Character transmission is prioritised as follows:

• Time-codes – highest priority
• FCTs
• N-Chars
• NULLs – lowest priority

Time-codes are highest priority because they are used to transfer time or synchronisation information and have to be delivered with low jitter. FCTs are higher priority that N-Chars, so that a large amount of data being sent in one direction does not stop FCTs being sent, thus causing the other end of the link to stop sending data because it has run out of flow control. Nulls are the lowest priority as they are only sent to keep the link running and synchronised when there is nothing else to send.