Recently a newly installed Vocus link was running 100mb Down but only 30mb up , multiple back an forths with support showed the link back to vocus was fine , however the speed was still bad.

Finally they told me the answer , the package ordered was not full 100mb up!

Best Effort Internet Access
VBU is delivered to site using Telstra Wholesale Ethernet Access (Fibre) Standard CoS (Class of Service) access tails. Note Standard CoS is 100% EIR (Excess Information Rate) which means, under congestion in the Telstra network, this traffic may be discarded. If the customer requires an Internet Service with continual sustained throughput or other medium to high performance requirements, please use Vocus IP Transit or Enterprise Internet rather than VBU.

Fix

Recommended VCT or VIE onnet service
or alternatively Telstra tail can be made premium.