Packet Definition | The Interactive Glossary

When data is transferred over the Internet, such as when a web server sends a website to your browser, the data isn't sent as one single large download. Instead, it is broken into very small pieces of data called network packets which are reassembled as they are received.

Each packet is made up of two basic components: the header and the data.

The packet header includes information about where the packet came from, where it's going, the packets that come before and after it, and a number of technical details that facilitate the transmission of the packet, enable reassembly and provide the ability to check for data loss. The second part of the packet, the data, is simply a small piece of the total data that is being transmitted.

Also See: Network, TCP/IP

Frequently Asked Questions

What is packet switching?

Packet switching is the term used to refer to the transfer of data over a network in the form of data packets. Transferring data in this way allows for a single communication medium to support multiple simultaneous communication sessions. In other words, packet switching allows multiple people to transfer information over the Internet, using the same physical infrastructure, and all do so at the same time. A network that transfer data using packets is called a packet-switched network.

A circuit-switched network is the alternative to a packet-switched network. In a circuit switched network a single communication session is guaranteed full access to the entire bandwidth offered by a physical network for the duration of the session. On one hand, this means that circuit-switched networks are less susceptible to data loss and can guarantee maximum bandwidth availability. On the other hand, the fact that only a single communication session can take place at a time means that a circuit switched network is unsuitable for a multi-user network. Traditional telephone systems are circuit-switched networks.

Why is data transmitted in packets?

Breaking data into packets is what makes a packet-switched network – one in which multiple users transfer information simultaneously – possible. The packetization process, including the use of headers, makes a packet-switched network very reliable, and capable of handling a wide range of bandwidth demands.

Are data packets ever lost in transmission?

When packets are transferred over the Internet, the packet headers contain enough information to allow the receiver to confirm that all of the packets have been received, and to line them up in the proper order to reassemble the transmitted data.

There are many protocols that can be used to transfer information over a packet-switched network like the Internet. Some of them, such as HTTP, will confirm that all of the packets have been received, and request retransmission of any lost packets before assembling and delivering the data. Others, such as those used for VoIP services, deliver packets as soon as they are received, which means some packets may be lost or delivered out of order – the result being a jump in a video feed and momentary breaking up of the audio content. However, services that depend on real-time packet delivery, such as VoIP, would suffer greater harm if they instead waited on all of the packets to be delivered, and then re-requested any lost packets, as opposed to simply delivering the packets as they are received and accepting a small amount of data loss.