Panasonic KX-TDA0490 Getting Started page 51

A1 VoIP Requirements
Is there only a single IP network between 2 ends of a call?
A huge degradation in speech quality will be produced when calls are made through multiple IP
networks as shown below; therefore, it is recommended that you avoid establishing a VoIP network
in this fashion.
PSTN
IP Network 1 IP Network 2
IP Network 1 IP Network 2
Getting Started 51