Circuit Switching and Packet Switching

There are two types of switched networks, packet-switched and circuit-switched.

  1. Circuit Switched - most notably employed by the telephone system
  2. Packet Switched - used for the overwhelming majority of computer networks and will be the focus of this book. Wifi

In packet-switched networks, nodes send discrete blocks (packets) of data to each other.


Packet Switched

Allows a more efficient use of the circuit.

For voice, you gotta bridge this gap, when there is a packet missing.

Human beings can’t detect, we don’t notice. The human mind is great at filling in.

  • Voice doesn’t have retransmission
  • Data has retransmission, above we have the Transport protocol

Circuit Switched

Our phone number is like an IP address, it’s a way of finding location!

416-534-4917 These each represent different parts 416 534 4917 Local Exchange

You have two circuits, so you have both directions. However, this results in a lot of inefficiency, because most of the time, only 1 of the 2 callers speak.

But what if you are moving, say you have a BC number but are in Ontario? I think it has to be packet switched? NO.

Question on the phone stuff: Nowadays, on my iphone, I can merge calls. And make group calls. Do you know how do they do that?

However, we have been moving from circuit switched to packet switched.

Traditionally, phones are circuit switched, so it seems that we are transitioning towards packet switched.

Three people talking at the same time, stream of voices will get merged together. Mixed version of the voice gets together. This is interesting How group calls are managed, when things are in parallel


Packet switching wins. It took decades because it was expensive at first.

  • PS wins because it is ultimately more cost effective (at around 2010) › Increased network utilization › Cheaper transmission options (than CS) › Cheaper hardware (than CS) › One network to manage for all media

2G and 3G did this:

  • CS for voice
  • PS for data