1 00:00:00,680 --> 00:00:05,380 I think all of us have experienced congestion management in our lives. 2 00:00:05,390 --> 00:00:07,740 You get to the airport and you want to check in. 3 00:00:07,760 --> 00:00:13,070 There's a queue or a line so you have to wait before your bags can be processed. 4 00:00:13,100 --> 00:00:19,670 You get two security at the airport and you have to wait in a queue or a line you're driving on the 5 00:00:19,670 --> 00:00:23,720 highway or motorway and lanes have been closed. 6 00:00:23,720 --> 00:00:30,230 It results in congestion which results in a queuing mechanism being used to filter the traffic. 7 00:00:30,230 --> 00:00:38,330 So queuing mechanisms manage congestion different queuing mechanisms can be used in the US as an example. 8 00:00:38,330 --> 00:00:43,070 You have TSA pre check so that helps you get through security quicker. 9 00:00:43,070 --> 00:00:48,650 If you've got a first class airplane ticket you're going to be processed quicker or better at check 10 00:00:48,650 --> 00:00:51,930 in than if you've got an economy class ticket. 11 00:00:51,980 --> 00:00:58,070 An ambulance will take priority on a motorway or a highway when there's congestion versus a standard 12 00:00:58,070 --> 00:00:58,940 car. 13 00:00:59,120 --> 00:01:06,170 So different queuing mechanisms can be used to determine how traffic is processed with round robin queuing 14 00:01:06,170 --> 00:01:06,820 mechanisms. 15 00:01:06,830 --> 00:01:09,050 All traffic is treated the same way. 16 00:01:09,050 --> 00:01:15,910 That means that everyone is treated the same way that results in delay for real time traffic. 17 00:01:15,920 --> 00:01:21,980 You could also implement a strict queuing mechanism where high priority traffic is always processed 18 00:01:21,980 --> 00:01:23,120 first. 19 00:01:23,120 --> 00:01:28,790 The advantage of that is voice packets will be transmitted first but if there is a lot of voice traffic 20 00:01:28,910 --> 00:01:35,180 or high priority traffic it could result in starvation of less important traffic. 21 00:01:35,210 --> 00:01:40,760 If you're constantly sending a lot of voice and video your FTE traffic may never be transmitted because 22 00:01:40,760 --> 00:01:46,670 you are always transmitting video and voice first in a strict priority queuing mechanism. 23 00:01:46,670 --> 00:01:52,670 So with congestion management we have queuing or buffering which determines the ordering of packets 24 00:01:52,670 --> 00:01:54,420 in the output buffers. 25 00:01:54,470 --> 00:02:01,100 In other words it determines how traffic leaves a road interface or leaves a switch interface. 26 00:02:01,100 --> 00:02:06,950 You do have ingress queues but for now we'll just concentrate on egress queuing mechanisms queuing is 27 00:02:06,950 --> 00:02:09,350 only required when there's congestion. 28 00:02:09,350 --> 00:02:14,840 If you're driving on the highway or motorway late at night and there are six lanes and there are only 29 00:02:14,840 --> 00:02:21,660 a few cars there's no need to have a queuing mechanism so queuing is used when there's congestion. 30 00:02:21,710 --> 00:02:28,490 Hence the term congestion management when queues fill up packets are reordered so that high priority 31 00:02:28,490 --> 00:02:34,130 packets are sent out of a rather interface first rather than lower priority packets. 32 00:02:34,130 --> 00:02:36,350 So again when this congestion. 33 00:02:36,350 --> 00:02:42,110 You may have high priority packets and low priority packets arriving a queuing mechanism is used to 34 00:02:42,110 --> 00:02:47,060 determine which packets should be processed first and then they are scheduled for transmission out of 35 00:02:47,060 --> 00:02:48,470 the interface of a rider. 36 00:02:48,650 --> 00:02:55,190 So when packets arrive they're put into classes and will be processed on how important they are or based 37 00:02:55,190 --> 00:02:57,700 on the queuing algorithm used. 38 00:02:57,920 --> 00:03:02,120 More important packets will be transmitted first before less important traffic. 39 00:03:02,120 --> 00:03:08,360 As an example so they will be scheduled for sending out of the interface of the router before less important 40 00:03:08,360 --> 00:03:16,400 packets so queuing is the logic of ordering packets and output buffers scheduling is a process of deciding 41 00:03:16,400 --> 00:03:18,790 which package should be sent out next. 42 00:03:18,800 --> 00:03:25,130 Scheduling occurs regardless of whether there is congestion on the link queuing is only activated when 43 00:03:25,130 --> 00:03:32,210 congestion occurs when queues fill up packets are reordered so that higher priority packets can be sent 44 00:03:32,210 --> 00:03:34,910 out before lower priority packets.