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Quality of Service Enhanced Routing in Mobile Ad Hoc Networks

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					                                                              (IJCSIS)International Journal of Computer Science and Information Security,
                                                                                                               Vol. 8, No. 5, August 2010

      Quality of Service Enhanced Routing in Mobile
                     Ad Hoc Networks
                                                D.S. Thenmozhi 1, R. Lakshmipathi 2
                       1
                           Lecturer, Institute of Road and Transport Technology, Erode, Tamilnadu, India.
                                                vivek_thenmozhi@rediffmail.com
                                       2
                                           Professor, St. Peter’s Engineering College, Chennai
                                                         Tamilnadu,India.

Abstract—The importance of Mobile Ad hoc Networks                       factor. The radio transmission channel is limited in bandwidth.
(MANETs) has been increasing everyday. Attractive features of           Channel bandwidth is shared among neighboring nodes.
MANETs are no need for infrastructure and decentralized                 Nodes in the MANETs can move freely. Nodes mobility
nature. Many applications that use MANETs include multimedia            makes determining and maintaining the network topology the
data that require Quality of Service (QoS) support for effective
communication. Also QoS routing feature is important for a
                                                                        most challenging issue. Networking mechanisms such as
mobile network to interconnect wired network having QoS                 routing protocols for MANETs require high efficiency
support. We approach the problem of providing        Quality of         because of limited resources in a mobile node such as network
Service for mobile ad hoc networks (MANETs) by the technique            bandwidth, memory capacity and battery power. Routing
of bandwidth based path finding. The Ad hoc On demand                   protocols in ad hoc networks must manage frequent topology
Distance Vector routing protocol provides efficient route               changes caused by node mobility. The nature of dynamic
establishment between nodes with minimal control overhead and           changing topology in ad hoc networks introduces difficulties
minimal route acquisition latency. The normal route finding             in end-to-end route finding. A new technique designed for ad
method of AODV is improved as Quality of Service Enhanced Ad            hoc networks is ‘On-demand’, or reactive routing. In this
hoc On demand Distance Vector (QEAODV) routing. In our
                                                                        technique nodes are not maintaining the full topological view,
work QEAODV establishes a path between the source and the
destination meeting the application stipulated throughput               but nodes construct routing tables having only routes to nodes
requirement. Contention which is the inherent problem in                that a source needs to communicate with, that are established
MANET is considered effectively in QEAODV. QEAODV is                    on demand with the help of source flooding.
implemented so that additional overhead requirement will be
very less. In this paper, we present a scalable and efficient
                                                                           A lot of work has been made on routing in ad hoc networks:
QEAODV to support QoS in ad hoc networks. Simulation results            the destination - sequenced distance vector (DSDV) protocol
show significant performance advantages of our protocol when            [5], the wireless routing protocol [6], the temporally-ordered
compared with normal AODV.                                              routing algorithms [7], the dynamic source routing protocols
                                                                        [8], the associativity based routing protocol [9], and the zone
Keywords—Mobile Ad hoc Networks (MANETs), quality of                    routing protocol (ZRP) [10], etc. These protocols tend to
service routing, bandwidth estimation, contention, admission            establish a path with least number of hops and achieving a
control, simulations.                                                   high degree of availability of nodes involved in the active path
                                                                        where the network topology changes quickly. Also, all the
                                                                        previous routing solutions only deal with the best-effort data
                        I. INTRODUCTION                                 traffic.
   Ad hoc networks are communication networks formed by a
number of nodes which are small radio devices with limited                 Though, the vast array of technological solutions for ad hoc
computational capacity and memory. The most desirable                   networks, their practical implementation and use in the real
advantage of ad hoc networks are their easy deployment.                 world has been limited so far. Because entertainment and
Ideally it should be possible to deploy the nodes in the area of        other multimedia based applications are naturally what drive
operation and have them self-organize to route traffic as               the mass users of a technology. In order to support above
required. Such an easy deployment would be most                         services best-effort routing solutions are not sufficient.
advantageous in a variety of applications ranging from                  Normally multimedia applications often have stringent delay
military operations and disaster relief to commercial                   and reliability sensitive service requirements. Any networks
applications.                                                           supporting multimedia applications must cater above
                                                                        requirements. Hence focus has been shifted from best-effort
  MANETs (Mobile Ad hoc Networks) [12] inherently                       services to the provision of better defined QoS in ad hoc
possess many challenges for its easy deployment, the nodes              networks. Shared nature of the medium in MANETs needs
should not depend on an external energy supply, so they are             additional care at the time of Quality of Service support. QoS
normally battery powered, and battery life is often a limiting          supportive routing protocols [2], [3] find important role in




