There are two major command using by Gen2, which are QueryAdjust and QueryRep. Specifically, these two commands are used by Reader. Also, as we may find out that Reader's transmission rate is 4 times slower than Tags' rate.
So the length of these two commonly using commands becomes critical in performance when doing time measurement.
Gen2 does very well in shortening their length:
QueryRep >> command type(2 bits) + Session (2 bits) = 4 bits
QueryAdjust >> command type(4 bits) + Session (2 bits) + Up or Down (3 bits) = 9 bits
There is only two 2 bits long command types, one is QueryRep, as it uses every time to order tags to downcounter by 1. Base on performance of Gen2, averagely, every tag needs 3 query rounds to be identified. So if there is 1000 tags, QueryRep is sent 3000 times roughly.
QueryAdjust is used to change the value of Q in the Q-algorithm. Instead of telling the value of Q directly in its command, it only tells how to change its value, as Q is changed step by step, one by one.
This efficient side of Gen2 compensates the upper limit performance of Aloha algorithm. These two succinct command lines reduce huge time in the whole process.