1 00:00:00,990 --> 00:00:07,560 So in a situation like this, the phone has to indicate to the switch that its traffic is important. 2 00:00:07,860 --> 00:00:18,720 So it needs a mechanism or a way to tell switch one that its traffic is more important than the PC traffic. 3 00:00:19,170 --> 00:00:21,430 Now, there are two main ways to do this. 4 00:00:21,450 --> 00:00:25,350 We either mark at layer two or mark at layer three. 5 00:00:25,680 --> 00:00:33,420 So in the same way that FedEx or DHL will mark a parcel, in other words, they put a sticker or a barcode 6 00:00:33,420 --> 00:00:39,810 on the parcel to indicate that the parcel is of great importance and should be delivered. 7 00:00:39,810 --> 00:00:46,890 The next day, the phone will mark the packets that it sends to the switch, either at layer two or 8 00:00:46,890 --> 00:00:50,820 at layer three, to indicate that the packets are important. 9 00:00:51,510 --> 00:00:54,540 Assuming that switch one accepts those markings. 10 00:00:55,560 --> 00:01:00,300 It will send the packets to switch to with the relevant markings. 11 00:01:00,480 --> 00:01:07,290 Markings are important in packets because when they arrive at a switch such as switch to it needs to 12 00:01:07,290 --> 00:01:08,340 make a decision. 13 00:01:08,550 --> 00:01:13,110 Which class does the packet belong to? 14 00:01:13,260 --> 00:01:15,510 In other words, is a platinum? 15 00:01:15,510 --> 00:01:16,340 Is it gold? 16 00:01:16,350 --> 00:01:17,140 Is it silver? 17 00:01:17,160 --> 00:01:18,300 Is it bronze? 18 00:01:18,420 --> 00:01:26,490 Or to use a airline analogy, is it first class or business class or economy class? 19 00:01:26,850 --> 00:01:32,850 Packets within a class will be treated the same way, so the switch needs to determine which class the 20 00:01:32,850 --> 00:01:34,050 packets go into. 21 00:01:34,080 --> 00:01:41,040 So again, platinum, gold, silver and so forth, and then it will treat those packets accordingly. 22 00:01:43,760 --> 00:01:51,080 So how does a phone or a switch indicate to another switch or rather the level of importance of packets? 23 00:01:51,440 --> 00:01:56,810 Now, to use the airline analogy, again, this is very similar to a ticket that you get. 24 00:01:57,260 --> 00:02:03,740 So does your ticket indicate that you're a first class passenger or business class or economy class? 25 00:02:03,950 --> 00:02:06,750 Think of the markings as a ticket. 26 00:02:06,770 --> 00:02:11,720 The ticket is an indicator of the service that you'll receive. 27 00:02:12,590 --> 00:02:21,260 So when the phone sends a voice packets to the switch, it's going to mock them at a layer two using 28 00:02:21,260 --> 00:02:23,690 an eight or 2.1 Q Marking. 29 00:02:23,900 --> 00:02:27,770 I'll show you the details of the markings when I do a Wireshark capture in a moment. 30 00:02:28,010 --> 00:02:31,550 But for now, understand that when you speak into a phone. 31 00:02:31,550 --> 00:02:33,650 So let's assume these are your voice waves. 32 00:02:34,640 --> 00:02:41,120 A phone trance codes that into a digital signal of zeros and ones they are put into UDP packets that 33 00:02:41,120 --> 00:02:48,620 are encapsulated in IP, which are in turn encapsulated in Ethernet and or sent to the switch. 34 00:02:49,040 --> 00:02:52,670 So at layer two, we have an ADA two, two, one, Q header. 35 00:02:52,760 --> 00:02:58,330 The reason why is that Ethernet doesn't have these additional markings. 36 00:02:58,340 --> 00:03:04,910 As an example, if you're using Ethernet to it has no way to indicate the importance of a packet. 37 00:03:05,180 --> 00:03:09,680 So when we capture the frame, you'll see in a moment that we have a destination address. 38 00:03:10,910 --> 00:03:12,590 We'll have a source address. 39 00:03:14,210 --> 00:03:20,090 And then we'll have an attitude or one Q header and then the actual voice within the packet. 40 00:03:20,390 --> 00:03:28,070 So the attitude of one Q header has a priority filter to this is three bits in size also called Cos 41 00:03:28,070 --> 00:03:32,390 or cos of service or cos it's three bits in size. 42 00:03:32,390 --> 00:03:38,540 So the binary values go from 000 all the way to 111.