Week 4: Networking and communications

Introduction

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CORY DOCTOROW

Over the past three weeks, we've explored the many potential threats to our digital lives. We've also taken a closer look at ways of keeping attackers from impersonating you online or infecting your devices with malware. Now we're going to delve a little deeper into the technology that underpins information security, focusing first on how to protect the internet itself and the network security problems that can affect it.

By the end of the week you'll be aware of some of the networking standards that allow different devices to connect to the internet and exchange information. You'll also be able to explain how data is transmitted across networks. And you'll understand the difference between the internet and the world wide web.

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Cory introduces the networking and communications topic.

You’ll learn how data is transmitted across the networks, including wireless networks and understand the difference between the internet and the world wide web.

1 What is the internet?

Figure 1

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This is a photograph of Vinto Cerf.

Figure 1

The internet is not a single entity with a single owner; instead it comprises a hierarchy of individual networks that have been connected to one another. These networks range from local area networks (LANs) that can be found in many businesses and universities to the telephone and data networks that link cities and countries by fibre optic cables and satellite links.

A definition often used is that the internet is a network of networks. Before looking at the design of the internet in more detail, let’s hear from Vinton Cerf, one of the engineers who was involved in the creation of one of the earliest computer networks:

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SPEAKER

Vinton Cerf is vice president and chief internet evangelist for Google. He has been involved in internet technology right from the very start. Ten years ago, the Open University interviewed him for a series called TheWebStory.com.

His involvement with internet technology started in the 1960s, when he was working on a computer networking project funded by the US Defense Advanced Research Project Agency, ARPA. He is widely known as the ‘father of the internet’.

VINTON CERF

Well I think people have gotten a little carried away at least in our culture there seems to be a need to focus a lot of attention on just one or two people. That’s not right. There are many fathers of the Internet depending on how far back you want to go and the evolution of the technology. At UCLA I was a graduate student along with Steve Parker, John Postel, Bob Braden, and a number of others, all working for Professor Len Kleinrock, who had the network measurement centre at UCLA. And so our job was to put the first computer up on the ARPANET and particularly the one that did network measurement.

SPEAKER

The ARPANET was a network of computers set up in 1969 to link research departments in universities around the United States. The big challenge was to get the different computers to talk to each other.

VINTON CERF

No one was really in charge of the development of the host protocols to connect computers up to the underlying network that Bolt Beranek and Newman was building, and so the graduate students just sort of gravitated to try to work on that. We always expected that someone would come out who was professional and would run the show. Steve Parker, who was my good friend then and still is, ran the network working group and we always expected that somebody from the East Coast would show up to tell us what to do but they never did. So we just went on and did the best we could.

Protocol is of course it's a diplomatic term. It's something that you establish in agreement between countries and that’s called protocol. It also turns out to come from the Greek word ‘protocollum’, which was the table of contents of a scroll. Well we stole that word for computer communication conventions because packets of information that computers exchange have little headers on them to say where they're going, where they came from and how much there is in that piece. So we called the procedures computer protocols. They're simply conventions for communications between computers.

SPEAKER

To get information between the various computers that formed the ARPANET, the data was chopped up into small ‘packets’. The packet switching protocols Vint and his colleagues devised enabled the packets to be sent by different routes and recombined at the other end to recreate the original data.

VINTON CERF

When the first wide area packet switch network was being built the ARPANET there was some uncertainty whether it was going to work at all. That actually worked out quite well. It was a very powerful and useful tool for computer science departments that were part of that system. In fact packet switching was so successful that we at ARPA anyway decided it would explore using packet switching in radio and satellite communication. That led to the development of the mobile packet radio network and an Atlantic satellite net that linked the US to Europe using packet switching technology. Well once those projects were under way Bob Kahn who was at ARPA at the time realised that these networks would ultimately have to be inter connected to each other. And we didn’t have any protocols, no procedures, no conventions that would allow computers that were on different networks to smoothly intercommunicate with each other. That led to the inter net project which Bob started at ARPA around 1970 – late ’72 or early ’73 and he posed that problem to me when I was at Stanford in March of ’73 and we worked together on solving that problem: how could computers on different networks communicate with each other uniformly. And that led to the design of what is now called TCP/IP.

This really was a back of the envelope moment. I was sitting in San Francisco in a hotel lobby waiting for some session to start at a conference and had an envelope in my pocket and I pulled it out and I was just sketching what the implications were of the architecture that Bob and I had talked about, eventually leading to what we called gateways and are today called routers. And so in a sense the system’s basic architecture was forced on us because we weren't allowed to change any of the networks themselves we had to work outside of them and then figure out a way to achieve uniformity. So that little sketch, which is long since lost, I had no idea it was an important sketch at the time, it was just getting my thoughts in order, was the beginning of at least for me of understanding how the structure would work.

