Re: Hope a discussion for draft-li-quic-optimizing-ack-in-wlan-00

[Christian Huitema <[e-mail]>]

Hello Jiao,

Your draft is motivated by specific data about running high bandwidth
applications over wireless local area network. It would be interesting
to compare behavior of these applications using different
acknowledgement policies, probably using simulations. Do you have
definitions of the application and of the WLAN that we could enter in
simulations?

The draft draft-iyengar-quic-delayed-ack-00 provides a way for senders
to specify both the maximum delay between acknowledgements and the
maximum number of packets between acknowledgement, with receivers
sending acknowledgements when one of the conditions is true. Several
servers set the delay to a fraction of the RTT, and the number of
packets to a corresponding fraction of the number of packets per
congestion window -- RTT/8 is often suggested. How is that different
from setting the "ACK intensity" suggested in
draft-li-quic-optimizing-ack-in-wlan-00?

The draft draft-li-quic-optimizing-ack-in-wlan-00 mentions using one way
delay measurements. Is that a reference to draft-huitema-quic-ts-00 ?

-- Christian Huitema

On 7/6/2020 7:35 AM, Kangjiao wrote:
>
> Dear Martin,
>
>  
>
> Here are the two drafts:
>
> draft-li-quic-optimizing-ack-in-wlan-00:
> https://tools.ietf.org/html/draft-li-quic-optimizing-ack-in-wlan-00  
>
> draft-iyengar-quic-delayed-ack-00:
> https://tools.ietf.org/html/draft-iyengar-quic-delayed-ack-00
>
>  
>
> I have outlined some distinction and connection between these two drafts:
>
>  
>
> a)       Both draft-li-quic-optimizing-ack-in-wlan-00 and
> draft-iyengar-quic-delayed-ack-00 propose a solution to reduce the ACK
> frequency for QUIC. draft-iyengar-quic-delayed-ack-00 makes the two
> parameters in delayed ACK, i.e., "Packet Tolerance" and "Max Ack
> Delay", be tunable by the sender. These two tunable parameters do not
> include RTT as a factor. Sara Landstrom et al. [1] has demonstrated
> that, in theory, the endpoint should acknowledge data at least twice
> per send window (RTT) to ensure utilization. In this case, reducing
> ACK frequency without considering the RTT as a factor of Max Ack
> Delay, might cause performance issues. On the other hand, the purpose
> in draft-li-quic-optimizing-ack-in-wlan-00 is to minimize the ACK
> frequency required by the transport, thus the ACK frequency is
> computed as *MIN*{bw/(packet_tolerance *max_packet_size), beta/RTTmin}
> (beta indicates the number of ACKs per RTT). While
> draft-iyengar-quic-delayed-ack-00 adopts the extended delayed ACK as
> specified in the legacy TCP, whose ACK frequency is computed as
> *MAX*{bw/( packet_tolerance *max_packet_size), 1/ max_ack_delay}. A
> paper [2] (to be appeared in SIGCOMM2020) has demonstrated that using
> a *MIN* instead of a *MAX* can also achieve equally good performance.
>
>  
>
> b)       draft-iyengar-quic-delayed-ack-00 provides a way for the
> sender to customize the ACK frequency. This means the ACKs might be
> excessively delayed when the Max Ack Delay is large. When sending
> fewer ACK frames, many data packets might be received during the ACK
> interval, generating only one RTT sample among multiple packets is
> likely to result in biases. For example, a larger minimum RTT
> estimate. In draft-li-quic-optimizing-ack-in-wlan-00, we propose a
> one-way-delay-based method to compute the minimum RTT more accurately.
> Apart from the ACK scheme, this is another point that we would like to
> discuss and get feedback from QUIC WG.
>
>  
>
> c)       With some minor extensions such as adding one more field of
> ACK-INTENSITY, the proposed ACK scheme in
> draft-li-quic-optimizing-ack-in-wlan-00 may be able to reuse the
> ACK-FEQUENCY frame specified in draft-iyengar-quic-delayed-ack-00 to
> sync the ACK intensity between sender and receiver.
>
>  
>
> Some reference mentioned above:
>
> [1] Sara Landstrom and Lars-Ake Larzon. 2007. Reducing the TCP
> acknowledgment frequency. ACM SIGCOMM CCR 37, 3 (2007), 5–16.
>
> [2] Tong Li, Kai Zheng, Ke Xu, Rahul Arvind Jadhav, Tao Xiong, Keith
> Winstein, Kun Tan. "TACK: Improving Wireless Transport Performance by
> Taming Acknowledgments", ACM SIGCOMM, 2020. (
> http://www.thucsnet.org/uploads/2/5/2/8/25289795/tong_sigcomm20.pdf )
>
>  
>
> Best Regards,
>
> Jiao
>
>  
>
> -----Original Message-----
> From: QUIC [mailto:[e-mail]] On Behalf Of Martin Thomson
> Sent: Monday, July 6, 2020 8:41 AM
> To: [e-mail]
> Subject: Re: Hope a discussion for draft-li-quic-optimizing-ack-in-wlan-00
>
>  
>
> Can you speak a little about the relationship with
> draft-iyengar-quic-delayed-ack ?
>
>  
>
> On Sat, Jul 4, 2020, at 16:05, Kangjiao wrote:
>
> >  
>
> > Dear QUIC WG members,
>
> > 
>
> > 
>
> > We uploaded a draft describing a mechanism for ACK optimization to
>
> > QUIC group. The link is
>
> > https://datatracker.ietf.org/doc/draft-li-quic-optimizing-ack-in-wlan/..
>
> > This solution comes from our practice and the results show it is a
>
> > good replacement of the traditional ACK mechanism to compensate for
>
> > scenarios where the acknowledgement overhead is non-negligible (i.e.,
>
> > wireless scenarios).
>
> > 
>
> > 
>
> > The key points for this solution can be:
>
> > 
>
> > 
>
> > 1. We conclude the formula of the minimum ACK intensity required for
>
> > QUIC transport.
>
> > 
>
> > 
>
> > 2. In order to alleviate the error in RTT estimation, we use protocol
>
> > extensions and a one-way delay factor. We think this round-trip timing
>
> > method can also be applicable for the ack thinning mechanisms (such as
>
> > ”Changing the Default QUIC ACK Policy”#3529) that have been discussed
>
> > in QUIC group..
>
> > 
>
> > 
>
> > 3. For implementation and interoperability, we define a new
>
> > ACK-INTENSITY Frame in which ACK Intensity is set. ACK Intensity is a
>
> > variable-length integer indicating the updated intensity of QUIC ACK
>
> > Frame calculated by our formula.
>
> > 
>
> > 
>
> > We look forward to your valuable comments and suggestions. Thanks.
>
> > 
>
> > 
>
> > Sincerely,
>
> > 
>
> > Jiao
>
> > 
>
>  
>