Abstract: A system for synchronizing one or more decoders with a network sync signal at a headend of a television communication network. The system allows decoders to transmit upstream messages synchronously in time slots which are defined according to the network sync signal, thereby improving system throughput. Identifying data is provided in a blanking interval (VBI or HBI) of one or more television signals to designate a horizontal scan line of the respective television signal which follows a reference point in the network sync signal by a predetermined delay. At each decoder, the identifying data is recovered, and the onset of the designated scan line can be used to signal the start of a transmission for the decoder. Preferably, the identifying data is provided in each television signal so the user is not forced to tune to a particular television channel to transmit a message. Various channel access protocols may be used, such as a session oriented protocol, or a synchronized ALOHA protocol.