AVL subsystem interfaces

Most traditional automatic vehicle location (AVL) systems covering large areas require large infrastructure investments. The paper presents a way to cut AVL infrastructure costs, by introducing an open architecture in the localisation system. The architecture uses existing infrastructure in combination with industry standard components and the paper focuses on the AVL subsystem interfaces in this architecture. In an AVL system positions are determined, distributed, used and displayed. A position determining device internally produces a more or less continuous one-way data flow. An AVL application, position user, needs data upon demand, e.g. polled data or periodically transmitted data. The paper describes an attempt to handle these functions and presents a generalised protocol-"the AVL macro-language"-which handles polled navigation data as well as periodically transmitted data. With this protocol the applications can access mobile AVL units through one or more communication systems. Results from field trials are presented as well as a range of interesting products from independent manufacturers.<
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