Warning: the use of the term Accept Level Acknowledgement is ambigious in HL7 v2. In HL7 v2 the functionality of the accept level acknowledgement is quite often combined with that of the Commit Acknowledgement. In HL7 v3 the Accept Acknowledgement has been explicitely defined NOT to overlap with the functionality of the Commit Acknowledgement.
A commit-level acknowledgement is sent once the transmission has been saved to reliable storage by the protocol software on the receiving system. The implementation of the commit-level acknowledgement will differ depending on the underlying Transport Protocol. The commit-level acknowledgement is not an HL7 interaction, and is out of scope of the standard itself.