Wired and Wireless Networks, Protocols and Layers

1 State what is meant by a protocol. 2

One mark for each of the following, to a maximum of 2.

• A set of rules
• Governing how data is transmitted or communicated between devices

Model answer. A protocol is an agreed set of rules that governs how data is transmitted and communicated between devices on a network, covering things such as how the data is formatted, how it is addressed and how errors are handled, so that different systems can understand each other.

2 Explain two differences between an IP address and a MAC address. 4

One mark for each of the following, to a maximum of 4.

• An IP address identifies a device on a network, a MAC address identifies a specific piece of hardware
• IP addresses are assigned by the network, MAC addresses by the manufacturer
• An IP address can change, a MAC address is fixed
• IP addresses route data between networks, MAC addresses deliver data within a local network

Model answer. The first difference is what they identify and who assigns them. An IP address identifies a device's position on a network and is assigned by the network itself, which means it can change, for example when a laptop joins a different Wi-Fi network. A MAC address identifies one specific piece of network hardware, is assigned by the manufacturer when the network interface card is made, and does not change. The second difference is their purpose. IP addresses are used to route data between different networks across the internet, whereas MAC addresses are used by switches to deliver data to the correct device within a single local network once it has arrived.

3 Explain why network protocols are organised into layers. 4

One mark for each of the following, to a maximum of 4.

• It breaks a complex process into smaller self contained parts
• Each layer has a specific role and only interacts with adjacent layers
• A layer can be changed or replaced without affecting the others
• It allows equipment and software from different manufacturers to work together

Model answer. Network communication is a very complex process, and layering divides it into smaller self contained parts so that each part can be designed, understood and maintained separately. Each layer is given one specific responsibility and only interacts with the layers immediately above and below it, which means a layer can be changed or replaced entirely without the rest of the stack being affected. For example, a network can switch from Ethernet cabling to Wi-Fi at the link layer while HTTP, TCP and IP continue to work exactly as before. Layering also allows manufacturers to build hardware and software that only has to comply with the rules of one layer, which means equipment from different companies can interoperate, and it makes fault finding easier because a problem can be isolated to a single layer.

4 A hotel is installing a network for its guests. Discuss whether it should use a wired or a wireless network. 6

One mark for each of the following, to a maximum of 6.

• Recommends wireless
• Guests need mobility and use their own devices in rooms and public areas
• Cheaper and less disruptive than running cable to every room
• Wireless is slower and less reliable, with signal weakened by walls and distance
• Wireless is less secure as the signal can be intercepted, so encryption is essential
• Reaches a justified conclusion, possibly a hybrid with wired backbone

Model answer. The hotel should provide a wireless network for guests. Guests arrive with their own phones, tablets and laptops and expect to use them in their rooms, in the lobby and in the restaurant, so mobility is essential and a wired connection that ties a device to one socket would not meet that need. Installing wireless access points is also considerably cheaper and far less disruptive than running Ethernet cable to every guest room in an existing building, where floors and walls would have to be opened up. There are real disadvantages. Wireless is slower and less consistent than cable, and the signal is weakened by the thick walls and long corridors typical of hotels, so careful placement of multiple access points is needed to avoid dead spots. It is also less secure, because the signal travels through the air and can be intercepted by anyone in range, so strong encryption such as WPA3 and an isolated guest network are necessary to stop guests seeing each other's traffic or reaching the hotel's own systems. The sensible solution is a hybrid: a wired backbone connecting the access points, the reception computers and the booking system, since those machines never move and benefit from the speed and security of cable, with wireless provided throughout the building for guests. This gives guests the mobility they expect while keeping the hotel's own critical systems on the faster and more secure wired network.

5 Describe the roles of the TCP and IP protocols and explain why they are used together. 4

One mark for each of the following, to a maximum of 4.

• TCP splits data into packets and numbers them
• TCP checks all packets arrive and reassembles them in the correct order
• IP addresses each packet and routes it to the correct destination
• Together they provide addressing and reliable delivery, which are both needed

Model answer. TCP, the Transmission Control Protocol, takes the data being sent and splits it into numbered packets. At the receiving end it checks that every packet has arrived, requests the retransmission of any that are missing or corrupted, and then reassembles the packets back into the original data in the correct order. IP, the Internet Protocol, is responsible for addressing: it attaches the source and destination IP addresses to each packet and determines the route the packet should take across the networks between them. They are used together because each solves only half the problem. IP can get a packet to the right destination but offers no guarantee that it arrives or that packets arrive in order, while TCP can guarantee complete, correctly ordered delivery but has no mechanism for finding the destination in the first place. Combined as TCP/IP they provide both reliable delivery and correct routing.