Symptoms
When launching any virtual machine running on Parallels Workstation Extreme, the host network speed drops up to 3 times slower.
Cause
The issue is caused by
Windows Vista sound card handling. When a multimedia application begins playback, the multimedia APIs it uses call the MMCSS service to boost the priority of the playback thread into the real-time range.
Workaround
1. Go to Virtual Machine Configuration > Hardware
2. Remove the sound card from Virtual Machine Configuration and save the changes