Methods and apparatuses are presented for conducting communications over a shared communication medium involving a plurality of nodes, involving (a) sending a request from a first node, the shared communication medium organized to include a request signal space and a scheduled transmission signal space, the request signal space including request segments each having a different location within the request signal space, the scheduled transmission signal space including scheduled transmission segments each having a different location within the scheduled transmission signal space, the request sent in a request segment, (b) obtaining an assignment associating the request with a scheduled transmission segment, taking into account location of the request within the request signal space, (c) from the first node, sending a data transmission in the scheduled transmission segment associated with the request, and (d) wherein the plurality of scheduled transmission segments include multiple categories of scheduled transmission segments associated with different service types.