Comparative study on priority based qos

International Journal of Wireless & Mobile Networks (IJWMN) Vol. 6, No. 5, October 2014
COMPARATIVE STUDY ON PRIORITY BASED QOS
AWARE MAC PROTOCOLS FOR WSN
Shouman Barua1, Farhana Afroz2 Sikder Sunbeam Islam3, Afaz Uddin Ahmed4,
Pantha Ghosal1 Kumbesan Sandrasegaran1
1,2Faculty of Engineering and Information technology, University of Technology, Sydney,
Australia
3Department of Electrical and Computer Science, International Islamic University,
Chittagong, Bangladesh,
4Department of Electrical Engineering, University of Malaya, Kuala Lumpur, Malaysia
ABSTRACT
In Wireless Sensor Network (WSN), QoS (Quality of Service) in sensor application plays a very important
role. QoS based routing is required to ensure the best use of nodes in WSN. In this paper, a comparative
study of QoS based routing in Media Access Control (MAC) protocols are presented based on the traits to
solve problems like prioritization, timeliness, reliability etc. The study mainly focuses on some priority
based QoS protocols used in WSN and a comparison among them. The study reveals that among the five
mentioned protocols; QMAC, PRIMA, DB-MAC, RAP, GTS; PRIMA shows the best performance in the
category of Packet Prioritization, Scheduling Scheme, Queue Type, Energy Awareness and QoS.
KEYWORDS
Network Protocols, Wireless Network, MAC Protocol, QoS.
1. INTRODUCTION
Wireless Sensor Network (WSN) is a wireless network consisting of small sensing nodes, which
have computation and communication capabilities, operates in an unattended environment [1].
WSN routes data back to Base Station (BS) based on the priority based service of the MAC
protocols. Data transmission processes from node to node or Multi hop towards the BS or
gateway. A wide variety of applications could be supported by deploying WSNs in many
different situations, whether they are composed of mobile or stationary nodes. Considering the
dynamic nature of the network, several new protocols have been proposed that are more concern
about QoS [2]. In WSN, there are two types of protocols used to carry out the communication
process between the nodes; they are Routing protocols and Media Access Control (MAC)
protocols. The basic communication type considers send periodic data or event-driven data to the
base station or to the sink. The sensor node extracts data from a particular location and then
multicast or broadcast of data is needed. Routing protocols needed to fulfil these requirements
along with energy conservation and QoS factors. The MAC protocol also plays an important role
in accessing the channels using sensor nodes, and maintains energy saving, throughput, QoS and
minimum delay. However, these protocols can be grouped based on problems they solve, like
Prioritization: Differentiate services based on definition of class of traffic, Timeliness:
Guaranteed delivery within a given time, Reliability: Ensuring probability of delivery etc. [3].
DOI : 10.5121/ijwmn.2014.6515 175

Many MAC layer protocols were proposed for WSN. Some of them are contention based like,
T-MAC [4], S-MAC [5]; some are QoS based such as Q-MAC [6] and along with that, many QoS
based routing protocol have been proposed like, SAR [7], SPEED [8] and also some comparative
study has been done in article [9]. However, in this paper we only considered the priority based
QoS MAC protocols for the analysis to develop a comparison. The rest of the paper is organized
as follows: Priority based QoS MAC protocols in section 2 and Comparison of the protocols in
section 3 and Conclusion in section 4.
176
2. PRIORITY BASED QOS MAC PROTOCOL
Reducing waste of energy caused by overhearing, collisions, excessive overhead, and idle
listening is the main purpose of most MAC-layer protocols. QoS provisioning in the MAC layer
deals mainly with the scheduling of packets on the wireless channel subject to local limitations.
Access to the channel that is maintained by the protocols is based on a schedule. Channel access
is fixed to one sensor node at a time. Using scheduling collision of packets during accessing the
channel can be avoided. However, due to dynamic nature of WSN, providing certain quality of
service (QoS) guarantees in a multi-hop wireless networks, where prioritizing data packets and
providing different services based on application specifics is very important. Here, we are going
to discuss on some priority based QoS MAC protocol briefly.
Q-MAC [6] is an energy-efficient; Priority based QoS-aware media access control (Q-MAC)
protocol. Figure 1 shows the priority scheduling in Q-MAC. Q-MAC tries to minimize energy
consumption while maintaining the QoS. Q-MAC uses the MACAW protocol as an under laying
protocol to access the wireless channel. To satisfy QoS requirements for different traffic types,
the Q-MAC introduces a queuing model where priority levels are set for different queues to
reflect the criticality of data packets that is originating from different sensor nodes.
Figure 1. Priority scheduling in Q-MAC [6]
The Q-MAC consists of intra-node and inter-node scheduling in WSN. The intra-node scheduling
scheme takes a multi-queue First-In First-Out (FIFO) based queuing style to classify data packets
agreeing to their MAC layer abstraction and application while the inter node scheduling handles
channel access with the goal of minimizing energy consumption through reducing collision and
idle listening. For intra node scheduling in Q-MAC, five extra bits of information are added to
every message, two for identification of the types of applications and three for the types of
sensing data. Packets that have gone through more hops have a higher priority. In Q-MAC, the