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QoS mechanisms. Since their role is to find which nodes in performance of Quality of Service Enhanced AODV is
the network will meet application requirements in the wireless, compared with its counter part AODV using NS-2 simulator.
mobile ad hoc network environment.
                                                                   The rest of the paper is organized as follows. Next section
                     II. RELATED WORKS                          presents basics of QEAODV protocol. Section IV explains the
   In MANETs Quality of Service based routing is a relatively complete functioning of Quality of Service Enhanced AODV.
new problem. In this section we present an overview of the Section V deals with QEAODV route discovery process. The
existing solutions. Chen and Nahrstedt [4] proposed a ticket protocol simulation and results are discussed in section VI.
based QoS routing algorithm for ad hoc networks. This ticket
based probing scheme achieves a balance between the single-
path routing algorithms and the flooding algorithms. It does                    III. PROTOCOL DESCRIPTION
multipath routing without flooding. The required QoS is
ensured during the time when an established path remains           Basic AODV [13] is based on flooding the network with
unbroken. The QoS support however is disrupted during the Route Request (RREQ) messages. The source node broadcasts
rerouting time. They consider only the type of networks a RREQ message with a time-to-live value equal to 1. i.e. a
whose topologies are relatively stable because their routing, broadcast is limited one hop neighborhood. Each RREQ is
rerouting architectures do not support ad hoc networks with uniquely identified through a sequence number, so that the
violently changing topologies. Lin and Liu [11] proposed a first copy of a RREQ received by a node is processed, while
new bandwidth routing scheme which contains bandwidth duplicated messages are discarded. When a node receives the
calculation and reservation for mobile ad hoc networks. They first copy of a given RREQ it records the address of the node
suggested a TDMA-based approach. This approach requires that sent the message. When the first RREQ reaches the
effective synchronization between all nodes in the networks. desired destination, a route reply (RREP) message is
Applying highly synchronized solutions in ad hoc networks generated and sent back to the source node through the
becomes expensive and synchronization may fail when the recorded reverse path, ensuring a path from the source to the
nodes are mobile. The free slot allocation algorithm based on destination. Normally this approach minimizes the number of
TDMA scheme is vulnerable to node mobility in the networks hops of the chosen path. The basic functionality of the
since slot allocations must be reconfigured whenever there are QEAODV is much similar to the AODV protocol. QEAODV
changes in available bandwidth or changes to routes in the differs from AODV in the way the route discovery process is
network. Also they have not considered the routing optimality modified to provide quality of service support by performing
(i.e. shortest path). Hanzo et. al [14] proposed Quality of bandwidth constrained admission control at each node in the
Service routing in ad hoc networks. They suggested network. Similar to AODV, the QEAODV also uses the Route
throughput constrained Quality of Service routing utilising the Request, Route Reply and Route Error packets for the route
Dynamic Source Routing (DSR) protocol. DSR is based on discovery and maintenance process, except the Route Request
source routing in which each data packet carries complete and Reply packet formats are modified to carry additional
path information. This requires more overhead compared to information through the network
AODV.
   Normally QoS can be achieved by coordinating the                                    IV. FUNCTIONING OF QEAODV
transmission schedule of packets between nodes. Actually
                                                                           The main problem of the MANET comes from the shared
existing above discussed approaches are mostly based on local
                                                                        nature of the wireless medium in single-channel networks.
decisions. All are focusing on the packet level and only deal
                                                                        Essentially, nodes that cannot communicate with each other
with required resource allocation at individual node point of
                                                                        directly may still contend directly with each other for the same
view. In order to support Quality of Service, guarantees for
                                                                        resources. This extended contention area, known as
end to end flows, path finding approaches need to be
                                                                        ‘neighborhood contention’ affects resource allocation at
combined with suitable admission control strategy. At the
                                                                        individual nodes in two-ways. First allocation decisions at an
time of making admission control decisions,              a node
                                                                        individual node require bandwidth information of nodes
considers its local resources simultaneously it must account
                                                                        outside of its communication range and along the entire route.
the resource of this contention neighbors because nodes flow
                                                                        Second, contention for resource may involve multiple nodes
may consume their resources through contention. This paper
                                                                        along a route. QEAODV performs admission control based on
fulfils this objective by modifying AODV to perform
                                                                        knowledge of these characteristics of MANET. We focus on
admission control logic at every node and also to consider
                                                                        ad hoc networks based on single-channel MAC layers like
both node's local resources and resources at contention-
                                                                        IEEE 802.11 because these single channel protocols are
neighbors while making admission control decisions.
                                                                        widely available and typically support ad hoc communication.
Admission control is based on the knowledge of available
                                                                        Moreover, these protocols are simple to implement and robust
bandwidth information. We only consider bandwidth as the
                                                                        and do not rely on stringent time synchronization that is hard
admission criteria. This is because bandwidth guarantee is one
                                                                        to implement in ad hoc network. The physical characteristics
of the most critical requirement for real time applications. The
                                                                        of wireless channels introduce the two challenges. First