SPEAKER

TCP/IP was one of the great technological breakthroughs of the twentieth century. It allowed the internet to become what it is today.

VINTON CERF

The easiest way to understand how the Internet works is to think of Internet packets as electronic postcards. Just like postcards: they have a 'to' address and a 'from' address and a finite amount of content on them. And the fact that they're electronic means that they go through the system about a hundred million times faster than the postcard that goes through the post office. But they behave just like postcards. They don’t necessarily arrive in the same order they were sent. They might not even arrive on the same day. Some of them get lost. That’s true of the Internet packets as well as postcards and so if you think about Internet packets as postcards you have a pretty good model. To understand TCP you need a little bit more thinking. Suppose that you were sending a novel to someone and the only way you could send it was by sending postcards so you cut the pages of the novel up, put them on postcards and then you realise that you have to number the postcards in order to let the party at the other end put them in the right order. Then you wonder you know if some of them got lost you'd have to re-transmit them so you keep copies to send. Then you realise that you need to find out whether you need to send any copies and you have acknowledgements coming back in the form of post cards, some of which might get lost. And so you have time outs that say if I haven't heard anything I'll start sending copies. It's basically the way the TCP works. It essentially allows us to send novels in sequenced order on top of postcards except of course we do it electronically and much faster.

SPEAKER

So the internet is essentially a giant game of pass the packet, using a set of rules or protocols called TCP/IP. When the protocol was first used to create an inter network from three separate networks, it was a milestone in internet history.

VINTON CERF

Interestingly enough there are two big milestones, neither one of which were very noted at the time by anybody except those of us deeply involved. In 1977, late in the year we actually got all three, packet radio, sat net and ARPANET networks to function together using the Internet protocols and gateways in between and that was very exciting for a few of us who were a part of that, but not noted anywhere. We didn’t call a press conference or issue a press release or anything. We just breathed a great sigh of relief. In 1983 in January we actually insisted on the deployment of those protocols by all the computers that were part of the ARPANET and satellite net and packet radio net. And that was a big moment for the people who had to get their machines up but there were only about two hundred and at most four hundred computers involved. Today there are fifty million computers on the Internet. And so any such similar kind of transformation can't be done in what's called a flash cut. It wasn’t even a flash cut in the Internet’s case. It took several months to get everybody up and running on the new protocols. But that was a forced change. Today you can't force that change.

The only real regret I have is that I didn’t argue that we should have a larger address space for the Internet than we decided on. In 1977 I picked a thirty-two bit address space which was enough to identify up to four billion things. It's now very clear that there will be many hundreds of billions of things on the Internet in the future and we should have picked a bigger address space but at the time it was an experiment and it never dawned on me or most everyone else that we needed anything like the scale that we will ultimately require.

SPEAKER

Although he resists being called the father of the internet, Vint Cerf is one of its greatest pioneers. When he first sketched out his ideas for the TCP/IP protocol, did he imagine that the internetworking project would turn out the way it did?

VINTON CERF

Certainly not in the form which it has ultimately materialised in. Tim Berners-Lee’s world wide web is something that’s truly phenomenal at the rate at which it has been absorbed and adopted. We knew however that we were working with very powerful technology. We knew that computing and the distributed programmes that are around the network would be very, very powerful engines. We just didn’t know exactly what they were going to do at the time. Software is sort of the ultimate clay – you can make anything you want to out of software if you can figure out how to programme it and so the Internet simply underscores the possibilities by creating an endless frontier of software that sits on top of the computers in the networks that communicate. So although in detail we didn’t know how this would all evolve and economics has played a big role in the evolution. Lower cost of networking, lower cost of computing making it available to many more people. But I think we knew we were working with something that was very powerful and that ultimately might make a big difference.

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Two key factors in the design of the internet were:

1. The network would not have a central controlling computer. Each computer on the network would be assumed to have the same authority as every other computer.
2. The network should be able to deliver information between any two computers on the network even if some of the machines in the network had failed (or given its Cold War origins, been blown to pieces). There would be a large number of alternative routes through the network, so it was not necessary for information to travel by the most direct route, instead it could travel in a roundabout route, avoiding the damaged parts of the network.

In the next section, you’ll see how this works.

1.1 How data moves around the internet

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TEACHER

When we talk about the internet, it's very tempting to think of it as a single computer network. But in reality, it's made up of thousands of separate networks owned by governments, corporations, and individual users. The computers and links that make up the internet are built by a huge number of companies, and use a large range of different technologies to store and transmit information. The internet is made possible, because although there are a large number of different types of computer and networking equipment, they all understand a relatively small number of communications protocols.

