With VPN connections, all data is elaborately encrypted before transmission and decrypted again after transmission. The maximum achievable throughput over a VPN connection is therefore lower for integrated systems like the FRITZ!Box due to the architecture than for dedicated VPN servers, for example. Throughput is influenced by

• the speed (upload and download rate) of both internet connections.
• the VPN technology used (IPSec or WireGuard).
• additional overhead caused by VPN encryption.
• the overhead of the software or communication protocols used (SMB, FTP, VoIP).
• the processing power and utilization of the FRITZ!Box models used.

Depending on the file type and communication protocol, the overhead can account for up to 74% of the transmitted data. However, the upload rate of the internet connection of the VPN remote site and the FRITZ!Box models being used normally limit data transmission the most.