Lesson video

Hi, I'm Alan, your computing teacher for this network's unit.

and this is lesson five of six and this is called the IP suites and packet switching.

You only need pen and paper for this lesson as you will be required to write some answers down for one of the tasks, turn off any notifications on mobile phones, remove any distractions that are nearby.

And when you're ready, we can make a start.

Okay, in this lesson we'll list and explain standard protocols.

We'll explain and give advantages and disadvantages of circuit switching and packet switching.

And we'll list and explain the four different layers associated with the TCP/IP model.

So all network data transmission, amounts to computers sending information as either electrical current, which is wired, radio signals, which we know is wireless or light, which will be fibre optics.

When a computer sends data across a network, it must first break the data down into signals that can be transmitted through the transmission media.

Be that electrical, light or radio.

At the other end, the receiving computer must be able to take those signals and reconstruct them into the data.

But what if somebody is sending an email from a Mac to someone on a Windows PC? Let's go through a set of strict rules that govern the different types of communication between devices.

Protocols are there to ensure different machines with differing implementations of software, can still communicate with one another.

Look at the following four activities that are commonly performed on a computer.

Browsing web pages, sending emails, streaming media and transferring files.

Each one of these has one or more protocols associated with them.

The Domain Name System servers share the task of keeping track of all the mappings of IP addresses to domain names across the internet.

It's like the phonebook of the internet.

Humans use domain names to look up information, but computers need the IP addresses to find that information.

Your HTTP or HTTPS which we'll look at in a second is a Hypertext Transfer Protocol.

This is the protocol for retrieving information from remote servers across the worldwide web.

It's primarily used to access web pages, but it's the underlying protocol for many apps.

Web browser requests to resource from a web server.

The server responds with a requested resource and any other linked resources such as Cascading Style Sheets, JavaScript or images.

The secure version of HTTP encapsulates all of the requests information into an encrypted data stream so that only the web browser and the web server can see the contents of this information.

Next up is FTP, which is File Transfer Protocol.

This is the protocol for transferring files across the internet.

These don't have to be web pages like they do in HTTP but quite often web developers will transfer their web pages from that computer to the web server.

Like HTTP, FTP is unencrypted meaning that the data is transmitted between client and server can be intercepted.

It's now considered insecure by many developers and alternatives are often used instead.

Next step SMTP which stands for Simple Mail Transfer Protocol.

This is the protocol used when Outlook applications or Apple Mail for instance, wants to send an email.

The emails are sent across the network through email service.

SMTP servers will listen for SMTP requests from email clients.

If the clients authorised to send the email from the server, the SMTP server will attempt to relay the message to the email server that handles the emails for the recipient.

We also have POP which stands for Post Office Protocol, and this protocol is another one used in email and is responsible for the retrieval of emails by an email client like Microsoft Outlook from the email server to the local client applications.

The latest version of this is version three.

So this is known as POP three.

With POP emails are downloaded from the server to the client's computer.

Next up we have IMAP which is Internet Message Access Protocol.

This is another protocol that's responsible for the retrieval of emails from servers to client applications.

The difference between IMAP and POP is that IMAP normally leaves the email on the server.

This means that if you check your emails from an app on you phone and from your laptop through a web browser you'll see the same emails in both clients.

Also, deleting an email on the app that uses IMAP will also delete it from the server.

All of these networking protocols exist in something called the application layer which we'll look at shortly.

So task one, using the worksheet complete the table on protocols.

You can pause the video and complete the task.

Okay, let's take a look at Packet Switching.

If your data is large enough that you want to send across the internet it will be split up into smaller packets.

Each packet contains a source IP address, a destination IP address and a sequence number.

As packets arrive at their destination, an acknowledgement is sent to confirm this.

Packets with no acknowledgement or lost packets are then resent.

So let's take a look at some advantages and disadvantages of Packet Switching.

Well, a Bandwidth is more efficiently used and packets can be redelivered if they're not acknowledged as received and packets can take different routes to avoid congestion.

However, the disadvantage of Packet Switching, data can take a long time to receive.

Packets can be lost.

It's also less secure, packets must contain the source IP address and the destination IP address.

In a Circuit Switch Network like the one you can see here, each node is connected to the other by one or more circuits.

The diagram here shows a simple follow network using a single circuit between each node.

If Node A wants to talk to Node B, then the circuit between these two nodes is dedicated to the communication for the entirety of the transmission.

If Node A wants to talk to Node D, then there are two paths in this circuit that can be used.

In the example shown it's going through B.

That means B will not be able to be used for the entirety of the communication between A and D.

The only way to increase capacity on this type of network design is to add more circuits.

The most common place to find Circuit Switch Networks nowadays is in the Telephone Network System.

Any image opposite, you can see there are multiple paths between any two destinations.

Pockets are sent in order, however, due to network congestion, it's unlikely that all packets will travel through the same route.

Packets can arrive in the wrong order, but thankfully due to the sequence number in each packet they can be reassembled once they reach their destination.

Some advantages of Circuit Switching, well it's more reliable, it's a dedicated connection and there's less chance of congestion.

This advantages however, it's possible wasted Bandwidth as you're waiting for communication to end and those nodes are unable to take on any more communications and it's expensive as more of them needed.

Okay, task two Packet Switching.

Using the worksheet, follow the link to the video of the team that pioneered Packet Switching back in 1965.

Pause the video and complete the task.

Okay, let's take a look at the TCP/IP Model.

This is a combination of the Internet Protocol and the Transmission Control Protocol.

This is abstracted into four layers to describe the functions involved in moving data from an application on one host, to another application on a different host across the network.

Okay, the top layer in this model is the Application Layer.

So this is the data that we want to transmit across our network, for instance, HTTP.

Okay, the Transport Layer is where we have the header and the data.

And depending on the type of communication, this can either be Transfer Control Protocol, header and data, or it can be a User Datagram Protocol.

This protocol is used for things like online gaming.

So if you suddenly see your screen glitching, for instance but that's the point where you've lost some information.

There's no point in sending you that information again because the game is continuing.

So you see the glitch and then it jumps back into the game.

Okay, the Internet Layer next, this contains the IP address of the destination and the sender and then the rest of the packet is the data to be sent.

The Internet Layer and the associated Incident Protocol Functions that define host to host communication and addressing across the network.

The most basic layer is the Link Layer.

This layer is responsible for the actual electrical signalling of data across the network.

It also handles transmitting of datagrams from one host internet layer, to a neighbouring hosts internet layer.

Okay, that's the end of this lesson and as always, there is a quiz to complete.

I'd love to share your work with Oak National.

So if you'd like to you can please ask your parent or carer to share your work on Instagram, Facebook, or Twitter tagging @OakNational and #LearnwithOak.

I'll see you next time.