Computer ScienceCBSE Class 12 · Data Communication

Switching Techniques and Transmission Media: Wired and Wireless (Class 12 Computer Science)

Updated 17 October 2026 · Fact-checked

Circuit switching sets up a dedicated path between sender and receiver for the whole session, while packet switching splits the message into packets that travel independently and are reassembled at the destination. Wired media are twisted pair, co-axial cable and optical fibre; wireless media are radio waves, microwaves and infrared.

Understand Switching Techniques and Transmission Media

Switching decides how data finds a path through a network.

Circuit switching. A dedicated path is set up before the data is sent and stays reserved for the entire session, even in silent moments. All data follows the same route in order. Example: a traditional telephone call. Good for steady real-time traffic; wasteful when the line is idle; set-up takes time.

Packet switching. The message is divided into small packets. Each packet carries the addresses and a sequence number, and travels independently, possibly by a different route. Packets are reassembled in order at the destination. No dedicated path, so the links are shared efficiently. The Internet uses packet switching.

Transmission media are the paths for the signal.

*Wired (guided) media*

Twisted pair: two insulated copper wires twisted together, in unshielded (UTP) or shielded (STP) form. Cheap and easy to install, used in LANs and telephones; limited distance and affected by interference.
Co-axial cable: a copper core with insulation and a metal shield. Carries higher bandwidth than twisted pair over longer distances, with better protection from interference; used in cable TV.
Optical fibre: thin glass or plastic strands carrying light signals. Very high speed and bandwidth, long distance, free from electromagnetic interference, secure; costly and needs skilled installation.

*Wireless (unguided) media*

Radio waves: travel in all directions and pass through walls; used for FM radio, Wi-Fi and mobile phones. Can be affected by interference.
Microwaves: travel in straight lines (line of sight), need towers or satellites; used for long distance links across hills and for satellite links. Rain can reduce the signal.
Infrared: short range, line of sight, cannot pass through walls; used for TV remote controls and short data transfers.

Switching Techniques and Transmission Media: key facts

Circuit switching: Dedicated path set up before sending
Path reserved for the whole session
Data follows one route in order
Example: telephone call; Wastes capacity when idle.
Packet switching: Message split into packets
Each packet travels independently
Reassembled at the destination
No dedicated path
Example: the Internet; Efficient sharing of links.
Wired media: Twisted pair cheap, short distance
Co-axial higher bandwidth, cable TV
Optical fibre light signals, highest speed, free from interference, costly; Fibre is the best wired medium for speed and distance.
Wireless media: Radio waves all directions, pass through walls
Microwaves line of sight, long distance, satellites
Infrared short range, line of sight, remote controls; Wireless does not need cables.

Twisted pair	cheap, short distance
Co-axial	higher bandwidth, cable TV
Optical fibre	light signals, highest speed, free from interference, costly

Radio waves	all directions, pass through walls
Microwaves	line of sight, long distance, satellites
Infrared	short range, line of sight, remote controls

How to answer Switching Techniques and Transmission Media questions

For a medium or switching question use property words, and pick the medium from the need.

1Underline the need: cheapest, fastest, longest distance, no interference, wireless, or through walls.
2Match: cheapest and short, twisted pair; interference-free and fast, optical fibre; cable TV, co-axial; through walls, radio waves; hills or satellites, microwaves; remote control, infrared.
3Give a one-line reason from the properties above.
4For switching, compare along the same points: path, order of data, use of the line, example.
5In a network-design case state the best wired medium (optical fibre is expected for long, fast links) and the wireless alternative with its limitation.

Switching Techniques and Transmission Media in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Phone call versus message packets

Suppose a landline call keeps one line busy until the call ends, while a chat message is broken into pieces that travel separately and join at the receiver.

Name the switching technique of each.

Try it first, then show the solutionSolution

The call reserves a path for the entire session: circuit switching.
The chat message is split into packets and reassembled: packet switching.

