Methods and systems for controlling access to resources. Receiving, at a server from user devices, requests associated with a resource. Transmitting, by the server to the user devices, tickets associated with the requests, each ticket associated with a respective one of a plurality of groups, the groups identifying requests received in successive windows of time. Receiving, at the server from one of the user devices, a subsequent request, the subsequent request identifying one of the tickets previously transmitted to that user device. Determining that the identified one of the tickets should be accepted and the subsequent request should be serviced.