1 00:00:00,750 --> 00:00:01,860 OK, great. 2 00:00:03,040 --> 00:00:09,240 In the last lecture, we have seen the introduction to Grierson's multiple axes with collision detection, 3 00:00:09,240 --> 00:00:15,880 which is mostly used in the wild at network, and Clemencia is used for wireless networks. 4 00:00:16,980 --> 00:00:19,950 Now, how the system really works? 5 00:00:20,400 --> 00:00:28,500 Well, the convention method is used in Ethernet and the mechanism it helps to minimize, but it does 6 00:00:28,500 --> 00:00:30,020 not eliminate collisions. 7 00:00:30,030 --> 00:00:36,660 I have already said in the previous lecture that the first step is when a device needs to transmit. 8 00:00:36,990 --> 00:00:38,120 It checks the wire. 9 00:00:38,700 --> 00:00:42,750 If the transmission is already under the way, the device can tell. 10 00:00:43,260 --> 00:00:45,210 This is called a carrier sense. 11 00:00:45,720 --> 00:00:47,760 Now, why did I use the word wire? 12 00:00:48,240 --> 00:00:55,380 Because in this lecture, in this convention method, the medium is actually the wire, whereas in the 13 00:00:55,380 --> 00:00:58,780 case messier method, the medium was wireless medium. 14 00:00:59,820 --> 00:01:07,320 Second step, if the wire is clear, the device will transmit even as it is transmitting as it performs 15 00:01:07,320 --> 00:01:08,420 carrier sense. 16 00:01:08,640 --> 00:01:10,880 OK, so we have finished this step. 17 00:01:10,890 --> 00:01:12,330 We have finished this step. 18 00:01:12,930 --> 00:01:13,610 Third step. 19 00:01:14,070 --> 00:01:19,740 If another host is sending simultaneous need, there will be a collision, right? 20 00:01:20,160 --> 00:01:25,680 The collision is detected by both devices through carrier sense. 21 00:01:27,090 --> 00:01:31,140 Now both devices will issue a jam signal. 22 00:01:31,290 --> 00:01:39,150 Both the devices will issue a jammed signal to all the devices, which indicates them to not transmit 23 00:01:39,150 --> 00:01:39,930 any frames. 24 00:01:41,070 --> 00:01:45,180 Then both of the devices will increment retransmission counter. 25 00:01:46,410 --> 00:01:53,640 Now, this is a cumulative total of the number of times this frame has been transmitted and the collision 26 00:01:53,640 --> 00:01:54,330 has occurred. 27 00:01:55,230 --> 00:02:01,490 So the counter has a maximum number at which the device aborts the transmission of the frame. 28 00:02:02,370 --> 00:02:09,600 And finally, both the device calculate a random amount of time and will wait for that amount of time 29 00:02:09,600 --> 00:02:11,070 before transmitting again. 30 00:02:12,240 --> 00:02:18,510 Now, in both in most of the cases, because both the devices choose random amounts of time to it, 31 00:02:18,780 --> 00:02:23,700 another collision will most probably not occur because the time is not the same. 32 00:02:24,600 --> 00:02:27,750 The time is not the same for both the devices as it can vary. 33 00:02:28,020 --> 00:02:32,250 And that is why this message works perfectly in the Wired network. 34 00:02:33,510 --> 00:02:35,580 This was all for the content and methods. 35 00:02:35,580 --> 00:02:39,210 We have seen two contention methods to summarise. 36 00:02:39,210 --> 00:02:48,060 The two methods are seen as messy and systemically see media works perfectly for wireless networks and 37 00:02:48,060 --> 00:02:52,510 CDMA city works best for the Wired network that is the Internet. 38 00:02:53,160 --> 00:02:58,580 The CEO stands for collision avoidance and the steady stands for collision detection. 39 00:02:59,580 --> 00:03:01,650 That's it, folks, for this lecture. 40 00:03:01,950 --> 00:03:08,220 In the next lecture, we will have introduction to one of the most important servers in the computer 41 00:03:08,220 --> 00:03:15,020 network history, and that is the DHC piece, or that is the dynamic host configuration protocol. 42 00:03:15,390 --> 00:03:17,280 I will see you in the next lecture.