Re: [rtcweb] -transports- discussion of DSCP

On 08/13/2014 09:07 PM, Martin Thomson wrote:
> On 13 August 2014 09:10, Ted Hardie <ted.ietf@gmail.com> wrote:
>> My concern here is that access to the ability to set different DSCP markings
>> on a per packet basis for a flow may not be available generally on all
>> platforms.  Even if we want to make a forward looking push toward that
>> ability, naming what we think is the appropriate alternative may make sense.
> Yeah, requiring per-packet DSCP seems overly enthusiastic.

I know it's possible to do this on Linux (for UDP, of course). I think 
it still requires an extra sysctl before sending each packet, which is 
reasonably high overhead if your app is sysctl-limited. But I don't know 
of any case where you would be allowed to set per-flow DSCP markings and 
would not be allowed to set per-packet DSCP markings; all the reasons to 
not do marking seem to be reasons to not do marking.

I'd like to know if the APIs exist on other platforms (whether they're 
overridden by default policy or not).

The two alternatives if we don't get per-packet setting are:

- Deaggregate, so that per-port-flow classifiers can do their thing
- Don't ask the network to differentiate, keep precedence of flow a 
sender-stack thing only

I don't know which is the more (or less) distasteful / useful of those 
two paths.

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