Q. What is Retransmission timer?
Retransmission timer
- if an ACK is received previous to the timer goes off - destroy the timer
- if the timer goes off before ACK arrives - retransmit the segment & reset the timer
- Retransmission time = 2* RTT
- not fixed because paths that IP packets take may differ
- If too short - retransmissions -> waste of bandwidth
- If too large - delay for the application program
RTT = * previous RTT + (1- ?)*current RTT, usually 90 %
Karn's algorithm:
- don't consider the RTT of a retransmitted segment in the calculation of the new RTT