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Updated on 03 Oct, 202518 mins read 185 views

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:

ServiceOld DaysToday
Landline voice callsCircuit switchingMostly 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/videoPacket switchingPacket 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

AspectCircuit SwitchingPacket Switching
Path setupDedicated end-to-end pathNo fixed path; each packet chooses its route
Resource usageResources locked for the whole sessionResources used only when packets are sent
Data flowContinuousBroken into small packets
ReliabilityGuaranteed bandwidth, but not fault-tolerantFault-tolerant, reroutes around failures
EfficiencyWastes bandwidth when idleVery efficient and scalable
Example (Old)Traditional telephone landlineARPANET, Internet
Example (Modern)Obsolete in new networksWeb, streaming, VoIP, Zoom, WhatsApp etc.
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