a seismic survey system having remote acquisition modules for acquiring seismic signals and communicating with a central recording system via a network of cables , other rams , and line tap units , arranged in a matrix of receiver lines and base lines . each ram cyclically converts analog signal values to digital , forming data packets . interrogation commands emanating from the cru and relayed with strategic delays by intervening ltus and rams are received by the ram . each command causes the ram to transmit a data packet . strategic delays are set such that the transmission capacity of the line is best utilized . power and frequency of transmission are selectable by the cru to optimize performance . cables contain multiple communication pairs . the network path between the ram and the cru is established from the cru and altered in event of malfunction . all types of network elements are interconnectable . recorded samples are synchronous .