Communications in a distribution network

A method of communicating information between a central station and a plurality of terminals in a distribution network, comprising the steps of:

• at the central station, determining downstream TDM frames, for transmission of distribution information and overhead information from the central station to the plurality of terminals, and upstream TDMA frames, for transmission of information in respective time slots from the terminals to the central station, each upstream frame having a frame identity which is included in the overhead information of a corresponding downstream frame;
• in each terminal, buffering asynchronous information for transmission upstream, storing an upstream frame identity and a time slot identity assigned to the terminal, monitoring the overhead information in the downstream frames for the stored upstream frame identity, and, in response to detection of the stored upstream frame identity in the overhead information in a downstream frame, transmitting, in the assigned time slot of the corresponding upstream frame, information comprising an indication of a queue size of the buffered asynchronous information;
• at the central station, allocating time slots in the upstream frames to terminals in accordance with the queue size indications from the terminals, and including in the overhead information in the corresponding downstream frames an indication of each terminal which is allocated such a time slot and the time slot which it is allocated;
• and
• in each terminal having buffered asynchronous information, monitoring the overhead information in the downstream frames for the indication of the terminal and, in response to detection of the indication of the terminal in the overhead information in a downstream frame, transmitting buffered asynchronous information in the allocated time slot of the corresponding upstream frame.

A method of allocating upstream transmission capacities to terminals in a distribution network in which distribution information and overhead information are transmitted in TDM frames in a downstream direction from a central station to the terminals, comprising the steps of:

• providing, for transmission from the terminals to the central station, upstream TDMA frames in which there are at least two different sizes of time slots, and identifying each upstream frame by a frame identity in the overhead information in a corresponding downstream frame so that the terminals can determine the time slots for each upstream frame;
• assigning time slots of a first size to at least some of the terminals for transmitting upstream queue size information for buffered asynchronous information to be transmitted upstream from the terminal, each such terminal storing an identity of an assigned time slot and an upstream frame identity for transmitting the queue size information, monitoring the overhead information in the downstream frames to detect the assigned frame identity, and transmitting the queue size information in the assigned time slot in the corresponding upstream frame;
• and
• allocating time slots of a second size to terminals in dependence upon the queue size information by transmitting from the central station in the overhead information in the downstream frames an indication of each terminal which is allocated such a time slot and the time slot which it is allocated, each terminal having buffered asynchronous information to be transmitted monitoring the overhead information in the downstream frames to detect the indication of the terminal and transmitting buffered asynchronous information in the allocated time slot of the corresponding upstream frame.

A terminal for a communications system in which information is communicated in TDM frames in a downstream direction from a central station of a distribution network to a plurality of terminals of the network, and in TDMA frames in an upstream direction from the plurality of terminals to the central station, the downstream frames comprising distribution information and overhead information, the overhead information comprising synchronization information for synchronizing the terminals to the upstream frames and authorization information for authorizing selected terminals each to transmit in an upstream frame, the terminal comprising:

• a store arranged to store information allocated to the terminal, said information including an identity of the terminal and allocation information communicated to the terminal by the central station, and delay information inversely dependent upon a distance of the terminal from the central station;
• and
• a control unit arranged to store said allocation information received from the central terminal in the store, the control unit also being responsive to the authorization information in the downstream frames and the stored information allocated to the terminal for selectively communicating information from the terminal to the central station in selected upstream frames at a time dependent upon the synchronization information and the stored delay information.