13.8.3 How Does Packet Switching Make the Internet Possible?
- What Is Packet Switching?
- Why Divide a Message into Packets?
- How Do Many Users Share the Same Network?
- How Does a Packet Reach Its Destination?
- Do All Packets Follow the Same Route?
- What Happens If Packets Arrive Out of Order?
- Why Is Packet Switching Better Than Circuit Switching for Data?
- Does Packet Switching Have Any Disadvantages?
- How Does Packet Switching Support Different Applications?
- Is the Internet One Giant Packet-Switched Network?
- How Has Packet Switching Changed Communications?
- Will Packet Switching Continue to Dominate?
- What Should You Remember?
Short Answer
The Internet is able to support billions of users because it uses packet switching. Instead of establishing a dedicated communication path between two users, information is divided into small packets that are transmitted independently across a shared network. Packets belonging to many different users are interleaved on the same communication links, making much more efficient use of available bandwidth. Packet switching provides the scalability, flexibility, and resilience required for modern data communications.
What Is Packet Switching?
Packet switching is a method of sharing communication resources among many users.
Instead of transmitting an entire message as one large block, the message is divided into numerous smaller units called packets. Each packet contains:
- user data;
- source and destination addresses;
- sequencing information;
- protocol information; and
- error-detection data.
The packets travel independently through the network and are reassembled into the original message after reaching their destination.
Why Divide a Message into Packets?
Breaking information into packets offers several important advantages.
It allows:
- many users to share the same communication links;
- transmission resources to be allocated dynamically;
- damaged packets to be retransmitted individually;
- alternative routes to be selected if necessary; and
- long messages to avoid monopolising network resources.
These advantages make packet switching particularly suitable for computer networks, where users generate highly variable traffic.
How Do Many Users Share the Same Network?
One of the greatest strengths of packet switching is statistical multiplexing.
Rather than reserving bandwidth for individual users, the network shares its communication links dynamically. Suppose ten users are connected to the same network. It is extremely unlikely that all ten users will transmit large amounts of data continuously.
Instead:
- one user may be browsing a website;
- another may be reading email;
- another may be streaming video;
- another may be downloading a file; and
- several may be temporarily inactive.
Packet switching exploits these natural traffic variations by allocating transmission capacity only when packets are actually available.
This greatly improves overall network efficiency.
How Does a Packet Reach Its Destination?
Each packet contains the address of its intended destination.
As the packet passes through the network, routers examine this address and decide where the packet should be sent next. Each router makes an independent forwarding decision based upon:
- the destination address;
- available routes;
- network congestion;
- link failures; and
- routing information received from neighbouring routers.
Eventually the packet arrives at its destination, where the receiving device reconstructs the original message.
Do All Packets Follow the Same Route?
Not necessarily.
In many IP networks, each packet is routed independently. Two packets belonging to the same message may therefore follow completely different paths through the network. This flexibility provides important advantages. If one communication link becomes congested or fails, subsequent packets can often be diverted automatically along alternative routes.
This contributes greatly to the Internet's resilience.
What Happens If Packets Arrive Out of Order?
Since packets may travel along different routes, they may not always arrive in the order in which they were transmitted.
This is not normally a problem. Each packet contains sequencing information that allows the receiving device to reconstruct the original message correctly. If a packet is delayed or lost, higher-layer protocols such as the Transmission Control Protocol (TCP) can request retransmission.
The user is usually unaware that any packets were lost or reordered during transmission.
Why Is Packet Switching Better Than Circuit Switching for Data?
Traditional circuit switching reserves a dedicated communication path for the entire duration of a connection.
This approach works well for continuous voice conversations. Computer traffic, however, is typically bursty. Users alternate between periods of activity and inactivity. For example:
- a user reads a web page before requesting another;
- emails are downloaded only occasionally;
- cloud applications exchange short bursts of data; and
- sensors transmit only when measurements are available.
If dedicated circuits were reserved during these idle periods, most network capacity would remain unused.
Packet switching allows that capacity to be shared by other users instead.
Does Packet Switching Have Any Disadvantages?
Like every engineering solution, packet switching involves compromises.
Potential disadvantages include:
- variable transmission delay;
- packet loss during severe congestion;
- packet reordering;
- protocol overhead; and
- the need for buffering and retransmission.
Modern communication protocols have been specifically designed to manage these effects efficiently.
For most applications, the advantages of packet switching greatly outweigh its limitations.
How Does Packet Switching Support Different Applications?
Modern packet networks simultaneously carry many different forms of communication.
These include:
- web browsing;
- email;
- voice calls;
- video conferencing;
- television streaming;
- online gaming;
- cloud computing; and
- industrial control.
Although each application has different performance requirements, they all share the same underlying packet-switched infrastructure.
Quality-of-service (QoS) mechanisms may be used to give delay-sensitive applications, such as voice and video, higher priority when required.
Is the Internet One Giant Packet-Switched Network?
Essentially, yes.
The Internet consists of millions of interconnected networks. Although these networks are owned and operated by many different organisations, they communicate using the common Internet Protocol (IP). Each router forwards packets independently towards their destinations. This distributed architecture allows the Internet to continue operating even if individual links or routers fail.
It is one of the principal reasons for the Internet's remarkable scalability and resilience.
How Has Packet Switching Changed Communications?
Packet switching has transformed the communications industry.
Instead of maintaining separate networks for:
- telephone services;
- television;
- computer data;
- messaging;
- video; and
- industrial communication,
modern operators increasingly transport all these services across a common packet-switched infrastructure.
This convergence has reduced costs, simplified network management, and enabled entirely new communication services.
Today, virtually every broadband network relies on packet switching.
Will Packet Switching Continue to Dominate?
Almost certainly.
Emerging technologies such as:
- cloud computing;
- 5G and future 6G networks;
- satellite Internet;
- software-defined networking (SDN);
- network function virtualisation (NFV); and
- the Internet of Things (IoT)
all depend upon packet-switched communication.
Although networking technologies will continue evolving, packet switching is expected to remain the foundation of global data communication for the foreseeable future.
What Should You Remember?
- Packet switching divides information into small packets that are transmitted independently across a shared network.
- Statistical multiplexing allows many users to share the same communication resources efficiently.
- Routers examine packet addresses and forward packets towards their destinations.
- Packets belonging to the same message may follow different routes and arrive out of order.
- Higher-layer protocols reconstruct the original message and recover any lost packets when necessary.
- Packet switching is much more efficient than circuit switching for bursty computer traffic.
- The Internet, cloud computing, modern broadband networks, and most digital communication systems are all built upon packet-switching principles.