How to diagnose slow speeds on Broadband or FTTP

If your broadband or FTTP service is running slower than expected, there are a few checks you can carry out before contacting the Fastnet Helpdesk.

This guide is for SoADSL, SoGEA, FTTC, and FTTP services where Fastnet has supplied a Zyxel router.

To get an accurate result, speed tests should be carried out using a device connected directly to the Zyxel router with an Ethernet cable. Wi-Fi speed tests are not reliable for diagnosing broadband speed faults, as wireless performance can be affected by distance, signal strength, interference, building layout, and the device being used.

Test directly into the router

Before running a speed test, please connect a laptop or computer directly into one of the LAN ports on the Zyxel router using an Ethernet cable.

Where possible, disconnect your internal network from the router while testing. This includes switches, firewalls, wireless access points, and other connected devices.

This helps ensure the speed test is measuring the broadband or FTTP service itself, rather than traffic or limitations from the internal network.

Please make sure:

• The test device is connected by Ethernet directly to the Zyxel router.
• The device is connected to one of the router’s LAN ports.
• Other network equipment is unplugged from the router during the test.
• Wi-Fi is disabled on the test device so it does not accidentally test over wireless.
• No downloads, cloud backups, updates, or streaming services are running on the test device.
• The Ethernet adapter on the test device supports the speed being tested.

Check whether the issue affects wired, wireless, or both

Before assuming the broadband service is slow, it is useful to confirm where the issue is being seen.

Please check:

• Are wired devices slow?
• Are wireless devices slow?
• Is the issue affecting one device or all devices?
• Is the issue constant or only at certain times of day?
• Does the speed improve when testing directly into the router?

If wired speeds are normal but wireless speeds are poor, the issue may be related to Wi-Fi rather than the broadband or FTTP service.

If speeds are still poor when testing directly into the router by Ethernet, further investigation may be required.

Reboot the router

A reboot can sometimes resolve temporary performance issues.

To reboot the Zyxel router:

1. Switch the router off at the power.
2. Leave it switched off for 15 minutes.
3. Switch the router back on.
4. Allow several minutes for the router to reconnect before testing again.

Please do not factory reset the router unless we have specifically asked you to do so. A factory reset may remove the configuration required for your service to work.

Run a speed test

Once the test device is connected directly to the router by Ethernet, run a speed test.

For SoADSL, SoGEA, and FTTC services, a standard speed test is usually suitable for checking the connection speed.

For FTTP services, especially higher-speed services up to 1Gbps, browser-based speed tests can sometimes be affected by the device, browser, operating system, Ethernet adapter, or the speed test server being used. If results appear lower than expected, it is worth testing with more than one speed test provider and, where possible, using a modern device with a Gigabit Ethernet port.

When running speed tests:

• Use a wired Ethernet connection.
• Test directly into the Zyxel router.
• Disconnect other network equipment from the router.
• Make sure no other devices are using the connection.
• Run more than one test.
• Test at different times of day if the issue is intermittent.
• Take screenshots of the results.

Please make a note of the download speed, upload speed, latency/ping result, date, and time of the test.

FTTP and higher-speed testing

For higher-speed FTTP services, a normal browser-based speed test may not always show the full available speed, especially on services close to 1Gbps.

This can be due to limitations with the test device, browser, Ethernet adapter, local network, or the remote speed test server.

If further testing is required, Fastnet may ask you to complete an iPerf test. This can provide a more controlled throughput test and may be useful when investigating higher-speed FTTP performance.

You do not need to complete an iPerf test unless requested by the Fastnet Helpdesk.

Check the cables and link speed

Poor speeds can sometimes be caused by cabling or link speed issues.

Please check:

• The Ethernet cable is securely connected at both ends.
• The test device is connected directly to the Zyxel router.
• The cable is in good condition.
• The device has connected at the correct Ethernet speed.
• A different Ethernet cable has been tried, if available.

For faster FTTP services, the device should ideally connect at 1Gbps over Ethernet. If the device only connects at 100Mbps, the speed test will not be able to exceed that, even if the broadband service is faster.

Check the FTTP ONT

If you have an FTTP service, please also check the ONT.

The ONT is the fibre termination box installed at your premises.

Please check:

• The ONT has power.
• The cable from the ONT to the Zyxel router is securely connected.
• The ONT lights are showing as expected.
• There are no red or unusual flashing lights.

If any ONT lights appear unusual, please make a note of them before contacting us.

When to contact Fastnet

If speeds are still lower than expected after completing these checks, please contact the Fastnet Helpdesk.

When contacting us, please provide:

• Your company name
• Your site address
• Your circuit ID or customer reference, if known
• The type of service, if known, such as SoADSL, SoGEA, FTTC, or FTTP
• Whether the issue affects wired, wireless, or both
• Whether the test was completed directly into the Zyxel router by Ethernet
• Confirmation that other network equipment was unplugged during the test
• The speed test results, including download, upload, and latency/ping
• The date and time of the tests
• Whether the issue happens all the time or only at certain times
• The lights showing on the Zyxel router
• For FTTP, the lights showing on the ONT
• Any recent changes to your network or equipment

Providing this information helps us investigate the issue more quickly and confirm whether the problem is with the broadband service, FTTP service, router, internal network, or wireless setup.