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Thu, 06 Mar 2025 07:50:41 -0800 (PST) Received: from smtpclient.apple ([2600:1700:841:34f0:9dd1:c9cc:79d1:efb]) by smtp.gmail.com with ESMTPSA id 3f1490d57ef6-e634b842159sm354639276.18.2025.03.06.07.50.40 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 06 Mar 2025 07:50:41 -0800 (PST) From: Cheng Cui Message-Id: <979E9D00-755F-4E4D-9687-CAB957F4C8C8@freebsd.org> Content-Type: multipart/alternative; boundary="Apple-Mail=_33C3C34F-6F43-4C39-A322-D59D095948EC" List-Id: Networking and TCP/IP with FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-net List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-net@FreeBSD.org Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.400.131.1.6\)) Subject: Re: Sending empty segment upon receiving partial ACK Date: Thu, 6 Mar 2025 10:50:09 -0500 In-Reply-To: Cc: freebsd-net@freebsd.org To: jaeyong yoo References: <38B72ADC-B796-4BFC-8F94-2BD6E40C4231@freebsd.org> X-Mailer: Apple Mail (2.3826.400.131.1.6) X-Spamd-Result: default: False [-0.78 / 15.00]; NEURAL_HAM_LONG(-0.95)[-0.949]; NEURAL_HAM_SHORT(-0.60)[-0.600]; MV_CASE(0.50)[]; FORGED_SENDER(0.30)[cc@freebsd.org,ccfreebsd@gmail.com]; R_SPF_ALLOW(-0.20)[+ip4:209.85.128.0/17]; NEURAL_SPAM_MEDIUM(0.17)[0.168]; DMARC_POLICY_SOFTFAIL(0.10)[freebsd.org : SPF not aligned (relaxed), No valid DKIM,none]; MIME_GOOD(-0.10)[multipart/alternative,text/plain]; RCVD_TLS_LAST(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; FREEMAIL_TO(0.00)[gmail.com]; ARC_NA(0.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; MIME_TRACE(0.00)[0:+,1:+,2:~]; RBL_SENDERSCORE_REPUT_8(0.00)[209.85.219.169:from]; TO_DN_SOME(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_IN_DNSWL_NONE(0.00)[209.85.219.169:from]; TO_MATCH_ENVRCPT_SOME(0.00)[]; PREVIOUSLY_DELIVERED(0.00)[freebsd-net@freebsd.org]; RCVD_COUNT_TWO(0.00)[2]; FROM_NEQ_ENVFROM(0.00)[cc@freebsd.org,ccfreebsd@gmail.com]; ASN(0.00)[asn:15169, ipnet:209.85.128.0/17, country:US]; MLMMJ_DEST(0.00)[freebsd-net@freebsd.org]; MID_RHS_MATCH_FROM(0.00)[]; R_DKIM_NA(0.00)[]; RWL_MAILSPIKE_POSSIBLE(0.00)[209.85.219.169:from]; TAGGED_RCPT(0.00)[]; FROM_HAS_DN(0.00)[] X-Rspamd-Queue-Id: 4Z7v5b16DFz3qJ0 X-Spamd-Bar: / --Apple-Mail=_33C3C34F-6F43-4C39-A322-D59D095948EC Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 I see Bug=C2=A0285158 = is created. = Let's talk/track it there. thanks > On Mar 5, 2025, at 16:58, jaeyong yoo wrote: >=20 > Yes it is data retransmission but my concern is that the > retransmission packet has the segment length of zero. > If there is nothing to send, why don't we just not send it. >=20 > What I meant by "no packets going out" is, that zero-length-segment > can be considered as ACK to acknowledge some received packets but the > sender of "zero-length-segment" did not receive any packets hence > nothing to ACK. That said, those retransmission packets are the pure > purpose of retransmissions and its segment length is zero, which seems > pure overhead. > Hope this makes it clear. >=20 > Thanks, > Jaeyong >=20 > 2025=EB=85=84 3=EC=9B=94 5=EC=9D=BC (=EC=88=98) =EC=98=A4=ED=9B=84 = 12:30, Cheng Cui =EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1: >>=20 >>=20 >>=20 >> On Feb 26, 2025, at 10:21, jaeyong yoo wrote: >>=20 >> Yes that behavior was observed during recovery phase and during that >> time frame, there were no packets going out to the other direction so >> there is no reason to send pure ACK (and the ack number for those 3 >> acks are the same and no possibility of challenge ack as well). >>=20 >>=20 >> Isn't loss recovery phase used for data retransmission? There should = be retransmitting packets. But what do you mean "no packets going out"? >>=20 >> Best Regards, >> Cheng Cui >>=20 >>=20 >>=20 Best Regards, Cheng Cui --Apple-Mail=_33C3C34F-6F43-4C39-A322-D59D095948EC Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8 I see Bug=  285158 is created. Let's talk/track it there. = thanks

On Mar 5, 2025, at 16:58, jaeyong yoo = <y.jaeyong@gmail.com> wrote:

Yes it is data = retransmission but my concern is that the
retransmission packet has = the segment length of zero.
If there is nothing to send, why don't we = just not send it.

What I meant by "no packets going out" is, that = zero-length-segment
can be considered as ACK to acknowledge some = received packets but the
sender of "zero-length-segment" did not = receive any packets hence
nothing to ACK. That said, those = retransmission packets are the pure
purpose of retransmissions and = its segment length is zero, which seems
pure overhead.
Hope this = makes it clear.

Thanks,
Jaeyong

2025=EB=85=84 3=EC=9B=94 = 5=EC=9D=BC (=EC=88=98) =EC=98=A4=ED=9B=84 12:30, Cheng Cui = <cc@freebsd.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:



On Feb 26, 2025, at 10:21, jaeyong yoo = <y.jaeyong@gmail.com> wrote:

Yes that behavior was observed = during recovery phase and during that
time frame, there were no = packets going out to the other direction so
there is no reason to = send pure ACK (and the ack number for those 3
acks are the same and = no possibility of challenge ack as well).


Isn't loss recovery = phase used for data retransmission? There should be retransmitting = packets.  But what do you mean "no packets going out"?

Best = Regards,
Cheng = Cui




Best Regards,
Cheng Cui



= --Apple-Mail=_33C3C34F-6F43-4C39-A322-D59D095948EC--