1. A method comprising: receiving, by an assistance server and from a mobile communication device, a request for assistance data of a data type, wherein the request includes a period parameter defining a period in which the assistance server is to transmit information related to the assistance data based on the request and at least one rate parameter defining at least one rate condition on when the assistance server is to send the assistance data during the period; during a period in which the assistance server is transmitting the information related to the assistance data based on the request, sending a plurality of transmissions based on the request to the mobile communication device, the plurality of transmissions comprising a first transmission of the assistance data and a second transmission of the assistance data in accordance with the period parameter and the at least one rate parameter; receiving, by the assistance server, a modification request for the assistance data of the data type, wherein the modification request includes a modification period parameter that defines a modification period in which the assistance server is to stop transmitting the information related to the assistance data based on the request and instead is to transmit the information related to the assistance data based on the modification request; during a period in which the assistance server is transmitting the information related to the assistance data based on the modification request, sending one or more transmissions based on the modification request, the one or more transmissions comprising at least a portion of the information related to the assistance data; and after sending the one or more transmissions based on the modification request, sending one or more additional transmissions based on the request.