Circuit Switching vs Packet Switching

In the world of networking, there are two fundamental ways to send data from one place to another.

1. Circuit Switching – The old traditional way (used in telephone networks)
2. Packet Switching – The modern way (used in modern networks and the internet).

Understanding these two will help you see why the internet works the way it does.

Circuit Switching – The Telephone Way

How It Works

Imagine you want to call a friend on the phone.

• When you dial the number, the network sets up a dedicated path (circuit) between your phone and your friend's phone.
• This path stays reserved for you two until any of both hang up.
• All your voice data flows along this same fixed path.

Key Features

• Dedicated connection: A single path is reserved end-to-end.
• Continuous data flow: Data travels like water through a pipe.
• Fixed bandwidth: You get a constant data rate through the call.

Advantages

• Simple design
• Guaranteed bandwidth (no delays or congestion during the call)
• Good for real-time, continuous data like voice

Disadvantages

• Wastes resources: The path stays reserved even when you are silent.
• Not flexible: If any part of the path fails, the entire call is dropped.
• Not scalable: Hard to handle millions of users at once.

Example: Traditional landline telephone networks are circuit-switched.

Packet Switching – The Internet Way

Now imagine sending a letter by post – but instead of one big envelope, you cut it into pieces and send each piece separately.

The computer breaks your data into small chunks called packets.

Each packet gets a header with important info like:

• Source address
• Destination address
• Sequence number

Packets are sent independently through the network, possibly along different paths.

The destination computer reassembles them in order to rebuild the original data.

Key Features

• No dedicated path: Packets travel over shared network links.
• Dynamic routing: Each packet finds the best route available.
• Statistical multiplexing: Many users can share the same network links.

Advantages

• Efficient use of network resources (only use bandwidth when sending)
• Robust and fault-tolerant (if one route fails, packets can take another)
• Scalable (can support millions of users easily)

Disadvantages

• Packets may get delayed or arrive out of order
• Requires extra processing to reassemble and check errors

Modern World: Almost Everything Uses Packet Switching

Today, even voice calls mostly use packet switching.

Here's how:

Mobile Calls (4G, 5G)

1. Older 2G/3G networks uses circuit switching for voice.
2. Modern 4G and 5G use VoIP (Voice over IP) which is packet switching
3. Voice is converted into digital data -> Split into packets -> Sent over the internet-like mobile network.

This is called VoLTE (Voice over LTE) or VoNR (Voice over 5G).

It's packet-switched.

Internet Calling Apps (WhatsApp, Zoom, Teams, Skype)

• Always use packet-switching (they run over the internet)
• You voice is sent as small audio packets using real-time protocols (RTP/UDP)

Traditional Landline Calls

• The old PSNT is still circuit switched, but it's being phased out globally.
• Many landline providers have already migrated to VoIP, which uses packet switching internally.

Summary:

Real World Analogy

Circuit Switching – Like Reserving a Private Road

• Imagine you and your friend live in two different cities.
• When you want to talk, the government builds a private road just for you two.
• No one else can use this road while you are talking, even if you are silent.
• Your cards (voice data) can go back and forth quickly because the road is dedicated and empty, but it's wasted whenever you stop sending anything.
• If any part of the road breaks, the whole conversation stops.

Key Point from this analogy:

• Dedicated path
• Continuous flow
• No sharing with others
• Wastes resources when not in use

Packet Switching – Like Sending Many Letters Through Public Roads

• Now imagine you write a long letter to your friend, cut it into many small envelopers, and drop them in the post office.
• The postal system sends each envelope through whatever roads are available at the moment.
• Some go by highway, some by local roads, and they may arrive out of order.
• Your friend collects all envelopes and reassembles them in the correct order to read your message.
• While your envelopes are travelling, other people's letters are also using the same roads.

Key points from this analogy:

• No reserved path
• Shared network (roads)
• Efficient and scalable
• Might be delayed or come out of order

Summary: Circuit Switching vs Packet Switching