Answer: Call: circuit switching. Chat message: packet switching.

Memory hook: Reserved lane versus shared roads.

Cable choice for two blocks

Suppose a school wants a fast, interference-free link between two blocks that are far apart.

Which medium should it use?

Try it first, then show the solutionSolution

Long distance, high speed and no interference point to optical fibre.
Twisted pair would be cheaper but its distance is limited and it is affected by interference.

Answer: Optical fibre

Memory hook: Light does not suffer from electrical noise.

Tricks to remember Switching Techniques and Transmission Media

Short memory aids. Say each one aloud once, then use it on a question the same day.

Circuit = reserved lane, packet = shared roads
Circuit switching reserves one path; packet switching uses shared routes.
Use it when: Comparing the techniques.
Twisted, Coax, Light
Twisted pair is cheap, coax is for TV, fibre carries light.
Use it when: Ordering wired media by power.
Radio walls, micro hills, infra remote
Radio passes through walls, microwaves cross hills in line of sight, infrared is for remotes.
Use it when: Wireless media uses.
Fibre: fast, far, free of noise
Three F-words for optical fibre.
Use it when: Why fibre is the best medium.

Switching Techniques and Transmission Media: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Interference-free medium · 1 mark · MCQBoard level

Which transmission medium is not affected by electromagnetic interference?
(a) Twisted pair (b) Co-axial cable (c) Optical fibre (d) Radio waves

Try it first, then show the solutionSolution

Fibre carries light, not electrical current.

Answer: (c) Optical fibre

Example 2: Define the two techniques · 2 marks · Short answerBoard level

Define circuit switching and packet switching.

Try it first, then show the solutionSolution

Circuit switching: a dedicated path is set up for the full session before data transfer. (1 mark)
Packet switching: the message is divided into packets that travel independently and are reassembled at the destination. (1 mark)

Answer: As in the steps.

Example 3: Compare the techniques · 3 marks · Short answerHarder board level

Compare circuit switching with packet switching for the path used, the flow of data and the use of capacity.

Try it first, then show the solutionSolution

Path: circuit switching uses a dedicated path; packet switching has none. (1 mark)
Data flow: circuit data follows one route in order; packets may take different routes and are reordered at the end. (1 mark)
Efficiency: circuit switching wastes capacity during silence; packet switching shares links efficiently. (1 mark)

Answer: See the three points above.

Example 4: Pick the medium · 3 marks · Short answerHarder board level

Suggest the most suitable medium and a reason for: (i) a TV remote control; (ii) a high-speed backbone between two buildings 2 km apart; (iii) the cheapest connection inside a computer lab.

Try it first, then show the solutionSolution

(i) Infrared: short range, line of sight, enough for a remote. (1 mark)
(ii) Optical fibre: high speed, long distance and free from interference. (1 mark)
(iii) Twisted pair (UTP): cheap and easy to install for short distances. (1 mark)

Answer: (i) Infrared (ii) Optical fibre (iii) Twisted pair

Example 5: Case: hills and a campus · 4 marks · Case-basedHOTS / competency

Suppose a university has a main campus and a research station on a hill 25 km away; a cable cannot be laid across the forest in between. Within the campus the buildings are about 300 m apart.
(i) Suggest a wireless medium for the hill link, with a reason. (1 mark)
(ii) Suggest a wired medium for the campus links, with a reason. (1 mark)
(iii) Why is infrared unsuitable for the hill link? (1 mark)
(iv) Which switching technique would the Internet traffic of the campus use? (1 mark)

Try it first, then show the solutionSolution

(i) Microwaves, which travel line of sight over long distances between towers.
(ii) Optical fibre, which gives high speed and no interference over a few hundred metres (twisted pair is cheaper but has a limited distance).
(iii) Infrared is short range and cannot pass through obstacles.
(iv) Packet switching.

