Albert Greenberg is currently a Director of Microsoft Azure in Redlands, Washngton. He was my boss (Department head) at AT\&T Labs Research, where I was before joining Columbia in 2002. Hence, whatever I say here must be held suspect. I had the privilege of being the first department member in Albert's department when he first became a Department Head in 1996. We had both previously been in the Mathematical Sciences Research Center of Bell Labs (now part of Lucent Technologies). See the list of former members of the Math Center.
I have had the opportunity to work together with Albert both before and after he donned his new hat. Our 1993 paper (joint with the unforgettable Otmar Schlunk, who seems to be making quite a name for himself) drew on Albert's great expertise in parallel simulation. We applied parallel simulation to study the behavior of the departure process from a large number of queues in series. We were a veritable queueing MacDonald's - serving billions of customers each day.
Later, in collaboration with R. Srikant, who was at AT&T, but now is at the University of Illinois, we studied advanced reservation. This is a fascinating technical problem, but like much of Albert's work, this work arose from consulting at a business unit at AT&T.