DSCP-45 - from Zayo, Hurricane Electric, Lumen

["Livingood, Jason via NANOG" <nanog () lists nanog org>]

In support of IETF L4S and NQB dual queue low latency standards, Comcast (and other networks) have been actively 
deploying this technology. L4S uses ECN marks and, since ECN is rarely modified in packet headers, this generally works 
find across domain boundaries. The more challenging one is NQB, since this is predicated on the DSCP-45 mark crossing 
domain boundaries - and as I think we all know, network domains all implement DSCP differently and so tend to remark 
DSCP on ingress.

Thus, to support NQB, a network will allow DSCP-45 at ingress and classify the traffic as best effort (like default 
internet traffic). Comcast has done so and we have >10M homes with dual queue (aka Low Latency DOCSIS, a DOCSIS 
implementation of L4S and NQB).

The volume of DSCP-45 traffic is beginning to grow, so we have started to look at traffic sources as we quantify 
improvements in application quality of experience (e.g., lower loaded latency and lower jitter). Apart from the 
expected sources we have observed double digit Mbps (far <1% of DSCP-45 volume) - from Zayo, Hurricane Electric, and 
Lumen.

If you run one of those networks, you may want to look at the source of DSCP-45 traffic to ensure your DSCP policies 
are squared away. Feel free to ping me for more information if you have any questions.

Thanks
Jason


For more info:

  1.
TSV NQB draft is in the publishing queue (https://datatracker.ietf.org/doc/draft-ietf-tsvwg-nqb/).
  2.
In support of this, IANA have entered DSCP code point 45 into their registry 
(https://www.iana.org/assignments/dscp-registry/dscp-registry.xhtml).

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