What is a Network Packet?

Data flows in tiny groups when moving from one computer to another. These data often travel with identifiers, making it easy for the receiving computer to recreate the original information. If you wish to build a career as a network engineer, a clear understanding of how network packets work and why they’re relevant can be helpful. In this article, we provide the answer to “What is a network packet?” explain why it’s essential, define packet switching, and respond to several frequently asked questions.

What is a Network Packet?

A network packet is a multi-byte unit of data transmitted at one time by a host, such as a server, on a network. The actual packet consists of the user data, called the payload, and control information that the network uses to deliver the payload. The term packet is often used interchangeably with frame, although some people distinguish packets as messages at the network layer and above, while frames are defined as messages that include the data link and sometimes even the physical layers.

Packets are small segments of a full message. All data sent over computer networks, meaning 2 or more computers connected to one another, is broken up into packets and then reconstructed by the destination device. Breaking up larger messages into smaller packets helps keep the wires clear for other devices to send information, ensuring the network runs more efficiently. If computers sent messages in their full, undivided state, each device would have to wait its turn to send its messages to other devices.

Packets can be monitored for a variety of use cases, including network performance management and network security. The versatility and detail of packet data allow for unmatched visibility into your network, meaning that nothing can hide from you, whether it is a performance issue, or a bad actor trying to gain or expand access.

How does it work?

Every network packet or unit of data is sent to its destination address using the best route available. This is a route taken by all the other packets within a message or by none of them.  This makes the network more efficient, balancing a load across multiple pieces of equipment from millisecond to millisecond. If there’s a problem with one item of network equipment during the transmission of a message, packets can be redirected using routers to ensure the entire message gets delivered.  Depending on the network being used, packets can also be referred to as Frames, Blocks, Cells, and Segments.

Importance of network packets

It’s possible to send data from one computer to another in a long unbroken line of bits the receiving computer can interpret. This transfer method becomes inefficient when more than two computers are a part of the process. As the data passes from one computer to the other, a third computer can’t simultaneously access that information using that same channel. This delay makes it almost impossible to perform complex tasks. Packet switching makes it possible to send data to multiple computers simultaneously.

What is packet switching?

Packet switching involves taking data and grouping it into packets, which are then transmitted over a telecommunications network. It is the principal way data communications are conducted across computer networks around the world.  The packets themselves are composed of a header and a payload. The data contained in the header is utilized by hardware at the network level, directing the packet to its designated destination. Once the packet arrives at its destination, the payload is extracted, where it is processed by an operating system, higher layer protocols, or application software.

The Internet utilizes packet switching. In this type of network, network equipment is allowed to process packets independently from one another, allowing network packets to take different routes to their destination devices to ensure they all reach that destination efficiently. However, some protocols require the packets to arrive in the correct order to be processed properly, regardless of the path they took to get there.

Network Packet Content

A packet may contain any of the following components:

• Addresses – The routing of network packets requires two network addresses, the source address of the sending host, and the destination address of the receiving host.
• Error detection and correction – Error detection and correction are performed at various layers in the protocol stack. Network packets may contain a checksum, parity bits, or cyclic redundancy checks to detect errors that occur during transmission. At the transmitter, the calculation is performed before the packet is sent. When received at the destination, the checksum is recalculated, and compared with the one in the packet. If discrepancies are found, the packet may be corrected or discarded. Any packet loss due to these discards is dealt with by the network protocol. In some cases, modifications of the network packet may be necessary while routing, in which cases checksums are recalculated.
• Hop limit – Under fault conditions packets can end up traversing a closed circuit. If nothing was done, eventually the number of packets circulating would build up until the network was congested to the point of failure. Time to live is a field that is decreased by one each time a packet goes through a network hop. If the field reaches zero, routing has failed, and the packet is discarded. Ethernet packets have no time-to-live field and are subject to broadcast radiation in the presence of a switching loop.
• Length – There may be a field to identify the overall packet length. However, in some types of networks, the length is implied by the duration of the transmission.
• Priority – Some networks implement quality of service which can prioritize some types of packets above others. This field indicates which packet queue should be used; a high-priority queue is emptied more quickly than lower-priority queues at points in the network where congestion is occurring.
• Payload – Payload is the data that is carried on behalf of an application. It is usually of variable length, up to a maximum that is set by the network protocol and sometimes the equipment on the route. When necessary, some networks can break a larger packet into smaller packets.

What is the difference between packets and datagrams?

The packet is the primary unit of communication between a source and a destination in a network. Once the packet arrives at its destination, the receiving computer reassembles each packet to recreate the original content. A datagram represents units of data transferred in a network.

In a single transfer, a typical datagram contains small amounts of data of up to 65535 bytes. Just as a connection-oriented protocol (TCP) makes use of packets, datagrams use connectionless protocols (UDP) to transfer information. They also contain the IP address of the source and destination computers, the data, and a header.