How to read your router's line statistics

Line statistics in this sense belong to DSL connections: broadband over copper telephone wire. That means ADSL and ADSL2+, which run over copper from the telephone exchange, and FTTC, or part fibre (fibre to the street cabinet, then copper to your home, using a technology called VDSL2). If you are not sure which type you have, our A to Z of broadband jargon explains the labels on your contract.

G.fast also uses the existing copper from the cabinet, ISPreview explains; see our guide to what G.fast is and what is happening to it.

On copper and part-fibre lines the figures live in the router's web interface, reached by typing the router's address into a browser on a connected device. thinkbroadband notes that the speed shown there is the connection (sync) speed.

• BT Smart Hub: BT says the Hub Manager opens at 192.168.1.254 or http://bthomehub.home, with the admin password on the back of the hub unless you changed it. Our BT broadband deals page covers BT's part-fibre and full-fibre packages.
• Sky and other provider hubs: Sky's help points you to its online Service Checker for the speed to your hub and the speed Sky guaranteed you. If you can't find line figures in your hub's settings, ask your provider: Openreach says your provider can run tests on your line and home equipment.
• Your own router: Kitz points out that makes label the figures differently and may show slightly different attenuation, so track your line with the same router throughout. Our guide to using your own router covers what to check before swapping.

Sync speed (also connection speed or line rate) is, in Kitz's words, “the speed at which your router has synchronised” with the network equipment. It includes allowances for the overheads of carrying data, so it isn't the speed you actually get: thinkbroadband says you normally see about 86% to 96% of it as the maximum result from a speed test or download.

Attainable rate is, per Kitz, the sync rate you could reach if restrictions at the network end were removed. It is the router's own estimate and routers can differ, Kitz says, so treat it as a guide. Going by that definition, an attainable rate well above your sync speed points to a limit set at the network end, such as your product's top speed, while one close to sync suggests the line itself is near its limit.

Sync shows what your line achieves, but speed promises usually aren't measured against it:

• Your personal speed estimate under Ofcom's speeds code is an estimate of the speed you're likely to get at busy times (8pm to 10pm).
• Your minimum guaranteed speed: if your provider has signed Ofcom's voluntary Broadband Speeds Code of Practice, your speed falls below what you were promised, the problem is on its network and it isn't fixed within 30 days, it must let you leave without an early exit fee. Ofcom's list of signatories includes BT, EE, Sky and Virgin Media (checked October 2026).
• How it is measured: BT measures throughput to your BT Hub with its own tester, and Virgin Media measures to its Hub. Unlike BT and Virgin Media, Vodafone's terms (November 2025, clause 4.2) refer to sync: if it continuously or regularly falls significantly below the minimum guaranteed speed (except on fibre to the home) and can't be resolved, you may move to a lower speed product or leave without a termination fee.

If sync is healthy but speed tests are far lower, the line probably isn't the bottleneck; BT notes device speeds depend on how many devices are connected and on Wi-Fi versus a cable. See why speed tests give different results and our minimum speed guarantee guide.

SNR stands for signal-to-noise ratio: how strong the broadband signal is compared with background noise on the line. Routers usually show the SNR margin (or noise margin), which Kitz calls a “buffer zone”: the difference between the SNR the line actually has and the SNR needed to run at the current speed. Kitz's own example: if a line needs 35dB of SNR to run at 8Mbps and actually has 41dB, the margin is 6dB. If the margin gets too low, Kitz says, you may see slower throughput or frequent disconnections.

• Downstream matters most. Kitz says the downstream figure is normally the most important, and the higher the margin, the better.
• It moves, and that is normal. Kitz says it is perfectly normal for SNR margin to fluctuate during the day, and it is most likely to be at its lowest in the evening. Look for a margin that sinks at the same time as drop-outs or a burst of errors, not at one reading.
• Margin and speed trade off. A line running slower needs less SNR, so shows more margin. If sync has dropped and margin has risen together, the line may have been retrained to run slower and steadier, as DLM can do (see the recording steps above).

Target margin

At sync, the router and network equipment settle on a speed that leaves some “spare SNR” for normal fluctuations: the target margin. Kitz's ADSL-era page says BT's rate-adaptive ADSL products could typically be set to 6, 9, 12 or 15dB, with 6dB the default, and that longer lines are more susceptible to noise so often need a larger margin than shorter ones. We found no current equivalent for today's part-fibre (FTTC) lines, so treat these figures as background, not a pass mark.

Attenuation is measured in decibels (dB). thinkbroadband defines it as “a measure of how much signal has been stopped by the metal telephone line”, and Kitz says lower is better. thinkbroadband calls it the most accurate measure of your line's length, because it takes in all the cable and joints. A high figure mainly tells you the copper is long: it explains why a line is slow but doesn't prove a fault.

For ADSL lines from the exchange, Kitz says every 3dB of attenuation halves the signal power received, and gives a rough guide of 13.5 to 14dB of loss per kilometre, depending on the cable. Those are ADSL figures, so don't use them to estimate the length of a part-fibre line.

