The multi-hop wireless networks that provide the feasible means of communication and information access in real time services are named as Mobile Ad-hoc Networks (MANETS). The Dual Busy-Tone Multiple Access (DBTMA) mechanism concedes the RTS-CTS scheme to establish communication between two nodes and medium access for applications with a high QoS requirement by assigning two narrow band busy-tones to notify the on-going transmission. In this paper, we obtained results relative to the interest of AODV based reactive routing protocol for MANETS and DBTMA mechanism. The performance is governed under real time sound traffic through simulation using NS-2. The performance of the protocol is measured in terms of various QoS metrics that include route discovery time, throughput, delay and hops per route which are calculated , and graphs ha ve been plotted. A simulation result shows that very substantial improvements in terms of AODV performance parameters and minimum delay are attained due to increased routing responsiveness.
An ad-hoc network is a collection of wireless hosts also named as Data-D-Hoc networks without an infrastructure. The ad-hoc network is a temporary network, which deploys the applications like battlefield communication, disaster recovery, etc. The network does not rely on an established infrastructure or on a central control. The ad- hoc networks that are autonomous or multi-hop wireless extension to the internet are called Mobile Ad-Hoc Networks (MANETS).
Routing is the process of selecting a path to the destination to send the data traffic. Routing Protocols are of two classifications: Proactive Routing protocol and Reactive Routing. In proactive routing, table-driven method is used in which each node of the network will update to the network. A periodic update is made in the routing table and the information is transmitted throughout the network to maintain its consistency. Hence, the delay in reaching the destination is reduced. However, the protocol needs more resources for the updating of information in the table. The proactive routing protocols are like DSDV (Destination Sequenced Distance Vector), Wireless Routing Protocol (WRP), and Global State Routing (GSR). In Reactive Routing Protocols, it is initiated only when there is a demand for route by a node having information to transmit. For this, a node in the network has to initialize the route discovery. The route discovered is maintained by route maintenance mechanism until the destination becomes un-accessible. The nodes that act as routers are meant for maintaining the routes for active destinations. The reactive routing can reduce the communication overhead and also reduces the delay; ex: Ad-Hoc On-Demand Vector, Dynamic Source Routing (DSR) [
The routing in Ad-Hoc networks needs to be dynamic and multi-hop. The adaptive routing method for Ad-Hoc networks is AODV. The channel access procedure of AODV is shown in
does not need global periodic routing advertisements. As the number of route discoveries is more, the routing load of AODV is large (in the 50 node case, as many from 6.5 routing packets per data packet, and 2 routing bytes per data byte). The delay characteristic of AODV protocol [
The following presumptions are made in an AODV Protocol [
Deciding the placement of static nodes.
RTS/CTS control packets disabled.
Fragmentation of frame size is disabled.
Two-ray way propagation path loss and signal model is considered.
Traffic/application types are configured for AC-VO is Audio, for AC-VI, V is MPEG4, for AC-BE is CBR, for AC-BK is FTP.
The MAC protocols are introduced for the nodes to access the channel with reduced collision [
The Carrier Sense Multiple Access with typical Collision Avoidance (CSMA/CA). Carrier sensing is performed through physical and also virtual mechanisms.DCF is the Distributed Co-ordination Function that makes the basis for CSMA/CD. The medium is sensed by the station to determine if some other station is beaming in the physical mechanism. Distributing the reservation information with RTS/CTS exchanges in MAC is called as virtual carrier sensing. If the channel is found busy, the station waits for a DIFS (DCF Inter-frame Spacing) duration [
Point Coordination Function (PCF) is a premium, polling-based access mechanism which involves the presence of an AP (Access Point) that acts as Point Coordinator (PC). In the PCF mode, time is divided into super-frames. Each super-frame consists of a contention period where DCF uses a contention-free period (CFP). This protocol does not provide service differentiation and prioritization.
