Sony has announced that PlayStation Network will undergo routine maintenance on the 18th of August. During the downtime, Sony is going to work on deploying a series of back-end improvements to the network.
The maintenance is scheduled to take place from 4:30AM BST (8:30PM PDT) to 6:00AM BST (10:00PM PDT). Like usual, players that sign in before the maintenance starts will be able to continue playing online, but won't be able to access PlayStation Store, PlayStation Home, and Account Management.
With the Call of Duty: Black Ops III beta starting on the 19th, it may be that Sony is improving their network so that there aren't problems and the network remains stable during the event.