Which one of the given hardware components is used to establish communications between two computers that are connected either through LAN or Internet protocol?

1  Layered network protocols

• Network communication relies upon the interaction of many different protocols. These protocols are designed to implement a particular set of rules and conventions governing particular aspects of how devices in a network communicate.
• Network protocols are arranged in layers, with each layer providing a specialised service for the layer above. Because each layer consists of standardised protocols that perform functions to an agreed set of rules, it is possible to modify individual protocols within a layer without having to change protocols in other layers.
• To visualise this concept of layers, consider a conversation between two people:
  • Content layer: ideas exchanged in conversation.
  • Rules: agree to speak a common language, take turns speaking, not to interrupt when others are speaking.
  • Physical: face-to-face communication requires speakers to be close enough to hear each other.
• In this example, the conversation has been divided into three layers. The physical layer considers the fundamental requirements of exchanging information between two people using speech. This includes considering the distance between the speakers, which will affect how loud each person needs to talk in order for the other to hear. Speech is a movement of air, which is translated as sound waves. This means that the conversation could take place in a ‘near’ vacuum like outer space.
• The rules layer defines how the speakers will talk. To exchange information, a common language would need to be chosen. Once the language is agreed, how is the conversation to be managed? Taking turns is a reasonable way to converse with another person and interrupting would be considered rude. But what happens if one person misses something and wishes it to be repeated? Do they ask for it to be repeated verbally, or do they use an agreed signal such as raising a hand?
• The content layer considers the actual message exchanged between the two speakers, which in a conversation may be an item of news, plans for a holiday or just gossip.
• By dividing the conversation into layers, we have decided upon the particular functions that are required by each layer to support communication, and in our simple layered model, it should be possible to change some aspects within one layer without affecting the others. For example, if we now decide to have a telephone conversation, how does this change the requirements of our physical layer?
• Networking protocols can be layered in a similar manner to the voice conversation in the example above, but has a wider range of considerations and uses different terms:
  • Encoding: language to use.
  • Formatting: greeting, recipient identity, closing phrase, sender identity.
  • Message size: segmentation of data.
  • Timing: flow control and timeout.
  • Delivery: to one host (unicast), to all hosts (broadcast), to some hosts (multicast).
  We will discuss these terms in more detail as you progress through the course.

5  Internet layer

• This layer allows computing devices to exchange data across networks. It receives segments of data from the transport layer protocols and encapsulates them within packets. The packets contain address information identifying the source and destination devices, allowing packet switching devices such as routers to route them to the correct destination network.
• There are two Internet layer protocols currently in use:
  • Internet Protocol v4 (IPv4): this is the most popular TCP/IP Internet layer protocol, which uses 32-bit addresses, superseding historically previous versions. The networking industry is slowly phasing out IPv4 due to the rapid growth of the Internet and the increasing demand for IP addresses, which it can no longer support. However, this will take considerable time as there are many systems and devices still dedicated to IPv4.
  • Internet Protocol v6 (IPv6): this is the replacement for IPv4. It uses a 128-bit address and is capable of supporting the expected future growth of devices connecting to the Internet.
• The switchover from IPv4 to IPv6 was facilitated by the layered approach to network protocols. Because IPv6 can perform the same function as IPv4, there was no requirement to redesign the protocols above (TCP and UDP) or below the Internet layer.

Activity: Compare IPv4 to IPv6

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7.2.1  Switches

• Switches provide connectivity points within a network, allowing you to add a large number of devices to a network, typically using UTP cabling. Because the most common network access protocol is Ethernet, most switches will support it and are thus referred to as Ethernet switches. Ethernet switches have now largely replaced the older and much slower Ethernet hubs.

• Switches provide multiple Ethernet NICs, which are referred to as ports. You can use a UTP cable to connect multiple computing devices to the ports:

• The term used to describe the layout of your devices is ‘network topology’. The simple layout shown above is referred to as a star topology, as it resembles a multi-pointed star. Note that each of the UTP cables shown must be no longer than 100m.
• The number of computing devices you can connect using a single switch is limited to the number of ports that are available. If you need to add more devices, or you wish to extend the size of your network, you can connect two switches together. This topology is referred to as an extended star:

• The Ethernet network access protocol was originally designed to support data rates of 10Mbps. This is too slow to support modern networks, so the protocol has evolved to support greater data rates.
• Most Ethernet switches are capable of supporting several Ethernet variants on each port. Although it is possible to configure each port to operate at a particular data rate, most Ethernet switches will negotiate with the connected computing device and set themselves to the highest data rate that they both support. It is best practice to connect switches together using the fastest data rate port available.
• Switches forward data between computers using the destination MAC addresses contained in the frames they receive. This means that switches have no knowledge of the IP addresses of the packets contained within the frames, so they cannot be used to join together different IP networks. Referring to the diagram below, all the PCs are addressed within the same IP network and the switches will successfully forward data between them.