queue architecture consists of five queues with one specified as an instant queue. That means, any
packet stored in this queue will be served instantly as showed in figure 1. After a packet is
scheduled for transmission, the inter-node scheduling mechanism, Power Conservation MACAW
(PC-MACAW) [9], is executed to achieve Loosely Prioritized Random Access (LPRA) between
sensor nodes in which we use contention time of each node to maintain the order by which nodes
access the channel.
PRIMA [10] is an energy efficient and QoS aware MAC protocol that has been designed for large
wireless sensor networks. PRIMA protocol is composed of two components; a clustering
algorithm for providing scalability and a channel access mechanism for providing multi-hop
communications. The channel access is framed of a hybrid mode of CSMA and TDMA. To
communicate control messages, CSMA mode is used while data messages are assigned in TDMA
slots. So, packet collisions and energy consumption can be minimized. PRIMA protocol
minimizes the idle listening periods by forcing the nodes that have no data to send to go early to a
sleeping state in order to save energy that is considered as a primary source of the energy
consumption in sensor networks. PRIMA protocol provides QoS by employing a queuing model
where traffics are classified depending on their importance in four different queues with different
priorities such as, high (instant queue), medium, normal, or low. Queues with higher priority have
absolute preferential action on top of low priority queues. For doing that, PRIMA uses a sub
protocol named C-MAC (Classifier MAC)-a modified version of Q-MAC. The source node
identifies the degree of importance of each data packet that it is sending which can be converted
into predefined priority levels. By appending two extra bits at the end of each data packet, the
application layer sets the required priority level for each data packet. The queuing architecture of
the C-MAC is shown in Figure-2.
177
Figure 2. Priority Scheduling in PRIMA [10]
DB-MAC [11] in Figure 3 is a MAC protocol based on contention and it is designed for delay-bounded
applications based on hierarchical data gathering tree. Actually, a transmission is given
high priority when it is close to the source than a transmission that is close to the sink. Apart from
this, nodes will overhear contention time slots from other in order to ease early data aggregation
embedded. Therefore, a node will obtain medium access with a top probability if it is close to the
source. Meanwhile, it performs path aggregation in such a way that it is maximum possible close
to the sources. When a source starts transmitting, the priority Pr is set to the maximum PrMAX.
Pr is then decreased by one at each hop. The receiving node decrements the priority by one and
makes PrMAX to PrMAX -1, and forwards the packet to the next node, which will contend for

medium access with priority PrMAX - 1. The BI value is set between 0 and 1023 tics, depending
on the value of the priority. If a node is close to the source, then it will take medium access with a
high probability. The priority access enables decreasing latency and saving energy compared with
IEEE 802.11 scheme [11].
178
Figure 3. The contention mechanism in DB-MAC [11]
RAP [12] is a RT communication architecture designed for large-scale sensor networks. Figure 4
shows the architecture of RAP. Control and Sensing applications interact with RAP through
Query/Event service APIs. The communication is sustained by an efficient and scalable protocol
stack that integrates the transport-layer location-addressed protocol (LAP), geographic routing
protocol (GF), contention-based MAC with packet prioritization and velocity monotonic
scheduling (VMS) policy. LAP is almost same as UDP (connectionless). Only difference is that
all messages are addressed by location rather than IP address. GF provides a greedy localized
routing decision to forward packets into a neighbour node. VMS policy is the main key of RAP
that is based on packet requested velocity that reflects both timing and distance and constraints.
Here, packets are assigned a higher priority with higher requested velocity. End-to-end deadline
miss ratio is reduced by VMS by giving the packets with higher priority and higher requested
velocities. Moreover, to implement packet priorities, two components of the standard IEEE
802.11 implementation have been modified. The initial waiting time becomes idle after the
channel and the back off window increase functions are modified to ensure that packets with top
priority have high chance to get the channel in both contention avoidance phase and contention
phase. Simulations demonstrate that RAP has effectively reduced the deadline miss ratio. The
result shows that a multi-layer location-based communication stack with velocity-based
prioritization can improve the RT performance and QoS in WSNs.

