TImers

Question 1

Retransmission timer

Answer 1

A number of bytes are sent according to sending window

if data is confirmed in due time
timer stops

if not
data is retransmitted and timer resets

Question 2

Persistence timer

Answer 2

prevents blocking in case of receiver window, previously 0, becomes non zero but the packet informing the sender has been lost

Question 3

Keepalive timer

Answer 3

If the connection is inactive for a long period of time,
After timeout a probing segment is sent,

if no reply, connection closed