Wired and Wireless Networks, Protocols and Layers
Wi-Fi against Ethernet, IP and MAC addressing, every protocol on the specification with what it actually does, and why layering makes the internet possible.
Wired and wireless
Wired, usually Ethernet
- Faster and more consistent speeds
- More secure, since an attacker needs physical access to the cable
- More reliable, no interference from walls or other devices
- Lower latency, important for gaming and video calls
- But: devices cannot move, and installing cabling is expensive and disruptive
Wireless, Wi-Fi or Bluetooth
- Convenient, devices can move freely
- Cheaper and quicker to install, no cabling needed
- Many devices can connect easily
- But: slower and less reliable, signal weakens with distance and is blocked by walls
- Less secure, since the signal travels through the air and can be intercepted, so encryption is essential
Wired networks offer speed, reliability and security. Wireless offers convenience, mobility and lower installation cost.
Bluetooth is short range wireless, typically under 10 metres, designed for connecting a small number of devices directly, such as headphones to a phone. Wi-Fi is longer range and higher bandwidth, designed to connect devices to a network.
IP addresses and MAC addresses
IP address
An IP address identifies a device on a network and is used to route data between networks.
- IPv4 uses 32 bits, written as four denary numbers 0 to 255, for example
192.168.1.24 - IPv6 uses 128 bits, written as eight groups of hexadecimal, because IPv4 addresses have run out
- IP addresses are assigned by the network and can change, for example each time you join a different Wi-Fi network
MAC address
A MAC address, media access control, identifies a specific piece of hardware.
- 48 bits, written as six pairs of hexadecimal digits, for example
00:1B:44:11:3A:B7 - Assigned by the manufacturer and does not change
- Used by switches to deliver data within a local network
| IP address | MAC address | |
|---|---|---|
| Identifies | A device on a network | A specific piece of hardware |
| Assigned by | The network | The manufacturer |
| Changes | Yes, can change | No, it is fixed |
| Used for | Routing between networks | Delivery within a local network |
| Format | 192.168.1.24 or IPv6 hex | 00:1B:44:11:3A:B7 |
A common misconception is that one replaces the other. The IP address gets the data to the right network, and the MAC address then gets it to the right device on that network.
- The MAC address belongs to the hardware, so it stays the same wherever the laptop goes.
- The IP address is given by the network, so the same laptop has a different one at home and at school.
- MAC: manufacturer, never changes, local delivery. IP: network, changes, routing between networks.
Standards and protocols
A standard is an agreed way of doing something, so that hardware and software from different manufacturers can work together.
A protocol is a set of rules governing how data is transmitted between devices. Without shared protocols, two computers would be talking different languages.
| Protocol | Full name | What it does |
|---|---|---|
| TCP | Transmission Control Protocol | Splits data into packets, checks they all arrive, requests any that are missing, and reassembles them in the right order |
| IP | Internet Protocol | Addresses and routes packets across networks so they reach the right destination |
| HTTP | Hypertext Transfer Protocol | Requests and transfers web pages between a browser and a web server |
| HTTPS | HTTP Secure | The same as HTTP but the data is encrypted, protecting it from being read if intercepted |
| FTP | File Transfer Protocol | Sends and receives files between computers, typically uploading to a server |
| POP | Post Office Protocol | Retrieves email from a server and normally deletes it from the server |
| IMAP | Internet Message Access Protocol | Retrieves email but keeps it on the server, so it syncs across multiple devices |
| SMTP | Simple Mail Transfer Protocol | Sends email from a client to a server, and between mail servers |
SMTP sends. POP downloads and removes. IMAP downloads and keeps synced. If a question mentions reading the same emails on a phone and a laptop, the answer is IMAP.
TCP/IP working together
TCP and IP are almost always used as a pair.
- TCP handles the reliability: breaking data into packets, numbering them, checking they arrive and reassembling them.
- IP handles the addressing: making sure each packet is routed to the correct destination.
- Your message is too big to send in one go, so it is split into packets.
- Every packet carries the destination address and its own number.
- Each router picks the next hop, so packets can take different routes, even around a broken link.
- They arrive out of order, and the numbers put them back together.
- SMTP sends email, from the sender to their server and between mail servers.
- POP downloads mail and normally deletes it from the server, so it lives on one device.
- IMAP keeps mail on the server, so a phone and a laptop both show the same mailbox.
Layers
Network protocols are organised into layers. Each layer has a specific job and only interacts with the layers directly above and below it.
The four layer TCP/IP model:
| Layer | Job | Example protocols |
|---|---|---|
| Application | Provides services to the user's software | HTTP, HTTPS, FTP, SMTP, IMAP |
| Transport | Splits data into packets and ensures reliable delivery | TCP, UDP |
| Internet | Adds addresses and routes packets across networks | IP |
| Link | Handles the physical transmission over the medium | Ethernet, Wi-Fi |
Why layering is used
- It breaks a complex problem into manageable parts, so each layer can be designed and understood separately.
