With advances in networking technology, vendors began to introduce non-perpetual licensing models, such as subscription or pay-per-use licensing. In the pay-per-use, user is charged each time he/she uses the software, service or module and user does not own the software, rather uses it at on rent for the limited period. There is time based pay-per-use arrangement
and transaction based pay-per-use arrangement.
In a time based pay-per-use arrangement, consumers are charged for the amount of time that they used non-owned copies of the software.
In a transaction based pay-per-use arrangement, usage charges occur because a software module has been used. The duration of use is irrelevant.