[tsvwg] Follow-up to your DSCP and ECN codepoint comments at tsvwg interim

Bob Briscoe <ietf@bobbriscoe.net> Sat, 07 March 2020 00:34 UTC

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From: Bob Briscoe <ietf@bobbriscoe.net>
To: Steven Blake <slblake@petri-meat.com>
Cc: tsvwg IETF list <tsvwg@ietf.org>
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Date: Sat, 07 Mar 2020 00:34:22 +0000
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Subject: [tsvwg] Follow-up to your DSCP and ECN codepoint comments at tsvwg interim
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I had audio problems during the chairs slides at the tsvwg interim.
Now I see the following two comments of yours in the minutes, I'd like 
to follow-up:

> - Steve Blake mentioned that L4S could be made compatible with each.
Can you say more about what's behind this idea? or point me to where 
you've already said it?

> - Steve Blake noted anyone running these experiments will tinker with 
> boxes, so may handle the DSCP bleaching concern.
Unfortunately, that's only partially true. It's fairly true for 
CDN->user applications. However, for (say) conversational video or 
online gaming, AR, VR, etc, which are particularly important targets 
apps, the path is often either accessISP-accessISP or 
accessISP-cloud-accessISP. Altho most access ISPs nowadays are pretty 
tightly meshed with other access ISPs (with less intermediaries than 
there used to be), there are still significant numbers of cases where 
two access ISPs are not directly connected.

Anyway, if user B's downstream is the bottleneck for user A, even if ISP 
B doesn't bleach Diffserv, the DSCP is still no use if ISP A bleaches, 
or if an intermediary does.

for write-up of the pros and cons.

Network traversal is already a difficult problem, even with just a very 
few ECN problems. We really don't want to make this impossible. With a 
3-part (sender-bottleneck-receiver) L4S deployment, there is already 
enough deployment barrier without adding Diffserv traversal to make 4 or 
more parts (sender-border-bottleneck-receiver). For SCE, there's already 
4-parts to deploy (tunnels added), so let's not countenance making that 
5 or more.


Bob Briscoe                               http://bobbriscoe.net/