Re: [tcpm] Variable "recover" in F-RTO

[Pasi Sarolahti <Pasi.Sarolahti at nokia.com>]

Hi Alex,

Sorry that it took this long to reply.

The condition 'but not more than "recover"' is there just to cover  
the case of invalid ACKs arriving for some strange reason, and in  
such case revert to normal TCP operation, to be on a safe side. In a  
well-behaving environment one should not receive such an ACK.

- Pasi


On Mar 5, 2009, at 2:37, ext Alexander Zimmermann wrote:

> Dear all,
>
> I have an understanding problem with aforementioned variable "recover"
> in the current version (http://www.tools.ietf.org/html/draft-ietf- 
> tcpm-rfc4138bis-04)
> of the F-RTO Algorithm.
>
> Section 2.1 The Algorithm (F-RTO, Reno/NewReno Case)
>
> Step 2): When the first ACK after RTO rexmit arrives at the TCP  
> Sender,
> we store the highest sequence number transmitted so far in the  
> variable
> "recover".
>
> then
>
> Step 2a) Check if the ACK from Step 2) is a DUPACK OR the ACK covers
> "recover" but not more than "recover"...
>
>
> Why is the check like this? IMHO we can only get an ACK that cover  
> exactly "recover"
> (Lost Retransmission - SIGCOM Paper Section 4.2) or an ACK that  
> cover less than
> "recover", but we cannot get ACK that cover more than "recover".
>
> Alex
>
>
> //
> // Dipl.-Inform. Alexander Zimmermann
> // Department of Computer Science, Informatik 4
> // RWTH Aachen University
> // Ahornstr. 55, 52056 Aachen, Germany
> // phone: (49-241) 80-21422, fax: (49-241) 80-22220
> // email: zimmermann at cs.rwth-aachen.de
> // web: http://www.umic-mesh.net
> //