DBTMA is the extension of BTMA [
-a Data channel for data transmission
-a Control channel―to transmit the control signals along with Busy tones
When a node is ready for transmission it senses the channel for busy tone active. If not, it turns ON the busy tone signal and starts transmission. Otherwise, the packet for transmission is rescheduled after some random delay. Any other node that senses the carrier signal on the incoming data channel also transmits the busy tone signal on the control channel [
All the nodes sensing the BTt signal will determine that they cannot receive data. All other nodes will defer from transmitting on sensing BTr signal. This mechanism creates the hidden terminals to back-off and exposed terminals to use the channel. The transmitter produces the transmits the busy tone BTt and is done to protect the RTS packets. Another busy tone BTr, is put up by the receiver, acknowledges the RTS packet and provides uninterrupted protection for the incoming data packets. The RTS packet, and the receive busy tone make the chance of successful RTS reception. The DBTMA protocol is the fundamental on the packet and twice narrow-bandwidth, out-of band busy tones are implemented with enough spectral separation on the unicast shared channel. BTt (the transmit busy tone) and BTr (the receive busy tone), shown whether the node is forwarding RTS packets or receiving packet transfer data, respectively. The transmits the busy tone (BTt) provides security for the RTS packets to increase the chance of successful RTS reception at the designated receiver. All nodes sensing any busy tone are not admitted to send RTS requests. When the start of the better signal is felt, a node forward and transfers the RTS packet is required to abort such transmission immediately (8).
Node A continuously monitors the busy signal when it is in the WF-BTR state. When a signal is felt, it recognizes that its channel request has been verified and reached. Before node A sends the data packet, it waits a mandatory waiting time (twm = 2T) in the WAIT state. This mandatory waiting time is intended to permit all possible RTS transmissions in the orbit of the recipient to be aborted. Upon timeout in the WAIT state, node A into the S-DATA (Send-DATA) state and transports the information package. At the end of the its transmission, node A goes into the IDLE state. Based on the successful reception of the data packet, node B turns off the BTr signal and passes into the IDLE state, ending the communication. If node B does not receive the data packet before the timer expires, if will off the BTr signal passes into the IDLE state.
Upon timeout in the CONTEND state, node A turns its busy signal and sends its RTS packet if no busy tone signal is felt. Differently, it moves backwards into the IDLE state. From the position of the other nodes in the region, their operations can be identified as follows:
When the BTt and/or the better signal is felt, a node is not permitted to send any RTS request. When the beginning of a better signal is sensed while a client is in the S-RTS state, it aborts its RTS transmission, turns off its better signal, and moves back to the IDLE state.
The following are the assumptions for DBTMA protocol:
The wireless transmission [
The packet is not clearly observed by the receiver, when there is any overlap of transmission at the receiver side. Packet errors are caused by packet collisions.
The data information processing time is obtained.
The data signal and the busy tone signal have the unique transmission range.
The noise between the busy tone signals and the data signal is negligible. The bandwidth consumption of the data signal is more when compared to busy tone signal that is negligible.
The transmission time of data, the transmission time of RTS packet, and the one way propagation delay has its maximum value as δ, γ and τ respectively.
The busy tone detection delay is connected, which depends on the communication hardware and might not, in general, be negligible.
The compulsory (mandatory) waiting time is set to twm = 2T.
The transmission time of the RTS packet is larger than td + 4T.
The large number of nodes in a network generates a poisson traffic in, which mean aggregate rate is calculated as λ channel requests per second.
The DBTMA communication rules are mentioned below:
Initialization is made by powering up, a node goes into the IDLE state. We accept that both the transmitter (A) And the Receiver (B) are in the IDLE coefficient and non idle state before the CONTEND state.
RTS control packet transmission: When source A has a data packet for transmission to the destination B, it tries to sense the busy tones, BTr and the BTt signals. The busy-tone signal BTt is raised when no busy tone is available and it sends an RTS packet to B, and gets into the S_RTS state. If source node A senses a busy tone signal, it triggers a random timer (chosen from [0, BI]) and moves into the CONTEND state.
Wait for BTr signal: When RTS transmission is completed, BTt signal is turned off by station A and it sets a timer to (td + 2T) second, and moves into the WF_BTR state.
Wait time for data packet: When destination B receives the RTS packet from source A, it raises its BTr signal and sets a timer to (δ + td + 2T) second, and moves into the WF_DATA state.
Compulsory wait time: When A senses a better signal in the WF_BTR state, it sets a timer to (tωm = 2T) second and extends into the WAIT state.
Data transmission to S_DATA: When there is timeout in the WAIT state, node A transmits the data packet to destination and passes into the S_DATA state.
End of data transmission: At the end of the DATA transmission from A to B, node A goes into the IDLE state.
Receive data packet at the destination: When the information packet is received or timeout happens in the WF_DATA state, B puts off the BTr signal and moves into the IDLE state.
CONTEND stage-Timeout: When there is timeout in the CONTEND state, node A tries to sense the BTr and the BTt signals again. If no busy tone signal is sensed at the medium, it works on its busy signal and sends an RTS packet to B, and exits into the S_RTS state. If node A senses a busy tone signal BTr it moves backwards into the IDLE state.
