 Hello everyone and welcome to the session on MAC protocol. Myself, Mr. Mettigarh SM, I am working as assistant professor in computer science and engineering department at Walton Institute of Technology, SolarPore. Now let us see the learning outcomes of MAC protocol. At the end of session, the students will be able to identify different types of protocols and applications of each protocol. The students will be able to identify different types of protocols and implementation of each protocol by using client server concept. The agenda of this MAC protocol, about MAC protocol, channel allocation problem, the channel allocation problem can contain two different parts that are static channel allocation in local area network and metropolitan area network. Third main point is multiple access protocol. The MAC is a sub layer of data link layer and it is a one of the sub layer or one of the part of vice reference model. The MAC is responsible for transmission of data packets to and from the network interface card and to and from the other remotely shared network. The main basic function of MAC is to provide the address mechanism and channel access so that each node available on the network can communicate with each other and nodes available on the same network are different network. Next one, channel allocation problem. In the channel allocation problem, the users would have to allocate the different channels before going to transmit the data from one station to another station. Based on that only they have given two types of channel allocation problem, static channel allocation in LANs and MANs. In the static channel allocation, previously this concept they are using in telephone trunk for transmitting the data from one station to another station. If there are n number of users or that means the bandwidth is equally divided and distributed to n number of stations. By using that divided bandwidth, each user can transfer the data from one station to another station. The good example for this one is FDM, FDM is Frequency Division Multiplexing. It can be used for allocating the where the bandwidth is equally divided among different number of users. When the number of senders are large, then the user may face a traffic problem. It means here we have allotted only 10 number of users for transmitting the data. It means if the user want to transmit a 20 number of users, it means then that time the user may face a problem of traffic. Then that time the user should have to store the data in a buffer. The buffer can be used for temporary storing the data. When there is only a small and constant number of users, each of which has a heavy load for traffic, FDM is a simple and efficient allocation mechanism used to transmitting the data. Second one is dynamic channel allocation in LANs and MANs. In a dynamic channel allocation, here we won't fix any fixed number of users to each and every channels. Based on that only they have given different key assumptions. That first one is station model. Station model, the station model may be a computers or any communicating devices. Here there are we have to check out the station model and then how we have to transfer the data from one device to another device. Second one is single channel assumption. Here the only one single channel can be used for communicating. All the stations can be used single channel for transmitting the data from one station to another station. Collision assumption, if they are used more than two stations are simultaneously transmitting the data from one station to another station, it means the collision may occurs. To avoid that collision we have to go to the next point that is time. In this we have to use two types of times continuous time and shorted time. In the continuous time we won't use any digital clocks for transmitting the data. If the user have the data then suddenly they can transmit the data in a slotted time. They have to make the slots for transmitting the frames from one station to another station. Where the time is divided into discrete slots. Based on that only they have given two types. First one is a carrier sense, second one is no carrier sense. Before transmitting the data from one station to another station the station how to sense to the next station. If the next station is busy the current station how to wait. If it is free then he can to transfer the data. If it is not sensed then the data or frames may be collapsed or collision may occurs. No carrier sense. Here without sensing to the next station the current station can directly send the frames. The frames may collide. How to avoid that collision? It is there in next topic. This is the topic for think and write. The think and write phase can contains one question that is the least the difference between static and dynamic channel allocation. Now pass the video and think about the question and then answer the question. Answer for think and write is static channel allocation and dynamic channel allocation. First point in static channel allocation is it can form static and then compile time. It can be dynamic channel allocation performed at run time or dynamic time. It can be assigned to stack, it can be assigned to heap. The static channel allocation must be known at compile time. Dynamic channel allocation must be may be unknown at compile time. Static channel allocation first in last out. Dynamic channel allocation no particular order for assignment. The static channel allocation it is best if required size of memory known in advance. The dynamic channel allocation it is best if we do not have idea about how much memory requires. These are the difference between the above question. Now can go to the next topic that is Aloha. In the 1990 the name of this scientist Abraham and his colleagues they have find the new and elizant method that new and elizant method we can call it as Aloha. It can be used for solving the channel allocation problem. There are two versions of Aloha are there, pure Aloha and slotted Aloha. The basic difference with respect to timing is in pure Aloha does not requires global time synchronization in a slotted Aloha we want global time synchronization. The system is working as follows if the user how to transmit the data then they can transmit whenever they want to transmit the data then after transmitting the user should how to wait whether the data can go or it can the collision can occurs. If the collision can occurs obviously the data can be collided or it can be destroyed using feedback mechanism to know about the status of frame retransmit the destroyed frames. This is about the pure Aloha. In the pure Aloha there are three stations are transmitting the frames, station one, station two and station three. In the green color can identify the collision part, the ending end of the first frame and then starting end of the second frame can be collided. In the third phase then ending end of the second part and then starting end of the third part can be collided. Here in a pure Aloha there are four stations are there all four stations are simultaneously transmitting the frames, the frames can be collided. Station one the transmitting two frames first frame it is not collided, second frame can be collided with the station of the first second station first frame and then you have to allow the slots also. Then in that particular slots the station may collides pure Aloha the main advantage of pure Aloha is low channel utilization. This is expected due to features that all are transmit whenever they want. The throughput of Aloha system is maximized by having a uniform frame size rather than by allowing variable ends. Slotted Aloha before transmitting the data the user can slots the timing. In that particular slots only they can transmit the data here the pure they can avoid the collision. There is a limit for best channel utilization using slotted Aloha to reduce the chance of collision the station should be able to detect what other stations are doing. In LAN network this is possible therefore they can achieve better utilization than slotted Aloha. Then carrier sense protocol can be used for different purpose these are the references I use to prepare the PPT. Thank you.