Patent ID: 7206321

Claim:
A method of filtering upstream scheduling messages in a data communication system that includes a headend and at least one subscriber unit, wherein the system has an upstream and a downstream transmission path, the method comprising: obtaining a scheduling message from the headend, the scheduling message including a MAP message having a plurality of information elements (IE's), at least one IE including a service identifier (SID), an Interval Usage Code (IUC), a Minislot offset and a Minislot length value; filtering the MAP message to identify a plurality of IEs that correspond to a selected subscriber unit, and to generate a filtered MAP message having a plurality of data fields, where the MAP message includes at least one Null IE; and storing an information set based upon the plurality of IEs obtained in the step of filtering the MAP message into a filtered scheduling message that includes the following sub-steps: (1) before encountering Null IE, storing the information using a first process; (2) when encountering the Null IE, storing the information using a second process; and (3) after encountering the Null IE, storing the information using a third process.