Don't read much into small changes. Kitz explains that the router's figure is an average across the frequencies in use, so it can rise slightly when sync speed rises, and can be affected by ongoing changes in line conditions. The true attenuation measured at the exchange should stay fairly static, it adds, so our suggestion is to note any large, lasting change with its date and mention it if you report a fault.

Bins, cross-talk and vectoring

When a DSL modem syncs, thinkbroadband explains, it tests each small frequency band (a “bin”) and skips those hit by interference, which lowers the speed. On VDSL2, cross-talk from other lines in the same cable can pull speeds down as more people connect to a cabinet. Vectoring cancels cross-talk, but thinkbroadband says it is on only some UK cabinets and never fully matured on VDSL2.

Kitz explains the main counters; not every router shows all of them:

• Compare them with uptime. Kitz says experienced readers judge errors against uptime, and that this can't be pinned to fixed figures. A raw total means little, so note the count, wait, and see how fast it climbs.
• Check the channel mode. Kitz says routers show the mode as Fast or Interleaved, and that interleaving can be applied to help a line stay stable, which is why FEC counts on an interleaved line are expected. On part fibre, thinkbroadband describes G.INP as error correction without sacrificing speed.

Writing about BT's ADSL network, Kitz said BT used the errored-seconds count for its DLM. Kitz gives no numeric limits for any of these counters, so watch the rate of increase and whether it lines up with your problems.

Each pointer leads to the next check, not a diagnosis:

• Speeds lower than you were told to expect: BT says problems can come from internal extensions and suggests trying your test socket before you call. thinkbroadband adds that a speed test within 10 to 20% of your provider's estimate means everything is probably fine.
• Errors and drop-outs that cluster at particular times: think about what switches on then. thinkbroadband names boilers, water heaters and anything with a motor as the likeliest culprits, plus TVs, phone chargers, LED bulbs and dimmer switches. It suggests switching devices on one at a time, ideally in daylight, as atmospheric interference comes into play after sunset; watch the error count and margin as you go.
• Problems after wet or stormy weather: see our guide to a crackling line or broadband that gets worse in the rain. thinkbroadband says lightning can interfere with DSL signals, so one restart after a storm can help.
• Sync lower and margin higher than a week ago, after drop-outs or many restarts: this fits the DLM pattern described in the recording steps. Leave the router on and keep recording.
• Steady sync and few errors, but slow or patchy in use: ISPreview noted in 2012 that slow-speed fault rules concern the line, not a poor Wi-Fi signal, so test wired first.

Two published examples show how a provider might judge a slow line against its sync speed; neither is today's general rule:

• Andrews & Arnold, a UK internet provider, publishes slow-speed fault thresholds set against each product's sync speed (page last modified December 2020). For example, for an FTTC line with a 40Mbit/s downstream sync, the fault threshold rate is below 15Mbit/s. Before reporting, it asks for a packet-loss check (at least 100 pings) and repeated wired speed tests at different times of day with no other traffic on the line, warning that online testers are “not always 100% accurate”.
• ISPreview reported in December 2012 that BT's FTTC products then had a fault threshold rate for download speeds, and that a fault could also be declared if the line rate dropped by more than 25% over a 14-day continuous period.

Openreach says to contact your broadband provider first: it can test your line and home equipment, and only it can arrange checks or repairs with Openreach. Our guide on how to report a broadband fault covers the process, and why broadband keeps dropping out helps if disconnections are the main symptom. Have this ready:

• Your personal speed estimate and minimum guaranteed speed.
• Dated readings of downstream and upstream sync, SNR margin and attenuation.
• Error counts with the line uptime beside each, so the agent can see the rate.
• Dated, wired speed tests from different times of day, including your provider's own test if it has one.
• What you have tried: master or test socket, microfilters, extensions removed.

Then ask: is my sync speed right for this line? Has line management slowed it, and can it be reset? Is my speed below my minimum guaranteed speed on your test, and, if you've signed Ofcom's speeds code, when does the 30-day period to fix it start? Would an engineer visit be charged if the fault is inside my home?

Sometimes the stats show a healthy but long line: steady sync close to the attainable rate, few errors, high attenuation. thinkbroadband's fibre guide says that if a line can't reach the top of a 40Mbps FTTC product, a 55 or 80Mbps FTTC product won't increase the speed, because they all use the same VDSL2 technology. So if your sync is below the top of your current tier, a faster part-fibre tier is unlikely to help.

What changes things is a technology that doesn't depend on the copper: thinkbroadband says full fibre's speed is not affected by distance, and describes cable as fixed-speed too. Since 16 September 2024, Ofcom guidance (reported by ISPreview) has said providers should name the technology, such as full fibre, part fibre, cable or copper, at the point of sale and in the contract summary, so check that wording.

To see what is available, compare deals at your postcode or read our fibre broadband deals page. Our guide to UK broadband providers explains which networks each company sells on.

If that means changing provider, Ofcom's One Touch Switch process (since September 2024, ISPreview reported) means you contact only the new provider; your current provider must send you the switching information, including any early termination charges.