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challenge is available bandwidth estimation at a node, second            fraction of channel idle time based on the past history as an
challenge is estimation of flow bandwidth requirement in a               indication of local available bandwidth at a node. This
shared medium.                                                           approach is justifiable since it does not consider that some of
                                                                         the channel time cannot be used due to the idle time caused by
A. Node’s Available Bandwidth:                                           the exponential backoff algorithm in IEEE 802.11 and the
                                                                         collisions in the network. Using the fraction of idle channel
   In shared wireless medium, when a node starts to transmit a           time can be a simple approximation for local available
flow, it consumes bandwidth from its contention neighbors.               bandwidth. A node can perceive the channel as either idle or
Because each node has a different view of the network, the               busy. The channel is idle if the node is not in any of the
node cannot decide on its own whether its contention                     following three states. First, the node is transmitting or
neighbors have sufficient unused bandwidth for the new flow.             receiving a packet. Second, the node receives a RTS or CTS
Also, obtaining contention neighbor information is not easy              message from another node, which receives channel for a
since a node may consume the bandwidth of contention                     period of time specified in the message. Third, the node senses
neighbor but not able to directly communicate with that                  a busy carrier with signal strength larger than a certain
neighbors if that neighbors are located outside transmission             threshold, called the carrier-sensing threshold, but the node
range and inside carrier-sensing range.                                  cannot interpret the contents of the message. By monitoring
                                                                         the amount of channel idle time, Tidle, during every period of
B. Flow Bandwidth Consumption:                                           time, Tp, the local bandwidth available BWlocal , for a node can
                                                                         be computed using a weighted average [1] as follows
   Multiple nodes on a route may contend for bandwidth at a
single location and not know about each other. A node on the               BWlocal = ω BWlocal + (1-ω)(Tidle /Tp) BWchannel              (1)
route of flow cannot tell how much bandwidth the flow will
consume at its contention neighbors. The limited bandwidth of               Where BWchannel is the capacity of the channel and weight ω
wireless ad hoc networks requires the limitation of any                  ε [0,1].
message overhead from information collection. In addition,
due to mobility, information gathered about the network only
has limited lifetime. Hence, it is effective to collect                   2. Calculation of Contention Neighborhood Bandwidth
information as close as possible to the time and location that it        Available (BWc-neigh)
is needed.
                                                                            Each node perceives the network in a different state. Hence
C. QEAODV Admission Control:                                             a node's local bandwidth available cannot provide information
                                                                         about its contention neighbors. Since it does not know the
   The objective of admission control is to determine whether            amount of BWlocal at other nodes. Two approaches are
the available resources can meet the requirements of a new               normally used to obtain bandwidth information at contention
flow while maintaining bandwidth levels for existing flows.              neighboring nodes. They are active approaches and passive
Each node views a different channel state, the available                 approaches. In active approaches, neighbors voluntarily
bandwidth in the network is not a local concept. To tackle this          exchange bandwidth information between each other. Such
condition, two terms are introduced: local bandwidth available           exchanges normally incur high message overhead. In passive
(BWlocal), contention-neighborhood bandwidth available
(BWc-neigh). Local bandwidth available is the amount of
unconsumed bandwidth as observed by a given node.
Contention neighborhood available bandwidth is the
maximum amount of bandwidth that a node can use for
transmission without affecting the reserved bandwidth of any
existing flows in its carrier-sensing range. Since a node may
consume the bandwidth of nodes that are with in its contention
range, the contention neighborhood bandwidth available for a
given node is equal to the smallest local available bandwidth
of all its contention neighbors. Hence in order to admit a flow,
a node must have required local bandwidth and contention
neighborhood bandwidth.

 1. Calculation of Local Bandwidth Available (BWlocal)

   It is the unconsumed bandwidth at a given node. Each node
in the MANET can determine its BWlocal by passively
listening network activities. In our approach, we use the




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approaches, a node passively monitors the channel to calculate
its contention neighbors' local bandwidth available. During
the normal IEEE 802.11 operations, a node listens the medium
using a threshold value known as contention-carrier sensing
threshold, which is set to a value much lower than the carrier-
sensing threshold refers the range that covers the carrier-
sensing ranges of all of the sensing node's contention
neighbors as shown in the Fig.1. When the signal strength of
the carrier sensed by a node is smaller than the contention
carrier sensing threshold there is no communication in its
contention neighborhood and contention neighbors of the
node experience idle channels. The amount of time that the
channel is in this idle state, denoted as Tidlecontention, for every
period of time, Tp, contention neighborhood available
bandwidth, BWc_neigh is calculated using the following formula.

