All language subtitles for 1. How does data flow in hubs, switches and routers

In this video, I�m gonna show you how data flows through devices in a network.

So how does data flow for example, through a hub or a switch or router?

Is the flooded out of all ports or is it only send out of an individual port?

And when I talk about data, I�m implying that on a switch a frame is forwarded out

of a port and on a router I�m talking about a packet is forwarded out of a port.

So in networking, it�s important to understand those terms and it�s also very

important to understand how traffic flows through devices in the network.

If you have a router where does the traffic go?

If you have switch, out of which port does the traffic go?
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So let�s look at how data flows in a network.
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We firstly gonna start off with an introduction to the different types
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of communication that takes place in the data network.
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We gonna look at unicast traffic vs. multicast traffic vs. broadcast traffic.
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I�m then gonna explain the term CSMA/CD which means
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Carrier Sense Multiple Access Collision Detection
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I�m then gonna spend quite a bit of time
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looking at the differences between hubs bridges, switches and routers.
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And I�m gonna show you how packet flows through those different devices.
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I�ll be referring to the OSI model throughout this video.
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I�m assuming at this point that you understand what the OSI model is
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and the different layers of the OSI model.
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If you�re unsure review the OSI video that�s part of this course.
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So in this video I�m not gonna give you the details of where a device
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in the OSI model resides, I�m gonna refer to terms
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such as a router is a layer 3 device, a switch is a layer 2 device.
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If you aren't sure about what that means please review the OSI video.
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So let�s start off with the basic types of communication
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that you'll encounter in the data network.
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This is one of those fundamental building blocks that you need to understand.
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So the first type of communication is unicast.
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Unicast is essentially where one device speaks to one other device.
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It's one to one communication, in other words, device A is communicating with device B
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the second type of communication is a broadcast, a broadcast is where one device
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sends traffic to all devices in the same subnet or in the entire network.
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There are different types of broadcast and we'll talk about some of them later.
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But as an example a broadcast to the local subnet means that all devices
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in the same subnet have the broadcasting device receive the broadcast.
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A broadcast to all hosts or networks means that the broadcast
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goes everywhere in the entire network.
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However in a lot of real world implementation, broadcast are limited
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and blocked by layer 3 devices such as switches and routers.
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So a broadcast would typically not go everyway in a network.
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Broadcast can cause a lot of problems and are therefore contained or limited
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in data networks, but essentially the idea of a broadcast is that all devices
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on the local segment or local subnet will receive the broadcast sent by single device.
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Now broadcast can be useful as an example if 2 windows machines
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are configured with the same name, you'll receive a warning about that because
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a broadcast is sent by those devices on the local network.
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That�s how the devices learned about each other and realized that multiple
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devices have the same name. So broadcast do have the uses but do cause a lot of
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problems in IPv4 networks and therefore in IPv6 broadcast support has been removed.
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In an IPv6 network broadcast are not supported. Now, what about multicast?
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Multicast have some of the advantages of broadcast, in that a single device
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can speak to many devices but it gets rid of some of the issue related to broadcast.
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Broadcast send traffic to people that don�t necessarily want the traffic
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where as with the multicast only devices that subscribe to the multicast receive it.
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So devices have to explicitly ask for multicast traffic before they receive it.
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So they won�t receive the multicast if they for example
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unsubscribe from that multicast.
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So to use some analogies, a broadcast is like a spammer were sending mail or email
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or traffic to everyone even to people who don�t want it.
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A multicast on the other hand is kind of a like an opt in or subscription service
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to a mailing list, so you may subscribe to an email mailing system giving information
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about Cisco CCNA, you can always opt out of that mailing list which means
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you no longer receive the emails, well in theory at least.
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So the idea with the broadcast is you will receive the traffic
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even though you don�t want it.
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The idea with the multicast is you can optionally receive the traffic or
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optionally opt out of receiving the traffic.
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Now another analogy which is useful in a classroom base environment is
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if I were standing at the front of the class as an instructor I would be talking
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and everyone in the class would be listening to what I�m saying, that�s a broadcast.
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So typically that happens in the morning when the class first starts.
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I�m speaking everyone in the room is listening, however typically especially
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after lunch an example, the classroom turns into a multicast where some people
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have unsubscribe from what I�m saying and that maybe happening right now
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which is unfortunate but hopefully not.
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Hopefully you're still listening, so I might be speaking in front of a class of 10
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people but only 5 of those people are listening to what I�m saying
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The other 5 people have unsubscribed from what I�m saying
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and are no longer listening to me. That�s an example of a multicast.
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so I�m hoping that this video won�t turn into
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multicast where you unsubscribe from what I�m saying.