1 00:00:01,190 --> 00:00:08,180 So in a situation like this the phone has to indicate to the switch that its traffic is important so 2 00:00:08,180 --> 00:00:19,370 it needs a mechanism or a way to tell switch one that its traffic is more important than the P.C. traffic. 3 00:00:19,370 --> 00:00:21,490 Now there are two main ways to do this. 4 00:00:21,500 --> 00:00:25,800 We either mock at Layer 2 or mock at least three. 5 00:00:25,860 --> 00:00:31,160 So in the same way that FedEx or DHL will mock a parcel. 6 00:00:31,190 --> 00:00:37,790 In other words they put a sticker or a barcode on the puzzle to indicate that the parcel is of great 7 00:00:37,790 --> 00:00:41,300 importance and should be delivered the next day. 8 00:00:41,300 --> 00:00:48,410 The phone will mark the packets that it sends to the switch either at least to what Layer 3 to indicate 9 00:00:48,590 --> 00:00:51,560 that the packets are important. 10 00:00:51,560 --> 00:00:59,390 Assuming that switch one accepts those markings it will send the packets to switch to with the relevant 11 00:00:59,390 --> 00:01:06,950 markings markings are important in packets because when they arrive at a switch such as Switch two it 12 00:01:06,950 --> 00:01:13,460 needs to make a decision which class does the packet belong to. 13 00:01:13,460 --> 00:01:18,410 In other words is it platinum is it gold is it silver is it bronze. 14 00:01:18,650 --> 00:01:26,720 Or to use a airline analogy is it first class or business class or economy class. 15 00:01:27,020 --> 00:01:30,230 Packets within a class will be treated the same way. 16 00:01:30,230 --> 00:01:34,230 So the switch needs to determine which class the packets go into. 17 00:01:34,250 --> 00:01:37,570 So again platinum gold silver and so forth. 18 00:01:37,820 --> 00:01:43,900 And then it will treat those packets accordingly. 19 00:01:43,930 --> 00:01:51,360 So how does a phone or a switch indicate to another switch or rather the level of importance of packets. 20 00:01:51,600 --> 00:01:53,890 Not to use the airline analogy again. 21 00:01:53,920 --> 00:01:57,370 This is very similar to a ticket that you get. 22 00:01:57,430 --> 00:02:04,040 So does your ticket indicate that you're a first class passenger or business class or economy class. 23 00:02:04,060 --> 00:02:06,920 Think of the markings as a ticket. 24 00:02:07,000 --> 00:02:12,790 The ticket is an indicator of the service that you'll receive. 25 00:02:12,790 --> 00:02:22,030 So when the phone sends a voice packets to the switch it's going to mock them at least to using an attitude 26 00:02:22,030 --> 00:02:23,940 of one queue marking. 27 00:02:24,070 --> 00:02:29,890 I'll show you the details of the markings when I do a y shock capture in a moment but for now understand 28 00:02:29,890 --> 00:02:31,570 that when you speak into a phone. 29 00:02:31,570 --> 00:02:38,050 So let's assume these are your voice waves a phone transfer codes that into a digital signal of zeros 30 00:02:38,050 --> 00:02:45,520 and ones that are put into UDP packets that are encapsulated in IP which are in turn encapsulated in 31 00:02:45,580 --> 00:02:49,040 Ethernet and are sent to the switch. 32 00:02:49,270 --> 00:02:52,550 So layer two we have an attitude of one queue head. 33 00:02:52,960 --> 00:02:58,350 The reason why is that Ethernet doesn't have these additional markings. 34 00:02:58,360 --> 00:03:04,750 As an example if using ethernet too it has no way to indicate the importance of a packet. 35 00:03:05,350 --> 00:03:10,870 So when we capture the frame you'll see in a moment that we have a destination address. 36 00:03:11,050 --> 00:03:19,230 We'll have a source address and then we'll have an edited one Q header and then the actual voice within 37 00:03:19,230 --> 00:03:20,550 the packet. 38 00:03:20,550 --> 00:03:28,050 So the editor the one Q header has a priority field to this is three bits in size also called costs 39 00:03:28,140 --> 00:03:30,900 or class of service or S.O.S. 40 00:03:30,900 --> 00:03:32,390 It's three bits in size. 41 00:03:32,640 --> 00:03:38,310 So the binary values go from 0 0 0 all the way to triple 1.