BWc-neigh≈ ω BWc-neigh + (1-ω)(Tidlecontention/Tp)BWchannel      (2)


                                                                          Next important factor to be considered is multiple nodes on
 3.Calculation of Application's              Flow      Bandwidth          the route of a new flow may contend for bandwidth at a single
Consumption (BWa_flow)                                                    location. Every such node needs bandwidth equal to BWflow.
                                                                          The number of such kind of nodes is known as contention
   QEAODV needs to quantify the bandwidth that a new flow                 count (Cct). Hence the bandwidth consumption of the flow [1]
requires so that it can be decided whether the bandwidth                  at this location is expressed as:
available will satisfy the requirements of the flow. Foremost,
the application’s data rate has to be converted into the                           BWa_flow = Cct x BWflow                                (5)
corresponding channel bandwidth requirement. This
conversion includes the protocol overhead incurred in the                  In Fig.2, flow 1 passes through the path F->B->A->C. Flow
MAC layer and the network layer. As per IEEE 802.11, for                  2 passes through the path D->H->B->G. Both the flows are
every application data packet, the MAC layer performs                     within node X's contention range. Assume flow 1 requires 1
handshaking. During this RTS, CTS and ACK control packets                 Mbps at each node, flow 2 requires 0.5 Mbps at each node. At
are involved. Hence each data packet's transmission time is               node X, both flows will take off 6 Mbps because nodes
calculated as follows.                                                    involved in both the flows are within the carrier sensing range
                                                                          of node X. A node can learn its contention neighbors by
  Tdata =Trts+Tcts +Tack+Tdifs+3Tsifs+(P+Q)/BWchannel          (3)        passively listening the routes and information carried in
                                                                          control and data messages. This method does not impose any
  Where Tdata      - transmission time of each data packet                extra message overhead in the network. A node on the route
        Trts       - time for transmitting RTS                            can get its contention count (Cct) value if the complete path
        Tcts       - time for transmitting CTS                            information is available to it. Complete path information is
       Tack        - time for transmitting ACK                            made available in the route reply (RREP) packet of QEAODV.
       Tdifs       - DCF inter frame space defined in the                 Hence BWa_flow is computed (5) by a node on receiving RREP
                     IEEE 802.11 protocol standard                        packet. Final admission control at a node is based on this
          Tsifs    - short inter frame space defined in the               value
                     IEEE 802.11 protocol standard
           P       - size of the data packet
           Q       - IP and MAC packet header length                          V. QEAODV ROUTE DISCOVERY PROCESS
     BWchannel     - Channel capacity
                                                                             Like AODV [2], QEAODV is a reactive unicasting routing
  If at every second, the application generates ‘R’ packets               protocol for mobile ad hoc networks. It needs to maintain the
with average packet size 'P', the corresponding channel                   routing information about the active paths. In QEAODV,
bandwidth requirement is computed as follows.                             routing information in maintained in routing table at every
                                                                          node. Each node constructs a next-hop routing table, which
     BWflow = R x Tdata x BWchannel                            (4)        contains the destination to which it currently has a route. An
                                                                          entry in the table automatically expires, if it has not been used
                                                                          for a specified amount of time.




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                                                                            Fig. 4. Final Admission Control