The two most common are the Internet Protocol, IP, which is used to transmit information. And the Transmission Control Protocol, TCP, which provides a structure for sending data over a network. The two are so important that they're often written together as TCP/IP. Since all of our computers understand the same protocols, it appears that they all belong to the same network.

The internet is made up of a hierarchy of networks all communicating through TCP/IP. The lowest tier is made up of individual users, who might be connected together in a local area network. These small networks are connected to the next tier, which is made up from internet service providers or corporate networks who provide access to internet services. These, in turn, are connected to higher tiers, such as telecommunication companies who own the all-important cables that allow data to travel around the world. The topmost part of the internet is sometimes called the internet backbone, or tier one.

Before data can be sent across the internet, the TCP is used to break it into fixed-size chunks. These are known as datagrams, but are sometimes called packets. Each datagram contains a small amount of data, as well as information needed by the internet itself, including the addresses of both the sender and the recipient and a serial number. The addressed datagrams are passed by the sender's computer to a nearby router, such as one on their home network. The local router extracts the destination address of the datagram, and looks for that destination in a table of known addresses. If the destination address is known to the router, then the datagram is sent to the destination computer. However, if the destination address isn't known to the router, it forwards the datagram to a higher-level router, which has a more comprehensive list of addresses. A datagram 1 might be forwarded all the way up to the routers on the internet's backbone.

The higher-level routers only need to examine the first part of the destination address to determine where the datagram needs to be forwarded. Once its address is found in a router's address table, the datagram can be redirected to a lower-level router, which will in turn forward it to more and more local routers until it eventually reaches its destination.

Routers constantly inform one another about their status and how busy they are. When parts of the internet become congested, or the router becomes unavailable, other routers will find new paths for datagrams that to avoid the problem. IP's ability to constantly reroute data to ensure a reliable flow of traffic means it's entirely possible for datagrams containing parts of the same file to take completely different routes across the internet.

When datagrams finally reach their destination, TCP is responsible for restoring the data to its original condition. The serial numbers on each datagram allow them to be ordered so that the data can be correctly reconstructed. TCP also allows the receiver to request new copies of missing or damaged datagrams from the sender. Between them, TCP and IP offer an extremely reliable way of sending data over what might be an unreliable network.

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The video explains how data is routed across a network of computers and how the internet is resilient to failures of individual computers, known as nodes of the network, or connections between computers, known as the links.

Instead of using a dedicated circuit for all of the information, internet traffic is split up and may take any number of routes through the network moving from its origin to the destination by a series of hops.

Note: Early in the above the video [2:05], an example packet is shown with destination address 6.7.8.104. However, there are subsequently two separate examples of different packets being routed. In the first example, the packet is being sent to a host on the local network, 1.2.3.104 and in the second example it is being sent to a remote host, 6.7.8.101.

1.2 Introducing the datagram

Figure 2

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This is an image of a collection of envelopes of different colours.

Figure 2

When data, such as a picture, movie or a document is sent over the internet, it is not sent as a single chunk. Instead it is split up into small, uniformly sized blocks called ‘datagrams’, also sometimes called ‘packets’.

Imagine that you have a large book that you want to post to a friend, but you only have small envelopes. One way to post the book is to tear it into a number of pieces, placing each piece in a different envelope. Each envelope is addressed to the recipient. It makes sense to label each envelope with a number to tell your friend where the pages belong in the whole book. When the envelopes are put in the postal system they may all travel through the same sorting offices and arrive on the same day, or they might take different routes and arrive on different days. However, your friend should be able to recreate the book when they receive all the envelopes.

A number of different datagrams are used by data travelling over the internet, but they all have a similar structure. One envelope and its contents correspond to a single datagram. The envelope (which is called the ‘header’) contains the sender and recipient’s addresses, a unique number, a date stamp and some error correction information, while the contents (called the ‘payload’) contains the actual information being delivered.

The address is an IP number that you will look at later in Week 4. You can look up the details of an address by using a ‘whois’ service. For example, you could use the site https://whois.domaintools.com/ and type open.ac.uk into the whois search box.

In the details returned you can see:

IP Address 137.108.200.90

Other details show that the domain belongs to The Open University. The IP location is in Milton Keynes, England, and is hosted on an Apache server.

1.3 Datagrams on the move

We have seen how, in theory, datagrams of information move around the internet. It’s actually possible to see this in action, often with surprising results.

Each datagram is sent through a series of computer nodes that form the backbone of the Internet. There are many thousands of these nodes and often many different routes between them. Each of these nodes has an IP address. If you look up the IP address of the node using ‘whois’, some will provide a geographical location for the node. Some will provide only the country of that node, and some provide no location information.

On most computer systems you can run software that will follow the route from your computer to a destination IP address, and it will return a list of the nodes that it passes through. These are usually known as ‘Traceroute’ apps. See the wikihow page for information on how to run this Traceroute tool on your computer: https://www.wikihow.com/ Traceroute. 

