13.8.4 What Is the Difference Between Circuit Switching and Packet Switching?
- Why Were Two Different Switching Techniques Developed?
- How Does Circuit Switching Work?
- How Does Packet Switching Work?
- Why Is Circuit Switching Well Suited to Voice?
- Why Is Packet Switching Better for Computer Data?
- How Do the Two Techniques Allocate Resources?
- Which Technique Is More Efficient?
- Which Technique Produces Lower Delay?
- Can Packet Switching Carry Voice Calls?
- Is Circuit Switching Still Used?
- Why Did Packet Switching Become Dominant?
- Is the Difference Becoming Less Clear?
- What Should You Remember?
Short Answer
Circuit switching and packet switching are two fundamentally different approaches to sharing communication resources. Circuit switching establishes a dedicated end-to-end communication path before information is exchanged, reserving network capacity for the duration of the connection. Packet switching divides information into small packets that share network resources dynamically with packets from many other users. Circuit switching provides predictable performance, while packet switching provides much greater efficiency and scalability for modern digital communications.
Why Were Two Different Switching Techniques Developed?
Communication networks have evolved to support very different types of traffic.
Traditional telephone conversations involve a continuous stream of information flowing at an almost constant rate. Computer networks, however, carry highly variable traffic consisting of short bursts of data separated by periods of inactivity. These fundamentally different traffic patterns led to the development of two different switching philosophies.
Circuit switching was designed for continuous communication. Packet switching was designed for bursty digital data.
How Does Circuit Switching Work?
Before communication can begin, a circuit-switched network establishes a dedicated communication path between the two users.
This path remains reserved throughout the entire conversation. Once established:
- bandwidth is reserved;
- intermediate switches maintain the connection;
- packets or messages do not compete with other users; and
- communication proceeds with relatively constant delay.
When the conversation finishes, the circuit is released and becomes available for other users.
Traditional telephone networks are classic examples of circuit-switched systems.
How Does Packet Switching Work?
Packet switching takes a completely different approach.
Instead of reserving a dedicated communication path, the message is divided into small packets. Each packet is transmitted independently through the network. Packets from many users are interleaved on the same communication links, allowing the network to allocate resources only when data is actually being transmitted.
This dynamic sharing makes much more efficient use of available bandwidth.
Why Is Circuit Switching Well Suited to Voice?
Traditional voice conversations generate a continuous stream of information.
During a telephone call, both participants expect:
- predictable delay;
- uninterrupted communication;
- constant transmission quality; and
- immediate response.
A dedicated circuit naturally satisfies these requirements because network resources remain reserved throughout the conversation.
Historically, this made circuit switching the ideal technology for public telephone networks.
Why Is Packet Switching Better for Computer Data?
Computer traffic behaves very differently from voice traffic.
A user browsing the Internet does not transmit continuously. Instead, information is exchanged in short bursts. For example:
- a web page is requested;
- the server responds;
- the user reads the page;
- another request is made; and
- the process repeats.
If a dedicated circuit were reserved during the reading period, it would remain idle for much of the time.
Packet switching avoids this inefficiency by allowing other users to share the available capacity whenever one user is inactive.
How Do the Two Techniques Allocate Resources?
The greatest difference between the two approaches lies in resource allocation.
Circuit switching:
- reserves communication resources before transmission begins;
- guarantees bandwidth throughout the connection; and
- prevents other users from using that capacity.
Packet switching:
- allocates resources only when packets are available;
- allows many users to share the same communication links; and
- continually reallocates capacity according to demand.
This dynamic allocation is one of the principal reasons why packet switching scales so effectively.
Which Technique Is More Efficient?
The answer depends upon the type of traffic.
For continuous communication, circuit switching can be highly efficient because the reserved connection is used continuously. For intermittent communication, packet switching is generally much more efficient because unused capacity immediately becomes available to other users. Most modern digital communication consists of bursty traffic.
Consequently, packet switching usually provides much better overall utilisation of network resources.
Which Technique Produces Lower Delay?
Once a circuit has been established, circuit switching provides relatively constant delay because the communication path remains dedicated.
Packet switching introduces additional variability because packets may:
- wait in queues;
- follow different routes;
- experience congestion; or
- require retransmission.
This variation is known as jitter. Modern communication networks minimise jitter through high-capacity links, quality-of-service (QoS) mechanisms, buffering, and traffic engineering.
As a result, packet-switched networks can now support high-quality voice and video communication despite their inherently variable delays.
Can Packet Switching Carry Voice Calls?
Yes.
In fact, most telephone conversations today are carried across packet-switched networks.
Technologies such as Voice over Internet Protocol (VoIP) divide speech into small packets that are transmitted across IP networks. Quality-of-service techniques prioritise these packets to minimise delay and jitter. From the user's perspective, the conversation appears almost identical to a traditional telephone call.
This convergence has allowed operators to replace many separate voice and data networks with a single packet-switched infrastructure.
Is Circuit Switching Still Used?
Although packet switching dominates modern communication networks, circuit switching has not disappeared completely.
Dedicated communication paths remain valuable in applications requiring:
- guaranteed bandwidth;
- deterministic delay;
- extremely high reliability; or
- specialised industrial or defence systems.
Many optical transport networks also establish dedicated paths through the network, even though the user traffic they carry is itself packet switched.
The underlying concepts of circuit switching therefore continue to influence modern communication-system design.
Why Did Packet Switching Become Dominant?
Several factors contributed to its success.
Packet switching:
- makes much more efficient use of network capacity;
- supports enormous numbers of users;
- adapts automatically to changing traffic;
- reroutes traffic around failures;
- integrates many different communication services; and
- scales readily as networks grow.
These advantages made packet switching the natural foundation for the Internet and virtually every modern broadband network.
Is the Difference Becoming Less Clear?
Increasingly, yes.
Modern communication systems often combine ideas from both approaches. For example:
- IP networks use packet switching to transport information;
- Multiprotocol Label Switching (MPLS) establishes predetermined paths through packet-switched networks;
- software-defined networking (SDN) controls traffic flows dynamically; and
- quality-of-service mechanisms reserve network resources for selected applications.
As a result, many modern networks combine the efficiency of packet switching with some of the predictability traditionally associated with circuit switching.
What Should You Remember?
- Circuit switching establishes a dedicated communication path before information is transmitted.
- Packet switching divides information into packets that share network resources dynamically.
- Circuit switching provides predictable delay and guaranteed bandwidth.
- Packet switching provides much greater efficiency for bursty digital traffic.
- Modern voice communication is increasingly carried using packet-switched technologies such as VoIP.
- Many modern networks combine concepts from both circuit-switched and packet-switched architectures.
- Packet switching has become the dominant communication technique because of its efficiency, scalability, flexibility, and ability to support a wide range of digital services.