Re: [tcpm] Comments on draft-blanton-tcpm-3517bis-01

[Yuchung Cheng <[e-mail]>]

Hi Ethan,

I have two questions:

1) IsLost (SeqNum):

      This routine returns whether the given sequence number is
      considered to be lost.  The routine returns true when either
      DupThresh discontiguous SACKed sequences have arrived above
      'SeqNum' or more than (DupThresh - 1) * SMSS bytes with sequence
      numbers greater than 'SeqNum' have been SACKed.  Otherwise, the
      routine returns false.

Does RFC require DupThresh discontinuous sack blocks? e.g.,
For example, if a sender sends 4 data packets
send pkt1: 1-100
send pkt2: 101-200
send pkt3: 201-300
send pkt4: 301-400
receive ack: ack1 with one sack block 101-400.
does IsLost(1) returns true?

2)
If the incoming ACK is a duplicate acknowledgment and the TCP is

   not currently in loss recovery, the TCP MUST increase DupAcks by
   one and take the following steps:

   (1) If DupAcks >= DupThresh, go to step (4).

   (2) If DupAcks < DupThresh but IsLost (SND.UNA) returns
       true---indicating at least three segments have arrived above
       the current cumulative acknowledgment point, which is taken
       to indicate loss---go to step (4).

can we combine (1) and (2)? go to steps (4) if IsLost(SND.UNA) is
true. I guess it depends on your answer of my first question.

Thanks,

Yuchung