Instead of looking up the ‘whois’ for each node to see where it is located, you can use an online utility that does this looking up for you and plots the results on a map. Open https://peter-thomson.com/ leaflet-map-tutorial/ traceroute-mapper.html in your browser and paste in the output from running ‘Traceroute’ on your computer.

1.4 Wireless networks

Figure 4

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The image is of a large mast with a number of satellite dishes attached to it.

Figure 4

Early computer networks depended on wires to move their data around the world, but engineers quickly realised that it would be useful to be able to use wireless (radio) connections to create a local wireless network.

Nowadays, wireless local area networks are commonplace. These wireless local networks have become known as Wi-Fi after the trademark of the Wi-Fi Alliance that certifies compatible products. If you have a laptop, tablet or smartphone, it probably has wi-fi access. Wi-fi is also being incorporated into an ever wider range of consumer goods including eBook readers, smart televisions, burglar and smoke alarms.

Wi-fi enables devices such as computers and printers to be connected together wirelessly to form a local area network (LAN). Instead of the signals going through cables and wires, they are sent through the air instead as radio waves.

The name ‘wi-fi’ refers in particular to wireless local area networking technology that is compliant with a particular family of standards maintained by the Institute of Electrical and Electronics Engineers (IEEE) and called the 802.11 family. You will see different variants of this standard on wireless routers, for example 802.11b, 802.11g and 802.11n.

In wireless LANs, the individual laptops, mobile phones and other devices, or nodes, are usually referred to as stations, acknowledging the fact that each communicating device acts as a radio station with a transmitter and a receiver.

In order to connect to a wi-fi network, a station needs to know the name of the network. This is also known as the service set identifier (or SSID) of the wireless LAN. The ‘service set’ referred to here is the set of wireless devices to be served by a particular wireless LAN.

The SSID allows the nodes on a wireless LAN to distinguish themselves from nodes on other wireless LANs that may be operating in the same physical space. For example, in many airports mobile phone companies provide free wireless LAN services to their customers and use the SSID to ensure that customers connect to the appropriate wi-fi network.

When you are trying to connect to an available network, you will see a list of SSIDs that are reachable from your device, some of these will have padlocks against them – more about what that means later.

2 Is your private information really private?

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SARAH SMITH

You might think you've got pretty good online security. You've devised long and complicated passwords. You only log onto trusted Wi-Fi networks. So how could anyone access your personal data? Well it doesn't take millions of pounds worth of high tech infrastructure. It's not only state security services that can do it. Anyone, with a bit of inexpensive kit, and a little bit of know-how, could be reading your emails right now. To show how easy it is to hack into just about anyone's emails, we invited a group of students to participate in a short experiment. We promised them a free lunch and that was enough to tempt them in. And we told them it had something to do with mobile phones. We did not tell them precisely what was about to happen.

We've invited you here to ask what your mobile phone says about you. And by the time we're all finished here, I think you're going to be pretty surprised when you find out just how much information your phone is giving away about you, all the time, without you even knowing it.

While they ate some free sandwiches and, inevitably, started playing with their phones, we started the electronic eavesdropping. They had no idea what we were up to next door. What our volunteers don't know is that hidden behind this bookcase, are our tech security experts. Right now, they are using a bogus Wi-Fi network to connect to our volunteers' phones and access all kinds of personal data.

Glenn and Daniel are here to show us, and our student guinea pigs, just how easy it is to hack into their phones and start reading their emails, tracking where their phones have been, and see what they're looking at online.

GLENN WILKINSON

So, Rachel Powell, we've got her Mac address.

DANIEL CUTHBERT

Can we find her?

SARAH SMITH

Using only a small receiver attached to their laptops, they're able to create Wi-Fi networks that look like the familiar trusted networks the students use all the time. Any of our students might have been wary if they had knowingly logged onto an insecure public network, like you might find at a bar or a coffee shop. But their phones are being tricked into automatically joining what looks like an approved and trusted network, sending all their traffic through our hackers' laptops. They had no reason to suspect anything, but while they dug into the egg and cress.

DANIEL CUTHBERT

Her Facebook profile is open. She shows where she lives.

SARAH SMITH

Glen and Daniel could see their Facebook pages, check where they'd been, even read their personal emails. Whilst you've been patiently waiting for us here, we have secretly had two tech security experts in the next room trying to find out as much as they possibly can about each and every one of you, without them knowing your names. They don't know your telephone numbers, none of that. But they've still been able to glean quite a lot of information about you.

Our students are about to discover just how much. By leaving their phones switched on, they've inadvertently given away their names, online identities, and allowed access to deeply private communications.

