 Hello everyone, myself, SM Mettigar, I am working as a student professor in computer science and engineering department at Walton Institute of Technology. And I welcome you all to the session on Mac layer protocol. Let us see the learning outcomes of Mac layer protocol. At the end of the session, the students will be able to identify different types of protocols and applications of each protocol. The first one is the students will be able to identify different types of protocols and implementation of each protocol using client server concept. This is agenda. The agenda contains carrier sense multiple access protocol, carrier sense multiple access protocol with collision detection and limited contents in protocol. Now let us see one by one in detail. First one is carrier sense multiple access. The carrier sense before transmitting the data to the next station, the current station how to send to the next station, whether the next station is free or busy. If it is free, then only the current station can able to transfer the data to the next station. Next station is free, then you have to wait. There are several versions of carrier sense multiple access protocols are there. First one is one persistent CSMA, second one is non persistent CSMA, third one is P persistent CSMA. First one is one persistent CSMA. One persistent CSMA can be used for sensing to the next station first time. A station prior to send data, it listen to the channel to see if anyone else is transmitting at that moment. If the channel is busy, the station waits until it becomes ideal. If the channel is ideal, the station transmit a frame. If a collision can occurs, the station waits a random amount of time and start all over once again. It means with current station how to sense to the next station, then check out the next station status. If it is free, then you can transfer. If it is busy, then it can waits until the random amount of time until the next station gets ideal. Although this protocol has disadvantages, it is better than aloha and slotted aloha. In the previous video, we have discussed about aloha and slotted aloha. In aloha, we have to use aloha concept simultaneously more than two stations want to transfer the data. Then after transmitting, the collision may occurs. Then again the user should have to resend the data in aloha protocol. Slotted aloha. In the slotted aloha, the user how to prepare slots for transmitting the data. If the current station is busy or in use, then according to slots only, the current user can forward the data to the next user. This performance depends on the propagation delay. There is a chance when two stations starts transmission at the same time, then the collision may occurs. Second one is non-persistent CSMA. In non-persistent CSMA, the user won't sense to the next user directly he can forward. That is station makes conscious attempts to sense the channel. After the first attempt, if the channel is ideal, then only it sends however, if the channel is already in use, it waits a random period of time and repeats the algorithm. This algorithm has better utilization but longer delays than one persistent CSMA. Third one is P-persistent CSMA. The P-persistent CSMA is in probability persistent CSMA. We have to find out the probability of collision in transmission process. A station transmits, if the channel is ideal with a probability P and with a probability Q equals to 1 minus P, it waits until the next slots. Q equals to 1 minus P. P is in probability if the collision is 1, then we have to apply that formula that is Q equals to 1 minus P. That is 1 is 1 minus P is 0, then there is no collision. The main advantage of persistent and non-persistent over ALOHA is that they ensure no station begins to transfer when it sends the channel busy. Now next point is think I write that is a reflection spot. The reflection spot can contains one question. Students can think over that question and write the answer for that question. That question is list the difference between persistent and non-persistent CSMA. Now pause the video and answer the questions. Now let us see the answer for this question. Non-persistent and persistent. In a non-persistent, HTTP 1.0 version can be used. In persistent, HTTP 1.1 version by default we have to use in persistent. In non-persistent, server parses request and responds and closes a TCP connection. In a persistent, on same TCP connection server parses request, responds, parses new request. Third difference is non-persistent, two RTTs to fetch each object, RTTs in real-time transmission. In persistent, client sends a request for all the referenced object as soon as it resued base as TML. Each object transfers, suffer from slow start, in a persistent favor RTTs and less slow start. These are difference between persistent and non-persistent. Now CSMA with collision detection. If two stations are sending the data simultaneously, they will get collision immediately. If without sensing, if two stations are simultaneously transmitting the data to the next station without sensing to the next station, then after passing the data from current station to the next station, the collision may detect, then after collision the data should have two discards are avoided. Then again the user should have to resend the data. It is important that stations should terminate a transmission as soon as they detect the collision. This protocol is called as a CSMA that is carrier sense multiple axis collision detection. In this part, the mainly we have to find the collision. Two stations are simultaneously, two are more than two stations are simultaneously sending the data. Obviously, if they are not sensed to the next station, the collision is occurred. That collision can be a collided data we have to remove and then once again the current user have to send the data. It is mostly or widely used in a local area network of the MAC sublayer. It is a basis of popular Ethernet LAN. This is the block diagram of CSMA with collision detection, how and where exactly the collision can detects. In the transmission period, the number of frames or data the user want to transmit, then they can transmit in the transmission grid frames to the contention period. In the contention period all the frames will be stored. Then after stored frame in the content that which 1 by 1 frames will be, go to the contention slot. Then after passing the data from contention period to the contention slot all the data our frames will be stored in contention slot, the stored data from contention slot will go to the next user . 1 by 1, if the station is ideal, if the next station is ideal on BG. If it is busy the contents and slots data will not pass to the next station. If the station is ideal or free then the contents and slots frames will be go to the ideal station. That data will be used for finding the collision can occurred or not occurred. If the collision is occurred then again we have to restart the process that is frame transmission period to the contents and slots, contents and slots to the contents and slots then contents and slots to the ideal period. This is a CSMA CD can be in one of the three states, contents and periods are ideal. Then CSMA with collision detection. A collision can be detected by looking at the power or pulse width of the ratio signal and comparing it with the transmitted signal. Here before transmitting the user can make the pure aloha in pure aloha the user won't sense and directly they can forward the data in pure aloha there are so many times the collision may occurs. Then only the user how to send the data through slotted aloha in the slotted aloha the collision may not occurs because before transmitting they have to make the slots in that particular slots only they have to send the data for that they can avoid the data for collision detection that collision avoidance if they avoided the collision then they can easily pass the data to the next users. The collision can be avoided for finding this one we have to use one persistent non persistent and P persistent one persistent first time persistent non persistent without persistent P persistent is a probability persistent. After a station detects a collision it terminates its transmission waits a random period of time and then tries again assuming that no other station has started transmitting in the mean time it means more than two stations won't send the data to the next user if they are not transferred then only it is possible to find out the collision. These are the references however used for preparing the above PPD. Thank you.