179
Figure 4. RAP Architecture [12]
For RT-WSNs, although IEEE 802.15.4 protocol has provided GTS (Guaranteed Time Slot)
mechanism for time sensitive data, details of how to use it to maintain explicit QoS guarantees are
still being developed. It is possible to let the PAN coordinator distribute GTSs corresponding to
the deadline and bandwidth requirements of transmissions to support HRT guarantees [13]. On
the other hand, enhanced CSMA/CA MAC mechanisms may offer soft delay guarantees. For
example, priority-toning strategy is used in [14]. A tone signal will be sent by a node to the PAN
coordinator to request it alerting other nodes to defer their contentions to support a fast delivery of
high priority frames. In [15], traffics are categorized into high and low priority queues with
different CSMA/CA settings. The result presents a heuristic solution to provide different QoS for
messages of different priorities. Service differentiation of packets in MAC shows promising.
3. COMPARISON OF THE PROTOCOL
The comparisons of the above MAC protocols have been given below:
Table-1: Comparisons of the priority based QoS mac protocols
Name
Packet
Prioritization
Scheduling
Scheme
Queue Type
Energy
Awareness
QoS
Q-MAC
Packets go through
more hop have
more priority
Intra node and
Inter node based
Scheduling
Multi queue(five
queues) FIFO
type
High High
PRIMA
Packets are
prioritized
depending on their
importance
Packets are
scheduled
through hybrid
approach
(TDMA, CSMA).
four different
queues (as High,
medium,
normal, low)
FIFO type
High High
DB-MAC
Packets from a
node that Close
to source get high
priority
Contention based
scheduling
N/A High
High
(Delay
Bound
ed)
RAP
Here, with higher
requested
velocity packet is
assigned a higher
priority
Velocity
Monotonic
Scheduling
Multiple FIFO
queues each
corresponding to
a fixed
Priority level
based on
requested
velocity.
N/A High
GTS
Prioritization is
done using a
toning signal
N/A
High and low
queue only,
FIFO queue.
High High
3. CONCLUSION
In this paper, the priority based QoS aware MAC protocols have been introduced which are used
in wireless sensor networks. The protocols are first discussed briefly and then their comparisons
are done. In comparison, five categories are considered for marking the performance of the

protocols. However, it is seen from the above study among the five protocols the PRIMA shows
the best performance in all the five mentioned categories. Although, the Q-MAC shows most
likely the same performance of the PRIMA but in the case of packet prioritization the scheme of
PRIMA is found better.
180
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Authors

First Author-- Shouman Barua, PhD Research Scholar, Faculty of Engineering and Information
Technology, University of Technology, Sydney, Australia.
Second Author – Farhana Afroz, Postgraduate Student, Faculty of Engineering and Information
Third Author – Sikder Sunbeam Islam, Assistant Professor, Department of Electrical and Computer
Science, International Islamic University Chittagong, Chittagong, Bangladesh.
Fourth Author – Afaz Uddin Ahmed, Research Assistant, Department of Electrical Engineering,
University of Malaya, Kuala Lumpur, Malaysia.
Fifth Author – Pantha Ghosal, Graduate Research Assistant, Faculty of Engineering and Information
Sixth Author – Kumbesan Sandrasegaran, Associate Professor, School of Computing and
Communications, Core Member, Centre for Real-Time Information Networks , Faculty of Engineering
and Information Technology, University of Technology, Sydney, Australia.
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