iPhone audio frameworks

Question

Hello,

Does AVFoundation Framework internally speak to AudioToolbox Framework? Because AudioToolbox holds all these services

1. Audio Converter Services
2. Audio File Services
3. Audio File Stream Services
4. Audio Format Services
5. Audio Queue Services
6. Audio Session Services
7. Audio Unit Processing Graph Services
8. Extended Audio File Services
9. System Sound Services

If incase , AVFoundation framework wants to convert audio file, how does it do?

Thank You.