Troubleshooting LTE Connectivity Issues

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This guide provides general advice for troubleshooting LTE connectivity issues for Vigor routers with an integrated LTE modem. This is indicated by the "L" suffix on the model name, for instance the Vigor 2862Lac. The following steps will assist you in troubleshooting problems you may encounter such as frequent connection dropouts or the LTE router will not connect to internet. This guide applies to DrayTek LTE router models such as the Vigor 2620Ln and Vigor 2862Lac.

 For information on how to setup LTE internet access on the Vigor, visit this link

1. Check the signal strength level on the Vigor router

The signal strength value can be found on the dashboad page and also on the [Online Status] > [Physical Connection] page. Additional details on the LTE modem status can be found under [LTE] > [Status]

The router indicates signal strength by referring to the RSSI value. This table shows different signal strength levels and the correspondng RSSI values to help you determine the signal quality of your LTE Internet connection

Signal Quality

RSSI Values

Excellent Above -70 dBm (i.e. -60dBm)
Good -85 to -70 dBm
Fair -88 to -100 dBm
Poor -101 to -110 dBm
No signal Below -110 dBm

The minimum RSSI value is -100dbm, however the lower the RSSI value the better the signal strength. Poor signal quality can result in connection failure, this would mean that the router won't be able find a band or a network to connect to.

To resolve poor signal quality:

  • Check that the LTE antennas are firmly connected
  • Re-Position the antennas, placing them outside of a rack or other enclosure
  • Check your mobile service provider's coverage in your area
  • Test the SIM on a device such as a mobile phone, to ensure that it works correctly
  • Extend the antennas with extension bases to obtain better signal coverage

2. Check the validity and credit of the SIM card

Check if you can use another device such as a mobile phone to create an internet connection using the SIM card. Check that there's data and you have a suitable contract with your mobile phone company to use this SIM card on a router.

If you're unable to send text messages from your router, check that the SIM you're using has credit to send SMS text messages. Some data-only SIMs may require additional topping up to be permitted to send text messages.

3. Ensure that your router is running the latest firmware version

We always recommend the use of the latest firmware for your product, to ensure that you have the latest features as well as vital security improvements.

4. Unable to connect to the Internet with the router's LTE WAN

Here are some connectivity issues you may encounter, their possible causes and ways to resolve them.

a. Network is identified but no Internet access.

If you cannot access the Internet or obtain an IP address with the router's LTE WAN, it may be caused by the following:

Mismatched APN settings

When you try to connect to a 3G/4G network, the ISP requires some parameters to allow the connection. Go to [WAN] > [Internet access] > [LTE] and ensure that the APN name, username and password matches the settings required by your ISP. If you are unsure about these settings, you can contact your ISP to verify that you are using the correct settings.

Invalid PIN code

Some SIM cards require PIN code validation to operate. Check that you have entered the right PIN code. Leave the PIN code field blank if the SIM card does not have one, which is also quite common. This can be done on the [WAN] > [Internet access] > [LTE] page.

Poor signal quality

Check if there are available networks nearby by using the same SIM card on a phone, or change the 4G only setting on Vigor to Auto (4G/3G/2G) for a try.

b. LTE status displays SIM card not ready.

This means that the Vigor LTE Router doesn't detect the SIM card. If the SIM card is connected, it may happen after unplugging and plugging the SIM card to Vigor Router without a system reboot.

Syslog will show: “SIM Card SIM_NOT_INSERTED”

 [4G]<5> Please make sure the SIM card is inserted BEFORE router is powered on.

Reboot the router while the SIM card was connected and see if the SIM card can be detected after the reboot.

c. Registration denied message is displayed on the LTE status.

This means that the Vigor LTE Router has found an available network and sent the register request but the server rejects the connection.

Syslog will show:

[4G]<5> register state UNKNOWN -----> DENIED
[4G]<5> Network registration was denied by the visible LTE network.


  • Check if the configured setting, e.g. APN or the User Name and Password (required by some ISPs) on Vigor Router are correct.
  • Change the Auto (4G/3G/2G) setting to "3G only" to test.
  • Check if another device, e.g. a phone can use the same SIM card to create the Internet connection.

5. Disable the keep alive settings

If the LTE WAN drops frequently and you see 'keep alive timeout' in the syslog, go to [WAN] > [Internet access] > [LTE] and disable Enable PING to keep alive.

6. Speeds are lower than expected

Test a mobile phone with the same SIM card / same mobile network

If you see lower speeds than expected, try a phone with the same SIM card to see if the speeds are similar. If they are not, it's important to consider that signal results can be very variable. LTE networks are shared amongst all nearby users on the same network and download speeds can vary significantly based on the time of day.

If a phone achieves significantly higher speeds than the Vigor router's LTE modem, check the LTE Category of the mobile phone, it may differ from the DrayTek router's LTE modem.
A higher LTE Category modem can achieve higher speeds than a lower LTE Category modem, which can give very different results potentially, for the same mobile network and/or SIM card.

Check Signal Quality and Antenna Placement

Swapping the SIM card to a phone, check that the phone's signal RSSI levels are similar to the router's LTE modem.

Try changing the router's antenna placement to see if that helps throughput:

  • Try to place the antennas close to a window and outside of any metal enclosures.
  • Try changing the angle of the antennas to check for improvement.
Change allowed LTE bands

Your mobile network will typically connect your router's LTE modem to the best available cell tower. However, you can try forcing the router's LTE modem to a different cell tower, or frequency, by changing the Preferred LTE Band setting, which may give higher speeds potentially.

This settings is located in the  [WAN] > [Internet access] > [LTE] menu. It allows you to select which LTE bands the modem will connect to, if your modem usually connects to "E-UTRA Op Band 7" and gives you lower than expected speeds, you can disable Band 7 to try connecting to an alternative band. Changing this setting requires a restart of the router to take effect.

Check which bands your mobile provider supports before changing this setting. Disabling all bands that the mobile provider operates on, will either stop it from connecting to a network, or fall back to 3G.

Further Steps

If you have followed all the suggestions above and the issue still persists, please contact our technical support for further analysis with the following information.

  • The model name of the router and its firmware version.
  • The config file of Vigor Router.
  • APN name (Required from ISP) and your ISP name.
  • The WAN Syslog.
  • If another Vigor Router or device can use the same SIM card to create the Internet connection?

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