RFC 6298 application

Question

I got this? How many Fragments that are going to be sent are: 10800 / 1200 = 9 segments to Host B.

And the full time is: (9*1200) / 1600000 = 6.75 ms

According to RFC 6298 [1]: (2.2)

When the first RTT measurement R is made, the host MUST set

SRTT <- R

RTTVAR <- R/2

RTO <- SRTT + max (G, K*RTTVAR)

where K = 4.

(2.3) When a subsequent RTT measurement R' is made, a host MUST set

RTTVAR <- (1 - beta) * RTTVAR + beta * |SRTT - R'| SRTT <- (1 - alpha) * SRTT + alpha * R'

The value of SRTT used in the update to RTTVAR is its value before updating SRTT itself using the second assignment. That is, updating RTTVAR and SRTT MUST be computed in the above order. The above SHOULD be computed using alpha=1/8 and beta=1/4

How am i going to continue to apply RFC 6298 on this to calculate SRTT,RTTVAR,RTO for each package that are being sent?

Answer 1

Fragmentation doesn't change TCP's RTT detection and calculation.

A segment is only received by TCP after all its fragments (or rather the original IP packet's) have been received and reassembled. TCP cannot see any fragmentation or reassembly as that all happens in the network layer below.

Accordingly, you don't calculate TCP RTT for each fragment but only for the last fragment. Total transmission time begins with the transmission of the first fragment and ends with the reception of the last.