Hello and welcome to a course on data communication.

We will start by looking at protocols and standards.

The goal of this course is to get an overview of protocols as concepts and what protocols do.

We will look at Ethernet for local networks.

If we start with rules for communication.

If we are going to communicate in any way, it depends on the type

it is important that we have certain rules for how this communication should go.

And within data communication, These rules are called protocols.

And a typical protocol is that in order for this to work you need to be able to identify the sender and

Here are some examples from non-communication.

For example, a letter, a media, if we are going to write something, a phone if we are going to talk, or face to face if we are talking to someone.

Then We also need to have a communication situation.

It should be written, one-way, interactive.

We need to come to an agreement on what language it is.

We need to stick to some kind of grammar and meaning structure that is reasonable.

to say everything in 1 sentence without having

We can't talk fast, because the other person

might not be able to understand everything.

So all these rules, all the protocols in data communication, can be

If we are to communicate with another person for example, we need to do all of this

Now it can be as serious in analog communication as in digital.

But if we look at some examples of conditions for a communication.

We will look at more advanced communication models like the OSI model.

If we take something we want to communicate today, for example what kind of weather it is.

If I speak, then this person may have to listen to understand what I have to say.

We should choose a language, maybe we choose English.

And we will physically use a medium for the transfer, which is a traditional old telephone.

If we call the other person, we have to identify the recipient, hit the phone number and the like.

So the person answers and hears that I speak English.

he or she on the other hand can speak English, then he or

she can understand what I say and start listening while I speak and perceive what I want to say, that is, to communicate what it means today.

So this is a pretty good example of a simple communication.

And it works the same when computers communicate.

If we look at the standard for local networks, which is what is most interesting in this context, it is Ethernet, which was created in 1973, a very old standard.

And since 2000, there is basically nothing else used for local networks, Even though there were several different standards that competed on the computer network side.

Then there are other standards that are perhaps used not for local networks but for other types of networks.

But Ethernet is the standard used for local networks for ordinary computers.

And then I also came to standardization organs.

The standard for Ethernet is actually IEEE

and IEEE stands for Institute of Electrical and Electronic Engineers which is a professional association of engineers, so to speak, all over the world over 3, 750, 000 members in 160 different countries.

And what IEEE does is that they develop standards for physical communication.

And Ethernet has a few different variants and standards.

If we look at it from 10 Mbps, which can't be used that much longer.

Because it's up to 100 Gbps which is very fast and maybe a little more unusual.

The Ethernet standard is a standard only for cables.

which is different standards for wireless networks, so called VLAN.

And then we look at some more standardization organs, we can be interesting in the context.

There is also Internet Engineering Task Force, IEFT.

They define and develop open standards for the internet.

And the most important thing here is the standards TCP and IP.

So it's actually hundreds of different protocols that are used.

Each of the TCP-IP is perhaps the most important protocol that is used.

So it's also important to know that there are a lot of different protocols that are used.

They are called as a collection name TCP-IP.

Most of the documents that are created by the IETF are known as Request for Comments, RFC documents with different numbers.

Some standards, for example IP, which we haven't talked about yet, but it was already available in the early 80s and has

Then we have another standardization up here on the right.

And the web and the internet are not really the same thing.

The physical network and the protocols used to make it work.

While the World Wide Web is a service that is used.

There are a lot of options for web usage of course.

But the most important standards that B1-3C has, or standardizes, is the HTTP protocol.

Which is the Hype Text Transfer Protocol.

Which is used by web readers and web servers.

It's the protocol used to retrieve websites.

are retrieved, there are a lot of different standards and things.

But the most important and common are the HTML, Hypertext, Markup Language and CSS, Cascading Style Sheets.

Which are used for, the most important in connection with the websites and the web.

There are a lot of other things that are used.

Then we have the International Telecommunication Union.

And it is a consortium via the UN, actually, the United Nations, with over 192 member states.

And they are important in this context, because they bring standards a little for telecommunication.

Among other things, the division of the radio spectrum.

That is, the different radio frequencies used for wireless technology.

You want to be able to standardize that, and

you have to agree globally or internationally

So if I buy a wireless router or a wireless access point, from the US or maybe manufactured in the US or China, I want it to be used here in Europe.

And it is important to agree on the frequencies.

Even satellite communication and telephony is handled by the International Telecommunication Union.

We will look at the cable types for Ethernet.

We will look at this again when we look at cables and contacts and the different network equipment.

There are Ethernet standards for bus networks.

The same type of cable that is used for TV antenna cables.

But anyway, the black 1 is copper cables.

So Contact types and cables that use optical cables.

As you can see there are many different types of cables.

And the cat in different categories is a TP cable, a twisted pair.

A standard of 100 meters is usual for compact cables.

In an Ethernet network, all computers in a network and units use Ethernet.

So everyone has a unique physical address called a MAC address.

This physical address has been assigned to the network cut that the computers and units use in production.

And when a host, so a unit on an Ethernet network communicates, it does so by sending so-called frames, which contain their own sender MAC address and the MAC address of the recipient.

A frame is translated as a frame in Swedish.

So everything that is sent in local networks is basically different frames.

Then these frames can contain different things.

They can contain, in turn, other types of packages, which in turn can contain other data units.

So it becomes a type of encapsulation that we will look at later.

