Communication

LAN hardware and routers

Networks including the internet AS Level 14 min read

On this page

What you need to be able to do
The devices in a LAN
The router
Mark-scheme focus
Worked examples
Summary
Can I do this?
Quiz

What you need to be able to do

Syllabus 2.1 Networks including the internet

2.1Describe the hardware used to support a LAN: switch, server, NIC, WNIC, WAP, cables, bridge, repeater.
2.1Describe the role and function of a router in a network.

You need: Network topologies. Next: Ethernet and CSMA/CD.

The devices in a LAN

Where each device sits in a typical LAN.

Device	Purpose (credited wording)
NIC (network interface card)	hardware that lets a device connect to a (wired) network; it has a unique MAC address that identifies the device on the network
WNIC (wireless NIC)	provides the interface to a wireless network, acting as an antenna; receives analogue radio waves and converts them to digital (and digital → radio waves to send); checks incoming transmissions for its MAC address and ignores the rest; encrypts / decrypts the data; gives the device a unique MAC address (not an IP address)
Switch	the central connection point of a star; stores the MAC addresses of the devices connected to it; receives packets and forwards them only to the intended recipient
Hub (older)	connects devices like a switch, but sends every packet to every device; more collisions, less secure
Server	a powerful computer that provides a service to the clients: file storage, printing, email, web pages, log-ins and security
WAP (wireless access point)	allows wireless devices to connect to a wired network, sending and receiving radio / Wi-Fi signals between the central device and the nodes
Cables	the wired transmission medium: copper (Ethernet twisted pair) or fibre-optic
Bridge	connects two LANs / segments that use the same protocol so they act as one network; it passes on only the packets meant for the other side
Repeater	restores (regenerates) the digital signal so it can be transmitted over greater distances: signals fade along a cable

Describe, don't expand. “A WAP provides a wireless access point” and “a WNIC acts like a NIC in a wireless network” were not credited (June 2022, November 2021): say what the device does.

A NIC / WNIC gives a device its MAC address (burnt in, unique). The IP address is a separate, logical address - often handed out by the router. Confusing the two was a frequent error (November 2021).

The router

A router connects different networks (e.g. a LAN to the internet) and directs packets between them along the best route.

It receives packets from the devices on the LAN or from the internet.
It analyses the destination IP address in each packet's header.
It looks up its routing table to find the most efficient route to the destination, and forwards the packet towards it (to the next router, or to the device on the LAN).
It maintains / updates the routing table as routes change.
On a home or office LAN it also: allocates private IP addresses to the devices (DHCP); gives the whole LAN one public IP address and translates between them (Network Address Translation, NAT); keeps a table of MAC and IP addresses; acts as a gateway and converts the packet format / protocol for the next network; and may run a firewall.

A router DOES	A router does NOT
receive packets and forward them towards the destination	send each packet to every device (a hub does that)
store the IP and / or MAC addresses of the devices attached to it	find the IP address of a URL (that is the DNS server's job)
hold a routing table and choose efficient routes	store websites

Answer in the context given. The November 2021 report: for a home network, generic lists and “it lets devices connect to the internet” (already in the question) scored little. “It allocates a private IP address to each of Andy's devices.”

Use the word packet, and mention IP / MAC addresses: a good description of a router's role “would include statements about the receipt and forwarding of packets and the appropriate use of IP and MAC addresses” (November 2022).

Mark-scheme focus

Describe the functions of a WNIC (4 marks)

(c) The school has several laptops. Each laptop has a Wireless Network Interface Card (WNIC). Describe the functions of a Wireless Network Interface Card. [4] — 9618/11/O/N/21 Q8Paper 1 · Theory fundamentalsPart (c)4 marksFull size

Credited

Provides an interface to the wireless network … as an antenna B1 B1
Receives analogue radio waves … converts them to digital / binary B1 B1
Checks incoming transmissions for the correct MAC / IP address … ignores transmissions not intended for it // encrypts / decrypts the data // converts digital to analogue waves and sends them via the antenna

Not credited

“A WNIC functions like a NIC but wirelessly”
“It provides an IP address” (it provides a MAC address)
Generic NIC descriptions

From: 9618/11/O/N/21 Q8(c)

Complete the table of network devices (4 marks)

(a) Complete the table: a device that receives and sends data between two networks operating on the same protocol; a description of a Wireless Network Interface Card (WNIC); a device that restores the digital signal so it can be transmitted over greater distances; a description of a Wireless Access Point (WAP). [4] — 9618/12/M/J/22 Q9Paper 1 · Theory fundamentalsPart (a)4 marksFull size