GLENN WILKINSON

I'm seeing your Facebook and your email. Your Yahoo mail, it turns out, was, it's not encrypted.

ALLIE KURTZ

Are you going through my email?

GLENN WILKINSON

We can go through your inbox. At that point, we have control. So Dan was looking at, like, a sent email.

ALLIE KURTZ

I do know I have quite an open online profile. But to see the emails come up on the screen, that was a bit shocking, all my work emails, personal things. So that was surprising. It's, like, really scary to know that can happen.

SARAH SMITH

And it's not just your email. Our hackers could identify the precise locations where our students' 2 phones had previously logged on to Wi-Fi networks.

GLENN WILKINSON

Someone went to the States and connected to a network with a unique name. So that's the only one that's in the database. So I know you've been there. And anyone from Romania or visited Romania?

SARAH SMITH

Did you realise that the phone in your pocket was practically a GPS tracking device?

RACHAEL PELLS

Not to that extent. I didn't realise it was that easy to track my whereabouts, even if, you know, even if they don't have anything on me in the first place, they can just find out everything they need to know through my phone.

GLENN WILKINSON

We are the good guys. We are on your side. This is an example to – if we were the bad guys, we wouldn't be showing you this. We'd be clearing out your bank accounts and running for the border.

DOMINIQUE BRUNDLER

I had no idea, really. We were just talking, eating sandwiches. So really just surprised and shocked.

SARAH SMITH

So at any point, somebody could be hacking into your phone and trying to access all this information about you. And you've realised there's no way you would know that was happening.

DOMINIQUE BRUNDLER

Yeah, basically, I will now turn off my Wi-Fi while I'm around.

SARAH SMITH

Worried now? You should be. So how can you carry on, using convenient Wi-Fi hotspots, without giving away all your secrets?

DANIEL CUTHBERT

They've got to be more aware of what they're connecting to. Mobile phones and smartphones today leak out a lot of information. The way we use the internet, we give away a lot of what we're doing.

SARAH SMITH

You're the white hat hackers. You are doing this for good purposes. Are other people out there using technology like this without quite such good purposes?

DANIEL CUTHBERT

Definitely. The criminal market is abusing this kind of technology now. Advanced malware, custom viruses, et cetera. And they're going after people. They want people's email boxes. They want access to computers. Because that way you can then start doing a lot more fraud than you could do with the old fashioned style attack.

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We all hope that the information we send wirelessly is private, but is that always the case?

Channel 4 News was able to learn personal information about unsuspecting people by intercepting their, supposedly private, but in reality completely public, wireless internet signals.

The attack shown in the video was possible because the hackers had set up their own wi-fi hotspot that either advertised the name of a common wireless hotspot provider, or the users chose to connect to a ‘free’ wi-fi network. The lesson here is to be careful about the public wi-fi networks you connect to, and the types of information you access using these networks.

2.1 Network security challenges

Figure 5

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This shows the back of a wireless router with a cable going into the port labelled 'INTERNET.

Figure 5

Internet routers are designed to move datagrams to their destination but how secure are they?

They have been programmed with strategies to overcome problems such as congestion or the failure of a part of the network. These strategies involve re-routing datagrams via any alternative path, as you saw from using Trace Route. Therefore, it is impossible to state with any assurance which route will be taken by a datagram travelling outside a local network.

The datagram may travel directly, or, more probably, travel through several routers located anywhere in the world. These routers will most probably not belong to either the sender or the recipient, but a third party. In most cases this will not matter, but datagrams can be copied, and their security compromised, as they pass through a router without alerting either the sender or receiver.

The process is known as packet sniffing and it has many legitimate purposes including analysing network performance and for law enforcement, but packet sniffing software is readily available to anyone who chooses to use it. In the past, packet sniffing required a computer that was wired to the network, but wireless networking means this is no longer the case.

2.2 Encryption in wireless networking

Figure 6

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This image shows three large satellite dishes.

Figure 6

Since wireless networks transmit data over a medium that is shared by everyone, anyone with a compatible receiver or transceiver is able to eavesdrop on the radio signals being sent.

Ensuring that the eavesdropper is not able to convert these signals into the original message is a desirable security property of any wireless network, referred to as ensuring confidentiality. (This was one of the three security essentials we mentioned earlier, along with integrity and availability.)

Another security problem with using a shared medium for transmission is that malicious users could interpose themselves between a sender and a receiver and modify the messages being exchanged or even destroy them entirely. This is sometimes called a ‘man-in-the-middle attack’, and it compromises the integrity of the data being transmitted across the network.

Finally, an attacker could transmit lots of random data on the frequency being used by the wireless network, congesting the network and thus preventing other users from sending data. As we saw earlier in the course, this is called a ‘denial-of-service’ (DoS) attack and is an example of an attack on the availability of the network.

