Circuit Switching vs. Packet Switching

Landlines and VoIP transmit voice data in different ways

The old telephone system (PSTN) uses circuit switching to transmit voice data whereas VoIP uses packet switching. The replacement of traditional landlines by internet-based communication protocols is due largely to the benefits of packet switching vs. circuit switching, although there are still advantages to using the latter.

Circuit Switching vs Packet Switching
Circuit Switching
  • Used for traditional landline phones.

  • Transmits data over a predetermined path.

  • Communication paths are exclusive to two parties.

Packet Switching
  • Used for cellphones and VoIP services.

  • Transmits data is the fastest way possible.

  • Multiple users share the same communication networks.

Packet switching and circuit switching are different methods for routing data from one destination to another. The journey the data takes is called the path, and the devices that make up the path (routers, switches, etc.) are called nodes. The major difference between the two approaches is that circuit switching relies on physical telephone lines to transmit data while packet switching uses the internet.

Circuit Switching Pros and Cons

  • More reliable connections.

  • Better audio quality.

  • Generally more secure.

  • Networks are more expensive to use, build, and maintain.

  • Inefficient use of network bandwidth.

In circuit-switching, the path is decided upon before the data transmission starts. The system decides on which route to follow based on a resource-optimizing algorithm, and the transmission goes according to the path. For the whole length of the communication session, the path is exclusive to both parties, and it is released only when the session terminates.

When you make a PSTN call, you are actually renting the lines. Therefore, if you speak for 10 minutes, you pay for ten minutes of a dedicated line. That's why international calls are so expensive. The benefit is that circuit-switching is more reliable than packet-switching, so you don't have to worry about dropped calls.

Packet Switching Pros and Cons

  • More efficient use of network bandwidth.

  • Networks are cheaper to build and maintain.

  • Automatic rerouting helps prevent dropped packages.

  • Poorer connections and call quality.

  • More vulnerable to outside data interference and security threats.

  • Unpredictable latency.

The Internet Protocol(IP) breaks data into chunks and wraps the chunks into structures called packets. Each packet contains information about the IP address of the source and the destination nodes along with the data load, sequence numbers, and some other control information. A packet can also be called a segment or a datagram.

In packet-switching, the packets are sent towards the destination irrespective of each other. Each packet has to find its own route to the destination. There is no predetermined path; the decision as to which node to hop to in the next step is taken only when a node is reached. Each packet finds its way using the information it carries, such as the source and destination IP addresses. Once they reach their destination, the packets are reassembled to make up the original data again.

Which Is Better?

With VoIP, you actually can use a network node even if there are other people using it at the same time. There is no circuit dedication; the cost is shared. The downside is that when you use a circuit that is open for other services, then there is a big possibility of congestion, and hence the delays or even packet loss. This explains the relatively lower quality of VoIP calls compared to PSTN. Fortunately, other protocols have been developed, such as the TCP protocol, that make VoIP connections more reliable.