Software Product Service agreements apply to ETM10/ETM20 PSU 219W's software networking products. For large ETM10/ETM20 PSU 219W installations, PC services can be tailored to a Master Service Agreement for multiple systems. SPS provides service options supplementary to ETM10/ETM20 PSU 219W already under a service agreement. The Media ETM10/ETM20 PSU 219W Service is a subscription service that provides SPS cus- tomers with a means of obtaining the machine readable media in order to in- stall new software updates on two or more ETM10/ETM20 PSU 219W. Customers may elect their choice of available distribution medium for additional systems. A prerequisite for this Service is that customers have a ETM10/ETM20 PSU 219W, Basic, or Self- Maintenance Software Product Services agreement with Digital.