Credited

Receives and sends data between two networks on the same protocol → router (a bridge fits the same description) B1
WNIC → hardware that allows a device to connect to a wireless network // provides a MAC address to identify the device on the wireless network B1
Restores the digital signal → repeater B1
WAP → hardware that provides radio communication from the central device to nodes on the network (and vice versa) B1

Not credited

WAP: “provides a wireless access point”
Descriptions only about connecting to the internet

From: 9618/12/M/J/22 Q9(a)

Describe the role and function of the router (3 marks)

(b)(ii) A router connects the LAN (four computers, a server and a switch) to the internet. Describe the role and function of the router in the network. [3] — 9618/12/O/N/22 Q10Paper 1 · Theory fundamentalsPart (b)(ii)3 marksFull size

Credited

Receive packets from devices / the internet; find the destination of packets using the IP address; forward packets to the destination B1 B1 B1
or: assign private IP addresses to devices on the LAN; store / update a routing table; find the most efficient path; maintain a table of MAC and IP addresses; provide the LAN with a public IP address; act as a gateway / protocol conversion / firewall

Not credited

“The router connects the LAN to the internet” (in the question)
“package” / “data” instead of packet

From: 9618/12/O/N/22 Q10(b)(ii)

Router role / functions: in most papers (2-3 marks): receive packets → read destination IP → routing table → forward; plus LAN jobs (private IPs, public IP, NAT).
Device tables: complete a device / purpose table (3-4 marks): switch, WAP, bridge, repeater, WNIC.

Worked examples

Example 1 · A school's router, switch, WAP and bridge (Paper 1, 6 marks) ★ Easy

A school has a LAN. (a) The LAN connects to the internet using a router. Describe the function of a router in a network. [3] (b) Complete the table by writing the purpose of each of these other hardware devices used to support the LAN: switch; Wireless Access Point (WAP); bridge. [3] — 9618/11/O/N/23 Q2Paper 1 · Theory fundamentalsParts (a) and (b)6 marksFull size

1 Read it with me what is actually happening?

(a) three separate router jobs. (b) one purpose each - say what the device does, not what its name means.

function of a routerwhat it does with packets
purposewhy the device is there

2 What is it asking for? the target, part by part

(a)three functions3
(b)three purposes3

3 What do we know? everything the question gives us

4 Plan the route work backwards from what we want

FindKey ideaAlready have itWork out firstTrap

(a)
- 1receives packets
- 2reads destination IP
- 3forwards via routing table
(b)
- Switchforwards to destination
- WAPradio link to wired network
- Bridgejoins two LANs, same protocol

5 Now solve it have a go on paper first, then open the worked solution

(a) Receives packets from the internet / external network B1; analyses the destination IP address of each packet B1; forwards the packet towards its destination using the routing table B1
(b) Switch: receives transmissions and forwards them to their destination // connects devices so they can communicate B1
WAP: allows wireless-enabled devices to connect to a wired network using radio / Wi-Fi signals B1
Bridge: connects two LANs / segments with the same protocol B1

6 Check it does the answer make sense?

No answer just expands an acronym ✓.

Example 2 · What does a router do - and not do? (Paper 1, 2 marks) ★ Easy

(c) Melinda connects her laptop to the internet through her router. (i) Tick one box in each row to identify whether the task is performed by the router or not: receives packets from devices; finds the IP address of a URL; directs each packet to all devices attached to it; stores the IP and/or MAC address of all devices attached to it. [2] — 9618/11/M/J/21 Q4Paper 1 · Theory fundamentalsPart (c)(i)2 marksFull size

1 Read it with me what is actually happening?

Four tasks; two belong to other devices. Who finds the IP address of a URL? Who sends a packet to everyone?

finds the IP address of a URLDNS
directs to all deviceshub / bus

2 What is it asking for? the target, part by part

(c)(i)four ticks2: one per pair of rows

3 What do we know? everything the question gives us

4 Plan the route work backwards from what we want

FindKey ideaAlready have itWork out firstTrap

5 Now solve it have a go on paper first, then open the worked solution

Receives packets from devices: performed
Finds the IP address of a URL: not performed (DNS server)
Directs each packet to all devices: not performed (it forwards to the destination)
Stores the IP and / or MAC addresses of attached devices: performed B2

6 Check it does the answer make sense?

1 mark for the first two rows correct, 1 for the last two ✓.

