Why do internet speeds fluctuate

Speed ​​fluctuations with cable and DSL: provider in the test

Fluctuations in speed are a nuisance, especially when the speed is no longer sufficient for streaming series and films.

When it comes to speed records, the COMPUTER BILD speed test delivers a clear result: cable providers such as Unitymedia or Vodafone Kabel Deutschland are many times faster than DSL. Unitymedia pushes the tube the hardest and delivers its customers an average download speed of 103 megabits per second (Mbps). For comparison: Telekom DSL connections only achieved download data rates of around 32 Mbps on average in the 2018 test. But the picture looks completely different if you look at the fluctuations in tempo. DSL providers like Telekom are suddenly great here, while some cable providers are really bad. Where are the tempo fluctuations particularly bad? And why? COMPUTER BILD has facts and backgrounds.

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When everyone uses the cable internet in the evening, things get tight: unlike DSL, every user cuts a piece of the same pie - if there is nothing left, the pace collapses.

Tempo fluctuations finally measured

There are always complaints about cable connections, the speed of which drops sharply in the evening or sometimes even comes to a complete standstill. You can often hear them among colleagues and acquaintances or read about them in forums. But so far it has been difficult to assess how often such problems really occur. After all, in forums you can find countless horror stories about almost every problem, while users remain silent without difficulty. For the 2018 speed test with 7.4 million measurements, COMPUTER BILD created various evaluation parameters in order to uncover the speed fluctuations and drops in speed hidden in the mass of data. Because it is also clear: On average, the speed of the cable connections is definitely right, just not in all houses and at all times of the day. The evaluation therefore focused on several questions: How high is the average and maximum fluctuation for the respective tariffs? What time of the day do you show up? And how bad are the problems?

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Vodafone Kabel: The pace slows down in the evening

The result: Vodafone Kabel and Pÿur customers are particularly hard hit. With the fastest tariffs from Pÿur, the speed sometimes drops by up to 25 percent. The reason for this: All households connected to the same distribution box share the available capacity. DSL connections are slower, but mostly more reliable and do not suffer so much from fluctuating speeds. Even more annoying than fluctuations are sharp drops in speed for customers. According to the measurement data, up to 22 percent of Vodafone cable customers with a 32 Mbps tariff sometimes surfed at less than 6 Mbps in the evening! Unitymedia shows that not all cable connections have the problem. Here the fluctuations are comparatively small, at around 10 percent in the 60 Mbps tariff. Cheeky, however: Unitymedia states in the small print of the terms and conditions that it is no longer possible to navigate the Internet at peak times. It is at least questionable whether the provider can slip out of responsibility so easily.

For HD video streaming in good quality, the connection should offer a speed of at least 6 Mbps (= 6,000 kilobits per second, Kbps). Taking measurements from Vodafone's cable connections with a 32 Mbps tariff as an example, it becomes clear over the course of the day: Between 7 and 10 p.m., around every fifth Vodafone user is threatened with a jerky picture.

VDSL from Telekom offers the most stable speed

Basically, the DSL providers have the problem of speed fluctuations better under control in the test. There are only a few fluctuations in DSL connections from Telekom, 1 & 1 and O2. The slightest risk of falling below the snail's pace limit of 6 Mbps during the day is at VDSL 50 connections from Deutsche Telekom: Only 5.4 percent are affected here. Vodafone's DSL connections come off surprisingly negative here: 19.8 percent of customers with 50 Mbps tariffs surf at least once a day with less than 6 Mbps.

Speed ​​comparison between cable and DSL providers

What is behind the slump in speed?

In principle, cable connections are more susceptible to fluctuations in speed than DSL connections: While the connection cables themselves often enable very high speeds, all households connected to the same distribution box share the available capacity at the same time. The example of Unitymedia shows, however, that this does not have to be a problem if a provider plans sufficient speed reserves and develops them quickly enough. This is obviously not the case with Vodafone Kabel. DSL is slower for each connection, but it is usually more reliable and does not suffer so much from fluctuating speed. It is astonishing, however, that the cable providers do not react flexibly to bottlenecks: In times when the total speed available in the connection area is used up to the limit, a targeted but discreet braking of all connections would be a better choice than the blind competition for enough data. For example, you could gradually throttle all connections down to 30, then to 20, 10 and finally to 6 Mbps. Even at 6 Mbps, video streaming would still be possible for at least one user in the household.

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What can those affected do?

Anyone who is affected by tempo fluctuations should repeatedly complain to the provider and request improvements. If the pace is regularly well below the contractually guaranteed performance, complain to the provider and ask him to make improvements within 14 days. If he does not succeed, you can withdraw from the contract or terminate it (special right of termination). The Federal Network Agency speaks of a "significant deviation" if one of the following criteria is met:
- Maximum speed: On two measurement days (ten measurements per day via LAN), 90 percent of the time is not reached at least once every day.
- Normal speed: You can find out this speed when booking or in the product information sheet. At least 90 percent of the measurements must reach it.
- Minimum speed: Must not be undercut on both measurement days. The minimum speed is also stated in the product information sheet.

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