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