In the world of networking, there are two fundamental ways to send data from one place to another.
- Circuit Switching – The old traditional way (used in telephone networks)
- 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)
- Older 2G/3G networks uses circuit switching for voice.
- Modern 4G and 5G use VoIP (Voice over IP) which is packet switching
- 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:
Service | Old Days | Today |
---|---|---|
Landline voice calls | Circuit switching | Mostly VoIP (packet) |
Mobile voice (2G/3G) | Circuit switching | — (obsolete now) |
Mobile voice (4G/5G) | — | Packet switching (VoIP) |
Internet apps (Zoom etc.) | — | Packet switching |
Web browsing/video | Packet switching | Packet switching |
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
Aspect | Circuit Switching | Packet Switching |
---|---|---|
Path setup | Dedicated end-to-end path | No fixed path; each packet chooses its route |
Resource usage | Resources locked for the whole session | Resources used only when packets are sent |
Data flow | Continuous | Broken into small packets |
Reliability | Guaranteed bandwidth, but not fault-tolerant | Fault-tolerant, reroutes around failures |
Efficiency | Wastes bandwidth when idle | Very efficient and scalable |
Example (Old) | Traditional telephone landline | ARPANET, Internet |
Example (Modern) | Obsolete in new networks | Web, streaming, VoIP, Zoom, WhatsApp etc. |
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