In streaming, the Aurora 64B/66B channel is used as a pipe. The streaming Aurora 64B/66B interface expects data to be filled for the entire s_axi_tx_tdata port width (integral multiple of eight bytes). When s_axi_tx_tvalid is deasserted, gaps are created between words that are preserved except when clock compensation sequences are being transmitted.
When data arrives at the RX side of the Aurora 64B/66B channel, if not read immediately, it is lost. If this is unacceptable, a buffer must be connected to the RX interface to hold the data until it can be used.