[e2e] Question on RFC6298, Managing the RTO Timer and additional lost pakets in Recovery state

[Ingemar Johansson S]

Hi

I am trying to understand the Linux TCP stack and how it rearms the RTO timer, in the process I  read section 5 in RFC6298.
It says quote "(5.3) When an ACK is received that acknowledges new data, restart the retransmission timer so that it will expire after RTO seconds (for the current value of RTO)."
What is the definition of new data ?. The strict interpretation is when SND.UNA advances, but it can also be that the highest SACKed sequence number increases. The former case it is more likely that RTO happens.

The second question is Linux related. Given that a lost packet puts the stack in Recovery state, the congestion window reduces one step as an effect on this. What happens if additional packets are lost when in Recovery state. I guess the congestion window should decrease more or ?.

I am currently porting the Linux TCP stack to fit our Java based system simulator, most things seem to be working but the above leaves me wondering.

/Ingemar

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Ingemar Johansson  M.Sc.
Master Researcher

Ericsson AB
Wireless Access Networks
Labratoriegränd 11
971 28, Luleå, Sweden
Phone +46-1071 43042
SMS/MMS +46-73 078 3289
ingemar.s.johansson at ericsson.com<mailto:ingemar.s.johansson at ericsson.com>
www.ericsson.com

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