This chapter summarizes everything related to the configuration, setup, and optimization of the WLAN (WiFi).

Basics

The first steps with the CTC modules and their WLAN often prove to be a major hurdle. That’s why we start here with some basics.

Generally, CTC uses the standard functionality of WLAN. The term WLAN is only commonly used in German and is too general—the standard used is called "4242WiFi4242." Even our CTC-Router is just a regular Fritz ox with a few setup steps performed for you (see the "Router Configuration" section below).

A typical WiFi network always has a name (4242SSID4242) and should have encryption (password) to prevent unauthorized access. The encryption standards are WPA, WPA2, and WPA3 .

  • WPA is largely ineffective as it can be cracked with little effort using freely available tools.
  • WPA2 is also crackable but requires significantly more effort. For most devices (including CTC modules), this is the maximum security supported.
  • If only WPA3 is enabled, the CTC module cannot connect to the WiFi.
  • Therefore, you should set your model railway WiFi to "WPA2" or "WPA2 + WPA3."

In addition to the non-unique SSID, there is also a MAC address for the WiFi. This is globally unique but is typically only used at a technical level and often not shown to the user.

A WiFi access point is a device that provides wireless network access without additional network functionalities. A WiFi router , on the other hand, includes the full range of network central functions and usually also enables internet access. For CTC, it is important that the WiFi router assigns the relevant IP addresses for communication via the DHCP function. The smallest variant of a WiFi router is the hotspot of a mobile phone.

Multiple WiFi networks can share the same SSID. This is used, for example, in mesh networks to extend WiFi coverage over a larger area using multiple WiFi access points (and a WiFi router). However, all these WiFi access points must be connected to the associated WiFi router. These WiFi access points are also called "4242WiFi repeaters4242." If the CTC module detects multiple WiFi networks with the same SSID, it is difficult to predict which one it will connect to.

A CTC module has three operating modes for WiFi:

  • In configuration mode , the CTC module sets up its own WiFi, acting like a mini-router. The WiFi of the CTC module has only an SSID but no password, meaning it is unencrypted. As of firmware 20260105 (CTC-App 4.46), the module is fully functional in this mode. Prior to this, the module could only receive configurations, particularly the SSID and password of the model railway WiFi.
  • In normal operation , the CTC module knows an SSID and a corresponding password and attempts to connect to the WiFi with this SSID at startup.
  • As of firmware 20260105 (CTC-App 4.46), the CTC module can have a temporary WiFi . This takes priority over the normal (configured) WiFi until it is deleted. If the temporary WiFi cannot be reached by the CTC module, it is automatically deleted.

WiFi Mesh

As of firmware 20250627 (CTC-App 4.40), CTC modules work reliably in mesh mode. The following should be noted:

  • From CTC’s perspective, a mesh exists when there is more than one access point with the same SSID, all connected to a common router.
  • At startup, the CTC module connects to the first access point with a matching SSID. The search typically begins on the WiFi channel it last connected to.
  • The CTC module remembers the WiFi channel it is connected to the model railway WiFi on. If the WiFi signal is too weak, the CTC module automatically searches for alternatives (routers with the same SSID), but only on the same WiFi channel . Only after 60 seconds without a connection to a WiFi does the CTC module search across all WiFi channels again.
  • Searching on the same WiFi channel takes about 300 ms. During this time, the CTC module is unreachable.
  • The signal strength considered "too weak" can be set in the WiFi config ("Signal min. dB") of the CTC module.
  • The WiFi Monitor not only shows the signal strength history but also the access point currently in use.

WiFi Icon

Since the WiFi signal quality has a significant impact on CTC, it is displayed in various places with the following symbols:

Symbol Meaning
ctc-app-doku-icon Optimal WiFi reception (> -67 dB)
ctc-app-doku-icon Good WiFi reception (> -70 dB)
ctc-app-doku-icon Acceptable WiFi reception (> -80 dB)
ctc-app-doku-icon Poor WiFi reception (<= -80 dB)
ctc-app-doku-icon CTC module with old firmware that does not transmit signal strength.
ctc-app-doku-icon CTC module has not reported in for at least 3 seconds.
ctc-app-doku-icon CTC module has not reported in for more than 10 seconds

The last two symbols (yellow and red) do not indicate the WiFi reception quality of the CTC module. It is quite possible that the CTC module is still well connected to the WiFi, but the CTC app has lost the connection to the WiFi. This is particularly likely if all CTC modules switch to yellow or red.

Router Configuration

This section collects documents on router configuration:

Tips for WiFi Connection

Both laptops and smartphones/tablets have an increasing tendency to connect to the internet. This means they are reluctant to connect to WiFis without internet access and may leave them spontaneously. CTC does not require internet access, so the model railway WiFi can be set up without an internet connection.

The challenge is to teach the devices running the CTC app to connect to the model railway WiFi and not leave it spontaneously. Here are some tips:

  • Connect PCs and laptops that do not need to be moved during model railway operation via network cable.
  • Ensure that PCs are connected to the model railway router either via LAN or WiFi, but not both simultaneously. Otherwise, the PC might see the CTC module but fail to load the config files.
  • Disable the "automatically connect" option for all WiFis or at least for the model railway WiFi.
  • Put the smartphone in airplane mode and only activate WiFi.
  • If problems occur, check whether the PC or mobile device is still connected to the correct WiFi.
  • Do not dismiss error messages or warnings from the smartphone regarding the WiFi; acknowledge them instead.

Tips for Optimizing WiFi Reception Quality

  • For stationary laptops or PCs, connect them to the WiFi router via LAN cable. Reception issues often stem from the laptop rather than the CTC module.
  • Use the 5 GHz WiFi for the device running the CTC app. This forces the connection through the WiFi router, which often has a much better position for communicating with the CTC modules.
  • For smartphones/tablets, use WiFi analyzer apps, e.g., the ad-free "WiFi Analyzer (open-source)" for Android. These allow you to move around your layout and check the reception quality of your model railway WiFi and the presence of competing WiFis. If necessary, consider changing the channel of your model railway WiFi.
  • Use the WiFi Monitor to display the signal strength of locomotives in detail and over time. The displayed graph can help you find the optimal position for your WiFi router.