Number of datagrams retransmitted by this source (LBT-RM only).

- n (Int32)
- Statistics set index

Number of datagrams retransmitted by this source transport.

This count is incremented under the same circumstances as
retransmissionBytesSent, below.
In a normal, light-loss scenario, most NAKs received induce a retransmission.
When losses become heavy and/or many receiver transports begin losing the
same datagrams, NCF-related no-retransmit counts (naksIgnored, naksShed and
naksIgnoredRetransmitDelay) may begin to inflate, and retransmissions
retransmissionsSent) may become significantly lower than NAKS
received (naksReceived).
This method returns a value from the nth set of statistics
encapsulated within this object.