I am doing master in TUM for communication engineering, this was way more clear then the lecture thanks :D i looked over the slides again and again but couldnt relate how 1 persistent differs from non-persistant except the behavior after collision.
1-persistent - while(!idle) { //keeps on sensing } //sends its data Non-persistent - while(!idle) { //senses time = random() wait(time) } //Sends its data
You said that, In O- persistent CSMA( sub part of Random access protocol), supervisory node decides the order of transmission. Whereas in Random access protocol u said there is no superior node, every node is equal. Can you please explain how this is possible?
You didn't explain p-persistent properly, especially the concept of probability.the probability is calculated randomly and has no relationship with time slots.
Correct me if I am wrong: I think P-Persistant means, after checking that the channel is free it checks if the current time slot allocated to the receiver station it wants to send a frame to. Then it only sends the frame with a certain probability. This is necessary because, if another sender has queued messages for this receiver and both senders would send their frames with a probability of 1 it would always lead to collisions. With a probability < 1 there is a chance to work off the transmission queues slowly.
Thankyou dear for the great work, I had a doubt, CSMA/CD is used by Ethernet. Ethernet is end to end, like between two nodes. It has different channel for transmission and receiption, I hope. Then how could a collision occur. Can't understand, correct me if I am wrong. Tell me what I am missing.
@@mohansurendar7429 different applications connecting same point is a bigger picture, my doubt is about node-to-node connection, where single Ethernet cable is connected.
A specified time might be assigned to multiple nodes, and another node might use the channel in that time slot so it is a good idea to sense the carrier before transmitting the data.
Sir please complete the full syllabus of computer networks ( network layer design issues) and other transport layer , session layer , presentation layer , application layer 🎉)
In p persistent csma it should be checking for two things. One is is it in the beginning of the time slot, and also check whether the channel is free. It is checking continuously right? Why can’t you send it the second time slot instead of sending at the beginning of the fourth time slot, I’m asking with respect to the picture 11:51
The first carrier sense protocol that we will study here is called 1-persistent CSMA (Carrier Sense Multiple Access). When a station has data to send, it first listens to the channel to see if anyone else is transmitting at that moment. If the channel is busy, the station waits until it becomes idle. When the station detects an idle channel, it transmits a frame. If a collision occurs, the station waits a random amount of time and starts all over again. The protocol is called 1-persistent because the station transmits with a probability of 1 when it finds the channel idle. A second carrier sense protocol is nonpersistent CSMA. In this protocol, a conscious attempt is made to be less greedy than in the previous one. Before sending, a station senses the channel. If no one else is sending, the station begins doing so itself. However, if the channel is already in use, the station does not continually sense it for the purpose of seizing it immediately upon detecting the end of the previous transmission. Instead, it waits a random period of time and then repeats the algorithm. Consequently, this algorithm leads to better channel utilization but longer delays than 1-persistent CSMA. The last protocol is p-persistent CSMA. It applies to slotted channels and works as follows. When a station becomes ready to send, it senses the channel. If it is idle, it transmits with a probability p. With a probability q = 1 - p, it defers until the next slot. If that slot is also idle, it either transmits or defers again, with probabilities p and q. This process is repeated until either the frame has been transmitted or another station has begun transmitting. In the latter case, the unlucky station acts as if there had been a collision (i.e., it waits a random time and starts again). If the station initially senses the channel busy, it waits until the next slot and applies the above algorithm.
