Where does mobile data come from?

Transmission

Phones work by sending and receiving radio signals between:

• 📡 Phone and cell towers (mobile network)
• ☁️ Phone and home router (local Wi-Fi network)
• 📱 Phone and other devices (Bluetooth, NFC...)

Networks and protocols

Different tasks and protocols operate on different networks:

• 📡 The mobile network carries
  • Regular phone calls (CSD, VoLTE)
  • Regular text messages (SMS, MMS)
  • Internet data (TCP/IP)
• ☁️ Wi-Fi carries only internet data (TCP/IP)
• 📱 Devices emit local signals (Bluetooth, NFC...)

Note that internet data (TCP/IP) can be transmitted via the mobile network ("mobile data") or Wi-Fi. Usually not both at the same time.

Internet data

Internet data encapsulates many more sub-protocols, such as HTTP for websites or XMPP for text messages. Since apps hide technical detail, it may not be clear if a particular app uses SMS (mobile network), XMPP (internet) or even HTTP (web).

Internet data can be transmitted over the mobile network ("mobile data") or Wi-Fi. Most apps are not aware which network they are using. Heavy-download apps should have an option to "download on Wi-Fi only", but this is not guaranteed.

Core mobile apps

For our purposes, Calls and Messages are core mobile apps. Typically, core apps use mobile network protocols and all other apps use internet data.

However, modern core apps may use internet data as a fallback, or to augment app features.

Sources and apps

The following diagram illustrates signal sources and apps that use them.

• Messages receives text messages from the Mobile Network. It may fall back on Mobile Data or Wi-Fi.
• Calls receives voice calls from the Mobile Network. It may fall back on Mobile Data or Wi-Fi.
• Wallet receives local signals via NFC, used to detect payment taps.
• Other apps receive data via Mobile Data or Wi-Fi, even if they are messaging or voice apps. They may also use local signals.

sequenceDiagram
    box Sources
    participant MobileNetwork as 📡 Mobile<br />Network
    participant MobileData as 📡 Mobile<br />Data
    participant WiFi as ☁️ Wi-Fi
    participant OtherSignals as 📱 Device<br />(NFC, Bluetooth...)
    end
    box Apps
    participant Messages
    participant Calls
    participant Wallet
    participant OtherApps as Other apps
    end
    MobileNetwork-)Messages: Text message
    MobileData--)Messages: .
    WiFi--)Messages: .
    MobileNetwork-)Calls: Voice call
    MobileData--)Calls: .
    WiFi--)Calls: .
    OtherSignals-)Wallet: NFC
    WiFi-)OtherApps: Data
    MobileData--)OtherApps: .
    OtherSignals--)OtherApps: .