This article is written for Internet Service Providers (ISPs), including fixed wireless, fiber, cable, and DSL operators, who want to understand bufferbloat, identify it on their networks, and eliminate it for their subscribers.
Bufferbloat (definition): A network condition in which excessively large or poorly managed data buffers in routers, switches, or access points cause high latency and degraded quality of experience (QoE), even when available bandwidth is not fully consumed. First formally identified circa 2010 by Jim Gettys and colleagues.
Key Takeaways:
- Bufferbloat is caused by large, unmanaged packet queues at network bottlenecks
- TCP’s behavior amplifies bufferbloat by deliberately filling available buffer space
- Symptoms include high latency, jitter, and increased support calls, even when subscribed speeds are being delivered
- The fix is Active Queue Management (AQM), specifically FQ-CoDel algorithms
- ISP-level deployment is required to resolve bufferbloat upstream of the subscriber’s equipment
For Internet Service Providers (ISPs), increases in high-bandwidth activity like online gaming and video calls can lead to Bufferbloat, a packet congestion issue that causes high latency, poor user quality of experience (QoE), and plenty of “slow internet” calls from increasingly frustrated subscribers. So, what is bufferbloat and how to fix it?
What is Bufferbloat?
If we consult our handy Preseem Fixed Wireless Glossary, it tells us that bufferbloat “refers to when network links become saturated with high bandwidth activity, such as online gaming or Zoom calls.” This results in high latency, causing the internet to feel slow for subscribers.
As Jim Gettys and Kathleen Nichols explain in this article, bufferbloat is also defined as “the existence of excessively large and frequently full buffers inside the network.”
Gettys should know—he was a core member of the group that first identified the existence of bufferbloat around 2010. Gettys co-founded bufferbloat.net with Dave Taht, who helped develop the FQ-CoDel AQM algorithm on which Preseem is based. As Taht’s Wikipedia page notes, his tireless work on bufferbloat issues helped prove that advanced algorithms like FQ-CoDel are “effective at reducing network latency, at no cost in throughput.”
During a webinar we hosted with Jeremy Davis and Brandon Yarbrough from Visp.net. They said the main bufferbloat symptom ISPs experience is an increase in latency, along with significant jitter and degradation of throughput. High latency causes a poor user experience. This can lead to a spike in support calls from subscribers where VoIP calls or gaming are occurring in the home.
It’s important to note that bufferbloat is not the same as the buffering that can happen when streaming video. This article is about packet buffering causing problems on a network that uses first-in, first-out (FIFO) queuing with large buffers.
As the article by Gettys and Nichols also explains, “Buffers are essential to the proper functioning of packet networks, but overly large, unmanaged, and uncoordinated buffers create excessive delays that frustrate and baffle end users.”
What Causes Bufferbloat?
It’s not surprising that internet users might be baffled by bufferbloat, as we don’t expect them to be technical experts. Ideally, however, ISPs should have an understanding of it. This way, they can explain it to their frustrated customers and, better yet, start fixing bufferbloat issues for them.
First, they should know what really causes bufferbloat in the first place.
Bufferbloat can happen anywhere on a network where packets can queue. Every network has a spot in the path that’s naturally slower, and that’s where bufferbloat will rear its ugly head. Typically, this happens at a bottleneck link where many packets are queued up.
How Do Queues Cause Bufferbloat?
Queuing occurs whenever a big pipe is narrowed or stopped down to a smaller pipe. This is a perfectly normal aspect of network design. However, poor queue management techniques at the bottleneck cause latency for each packet. This is because the newest packet in the queue has to wait for all the others to be transmitted. This in turn leads to a subpar quality of experience for the internet user. Physical interfaces often have queues thousands of packets deep, which is a classic case of bufferbloat waiting to happen.
As the slide below mentions, consider how a user might feel when the red packet at the back of the queue is important to how they’re experiencing service. Looks like they’re in for a long wait.
Though bufferbloat can occur on equipment in a subscriber’s home, particularly directly in the upstream of their internet connection, a common location for fixed wireless providers is at the Access Point (AP) level. A congested AP can cause suffering for everyone on the network. Capping the AP at less throughput than it can push (say 10 Mbps) could help reduce this problem. That said, non-maximum throughput on an AP could be due to signal degradation. This can cause packets to queue up in the first place, leading to bufferbloat symptoms.
