What is the relationship between the variable LastByteRcvd in Section 3.5.5 and the variable y in Section 3.5.4? In Section 3.5.4, we saw that TCP waits until it has received three duplicate ACKs...

What is the relationship between the variable LastByteRcvd in Section

3.5.5 and the variable y in Section 3.5.4?

In Section 3.5.4, we saw that TCP waits until it has received three duplicate ACKs before performing a fast retransmit. Why do you think the TCP

designers chose not to perform a fast retransmit after the first duplicate ACK

for a segment is received?