Just to clarify, we're talking about GigE Vision as a high-level protocol running on top of Gigabit Ethernet (GigE).
The GigE Vision protocol uses UDP (which of course is running on top of IP, which is on top of Gigabit Ethernet).
By using UDP, we decrease the overhead incurred when transmitting data. We also decrease the latency and jitter by using UDP.
Because UDP doesn't have any built-in delivery guarantees, the GigE Vision protocol specifies a retransmission scheme.
Hope this answers your question.