1 1 00:00:00,530 --> 00:00:03,070 When we talk about the way data flows in a network, 2 2 00:00:03,070 --> 00:00:05,400 there's really three different ways it can flow 3 3 00:00:05,400 --> 00:00:08,150 if you're talking about IP version 4. 4 4 00:00:08,150 --> 00:00:11,660 IPv4 allows us to have unicast, multicast, 5 5 00:00:11,660 --> 00:00:13,920 and broadcast data flows. 6 6 00:00:13,920 --> 00:00:15,480 First, we have unicast. 7 7 00:00:15,480 --> 00:00:17,310 And unicast is when data travels 8 8 00:00:17,310 --> 00:00:20,240 from a single source to a single destination. 9 9 00:00:20,240 --> 00:00:21,510 So, if you want to think about this like 10 10 00:00:21,510 --> 00:00:23,370 me picking up the phone and calling you, 11 11 00:00:23,370 --> 00:00:26,140 it's a one-way conversation between you and me. 12 12 00:00:26,140 --> 00:00:28,790 There's only two people who are talking, me and you, 13 13 00:00:28,790 --> 00:00:32,760 and it's unicast going from me to you, or from you to me. 14 14 00:00:32,760 --> 00:00:34,650 Second, we have multicast. 15 15 00:00:34,650 --> 00:00:37,650 And this allows data transfer from a specific source 16 16 00:00:37,650 --> 00:00:40,610 to multiple but specific destinations. 17 17 00:00:40,610 --> 00:00:42,450 For example, maybe I'm at a classroom 18 18 00:00:42,450 --> 00:00:43,950 with three different people. 19 19 00:00:43,950 --> 00:00:46,410 I can now talk to all three of them at once, 20 20 00:00:46,410 --> 00:00:48,370 because I'm talking to the three people 21 21 00:00:48,370 --> 00:00:49,880 who are sitting in that classroom, 22 22 00:00:49,880 --> 00:00:53,050 that's going from me to those three specific people. 23 23 00:00:53,050 --> 00:00:54,610 Now, broadcast, on the other hand, 24 24 00:00:54,610 --> 00:00:56,750 is when data travels from a single source 25 25 00:00:56,750 --> 00:00:59,640 to all the sources on a destination network. 26 26 00:00:59,640 --> 00:01:02,850 If you think about this, if I go and do a radio broadcast, 27 27 00:01:02,850 --> 00:01:04,740 I might be speaking on the radio, 28 28 00:01:04,740 --> 00:01:06,380 and I don't know who I'm talking to. 29 29 00:01:06,380 --> 00:01:08,340 I just know that I'm talking to anybody 30 30 00:01:08,340 --> 00:01:10,290 who happens to tune in and listen. 31 31 00:01:10,290 --> 00:01:11,580 That's the big difference between 32 32 00:01:11,580 --> 00:01:14,460 unicast, multicast, and broadcast. 33 33 00:01:14,460 --> 00:01:16,300 Let's look at each of these a little bit closer 34 34 00:01:16,300 --> 00:01:17,910 by looking at some diagrams. 35 35 00:01:17,910 --> 00:01:19,230 First, we have unicast. 36 36 00:01:19,230 --> 00:01:21,520 And let's say I have unicast and I have one server 37 37 00:01:21,520 --> 00:01:24,910 who wants to send messages to PC1 and PC2. 38 38 00:01:24,910 --> 00:01:26,690 If I put that message in an envelope, 39 39 00:01:26,690 --> 00:01:28,980 also known as a packet, I can then send it out 40 40 00:01:28,980 --> 00:01:32,450 based on its IP address from the server to PC1, 41 41 00:01:32,450 --> 00:01:34,740 or from the server to PC2. 42 42 00:01:34,740 --> 00:01:36,750 And you can see that here on the screen. 43 43 00:01:36,750 --> 00:01:39,190 Now, when I go into multicast, I can send 44 44 00:01:39,190 --> 00:01:41,790 just a single message and it will be directed 45 45 00:01:41,790 --> 00:01:43,640 to whoever I want it to be into 46 46 00:01:43,640 --> 00:01:45,680 as part of their multicast group. 47 47 00:01:45,680 --> 00:01:48,250 So, my server, in this case, is sending out a message 48 48 00:01:48,250 --> 00:01:53,250 to multicast group number one at 239.2.1.3. 49 49 00:01:53,570 --> 00:01:54,920 When it gets to the switch, 50 50 00:01:54,920 --> 00:01:57,600 the switch determines who's part of that multicast group, 51 51 00:01:57,600 --> 00:02:00,230 and in this example, PC1 and PC2, 52 52 00:02:00,230 --> 00:02:02,110 both get a copy of that message. 53 53 00:02:02,110 --> 00:02:03,970 That's the great thing about multicast, 54 54 00:02:03,970 --> 00:02:05,920 is I don't have to repeat the message twice, 55 55 00:02:05,920 --> 00:02:07,450 even if it's the same message, 56 56 00:02:07,450 --> 00:02:09,500 because it's going out and hitting that switch, 57 57 00:02:09,500 --> 00:02:12,560 and getting repeated to everyone in that group. 58 58 00:02:12,560 --> 00:02:13,700 This works very much like 59 59 00:02:13,700 --> 00:02:15,630 when we're doing things like broadcasting video 60 60 00:02:15,630 --> 00:02:17,420 using a service like a live stream. 61 61 00:02:17,420 --> 00:02:19,960 And I can send the message once to my Facebook group, 62 62 00:02:19,960 --> 00:02:21,850 and then Facebook can multicast that out 63 63 00:02:21,850 --> 00:02:24,210 to all of the users who want it. 64 64 00:02:24,210 --> 00:02:25,860 Next, we have broadcast. 65 65 00:02:25,860 --> 00:02:28,090 And when you're dealing with a broadcast message, 66 66 00:02:28,090 --> 00:02:29,930 this is when the server sends it out and says, 67 67 00:02:29,930 --> 00:02:32,720 hey, switch, everyone who's connected to you, 68 68 00:02:32,720 --> 00:02:34,640 tell them all about this message. 69 69 00:02:34,640 --> 00:02:36,750 By doing that, it's going to broadcast that out 70 70 00:02:36,750 --> 00:02:38,520 to everybody on the network. 71 71 00:02:38,520 --> 00:02:41,080 So, if you're using a standard Class C network, 72 72 00:02:41,080 --> 00:02:45,760 that would actually go out to 255.255.255.255. 73 73 00:02:45,760 --> 00:02:47,220 And when it goes out to the switch, 74 74 00:02:47,220 --> 00:02:50,050 it's going to send it to everybody who's connected to it. 75 75 00:02:50,050 --> 00:02:54,420 And in this case, that's PC1, PC2, and PC3. 76 76 00:02:54,420 --> 00:02:55,720 Now, some students get confused 77 77 00:02:55,720 --> 00:02:58,430 between multicast and broadcast. 78 78 00:02:58,430 --> 00:03:01,310 The key distinction there is with broadcast, 79 79 00:03:01,310 --> 00:03:03,030 everybody is going to get it. 80 80 00:03:03,030 --> 00:03:06,500 But with multicast, only those who have opted into it 81 81 00:03:06,500 --> 00:03:07,990 are going to get that message. 82 82 00:03:07,990 --> 00:03:09,840 And that's the key distinction there.