But as soon as a unit receives a frame In an Ethernet network, a host will decode and control this frame and then check if it is the right MAC address.

If it is a MAC address to our computer, for example, or some MAC address that our computer will react to, it will investigate it more closely.

If it is a MAC address that is not to our computer, then this frame will be ignored and thrown away So on, you don't run the network scooter in a promiscuous mode, you can catch everything that is sent on the cable.

Now we will look at how to find your physical MAC address.

If we start graphically, right click and select Open Network and Sharing Center.

Also called Network and Sharing Center in Swedish.

And then we take Change Adapters Settings.

If we double click on this or right click and choose Status, we see information about logical addresses that we haven't talked about yet, IPv4 and IPv6.

And if we click on details, we find more detailed settings.

Here is something called physical address.

the command interpreter is to use the command run and type in cmd.

Then we use a command called ipconfig Which

So we get a lot of information about all network interfaces that exist And If we look at the physical network cutout we see that we have a physical address here.

If we continue to look at Ethernet frames, which is the unit, the frames that the data is sent in.

But the Ethernet protocol in itself decides a lot

What is going to be included in the frames.

And the timing that has to do with the speed.

When we send something, for example the link between our computer and the switch.

In the end, these frames are coded so that they are sent as digital signals to our media.

That is, our copper cable, optical cable or maybe as a wireless radio signal.

Sometimes you see that a frame is called a PDU.

And that actually depends on the context.

We will look at different protocols and levels in communication.

You remember this with the simple computer communication model.

There are different levels and protocols that work in computer communication that divide the data into units, smaller parts.

And as soon as you do that, you have a PDU, a Protocol Data Unit.

In some literature it says that PDU only applies to the upper layers.

But actually it is as soon as you share data with the help of a protocol in a unit, it becomes a PDU.

If we mean PDU when we talk about Ethernet, it's frames.

If we talk about PDU, when we talk about the IP protocol, it's called a package.

If we look at a frame, it is a maximum of

If for some reason we would get a frame that does not fit in this size, that does not follow the standard, then this frame will be ignored.

Then there are some exceptions, like jumbo frames and such, but for regular data networks locally, it's Ethernet frames.

For regular data networks, it's Ethernet frames.

If we look a little more in detail at these Ethernet frames, we see that there are 2 variants.

bytes maximum, And it consists of a couple of different things.

First and foremost we have a preamble, which is actually on 7 bytes.

This preamble is used as a synchronization.

And the first 7 bytes consist of 1's and 0's.

Then we have start frame delimiter, which is an 8-bit that marks the start of a frame.

Then we comes 6 bytes with destination address.

Here we see the MAC address where this frame is going.

And then we see the send address, 6 bytes MAC address.

So a MAC address consists of 6 bytes, as we saw before.

And it is written in hexadecimal form, as we saw before.

We have not gone through the hexadecimal number system, but a hexadecimal number can have a value between 0 and 15.

which is the decimal number system, we've added A for 11 and B for 12, CDEF and so on, F is 15.

It's very easy, because a hexadecimal number corresponds to 4 bits.

So it's very easy to represent binary data hexadecimal.

2 hexadecimal numbers, a string and a byte.

Then there is a 2 byte part, which is type and length.

And it is used to tell what type of data is encapsulated in this frame.

Because in a frame there is always something else encapsulated in it.

Then comes the data that can vary from 4600 to 1500 bytes as you can see.

And at the end we have something called a frame check sequence that consists of 4 bytes and is a CRC check.

It's a mathematical algorithm that can calculate and see if something has happened to the computer.

So you can easily see If something has changed in the frame, and then this will be thrown when the frame is broken.

Then below we see the same, but it has been added

And then a frame is 4 bytes larger, so then the maximum size is

And we will talk a little more about VLAN later, so we can't

We'll talk a little more about broadcasts.

We look from the previous video, where we talked a bit about broadcast messages.

Broadcasts are when you send from 1 unit to all units in the network that can receive this.

Broadcast messages are used from time to time, as we will see later on.

This means that a frame is sent to all hosts on a local network.

When we can only have 1 destination MAC address.

And all networks should have a unique MAC address.

So how can you get a frame sent to all on a network?

Yes, then there is a unique broadcast MAC address that consists of only 1's in the address, i.e.

And if we only have 1's, then the answer is of

1's, 4 bits with 1's, the answer is 15, i.e.

So these 48 bits that a MAC address consists of, are simply F.

And the network equipment that we will look at later can be identified.

If we want to send something to this macadress, it's out to everyone who is connected to this local network.

So that's how broadcast works on this level.

And if we talk about broadcast we get to talk a

We will talk a little more about that when we talk about switches and equipment.

But we can simply state that when a switch that we use to connect units on a network, when it receives a broadcast message, it sends this message to all PUTs.

And therefore, You can also call a local network a broadcast domain.

That means that a broadcast reaches all units in a local network.

So the limitation is the same as a local network.

And If we have too much broadcast traffic, it can be a problem.

If we are going to send data to all the units, it will be too much traffic.

Another important thing is that if we take routers, which I talked about earlier.

A router is used to connect the same network and a router that does not support broadcast messages.

However, you can configure a router if you want to to transmit certain types of broadcast.

So a router can be said to limit a broadcast domain.

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