2.3 Using wireless networking securely

Figure 7

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The image shows three internet cables sitting on top of a computer keyboard.

Figure 7

Use the network connection tool on your computer to identify how many wireless networks are within range of your current location.

How many of them use secure connections? If your home wireless network is not configured to use WPA2 or WPA3, find out how to set this up and make sure to do this. The user manual for your wireless router or your internet service provider’s website should have information that will help.

Consider how you connect to the internet when you are on the move. Do you connect to your home wi-fi network, your mobile service provider, the free wi-fi in a coffee shop?

Go through the online services you identified in Week 1. Which ones would you choose not to access using public wireless networks?

3 Why we need standards on the internet

Figure 8

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This image is a photograph of a complicated road layout, from above.

Figure 8

As you’ve learned, when you send data over the internet it is sent across several hierarchies of networks, using different technologies from many different providers and operated by different organisations.

These networks must use a standard form of communication so information from one network can be passed across to another network.

To some extent, the way any one of these separate networks works internally is nobody’s business but the owner and users of that network. However, where a network joins to other networks, where it becomes part of the internet, it has to conform to the standards of the internet.

The internet is not owned by a single organisation, so there is no one authority that dictates how it works. Yet all the different people and organisations with their own networks that together make up the internet have to work to common standards, or data would be unable to move between the different networks.

In the next section you’ll find out about the TCP/IP protocols.

3.1 Introducing the TCP/IP protocols

Figure 9

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This image shows the back of a computer with multiple cables.

Figure 9

The standards that allow different networks and differing communications equipment to talk to one another are formalised in digital rules known as ‘communications protocols’.

For the internet the two most important are the Transmission Control Protocol (TCP), and the Internet Protocol (IP). They are so inextricably linked that they are often written together as TCP/IP.

TCP

The TCP protocol is responsible for ensuring data can be sent reliably over the internet. It works through a number of software ports that act to keep data separate on the same computer – so it is possible to browse a web page, collect email and listen to streaming music at the same time.

To understand how TCP works you need to know something about ports. A port can mean different things depending on the context. A port can be a physical connection on a device such as the USB port into which you plug your printer or flash drive. But for TCP, it means a number which indicates how data is handled when it reaches its destination. Many ports represent specific protocols such as port 80 representing the well-known port of HTTP.

Common TCP ports include the following:

• port 20 and 21 – File Transfer Protocol (FTP) for sending and receiving files (port 20) and control (port 21)
• port 22 – Secure Shell (SSH) for secure logins to computers
• port 25 – Simple Mail Transfer Protocol (SMTP) for sending email
• port 80 – HyperText Transfer Protocol (HTTP) for browsing web pages.

Data being sent from an application on your computer is divided into TCP datagrams each containing the TCP port number. The TCP application running on the recipient’s computer will then examine this port number to determine which application should receive the information in the datagram.

Figure 10

TCP’s second major task is ensuring that all data sent from a computer is received by its destination. It waits for acknowledgements from the remote computer, and in the event that a datagram gets lost or damaged in transit, it can resend the missing datagram. For this reason TCP is reliable – but relatively slow.

Applications where timeliness is more important than absolute accuracy – such as streaming media, video games and video conferencing – will use less reliable, but faster, protocols such as UDP (User Datagram Protocol) to send and receive their data.

If you are receiving an email, you want the whole message to arrive with no gaps, but if you are streaming a TV programme, it doesn’t greatly matter if a few datagrams get lost.

TCP is not responsible for sending and receiving information; that is performed by a second protocol – most commonly, IP, that we will look at next.

3.2 The internet protocol and IP addresses

Figure 11

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The image is of a lorry driving along an empty road.

Figure 11

The Internet Protocol (known as IP) does the hard work of actually moving data across the internet. IP is only concerned with moving data, it doesn’t actually check that data actually arrives (that’s handled by TCP).

When IP receives data from TCP to be sent on to the internet it wraps the TCP datagram in its own IP datagram containing a sender’s and a receiver’s address as well as some other information.

When IP receives data from the internet, it removes the IP datagram information and passes it to TCP which will perform the checking of the contents and reordering of information before it can be passed through the appropriate port to an application.

3.3 From numbers to names

Figure 12

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This is a close up of '.uk' on a screen.

Figure 12

When we type an address (such as www.open.edu) into a browser, the address is translated into a unique IP address by a name server, called a Domain Name Server (DNS), located somewhere on the internet. This IP address is attached to every IP datagram destined for the Open University server.

As an example we will use an IP datagram belonging to an email being sent to Bob who works in the coffee bar at Big University in America (Bob’s address is bob@coffee.big.edu). The address is sorted from the most general part of the address to the most specific. First of all, the name server on the sender’s machine makes a request across the internet to a computer which holds the addresses of all American universities (most of which use .edu at the end of their address) asking for the IP number of big.edu. Assuming that big.edu exists, the .edu name server then responds with the IP number for the name server at Big University.

