British Rail´s distributed Band III radio network

British Rail (BR) split the UK into control areas each area having control equipment to link it into the trunk telephone network. A fully equipped control area can handle 40 fixed stations, four telephone trunk junctions, six direct lines to electric control rooms, one direct line to the train control office, one line to emergency operator and two interfaces into the BR teleprinter network. Fixed stations are arranged in non interfering groups and channel free ALOHAs are sequenced around these groups. All fixed stations operate on the same control channel but are allocated a separate traffic channel. The traffic channel allocation is arranged so that fixed stations can operate without the need for guarding although the control system can cater for this if future expansion dictates that guarding will be necessary. The ALOHA number is set at three