Example 3 · Three functions of a home router (Paper 1, 3 marks) ★★ Medium

Andy plays games over the internet; several devices connect wirelessly to the router in his house. (b)(ii) The router has a wireless access point (WAP). Identify three functions of the router in Andy's network. [3] — 9618/12/O/N/21 Q3Paper 1 · Theory fundamentalsPart (b)(ii)3 marksFull size

1 Read it with me what is actually happening?

Functions of the router (not the WAP) in Andy's home network.

of the routernot the WAP's radio job
in Andy's networkhome LAN context

2 What is it asking for? the target, part by part

(b)(ii)three functions3

3 What do we know? everything the question gives us

4 Plan the route work backwards from what we want

FindKey ideaAlready have itWork out firstTrap

Is “lets his devices connect to the internet” enough?

No: it repeats the question.

5 Now solve it have a go on paper first, then open the worked solution

Receive packets from devices or the internet B1
Forward / route packets to their destination (using the destination address / routing table) B1
Assign private IP addresses to Andy's devices // maintain a table of MAC and IP addresses // find the most efficient path B1

6 Check it does the answer make sense?

None of the three is a WAP job ✓.

Example 4 · The role of a switch (Paper 1, 3 marks) ★ Easy

(e) Describe the role of a switch in a network. [3] — 9618/12/M/J/25 Q6Paper 1 · Theory fundamentalsPart (e)3 marksFull size

1 Read it with me what is actually happening?

Three things a switch does with packets and addresses.

2 What is it asking for? the target, part by part

(e)three points3

3 What do we know? everything the question gives us

4 Plan the route work backwards from what we want

FindKey ideaAlready have itWork out firstTrap

5 Now solve it have a go on paper first, then open the worked solution

Stores the MAC addresses of devices connected to it B1
Receives packets from devices B1
Forwards packets directly to the intended recipient // central point of connection, enabling devices to communicate B1

6 Check it does the answer make sense?

“Directly to the recipient” is what separates a switch from a hub ✓.

Summary

NIC / WNIC: connect a device (wired / wireless); unique MAC address; WNIC converts radio ↔ digital and ignores other MACs.
Switch: central point, stores MACs, forwards only to the destination. WAP: wireless devices onto a wired network. Bridge: joins two LANs with the same protocol. Repeater: regenerates the signal.
Router: receives packets, reads destination IP, routing table, forwards; on a LAN also allocates private IPs, public IP / NAT, gateway, firewall.

If you see…	do this
“describe a device”	what it does, not what the letters stand for
“role of a router”	packets + IP addresses + routing table (+ LAN jobs in context)
“WNIC”	antenna, radio ↔ digital, MAC address check, encryption

Can I do this?

I can describe the purpose of a NIC, WNIC, switch, server, WAP, bridge and repeater.
I know MAC addresses come from the NIC and IP addresses are separate.
I can describe the role and functions of a router, including on a home LAN.
I know what a router does not do (find a URL's IP, broadcast to all).

Anything unticked: revise that section first. All ticked: take the quiz.

Quiz

The multiple-choice and guided questions need JavaScript. The concept checks and exam practice below work without it.

Concept checks

Answer each one in your head first, then open it.

1Why does a switch need MAC addresses but a router uses IP addresses?Show answer

A switch delivers within one LAN, where each device's hardware (MAC) address is known; a router moves packets between networks, where logical IP addresses describe where a network is.

2Why can a laptop have the same MAC address everywhere but a different IP address on each network?Show answer

The MAC is fixed in its network card; the IP address is given by whichever network it joins.

3Why does a home router give out private IP addresses?Show answer

There aren't enough public IPv4 addresses for every device; the LAN shares one public address and the router translates (NAT).

Exam-style practice

New questions, not used above. Do them on paper, then mark your work against the official mark scheme.

Q1Past-paper style3 marks

A long corridor in a school needs a network cable 180 m long, and two classroom LANs must be joined into one network.

(a)
Identify the device needed for the long cable and describe its purpose.
[2]
(b)
Identify the device used to join the two classroom LANs.
[1]

Show the mark scheme

Part	Answer / working	Marks
(a)	Repeater	B1
	Restores / regenerates the digital signal so it can travel further	B1
(b)	Bridge (same protocol) // switch	B1
Total: 3 marks

Q2Past-paper style3 marks

Describe three functions of a router in a home network.

Show the mark scheme

Part	Answer / working	Marks
	Receives packets from devices / the internet and forwards them to their destination	B1
	Allocates private IP addresses to the devices on the LAN	B1
	Provides the LAN with a public IP address / NAT // maintains a routing table // acts as a firewall	B1
Total: 3 marks

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