Mac Protocol

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This document is going to analyze the delays in the IEEE 802.11 MAC PROTOCOL. This analysis is prepared by observing the simulation results using the ns2 simulator. Here we are going to simulate in a WI-FI MODE and going analyze the total packet delay in different mechanisms by assigning different values depending upon the platform we have taken. The analysis identify when the packet delay with respect to the architecture is going to vary in the IEEE 802.11 wireless LANs.


WIRELESS LANS these are growing at a lightning speed in the field of communications and networks and they had achieved a lot from a decade. There are many researches going on these fields. In this layer the entire network was divided into character cell and these cells are named as BSS (basic service set). These are controlled by Access point. These can also be monitored without the Access points. Here all the Access points forms a backbone which is link among these and this backbone forms the network. This is called as the wireless LAN and sometimes called as Ethernet also. The connections of all the Access points with the each individual cell are named as Extended Service Set (ESS). Establishing the connections between the different LANs is done by a tool named as portal. If the Access point wants to access the each individual cell first the Access point needs to get a Active or Passive information from the cell depending on that information synchronization will be done. Here we are going to deal about the mobile network in the wifi mode where the mobile nodes are moving In the specified region where the nodes keep on changing there position at a particular time and packets are transferred from one node to other node through the network.

II. Related works

1.Calculating the delay limits in wireless lans: In this document calculating the of the delay lower limits and throughput upper limits are produced by varying the different values like data rate, control rates, propagation delay, payload size in bytes acknowledgement transfer time, size of acknowledgement packets, MAC header size, time slot for an individual packet. And functionality of the CSMA/CA protocol is explained where CSMA/CA is the protocol which is used to avoid the collision of the packets in the MAC layer it is called as the DCF (Distributed coordination function). The DCF gives the information about the RTS/CTS mechanism. Here the throughput delay and the packet delay are increasing irrespective if the overhead generated by the network


In this an individual analytical model was developed to calculate the packet delay, loss of packets, time and which the packets are dropped ion the wireless LANs. Here the RTS/CTS ( request to send/clear to send) mechanisms are used. Here comparison of the retry limits for the packets are done where the defined model uses the retries to send the lost packets with a limit, by doing this the delay of the packets is reduced for a packet transmission using this retry process. The packet delay depend upon the number stations making an attempt to resend the packet in the network.


in this document a mechanism is introduced to prove that the RTS/CTS mechanism does not effect on the packet delay in the small network. In the large networks this mechanism is working effectively to reduce the delay if only the packet size is large. Various calculations are done on this the mechanism used here the Markov chain and the simulations are done by taking the large packet size in the small networks and large networks and vice versa and the collision occurring among the packets is assumed as minimum in the network.


Now we are going to create a simulation model for our requirements for analyzing the packet delay. The simulator used here is ns2 and the IEEE802.11 is used here to demonstrate the requirements. The MAC type used here is Mac/802.11, and we are developing this mobile network where we are going to consider the mobile nodes which are moving in mobile network and the packets transfer is done among these nodes. The channel type used here is wireless channel. We are considering a two ray ground radio propagation model since there should be exchange of the data packets among the nodes we are considering the Omni antenna type for the transfer of the signal WIRELESS PHYSICAL TYPE is considered as a network type

We are considering mobile nodes and these nodes are allowed to move within the boundary. Let us imagine the boundary for this example is 1550*1500m. We have designed such that they move together and again they move aside while they are communicating among them. We have specified the network components above like Link layer, interface queue (ifq), mobile access control (MAC) layer.

These wireless nodes will receive the data and transit the data to the nodes which are connected to them. The simulator which we are taken is an Object Oriented simulator. The interpreter used by it is Otcl ns2 uses the Otcl interpreter as a frontend simulator. Mobile network layer contains four different types of the ad-hoc routing protocols. They are DSDV(destination sequence distance vector), DSR(dynamic source routing), AODV(ad-hoc on demand distance vector routing), and TORA

The protocol we are going to utilize her is the DSDV protocol. This protocol uses the 255 port number and the port address is dmux. Every packet that was sent by the mobile node is having the dmux address only. The responsibility of the dmux is to carry the packets to the destination. When packet does not know the route to its destination then it will be cached and at the same time the information is sent to all the routing agents about the cached packet.

