved independently of the other. Fig. 1 shows
the block diagram of the architecture. In this paper, we used weighted fair
queuing in our scheduler and as a result it provides throughput service
differentiation with in a node.
Fig. 1 Scheduler Architecture Our scheduler based
architecture provides several advantages to the regular QoS enhancements
suggested for the EDCF MAC protocol. In EDCF, each queue is provided with
separate QoS parameters and as a result, each queue makes an independent
attempt to achieve its own QoS requirements. There is no centralized control
to provide QoS with in a node. We provide more control in providing QoS for
the all queues within a node. Also, with our architecture, there are only two
parameters viz., Popt and CW at the
channel access level. Moreover, our architecture is very similar to the DiffServ architecture of the wired network thus,
increasing the compatibility between the wired and wireless networks. Simulation
OPNET Since,
we wanted to test our proposed idea as early as possible and owing to some
learning curve involved with OPNET; we did our initial work in ns2. We
modified the ns2 to incorporate the scheduler in the wireless node. Fig. 2
shows the placement of the scheduler in the protocol stack. The scheduler is
part of the PriQueue class and interacts with MAC
layer directly. We
will implement our next phase of work in OPNET from July 2005. Until then, we
will use OPNET for learning purposes
Fig. 2 modifications in ns-2 Simulation Results
Fig. 3 Effect of scheduler on the Core Mac protocol
Fig. 4 Scheduler based MAC protocol (CBR Traffic)
Fig. 5 System Throughput Vs Load (CBR Traffic)
Fig. 6 System Class Throughout Vs Load (CBR Traffic)
Fig. 7 Scheduler based MAC for on-off traffic
Fig. 8 System Throughput Vs Load (ON-OFF Traffic)
Fig. 9 System Class Throughout Vs Load (ON-OFF
Traffic) REFERENCES [1] IEEE Std. 802.11-1999, Part11:
Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) specifications, Reference number ISO/IEC
8802-11:1999(E), IEEE Std. 802.11, 1999 edition, 1999. [2] S. Blake, D. Black, M. Carlson, E.
Davies, Z. Wang, and W. Weiss, “An Architecture for Differentiated
Services,” RFC 2475, December 1998 [3] IEEE 802.11 Wireless Local Area
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Supplement to Part 11: Wireless LAN Medium Access Control (MAC) and Physical
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Frame Scheduling in IEEE 802.11-operated WLANs”, IEEE Journal on
Selected Areas in Communication, Vol. 22 (10), December 2004 [19] H. Zhu. M. LI and
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