Speeds (IAS) on Descent

[DBEnterprises]

All,

Looking for a source document/feedback on the following:

Aircraft is tracking via a STAR. The STAR has a speed restriction of NA250IAS below A100.

ATC instruct pilot to descend at 280KTS.

Q1. Does this mean that a/c will descend at 280 until approaching A100 then reduce to 250/A100 or remain at 280KTS below A100?

Q2. If instructed to descend at 230KT could the pilot increase to NA 250KT once below A100?

Overall - How do you interpret the speed assignment vs. airspace/procedure requirements for your operations??

Just interested.

DBE::