Abstract: A variable length data packet in a seismic system includes a fixed-length data portion and a variable-length data portion, the amount of data in the variable-length portion depending on the number of active channels. The data packet identifies the number channels which are in operation in the system, which may be the same or fewer than the number of installed channels. This signals the central recorder as to the length of the block of data in the data packet which includes seismic data. This feature permits the scaling of the system to accommodate varying numbers of channels, without reconfiguring the system. In another aspect, a method of sending data in a data system having a plurality of installed channels includes the steps of determining the number of active channels; assembling a packet of data comprising a fixed-length field and a variable-length field, the number of data bytes in the variable-length field being a function of the number of active channels; and sending the packet of data.