Apparatus comprises: first and second transmitter interfaces, each configured to transmit data over a respective communications path including one or more logical connections; first and second transmit buffers forming part of the first and second transmitter interfaces respectively, the first and second transmit buffers being configured to store packets of data for transmission over their respective communication path; one or more path capability determining modules configured to determine a measure of capability of each of the communications paths to transmit data; an input data buffer configured to store data for provision to the first and second transmit buffers for subsequent transmission; and a data handling module configured to respond to determining the presence of data in the input buffer for transmission by: using the measured capabilities of the communication paths and measures of the quantity of data stored in the transmit buffers to select one of the first and second transmitter interfaces for transmitting data; and providing at least one packet of data to the transmit buffer of the selected one of the first and second transmitter interfaces.