• The diagram below shows the same topology, but this time the PCs have been placed in different IP networks. While the switches will forward data between the PCs based on the MAC addresses in the Ethernet frames, the PCs will refuse to communicate with devices outside their own IP network.

Activity: Data rates

Research the data rates supported by the following Ethernet variants:

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7.2.3  Wireless Access Points (WAP)

• You can send data directly between two devices using WiFi provided that the devices have compatible wireless NICs fitted. This is very useful if you wish create a temporary connection between the devices, but it can prove difficult to manage as you try to connect more devices.
• Using a wireless access point in your network provides a central WiFi connection point to which all WiFi capable devices must connect in order to exchange data. In effect, you have created a star topology without wires:

• While a single star topology WiFi network can be useful, you are more likely to meet WAPs connected to Ethernet switches, allowing the network to provide both wired and wireless network access:

8  Network address translation

• You will have read about NAT when exploring IP packet forwarding, but it is covered in more detail here.

• If you examine the diagram below, you will see that the home LAN is using IP addresses in IP network 192.168.0.0/24, which will be the case for all the ISP’s customers who are using the same type of home router. This will cause problems, as the source and destination addresses have to be unique in every communication unicast (sending packets between two devices).

• Why do home routers use the same address on the home LAN if it will cause problems within the Internet? Remember, IPv4 cannot provide sufficient IP addresses for all the devices that want to use IP, so certain ranges of IP address, including 192.168.0.0/16, are set aside as private addresses.
• Private IP addresses can be used by anyone, at any time, within a private network. This addresses the issue of not having sufficient IP addresses, but creates a problem in that the IP address cannot be used to communicate over the Internet as it is not unique. However, you will have a unique, public IP address assigned to your home router on the interface that connects to the ISP, which in the diagram above is 82.10.250.19.
• The idea of NAT is to convert the source address from all outgoing LAN packets into the unique public address assigned to the home router, and vice versa for incoming packets from the Internet.

IP addresses in packets

• The image below shows a packet transmitted from the home PC towards the web server, which needs to be routed towards the Internet by the home router:

• Note that in the diagram above the source address is 192.168.0.101, which is private.
• The packet will be received by the home router, which will perform NAT, converting the source address to its own WAN interface IP address (82.10.250.19):

• The packet can now be forwarded through the Internet to the destination web server, which will return the requested webpage in a series of packets:

• The IP packet is now addressed with the web server acting as the source, and the public address of the home router WAN interface as the destination. The home router will accept the incoming packet, and translate the destination address back to the private IP address of the home PC:

• The use of NAT and private IP addresses has extended the life of IPv4 well beyond what would have been possible with the original range of addresses it provided. Private IP addresses and NAT are implemented within most home and business networks.

9  Using networks securely

• You need to consider the security of your home network in order to protect your personal security. If your network is not secured, or you use it in an insecure way, then you increase the risk of threats to yourself and your data.
• Consider some of the activities that you undertake via the Internet:
  • emailing
  • sending photographs
  • chatting
  • posting to wiki
  • shopping
  • banking.
• What would be the impact if someone was able to intercept any information you sent while doing these activities? It could range from personal embarrassment to severe financial loss. You would probably not do any of these things with a stranger sat next to you, but when you do them over the Internet, there is a risk that your data can be intercepted by others.
• What could be the motivation for trying to access your information? The list is long, but some popular reasons are:
  • general nosiness
  • a wish to bully or get you into trouble
  • a wish to steal your money or data
  • a desire to impersonate you while carrying out a criminal activity.
• To start securing your network, consider the passwords that you use to protect access to your online accounts, and to your network devices such as PCs, tablets and home routers.
  • Your passwords need to be strong. Use a mix of numbers, letters and special characters. Do not use anything that could be guessed, such as a pet’s name or a birthday.
  • You need to change your passwords regularly in case other people learn them.
  • Do not tell your passwords to anyone. Ever.
  • If you have set up a password hint, do not make the hint too obvious.
  • Do not use the same password across multiple accounts and devices. If someone learns it, they have access to everything.
  • Do not write your passwords down.
• You also need to consider how your devices handle your passwords, as some will try to be helpful and store them for you. If you are using a public computer to access a website that requires you to enter a password, the browser may offer to store it for you. This is not a good idea, as the next user of the computer can access your passwords.
• If you log into your account and then walk off to do something else, leaving the computer unattended, anyone else who is present can access your account. If you leave your PC or device, logout from it first. Most PCs, tablets and smartphones can be configured to automatically logout after a short period of inactivity, so find out how to set this up.