The sender’s machine then uses that IP number to make a link to the name server at Big University and requests the IP number of the coffee shop computer used by Bob. The big.edu name server will then respond with the address of the coffee shop. The IP datagrams can then all be addressed correctly and sent into the network.

Up until 2019, the DNS information requested was sent as plain text and could be intercepted even when the data being sent or requested was encrypted. From 2019, it has become possible for DNS requests to be encrypted. In Firefox browser go to Settings, then Network settings and select the enable DNS over HTTPS checkbox.

Chrome 78 is also experimenting with this feature, which can be enabled by browsing to ‘chrome://flags/’ in your Chrome browser, searching for ‘dns-over-https’ and enabling. You will have to restart the browser for this change to take effect.

3.4 The internet is not the world wide web

Figure 13 British physicist-turned-programmer Tim Berners-Lee devised the specifications for URIs, HTTP and HTML – technologies that underpin the internet as we know it

We’ve all done it. We’ve all been browsing a website and said ‘I’m on the internet!’.

This is true, but misleading, if for no other reason than the internet dates from 1982 (with its roots as far back as 1969) but the world wide web only came into being in 1990 thanks to Sir Tim Berners-Lee.

Before the advent of the world wide web, not only did fewer people use the internet (it took until 1998 for 100 million people to log on for the first time), but it wasn’t anything like the world wide web we know today – almost all commands had to be typed in – often using cryptic instructions, and what you got back – if you got anything at all – was plaintext. The world wide web not only meant that it was possible to use the internet’s resources without learning a whole new language, but it allowed for rich text, graphics, animation and sound to be delivered quite literally at the click of a button.

Interview with Tim Berners-Lee

Download this audio clip.Audio player: ou_futurelearn_cyber_security_aud_1009.mp3

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Transcript

NARRATOR

In 1980, a young software consultant called Tim Berners-Lee wrote a programme called ENQUIRE. It involved the use of hypertext, links that allow users to jump directly from one computer page to another. It's sowed the intellectual seeds of an information revolution – the world wide web.

In the late 1990s, Tim gave several interviews against rather noisy backgrounds for the Open University series TheWebStory.com.

TIM BERNERS-LEE

The web is an abstract space of information. The web is a space of pages, of documents, of pictures, which are linked together. And the links are abstract links. Now in fact, for the web to exist, all this information about the links and about the documents is transferred over the internet.

NARRATOR

Tim's pioneering idea for the world wide web emerged in 1989, when he was working for CERN, the European organisation for nuclear research.

TIM BERNERS-LEE

I was just frustrated with a lack of interoperability, the fact that people were championing different documentation systems and help systems. And I tried experimenting with actually taking all the documents in one system and making it appear as though they were in this help system. So I looked at the mapping between the two, and eventually I realised that this little hypertext programme I'd been playing with 10 years before was, in a sense, the key, and that if you made a global hypertext system, any of these systems could be represented in terms of it.

And so suddenly, this was the answer to making any system available without disturbing it, even. That was the key thing. Without putting constraint on somebody, forcing them to use a particular machine, forcing them to store their documents in a particular format.

It just said, all right, let's not force any of those issues. Let's just second-guess them. Let's step above them, and let's say, whatever format you put your document in, let's say that it's part of the one universal space. And let's find a way of making an identifier for it. And once you had that idea, it's really pretty unstoppable.

So when I said, hey, I think we should make a completely general global hypertext system, the very proper answer at CERN was, well, that's fine, but it's not what we're here for. So in fact, it was only because my boss, Mike Sandel, who had a sort of twinkle in his eye, and thought, hm, I don't know what exactly this is about, but I have a feeling that it sounds kind of exciting.

And he said, well, why don't you spend the next couple of months – you know, I won't complain if you just go and write the programme. If Mike hadn't said that, if I'd had to go through the process of trying to get a formal project approved, it would never have happened.

NARRATOR

Tim's brilliant idea was to make documents located on one computer appear to be located in a window on another computer. It took Tim and his colleague Robert Cailliau two years to develop and refine the protocols that could make this happen.

TIM BERNERS-LEE

When you're looking at a web page and you click on a hypertext link, then hidden behind the actual text of what's written there is the identifier of some other page. When you click on it, then the programme which shows you that page looks up the identifier. An identifier's one of these things which starts with http://.

Now the http means if you want to get at this thing, this is how you do it. You take the rest of the string, the rest of the characters, and the first bit is something like www.acme.com. And that is the is name of a computer, in fact.