- Layers can be changed independently. Switching from copper to fibre changes only the link layer, and everything above it carries on unchanged.
- It allows interoperability, because manufacturers only need to follow the rules of the layer they are working in.
- It makes fault finding easier, since a problem can be isolated to one layer.
- Different protocols can be used at the same layer without affecting the rest, for example choosing IMAP instead of POP.
Layers divide the complexity of network communication into self contained parts, so each layer can be developed, changed or replaced without affecting the others.
- Your message starts at the top, in the application.
- Transport splits it into segments and adds a port number.
- Internet wraps each segment in a packet and adds IP addresses.
- Link turns the packet into a frame with MAC addresses, and it goes out.
- At the other end the same four layers run in reverse, unwrapping it.
Key terms you must be able to define
- Protocol
- A set of rules governing how data is transmitted between devices.
- Standard
- An agreed specification that allows equipment from different manufacturers to work together.
- IP address
- An address identifying a device on a network, used to route data between networks.
- MAC address
- A unique address assigned to network hardware by its manufacturer, used within a local network.
- TCP
- Transmission Control Protocol. Splits data into packets and guarantees they arrive and are reassembled correctly.
- IP
- Internet Protocol. Addresses and routes packets across networks.
- HTTPS
- The encrypted version of HTTP, protecting web traffic from being read if intercepted.
- SMTP
- The protocol used to send email.
- POP
- A protocol that retrieves email and normally deletes it from the server.
- IMAP
- A protocol that retrieves email while keeping it on the server so it syncs across devices.
- Layer
- A distinct level of network functionality with a defined job, interacting only with adjacent layers.
Flashcards
Say the definition out loud before you flip the card. Retrieving it from memory is what builds recall, reading it again is not.
Reach the top grade on this topic
Two things earn the top marks here.
Never define a protocol as 'a set of rules' and stop. Every protocol is a set of rules. Say what the rules are for. TCP is the set of rules for splitting data into packets and ensuring they arrive complete and in order.
On layering, give a consequence not just a description. The strongest phrasing names a change and says what is unaffected: "Because Wi-Fi and Ethernet both sit at the link layer, a network can switch from cable to wireless without any change to HTTP, TCP or IP above it."
The email protocols come up almost every year, and the discriminator is IMAP against POP. Learn the scenario: multiple devices means IMAP.
- Match all eight protocols to their function without hesitation
- Explain the IP against MAC distinction using assignment and purpose, not just format
- Give three benefits of layering, each with a consequence
- Choose wired or wireless for a scenario and justify with the specific constraint in the question
Mistakes that cost marks here
- Saying HTTPS 'is more secure' with no mechanism. It encrypts the data so that intercepted traffic cannot be read.
- Saying POP and IMAP send email. They retrieve it. SMTP sends.
- Saying a MAC address can be assigned by the network. It is set by the manufacturer.
- Describing layers as 'to make it faster'. Layering is about manageability and interoperability, not speed.
- Giving TCP the job of addressing. TCP handles packets and reliability, IP handles addressing and routing.
Your MAC address is burned into the network card at the factory and the first half identifies the manufacturer. Given only a MAC address, you can look up who made the device, which is why some phones now randomise it for privacy.
Knowledge check
Exam-style questions
Five written questions in the style of the real paper. Write a full answer, then let the marker check it against the mark scheme.
- LA set of rules
- LGoverning how data is transmitted or communicated between devices
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.
- LAn IP address identifies a device on a network, a MAC address identifies a specific piece of hardware
- LIP addresses are assigned by the network, MAC addresses by the manufacturer
- LAn IP address can change, a MAC address is fixed
- LIP addresses route data between networks, MAC addresses deliver data within a local network
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.
- LIt breaks a complex process into smaller self contained parts
- LEach layer has a specific role and only interacts with adjacent layers
- LA layer can be changed or replaced without affecting the others
- LIt allows equipment and software from different manufacturers to work together
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.
- LRecommends wireless
- LGuests need mobility and use their own devices in rooms and public areas
- LCheaper and less disruptive than running cable to every room
- LWireless is slower and less reliable, with signal weakened by walls and distance
- LWireless is less secure as the signal can be intercepted, so encryption is essential
- LReaches a justified conclusion, possibly a hybrid with wired backbone
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.
- LTCP splits data into packets and numbers them
- LTCP checks all packets arrive and reassembles them in the correct order
- LIP addresses each packet and routes it to the correct destination
- LTogether they provide addressing and reliable delivery, which are both needed
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.