12  Activities

Activity: Investigating your home network

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Activity: Network devices and protocols – Packet Tracer

We connect our devices to the Internet and the Internet connects them all together. But what is the Internet made of? We say it interconnects all the devices, but how?

Network devices are mainly hubs, switches or routers. There are lots of other specialist bits, but the bulk of the interconnectivity is done by switches and routers. In this course you have looked at client server models, web requests and emails. What do these messages look like and how are they sent?

For each type of communication over the network there are a set of rules and specifications as to what format and order the information is sent. These are called protocols and they are fundamental in understanding how the Internet works.

This Packet Tracer lab explores the devices and protocols used in computer networks. You will need:

Activity: Password hints

Companies do not store a user’s passwords in clear text – they send it through a scrambling algorithm to produce a 'hash', and the hash is then saved. The hash algorithm does not work in reverse, so you can't unscramble a hash to get the original password. When you enter your password the site uses the same algorithm to make a hash, which it then compares to the hash saved against your details.

Some sites allow you to store password hints, and they save these as clear text. Adobe was hacked in 2013, and its hashed passwords and hints were stolen for thousands of customers. The hackers looked at all the hints that gave the same hash (hence were the same password). Because they had lots of hints for the same password it was easy to guess what they were.

Can you guess the passwords used in this puzzle based on the stolen hints?

13  Resources

For more information, take a look at the following resources.

• Watch this computer networking tutorial to explore what is a protocol:

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• For a detailed look at the complexity of what happens when you click a URL read Igor Ostrovsky’s blog post.
• Read Google's guide to online safety.
• Read How-To Geek’s guide to choosing a good password and watch the following video:

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• Read Action Fraud’s guide to phishing and watch the following video:

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• Watch this video on being cautious when using public WiFi:

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14  End of course quiz

Now it’s time to test what you’ve learned in a quiz.

15  Acknowledgements

Grateful acknowledgement is made to the following sources:

Figure 1: Birmingham City University (BCU)

Figure 2: Birmingham City University (BCU)

Figure 3: Cisco

Figure 4: Birmingham City University (BCU)

Figure 5: Birmingham City University (BCU)

Figure 6: CommScope. This file is licensed under the Creative Commons Attribution-Noncommercial-NoDerivatives Licence http://creativecommons.org/licenses/by-nc-nd/2.0/

Figure 7: tlsmith2000. This file is licensed under the Creative Commons Attribution-Share Alike Licence http://creativecommons.org/licenses/by-sa/2.0/

Figure 8: Bull3t Hughes. This file is licensed under the Creative Commons Attribution-Share Alike Licence http://creativecommons.org/licenses/by-sa/2.0/

Figure 9: Cisco

Figure 10: Cisco/Birmingham City University (BCU)

Figure 11: Cisco/Birmingham City University (BCU)

Figure 12: Cisco/Birmingham City University (BCU)

Figure 13: Cisco/Birmingham City University (BCU)

Figure 14: Cisco/Birmingham City University (BCU)

Figure 15: Cisco

Figure 16: Cisco/Birmingham City University (BCU)

Figure 17: Cisco/Birmingham City University (BCU)

Figure 18: Cisco/Birmingham City University (BCU)

Figure 19: Publisher unknown

Figure 20: Cisco/BCU

Figure 21: Birmingham City University (BCU)

Figure 22: Birmingham City University (BCU)

Figure 23: Birmingham City University (BCU)

Figure 24: Birmingham City University (BCU)

Figure 25: Birmingham City University (BCU)

Figure 26: Publisher unknown

Figure 27: Screenshot taken from Barclays, example of phishing.

Every effort has been made to contact copyright holders. If any have been inadvertently overlooked the publishers will be pleased to make the necessary arrangements at the first opportunity.

Which one of the given hardware components is used to establish communication between two computers that are connected either through LAN or Internet protocol?

What components are needed to work together when connecting a computer to the Internet?

What piece of hardware is used to allow a computer to communicate with another computer?

Which hardware is used to connect two or more networks?