So the first thing you do is you go out to another computer you know which knows about the native computer and says, hey, where do I find this? And you get back a computer number, like 28.34.6.12. Something looking more like a telephone number of the other computer. Then your computer uses that to start communicating with the other computer, which has got the information.

And what it does, it sends a very simple message. It just says get, and then it gives the rest of all the other characters left. So when you look at something which says http:// – that means use hypertext transfer protocol. www.something.com – that means go to this computer. Slash, gobbledy-gook-gobbledy-gook.

Gobbledy-gook-gobbledy-gook, you don't have to understand. All you do is you know that's what you asked for. So it makes a connection and it sends a very simple command, which is get gobbledy-gook-gobbledy-gook. And the response is that the information about how to put up that page comes back across the internet, across that connection.

So it's really very simple. It's just, get me gobbledy-gook. Here's gobbledy-gook.

NARRATOR:

To start with, the web was limited to developments within the CERN community. Then in August 1991, Tim and his colleagues launched the first publicly available website, a milestone in the history of the internet.

TIM BERNERS-LEE

A lot of people ask, what was it like when the web – when it suddenly exploded? When – but it didn't. It didn't suddenly explode. What happened was that it was, for the first two years, a big, hard slog trying to persuade everybody that the idea of global hypertext was not too crazy, or too complicated, or too confusing, or too expensive, or whatever. And in fact, that it was very simple, and in fact, it would save time, et cetera.

So with my fellow evangelist and colleague, Robert Cailliau, we went around to conferences and we went and talked to people individually within the high-energy physics community – which was basically paying our salaries, remember. So I had to persuade them this was important for highenergy physics. And we, at the same time, sent our some emails and some articles to newsgroups and things.

And it was not apparent that it was going to actually make it for a long time. But the interesting thing was that when I looked at the logs of the servers – the first server was called info.cern.ch. And the load on that server, which started off serving 10, 100 hits a day in the summer of '90 – the load on that server went up exponentially during the next 12 months.

And then when I looked back the year after that and made a graph of the second 12 months, it was again exactly the same-shaped exponential curve. So after a while, I started plotting it on a log scale so that you could see it as it went up from the hundreds to the thousands to the tens of thousands. And the load on that server was just – as the time went on from the summer of '91, summer of '92, summer of '93, summer of '94 – the load on the server just went on increasing by a factor of 10 every year.

NARRATOR

But the growing success of the world wide web only partially realised Tim's initial dream of what might be possible.

TIM BERNERS-LEE

The first part of it was, wouldn't it be great if we had this universal information space, and everybody could be in equilibrium with it so they could exchange information very fluidly through it? Wouldn't this do something amazing for humankind, if we were connected through this information space? That was the dream, part one.

And the other half of the dream was, suppose you have a situation where any idea which is worth typing in, worth clicking in with a mouse, is in the web? Then maybe we should bring back the computers, the computers which have gotten out the way. The computers which have hidden, made themselves scarce, and just produced this information for us. Maybe we'll be able to use them again. Maybe we'll be able to write programmes which can analyse what on Earth our society is like, what on Earth we are trained to do.

That was the second part of the dream. And that's not there at all. So that, we need a whole lot more technology in the web. We need machine-understandable information. We need digital signature. We need a web of trust. We need logical reasoning out there on the web. That is going to be yet another revolution.

I think it's going to be as dramatic as the web phase I, if you like. And we haven't started yet. So really, if you think everything's over, you're completely wrong. This is just the start. We're just figuring out how to make these global revolutions using technology, and how to make them be a good thing for humankind. So jump on board now, because it's just speeding up.

ANNOUNCER

From the Open University. For more information, go to www.open.ac.uk/use.

End transcript

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Listen to this interview. Towards the end, Tim Berners-Lee mentions a number of things that will be needed to make the world wide web achieve its full potential. One of these is digital signatures, which can be achieved using cryptography – our topic for next week.

Next, you have an opportunity to review your learning of the course so far in the Week 4 compulsory badge quiz.

4 Week 4 quiz

This quiz allows you to test and apply your knowledge of the material in Week 4.

5 Summary of Week 4

Figure 14

This week you have learned the basics of computer networking and communications, gaining an understanding of how data is transmitted across the networks, including wireless networks.

You are now aware of some of the networking standards that allow different devices to connect to the network and exchange information.

Additionally, you have learned about the difference between the internet and the world wide web, and can describe some security problems that affect networks.

You are now half way through the course. The Open University would really appreciate your feedback and suggestions for future improvement in our optional end-of-course survey, which you will also have an opportunity to complete at the end of Week 8. Participation will be completely confidential and we will not pass on your details to others.

You can now go to Week 5: Cryptography.

Acknowledgements

This course was written by Arosha K. Bandara.

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2 extract (including transcript) from Datababy: How easy is it to become a phone hacker? © Channel4/ITN

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