Subject: [tcpm] comments for draft-ietf-tcpm-rack-00.txt

From: Yoshifumi Nishida <[email-masked]>
Date: Fri, 30 Sep 2016 00:20:27 -0700

Hello,

Thanks for an interesting proposal.
I've read the draft-ietf-tcpm-rack-00.txt and have the following comments
on the draft.
Please point out if I miss something.

1: I think the draft should mention how to control pipe size during loss
recovery.
    When RACK identifies lost packets, how it reduces cwnd?

2: Similar to 1:, doesn't RACK have a certain back-off mechanism? I
couldn't find it in the draft.
    It is nice that it can find the lost of retransmitted packets, but does
it retransmits them again with the same settings?
    It seems to me that RACK might become aggressive under heavy
congestions as it keeps retransmitting packets with short intervals while
other TCPs wait for RTO.

3: I am not very sure if using the minimum value in all RTT measurements
for RACK.min_RTT is a really good option.
    If RTT is significantly increased all of sudden, it might cause lots of
spurious retransmits unless reordering window is dynamically adjusted.

4: It is a bit confusing to me that the abstract says "modern TCP
implementations that can support per-packet timestamps.." because I thought
it was referring timestamp option. But, RACK actually doesn't rely on it. I
might prefer to say something like keep tracking transmit time per packet.

5: I guess you might want to add explanations of "RACK packet" and
"RACK.ack_ts" in Section 4. I think their definitions are not very clear.

Thanks,
--
Yoshi