Timeout of back-off Timer: The timeout condition in the WF_BTR state, makes node A to move into the IDLE state.
When a node is ready with data and needs to determine the route to its destination, it sends a RREQ (Route ReQuest) message through flooding. Thus the route request is broadcast to their neighbors. The intermediate node will have the details on a reverse route to the originator. When the destination realizes that itself as the requested node, it gives the reply as RREP (Route Reply) message along the reverse path. The intermediate nodes through which RREP message travels will update the routing table with new route information.
Each node in a network maintains a route request buffer that contains a list of recently broadcasted route requests. The route request buffer consists of a pair of values in each entry as the address of the node originated the request, and the route request identification number (RREQ ID) [
Route discovery time τ ∞ Dsd
Number of nodes | Time (ms) | |
---|---|---|
AODV | DBTMA | |
165 | 0.92 | 0.85 |
345 | 0.81 | 0.77 |
525 | 0.77 | 0.68 |
705 | 0.63 | 0.55 |
885 | 0.52 | 0.45 |
1065 | 0.46 | 0.38 |
1245 | 0.38 | 0.29 |
1425 | 0.22 | 0.19 |
1605 | 0.18 | 0.08 |
1785 | 0 | 0 |
When a node requires a route to destination, the route discovery process is initiated within the network. Once a route or all the possible routes are discovered the route discovery process will be completed. Depending upon the number of hops per route, the shortest path will be selected and the route establishment is made. The information about route discovery is updated in the routing table of all intermediate nodes that helps in finding the number of hops per route. This hop-by-hop method of routing is based on the fact that different nodes of the network will have different views on the topology. Hop count is used to calculate the number of hops required by a node to reach the destination. This is explained using the
Node A can be reached using certain hops and the establishment of route is based on the hop count. The value on the link indicates the hop or cost values and this generates higher packet drops and collision rate probability.
The number of hops per route (for 50 Nodes) is shown in
Average end-end delay calculation is the sum or amount of time taken by a packet to go from source to destination and it is used to find delays caused during route discovery latency, queuing at the interface queue, vice-verse transmission time and delays are considered at the hybrid MAC layer, propagation delays and transfer times. Delay in AODV protocol is comparatively more and therefore the MAC protocol that is combined with AODV can improve its performance. The
The throughput of an AODV routing protocol can be calculated as the ratio between total number of data packets sent by the sender to the total number of data packets received at the receiver. The throughput of AODV and DBTMA can be compared using the
Destination | Next Hop | Cost |
---|---|---|
A | × | × |
B | B | 4 |
C | E | 2 |
D | E | 4 |
E | E | 1 |
No. of Hops per Route | Time (ms) | |
---|---|---|
AODV | DBTMA | |
180 | 1.58 | 1.56 |
378 | 1.52 | 1.51 |
576 | 1.51 | 1.5 |
774 | 1.5 | 1.49 |
972 | 1.5 | 1.47 |
1170 | 1.5 | 1.47 |
1368 | 1.5 | 1.47 |
1566 | 1.5 | 1.47 |
1784 | 1.5 | 1.47 |
Number of nodes | Delay (ms) | |
---|---|---|
AODV | DBTMA | |
50 | 1.0992 | 0.4992 |
75 | 0.1324 | 0.1946 |
100 | 0.3814 | 0.1626 |
125 | 0.2927 | 0.038 |
150 | 0.6762 | 0.0363 |
Number of nodes | Throughput (bps) | |
---|---|---|
AODV | DBTMA | |
50 | 64542.4 | 155850 |
75 | 81664 | 159200 |
100 | 81292.8 | 158750 |
125 | 80132.8 | 160200 |
150 | 78499.2 | 160200 |
PARAMETERS | AODV | DBTMA | |
---|---|---|---|
1 | DELAY | 4.6% | 1.78% |
2 | THROUGHPUT | 6.01% | 8.04% |
3 | PDR | 7.09% | 9.25% |
The results show that the impact of DBTMA on AODV has lower delay, an increase in throughput and efficiency in route discovery time, and number of hops per route. Thus, through implementation of On-Demand routing protocols like AODV along with the MAC protocol DBTMA can provide increase in its overall performance (shown in
Vanitha, S.V. and Mohankumar, G. (2016) Impact of DBTMA (Dual Busy-Tone Multiple Access) on AODV (Ad-Hoc on Demand Vector) Routing Protocol. Circuits and Systems, 7, 3604-3616. http://dx.doi.org/10.4236/cs.2016.711305