Within an activated instrument, Service Provider can optionally grant access to makers and takers via maker and taker whitelist. This is supported by Instrument where Service Providers can update the whitelist at any time. This whitelist affects the newly created issuances and engagements but does not affect the existing ones. Service Provider can also charge service fees from makers and takers by specifying service token, service address and fee receiver address. In a word, instrument is the place where Service Providers could enforce access control strategies.