Re: [tsvwg] Switch testing at 25G with ECN --SCE Draft

Greg White <g.white@CableLabs.com> Thu, 08 August 2019 22:58 UTC

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From: Greg White <g.white@CableLabs.com>
To: "Scaglione, Giuseppe" <giuseppe.scaglione@hpe.com>, "tsvwg@ietf.org" <tsvwg@ietf.org>
Thread-Topic: [tsvwg] Switch testing at 25G with ECN --SCE Draft
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Date: Thu, 8 Aug 2019 22:58:46 +0000
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Subject: Re: [tsvwg] Switch testing at 25G with ECN --SCE Draft
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Hi Giuseppe,

Thanks for sharing your work.   At the TSVWG meeting at IETF105 it was mentioned that there was a hardware implementation of SCE running in a 25Gbps switch (1:47:30 in https://www.ietf.org/audio/ietf105/ietf105-placeducanada-20190726-1220.mp3).  I presume this is the implementation that was being referred to.

If I’m reading this correctly, the marking implementation in the switch is actually DCTCP-style (marking CE based on instantaneous queuing delay) in a single queue, rather than SCE-style.   The CE marks are then transformed into SCE marking by the receiver itself before being handed to dctcp-sce or reno-sce.  So, in essence this test appears to be a study of various AQM ramp options and modified ECN congestion responses in a homogeneous DCTCP datacenter environment, rather than being an SCE experiment specifically.

Could you provide some information on the buffer size?  It looks like it may be ~200us.   How does this marking approach compare to existing DCTCP deployments (i.e. do they generally use a hard marking threshold or do they similarly use a ramp)?  Have you thought about adjusting the ramp so that 100% marking occurs before you reach the tail drop limit?  I wonder if that would eliminate the packet drops.

For comparison, you may as well use stock DCTCP which would avoid the receiver needing to translate the CE marks into SCE marks, since DCTCP can just interpret the CE marks directly.   But, I didn’t think that the goal of SCE was to replace DCTCP in datacenters anyway…

Are the tables missing some data?  I don’t see the bandwidth/retries/packet drop data for the continuous TCP connections.

Also, do you have an explanation for Pic 1, where the ping time when the link is idle is almost double the ping time when the link is saturated?

Best Regards,
Greg



From: tsvwg <tsvwg-bounces@ietf.org> on behalf of "Scaglione, Giuseppe" <giuseppe.scaglione@hpe.com>
Date: Tuesday, August 6, 2019 at 3:36 PM
To: "tsvwg@ietf.org" <tsvwg@ietf.org>
Subject: [tsvwg] Switch testing at 25G with ECN --SCE Draft

Greetings,

The attached document contains data collected testing with an Ethernet switch and the new TCP-dctcp-sce and TCP-reno-sce algorithms, draft-morton-taht-tsvwg-sce-00.

Best regards,


Giuseppe Scaglione
Distinguished Technologist
R&D Lab Hardware
Aruba Networks
Hewlett Packard Enterprise
8000 Foothills Blvd.  (MS 5555)
Roseville, CA   95747
Tel : 1-916-471-9189
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