Answer
Network bandwidth restrictions are fully controlled by Virtuozzo. The corresponding detailed documentation is available here:
Managing Network Accounting and Bandwidth
There is no thing like bandwidth guarantee.
First, provider configures the allowed maximum bandwidth for the network adapter (e.g. 10Gbs) on the Virtuozzo node, then the bandwidth is sliced into parts, given to VEs, controlled by RATE parameter in Virtuozzo VE configuration. If provider oversells the available bandwidth, giving out high limits to VEs, there is a probability that the network speed gets degraded in case of high network activity from all VEs at the same time, filling the bandwidth to maximum.
The OACI service template only defines the boundaries for the final bandwidth limits on the VE. Minimum bandwidth (guarantee) is not configured.