TCP timout rfc 2018 + rfc 793

dani1999

i ask befor but i find out somthing that not clear.
About TCP let's say that i have 3 segment to send,
Let's say that the cwind start from 1.
So i send segment 1 and get ack, so now the cwind is 2.
Then I send 2+3 , but segment 2 is gone.So i come to TIMEOUT (so cwind down to 1)
now what will happend?I ask before and see rfc 2018 and according to this article TCP Selective Acknowledgments (SACK) - PacketLife.net i understand that...
if i not use on SACK(on option on TCP) . so i will need send again 2+3 segment
but... someone told me that this artile is not correct because on rfc 793 (and not change from then) i will need send again only the 2 segment
on rfc 793

RETRANSMISSION TIMEOUT
For any state if the retransmission timeout expires on a segment in
the retransmission queue, send the segment at the front of the
retransmission queue again, reinitialize the retransmission timer,

and return.

and what i get from there that when i send segment number 2 i will get ack on 2+3( so i need send only segment 2)
but on the article on packetlife i understand that the recevier not save the segment 3 so i need send 2+3
i dont use SACK

who is right?(or this arcticle is right but not talk on timeout? i not think so)
i need prove that base on rfc
thanks!

james43026

Well RFC 793 was written in 1981, and RFC 2018 was written in 1996 and was an addition of sorts to TCP, so the selective acknowledgement option is a valid option and can be use to prevent a receiver from having to receive the same packets multiple times just because a packet was lost or arrived late. Without selective acknowledgement if three segments were transmitted from host A to host B, and segment 2 was lost, then segment 2 and 3 would have to be retransmitted and received by host B. Now with selective acknowledgement in the same scenario, host B can just ask for another copy of segment 2, with no need to get another copy of segment 3.