How Does TCP Affect Bufferbloat?
Bufferbloat is also made much worse by how TCP works. Checking our glossary again, TCP stands for Transmission Control Protocol, the communications standard that allows computers to exchange data with each other. TCP is a key component of how the internet works.
If you have large buffers, TCP learns that “this network can hold X packets before it gets a loss.” It then sets its rate so that X packets are always in flight, which creates a kind of “standing queue” phenomenon. This adds latency to every packet that flows through the network interface controller as long as the TCP connection is active. This is where bufferbloat happens and it causes big latencies that will negatively affect your subscribers.
Bufferbloat happens because networking vendors are primarily focused on throughput, which is typically how they measure their equipment. To run at really high rates with a single TCP flow, you need a lot of buffering. This tradeoff conflicts with optimizing for latency. This is a problem because low latency corresponds to improved subscriber QoE, which means happier customers.
The discovery of bufferbloat has led to speed tests that now show loaded latency—the ultimate measure of bufferbloat. The irony, however, is that bufferbloat causes the problems that get people to run speed tests, whereas if they just had a consistently good experience there’d be no need to run the tests!
How Can ISPs Fix Bufferbloat?
It’s not enough to measure bufferbloat, however. We want to fix it. In our experience, there are two ways to solve the link bottleneck problem:
- Stay below the bottleneck rate so that the queue doesn’t grow, or
- Wherever the bottleneck is, do something smarter than simple FIFO queue management to mitigate the issue
At Preseem, our focus is moving that bottleneck back to where we can use Active Queue Management (AQM) techniques to solve the problem rather than having to keep the absolute rate below the bottleneck bandwidth.
Active Queue Management refers to a set of algorithms that proactively manage packet queues in network equipment, dropping or delaying packets before a queue reaches maximum depth. Unlike FIFO (first-in, first-out) queuing, AQM prevents the deep queues that cause bufferbloat-related latency. Preseem’s use of AQM traffic management methods are based on the FQ-CoDel (Fair Queuing Controlled Delay) algorithm.
Using FQ-CoDel, traffic flows are isolated and automatically categorized into bulk or interactive flows based on how much queue they build up. This means they can’t “hurt” each other or slow each other down. This also means there’s no more guessing at rates per application or babysitting complex rule sets. Instead, you’ll go from FIFO packet queues that cause latency to getting short, isolated flows that produce very low latency, even when the network is busy.
As a result, good queue management strategy means subscribers can run their internet connection at full capacity without getting high latency and poor QoE. This means one household member’s large Minecraft update will no longer affect another’s important Zoom call, and your support team will be fielding far fewer “slow internet” complaints!
Taking Action on Bufferbloat
In a nutshell, when bufferbloat occurs on a network, the most obvious symptom providers see is increased latency and jitter. You’ll also get more support calls from gamers and those using VoIP, because bufferbloat will significantly degrade their experience.
Latency and throughput are the ultimate measures of QoE on a network. This is why Preseem measures latency at a fine grain level directly from subscriber traffic. By applying AQM techniques, devices in the home are prevented from hurting each other and traffic flows smoothly, even at peak times. Fixing bufferbloat really is possible. Using an AQM solution is the key to fixing this problem on your network for good.
Interested in reducing bufferbloat issues and providing a better experience for your subscribers? Contact us to book a live demo or start a free 30-day trial.
Frequently Asked Questions
What is bufferbloat in simple terms?
Bufferbloat is a network problem where large data buffers inside routers and other equipment cause unnecessary delays (latency) even when your internet connection isn’t fully congested. Instead of data flowing through smoothly, packets pile up in deep queues and wait their turn, making the internet feel sluggish even when your speed test shows a fast connection.
What are the symptoms of bufferbloat?
The most common symptoms ISPs and subscribers notice include:
- Noticeably high latency and ping times, especially during heavy usage
- Jitter (inconsistent latency) that disrupts VoIP calls and video conferencing
- Poor online gaming performance — lag spikes, rubber-banding, disconnections
- Video calls that freeze or degrade while someone else in the household downloads a large file
- An increase in “slow internet” support tickets, even though subscribed speeds appear correct on speed tests
- Degraded throughput during periods of network congestion
What causes bufferbloat?
