Re: [tcpm] ACK aggregation and congestion window growth

Ingemar Johansson S <ingemar.s.johansson@ericsson.com> Tue, 30 April 2019 05:44 UTC

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From: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
To: Rick Jones <perfgeek@mac.com>
CC: "tcpm@ietf.org" <tcpm@ietf.org>, Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
Thread-Topic: [tcpm] ACK aggregation and congestion window growth
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Date: Tue, 30 Apr 2019 05:44:14 +0000
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Subject: Re: [tcpm] ACK aggregation and congestion window growth
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Hi

 

No the ACK aggregator does not delay the 3WHS, I guess this can cause Cubic to exit slow start. Still I would expect that CWND would eventually increase, even in congestion avoidance.

 

Regards

/Ingemar

 

From: Rick Jones <perfgeek@mac.com>; 
Sent: den 26 april 2019 16:03
To: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>;
Cc: tcpm@ietf.org
Subject: Re: [tcpm] ACK aggregation and congestion window growth

 

Does your ACK aggregator also delay the ACKs of SYNchronize segments? If not, perhaps the congestion control sees the increase (?) in round trip time after connection establishment as a signal of congestion and behaves accordingly. 


On Apr 26, 2019, at 06:46, Ingemar Johansson S <ingemar.s.johansson@ericsson.com <mailto:ingemar.s.johansson@ericsson.com> > wrote:

Hi

 

I am experimenting with a simple test setup with 2 Ubuntu 18.04 PCs (Cubic CC). 

Between these two I have a simple setup that aggregates ACKs so that they are forwarded to the server only every 10ms. The min RTT is 18ms. 

The problem I see is that even though I should reach 1Gbps throughput, I only get around 200Mbps. 

I would believe that the congestion window should eventually increase enough to handle the burstiness given by the ACK aggregation but it seems like this is not the case. 

Is there a limitation in the Linux stack that prevents congestion window growth when ACKs arrive in bursts like this ? 

 

/Ingemar

==================================

Ingemar Johansson  M.Sc. 

Master Researcher

 

Ericsson Research

Network Protocols & E2E Performance

Labratoriegränd 11

971 28, Luleå, Sweden

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ingemar.s.johansson@ericsson.com <mailto:ingemar.s.johansson@ericsson.com> 

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