Re: [L4s-discuss] Irregularities in results from L4S testing

[Matteo Guarna S303434 <[e-mail]>]

Thanks a lot Sebastian Moeller, Koen De Schepper, Robert Joseph McMahon 
and Vihdi Goel, you've all been incredibly helpful.

I am really greatful for everybody's help, you helped me solve all my 
doubts!

I wish you all a great day

Matteo


Il 2023-09-05 21:44 Matteo Guarna S303434 ha scritto:
> Greetings,
> 
> I am currently conducting research for my thesis on the L4S suite. As
> part of my research, I have deployed a simple testbed to examine the
> behavior of a TCP-Prague data flow when deployed in conjunction with a
> TCP-Cubic flow on a congested, L4S-capable network link.
> 
> For the network configuration and host setup, I have utilized the
> source code available at the following GitHub repository:
> 
> https://github.com/L4STeam/linux/tree/testing .
> 
> While my initial tests have been generally successful, I have
> encountered two specific issues:
> 
> 1 - The TCP-Prague and TCP-Cubic flows do not seem to equitably share
> available bandwidth. In some cases, TCP-Prague appears to consume up
> to two/thirds of the channel's capacity.
> 
> 2 - Upon inspecting the packets to assess the correctness of the
> protocol's behavior, I observed that the proportion of TCP-Prague ACK
> packets with the TCP ECE (Explicit Congestion Notification Echo) flag
> is approximately 5/9 of the total ACK packets, while the percentage of
> transmitted packets marked by the queue remains consistently at around
> 8%. While I did not anticipate a strict 1:1 ratio, this result still
> strikes me as peculiar.
> 
> Additionally, I noted that all TCP-Prague packets inherently carry the
> CWR (Congestion Window Reduced) flag by default. It appears to me (if
> I'm not mistaken) to be an intentional implementation choice by the
> developers, as detailed in the source code found at
> https://github.com/L4STeam/linux/blob/testing/net/ipv4/tcp_prague.c ,
> specifically beginning at line 53. I would appreciate confirmation
> regarding this implementation choice and assurance that it does not
> adversely impact its compliance with the standard.
> 
> I extend my sincere gratitude in advance to anyone who can provide
> insights or assistance with these matters.
> 
> Best regards,
> 
> Matteo Guarna
> 
> 
> P.s.
> 
> I someone wants a more detailed insight regarding my testplant and my
> results, I had tried to ask for help by opening an issue on the
> repository's github, where I provided a more in-depth description of
> my experiment. The conversation is available here:
> 
> https://github.com/L4STeam/linux/issues/21