                                                                         certain time period in order to make use of them if final
                                                                         admission control fails for the first selected route. On
   During the route discovery process, the source broadcasts             receiving the RREP packet, a node performs final admission
route request (RREQ) packets. Each RREQ packet contains                  control as shown in Fig.4. Using the details available in the
the addresses of the source and the destination, the broadcast           RREP packet each node on the reverse path computes actual
ID, the last seen sequence number of the destination as well as          bandwidth consumption of the flow (BWa_flow). If the actual
the source node's sequence number. Broadcast ID is used as               bandwidth requirement of the flow (BWa_flow) is lower than
an identifier. Sequence numbers are utilized to ensure loop-             node’s local available bandwidth (BWlocal) and contention
free and up-to-date routes. Application's channel bandwidth              neighbourhood available bandwidth (BWc-neigh), final
requirement (BWflow) is computed by the source and included              admission control succeeds otherwise it fails.    On success
in the RREQ packet. In QEAODV, each node computes                        of admission control, a soft reservation of bandwidth is made
BWlocal and BWc-neigh as per (1) and (2) respectively. Every             in the routing table and RREP is forwarded to its immediate
intermediate node, on receiving RREQ performs preliminary                predecessor. On failure of final admission control, an
admission control as given in Fig.3. If the bandwidth
requirement of the flow BWflow is lower than node's local
available bandwidth BWlocal and contention neighborhood
available bandwidth BWc-neigh, preliminary admission control
succeeds, otherwise it fails. In case of failure, the RREQ is
discarded. On success of the preliminary admission control
the node sets up a reverse route entry in its routing table, adds
its identifier in the RREQ packet and rebroadcasts the route
request. Recording the sequence of hops in RREQ packet
enables to determine the lower bound of the contention count
of the complete route and also it can be used to eliminate
circular routes.
   When the intended destination receives, a route request, it
receives the full route and sends a route reply (RREP) back to
the source along the same route. If different routes arrive at
the destination, the destination chooses the shortest path route
and the remaining routes are cached at the destination for                          Fig. 5. Throughput of QEAODV.




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   Fig. 6. Throughput for different simulation times.                   Fig. 8. Control message overhead for pause time = 20sec


                                                                      of RREQ is modified to carry additional information. The
                                                                      routing table structure is also changed to hold the extra details.

                                                                          Simulations are run for different scenarios. Different
                                                                      scenarios are created using 10, 20, 30, 40 and 50 nodes.
                                                                      Protocol evaluations are based on the simulation of wireless
                                                                      nodes forming an ad hoc network, moving about over a
                                                                      rectangle. Rectangle size is 1000m x 1000m, simulation time
                                                                      is 200seconds. At medium access control (MAC) layer the
                                                                      802.11 protocol was used. Radio transmission range of a node
                                                                      is set to 250m and the carrier sensing range is set 550m. Node
                                                                      movement is set as per “random way point” model. Each flow
                                                                      generated 10 packets per second. Each packet size is 512
                                                                      bytes. Speed of nodes is 5m/s and the bandwidth of the
                                                                      channel is 2 Mbps.A number of simultaneous CBR flows are
 Fig. 7. Control message overhead for pause time = 10sec              made. Scenarios are run for different node pause time values.
                                                                      The performance of the QEAODV is compared with normal
                                                                      AODV in terms of throughput, overhead and network
                                                                      performance ratio. Throughput of QEAODV gets increased
admission failure message is sent to the destination via the          significantly as shown in Fig. 5. In Fig. 6 throughput of
same reverse route. It enables cancellation of bandwidth              QEAODV is high till the average simulation time of 130
reservation by the successor nodes. On receiving the                  seconds, beyond that throughput gets decreased. This is due to
admission failure message, the destination selects another            the effect of nodes mobility. From Fig. 7 and Fig. 8, it is
fresh cached route and sends a RREP. On successfully                  inferred that control message overhead as per QEAODV
receiving RREP, a source has enough end-to-end bandwidth              execution is comparatively lower than normal AODV
reserved entire route and communication can start at each             execution. Also as the nodes’ pause time value increases,
node on the path, bandwidth reservation is refreshed by the           control message overhead decreases drastically.
arrival of data packets. The bandwidth reservation at the node
automatically expires, if no data packet arrives due to link
breakages.                                                                                  VII. CONCLUSION

                                                                         In this paper, we proposed a QoS enhanced AODV
              VI. SIMULATION AND RESULTS                              (QEAODV) routing algorithm for ad hoc networks. The
                                                                      existing AODV performs routing with low control overhead
   The proposed QEAODV routing protocol is implemented                and effective packet transmission. But do not have QoS
using the NS-2 network simulator [15] by modifying the code           support. We modified the normal AODV to perform path
of AODV protocol. AODV protocol already exists in the                 finding that meets the application stipulated bandwidth
network layer. A modification is done in the MAC layer to             requirement. Our path finding approach is modified in such a
capture the signal strength. In QEAODV the packet structure           way that it deals with common medium sharing problem of




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                                                                                                     ISSN 1947-5500
the ad hoc networks effectively. The modified QEAODV                    [15] S. McCanne, S. Floyd, S. Fall, K. Varadhan: The
performs path finding with less overhead by adopting passive        Network Simulator NS2 (1995). The VINT Project, available
approach of listening to the medium. Simulations show that          at http://www.isi.edu/nsnam/ns.
QEAODV performs better than AODV in terms of throughput
and control message overhead. It improves packet delivery
ratio greatly without affecting the overall end-to-end
throughput of existing flows.


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