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[tcpm] Questions about TLP

Yi Huang <huanyi@microsoft.com> Thu, 02 May 2019 05:48 UTC

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From: Yi Huang <huanyi@microsoft.com>
To: "tcpm@ietf.org" <tcpm@ietf.org>
CC: Praveen Balasubramanian <pravb@microsoft.com>, Matt Olson <maolson@microsoft.com>
Thread-Topic: Questions about TLP
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Date: Thu, 02 May 2019 05:47:56 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tcpm/OnkmGITeDK_KDH8QS67FFXWCtac>
Subject: [tcpm] Questions about TLP
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Hi RACK/TLP authors,



I have the following questions (page numbers refer to draft-ietf-tcpm-rack-05):



1.In page 16, it says "Finally, if the time at which an RTO would fire (here denoted "TCP_RTO_expire") is sooner than the computed time for the PTO, then a probe is scheduled to be sent at that earlier time." What does this TCP_RTO_expire actually mean? Does it mean there is another RTO timer (possibly started some time in the past) running along with PTO or just RTT + 4*RTTVar + Now()? Also, why would another probe be sent at RTO expiration time instead of treating it like RTO and collapsing the cwnd?



2.In page 18 section 6.6, a new variable TLPRxtOut is defined and it is stated that TLPRxtOut is used to guarantee that there is only one outstanding TLP retransmission. However, it is not clear to me when TLPRxtOut should be really used. Should it be used in 6.5.1 Step. 1 (checking whether we should and can schedule a TLP) or in TLP_send_probe()?



Thanks,



Yi

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