Answer: (i) Microwaves (ii) Optical fibre (iii) Short range, line of sight (iv) Packet switching

Where students lose marks in Switching Techniques and Transmission Media

The slips examiners see most often, and what to write instead.

Mistake: Saying optical fibre carries electrical signals
Fibre carries light pulses, which is why it has no electromagnetic interference.
Wrong working
Optical fibre carries electrical signals through copper.
Right working
Optical fibre carries light signals through glass or plastic.
Do this: Write "light" in the definition.
Usually costs: 1 mark
Mistake: Wrong example for circuit switching
The standard example is a telephone call, not the Internet.
Wrong working
Circuit switching example: the Internet
Right working
Circuit switching example: a landline telephone call
Do this: Pair the Internet with packet switching.
Usually costs: 0.5 mark
Mistake: Choosing infrared for a long distance
Infrared has a short range and needs line of sight.
Wrong working
Infrared for the link between two cities
Right working
Microwaves or optical fibre
Do this: Choose from range and obstacles in the question.
Usually costs: 1 mark

Exam tips

In a differentiate question write three matched points, not two paragraphs.
Always give a reason from a property (speed, distance, interference, cost) for your medium choice.
Name optical fibre as the best wired medium for long, high-speed links, unless the question limits the budget.
Mention line of sight for microwaves and infrared.
Write the example: telephone call for circuit switching, the Internet for packet switching.

Practice questions on Switching Techniques and Transmission Media

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Which of the following is a wireless transmission medium?
(a) Co-axial cable (b) Twisted pair (c) Microwave (d) Optical fibre
Hint
No cable involved.
Answer
(c) Microwave
Q2 · 1 mark · Very short answerBoard level
Name any two guided (wired) transmission media.
Hint
Think of cables.
Answer
Any two of twisted pair, co-axial cable, optical fibre.
Q3 · 2 marks · Short answerHarder board level
Write two differences between twisted pair and co-axial cable.
Hint
Think of shielding and bandwidth.
Answer
Twisted pair is cheaper and easier to install but has lower bandwidth, shorter range and more interference; co-axial cable has a metal shield, so it gives higher bandwidth and better protection from interference over longer distances.
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The Internet uses packet switching.
Reason (R): In packet switching a dedicated path is reserved for each session.
(a) Both A and R are true and R is the correct explanation of A. (b) Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is true.
Hint
Does packet switching reserve a path?
Answer
(c) A is true but R is false: packet switching has no dedicated path.
Q5 · 3 marks · Short answerHOTS / competency
Suppose an online-class provider moves lessons as many small packets instead of reserving a line for each student. Give three reasons why this suits thousands of students at once, and name one risk.
Hint
Think sharing and independent routes.
Answer
Links are shared, so unused capacity is not wasted; packets can use different routes around busy or failed links; no set-up per session. Risk: packets may arrive late or out of order and must be reassembled, which can cause delays.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is a packet?Show answer
A small unit into which a message is divided for sending.
2.Which switching technique reserves a path?Show answer
Circuit switching.
3.Which medium uses light?Show answer
Optical fibre.
4.Which wireless medium passes through walls?Show answer
Radio waves.
5.Which wireless medium is used by a TV remote?Show answer
Infrared.
6.What kind of path do microwaves need?Show answer
Line of sight.

Switching Techniques and Transmission Media: frequently asked questions

What is the difference between circuit switching and packet switching?

Circuit switching reserves a dedicated path for the whole session; packet switching splits data into packets that travel independently and are reassembled at the destination.

Which transmission medium is the best?

For speed, distance and freedom from interference, optical fibre is the best wired medium; for no cabling, radio waves or microwaves are used depending on distance and obstacles.

What is the difference between guided and unguided media?

Guided (wired) media such as twisted pair, co-axial cable and optical fibre carry the signal through a cable; unguided (wireless) media such as radio waves, microwaves and infrared carry it through the air.

Why is twisted pair used in labs?

It is cheap, flexible and easy to install, and the distances inside a lab are short.