Bufferbloat is caused by a combination of oversized buffers in network equipment and the behavior of TCP (Transmission Control Protocol). When a network bottleneck exists, a point where a high-capacity link narrows to a lower-capacity one, packets queue up. TCP compounds the problem: it learns how many packets a network can hold before dropping them, then deliberately keeps that many packets in flight, creating a persistent “standing queue.” This adds latency to every packet traversing that interface, for the entire duration of active TCP connections.
How is bufferbloat different from regular network congestion?
Regular congestion means a link is genuinely overloaded, with more data being sent than the link can handle. Bufferbloat can occur even when a link isn’t at capacity. The problem is the size and management of the buffers: even at moderate utilization, large unmanaged buffers allow queues to grow deep, adding latency. A subscriber can have plenty of remaining bandwidth headroom and still experience bufferbloat symptoms.
Does bufferbloat affect both download and upload?
Yes. Bufferbloat can occur in either direction. Upload-direction bufferbloat is particularly impactful for VoIP calls and video conferencing, where outbound packets must traverse the subscriber’s upstream connection. A large upload (like a cloud backup or file share) can cause bufferbloat that degrades all simultaneous upload-dependent traffic, including voice and video.
How do ISPs fix bufferbloat?
The most effective fix is deploying Active Queue Management (AQM) at the bottleneck link. AQM techniques intelligently decide which packets to drop or delay, before queues grow excessively deep, rather than applying simple first-in, first-out (FIFO) queuing. This prevents queues from growing to the point where latency becomes a problem. The leading AQM algorithm is FQ-CoDel (Fair Queuing Controlled Delay), which also isolates individual traffic flows so that one subscriber’s bulk download cannot degrade another’s real-time traffic.
What is FQ-CoDel and how does it fix bufferbloat?
FQ-CoDel stands for Fair Queuing Controlled Delay. It is an AQM algorithm that works by:
- Isolating flows — separating individual traffic streams so bulk flows (like large downloads) cannot crowd out interactive flows (like VoIP or gaming)
- Managing queue delay — actively monitoring how long packets wait in the queue and dropping packets proactively before the queue grows too deep
- Automatic categorization — classifying traffic into bulk or interactive flows based on observed queue behavior, without requiring manual rules
The result is dramatically reduced latency even when the network is under heavy load, without sacrificing throughput.
Can subscribers fix bufferbloat themselves?
Subscribers can sometimes reduce the impact of bufferbloat in their home network — for example, by enabling SQM (Smart Queue Management) on a consumer router running OpenWrt or DD-WRT firmware. However, bufferbloat at the ISP’s access point (AP) level, or anywhere upstream of the subscriber’s equipment, can only be fixed by the ISP. This is why ISP-level AQM deployment is the most effective solution.
How do you test for bufferbloat?
The most common tool is the Bufferbloat test at waveform.com (formerly at DSLReports), which measures latency under load rather than just idle latency. A connection showing high idle latency but dramatically higher loaded latency is experiencing bufferbloat. Standard speed tests that only measure throughput will not detect bufferbloat — a connection can score well on a speed test while suffering severely from bufferbloat.
Does bufferbloat affect fiber internet connections?
Yes. While fiber connections have significantly higher bandwidth than DSL or fixed wireless, they are not immune to bufferbloat. The problem occurs at bottleneck points — wherever a higher-capacity link is throttled to match a subscriber’s purchased tier — and the queue management at that point determines whether bufferbloat occurs. Without proper AQM, even a gigabit fiber connection can exhibit bufferbloat symptoms when the subscriber’s line is busy.
Why do support calls increase when bufferbloat is present?
Because the subscriber’s experience feels like “slow internet,” but a standard speed test may show the correct subscribed speed. This creates confusion: the subscriber knows something is wrong, the ISP’s speed test shows the plan is delivering, and neither party can easily identify the root cause without measuring loaded latency specifically. Bufferbloat-related complaints tend to spike around online gaming (which is latency-sensitive) and video calls (which suffer from jitter).
Is bufferbloat the same as buffering when streaming video?
No. Video buffering (the spinning wheel on Netflix or YouTube) is caused by insufficient bandwidth where not enough data is arriving fast enough to play the video. Bufferbloat is a latency problem caused by packet queues growing too large inside network equipment. The two problems can coexist, but they have different causes and different fixes.