When the receiver node finds that it didn't receive any packet it will send an acknowledgement on to the route and after receiving this the packet which is cached is sent ot its destination. This is what the DSDV protocol does.

DSR (dynamic source routing) this protocol is different from the dsdv protocol. In this protocol it verifies the each packet individually and then it sends out on to the route and if the packet is not containing the destination address then it will provide the destination address of the node which is available with it. If it is not having the destination address then it will stop the packet and then send a query on to the network about the unaddressed packet.

Then the destination node will identify about the lost packet and retrieves it form the network. The acknowledgements that are sent by the router will be replied either by the target node or by the middle nodes. DSDV AND DSR are using the same port number it is 255 and it was assingned NULL agent.

Link layer by using this layer we can analyze the data link protocol, and many protocols like packet fragmentation reliable link are analysed using this onlythe address for the MAC HEADER set by this only this is one of its important application. Here we are specifying the path for the simple nodes and we are giving the packet size(ifq) for these.

Now we get .tr file after the simulation which will give the values in it they contains the sent, received, lost cached packets with the size in it .which are given a view about the network we are going to run the simulation for about 1550 sec

While in specifications we are going to mention about the node configuration interface where we are going to specify about the agent trace, router trace, and MAC TRACE movement trace. These are the node specifications available we have to take the specifications of these models here these will give the information regarding the network. If we want to trace the mac address we have on it and here we are using only router trace and mac trace and remaining are disabled.

The delay of packet can calculated as follows time taken by packet to reach the destination divided by sum of the link speed and delay in link. Here the delay is calculated in the seconds.

Here in the ns2 there are different agent objects are available. Like null objects, loss monitor objects, t6cp objects, tcp/reno object/ tcp/newreno objects and many others while of them we are going to consider only the null objects for our simulation.

Here after running the simulation for about 1500 sec the values are obtained

Now we are going to change the values for the total number of the nodes and then we are to assign the values to them like we are going to change the number of mobile nodes in the network and then we are going tokeep the packet size same for them 1000 ifq and the wwe are going to calculate the value and then we are keeping them in graph.



The above are the specifications that are used in the simulation we are going to conduct.

Here we are differing the values from 3 to 65 nodes and we have calculated the total packet delay for this the size of the packet is same it means keeping the packet size same we are changing the mobile nodes in the network.

By the graph we can understand that if the packet size is same then if the number of nodes are increasing the network then the delay of the packets will also we decreased but it completely depends upon the packet size now we are going to change the length of the packet and see at which rate the packet are transferred

Here we taking the constant 65 mobile nodes in the network and then we keep on varying the size of the packets and we are observing how many packets are being transferred in the network at a constant rate. Here we are not calculating the delays but here are going to check how the load will be maintained inth network if we are giving different packet sizes

From the graph we came to now that if are changing the packet size that is on x axis then how the packet number wiil be varying that is on y axis here on the x - axis is the length of the packet . we came to know that for a constant nodes if the packet length is varyingthen the number of packets sent per second will variy in an increasing manner which reults in the reducing the traffic in the network

THE AVERAGE packets sent in the network are 3146.8 these are the average number of the packets that are sent on the network to maintain the load.


Here from the entire document we have done simulation to obtain the packet delay and the packet number. From the graphs and simulation works that are we can understand that if the nodes in the network are changing frequently and if the packet lengths are also same then the delay will be varied depending upon the network. That is the delay will be constantly increasing, but it depends upon the packet length or size and the flow of traffic is also observed here and it is such that if the length of the packet is varying then the number of packets that are exchanged at a particular time is increased .