MS Software Assurance
Overview
Software Assurance (SA) is included in many Microsoft Volume Licensing agreements (Open Value, Open Value Subscription, Enterprise Agreement) and is an optional purchase in others (Open License, Select Plus, MPSA). SA is purchased at the same time as the corresponding license, and after SA payments have been maintained throughout an agreement, the SA may be renewed without the need to purchase a license again.
Benefits by Agreement

External Links
MS Software Assurance - Link