Packet Errors, Packet Discards, and Packet Loss: What’s the Difference?

Packet loss, packet error, and packet discard—they all seem to blur together. But these terms are not actually interchangeable.

So how do you tell them apart?

Before we jump into packet loss definitions and differences, let’s start with the basics.

What is a packet?

A packet is a segment of data sent from one device to another over a network. Packets are used because they divide large amounts of data into smaller chunks, making it easier to move across a network. A packet contains information like source, destination, data, and size to help a large file arrive at the correct location and be reassembled properly once it gets there.

But packet transfer is far from perfect and things can go wrong. Those “things” are in the form of errors, discards, and loss.

This article takes a deep dive into packet errors, packet discards and packet loss, to highlight what each term really means and how to easily differentiate between them. We’ll also highlight some of the common causes of these issues and how they can affect the network.

What is a packet error?

A packet error means there’s something wrong with the packet. There are two types of packet errors that usually occur:

• Transmission errors, where a packet is damaged on its way to its destination—like a fragile Amazon order that gets dinged up en route.
• Format errors, where a packet’s format isn’t what the receiving device was expecting (or wanting). Think ordering a Coca-Cola in a restaurant and getting a Pepsi instead.

Packets can easily become damaged on their way through a network. If a device—like a router, switch, or workstation—is connected to Ethernet through a bad cable, bad port, broken fiber cable, or dirty fiber connector, then a packet can be damaged.

Access points are also susceptible to packet errors. Offices often have multiple sources of high radio frequency interference—thanks to Bluetooth devices, unmanaged access points, microwaves, and more. So packets travelling wirelessly are easily damaged.

If a packet error occurs, TCP (Transmission Control Protocol) will resend the same information repeatedly, in hopes the data will eventually reach the destination without any problems, while UDP (User Datagram Protocol) will keep trucking forward even when packets fail to reach their destination.

What is a packet discard?

A packet discard happens when a received packet has a transmission or format error, or when the receiving device doesn’t have enough storage room for it.

While some discarding is inevitable, excessive discards can point to several problems including:

• A network device is misconfigured. Think of mismatched VLANs at two ends of a connection. If one end is a VLAN 9 but the other isn’t, the traffic coming from the VLAN 9 will be discarded because the receiving port isn’t configured for VLAN 9 traffic.
• A port that doesn’t have enough bandwidth
• Hardware—like switches, routers, and firewalls— experiencing high CPU or memory usage

Access points are susceptible to packet discards just as they are to packet errors, but not for the same reasons. If access points are experiencing a high number of packet discards, it may be that the wireless devices it’s trying to connect to are too far away from it.

To keep packet errors and packet discards separate in your mind, remember this simple saying: “All packet errors are discards, but not all packet discards are errors.”

What is packet loss?

You might have thought that packet loss and packet discard were interchangeable terms, since they both sound very similar. But there’s one key difference: Packet loss happens before a packet reaches its destination, which means it can happen anywhere in a network.

And while packet loss is a common problem across networks, it typically doesn’t affect network performance. In some cases, slowdowns caused by packet loss may not even be noticeable. Legally downloading a movie from Netflix might take 45 seconds instead of 30, for example.

However, persistent packet loss should still be addressed, and there are several potential culprits behind it:

• There are more packets on a link than it’s designed or configured to handle.
• A device is receiving packets faster than it can process them, causing extra packets to be dropped while they wait.
• There’s old, faulty, or poorly laid out hardware on the network.
• There’s high radio frequency interference in the office.
• There’s a large distance or weak signal between a device and an access point.

And there you have it—a definitive answer to the common question, “What’s the difference between packet errors, packet discards, and packet loss?”