[Cerowrt-devel] cerowrt-3.10.24-5 dev build released

Rich Brown richb.hanover at gmail.com
Tue Dec 17 22:06:14 EST 2013

Hi Sebastian,

>> And while trying to make an intelligent guess, I wonder how to map none/tc_stab into DSL and/or ATM; if adsl is the same as DSL;
> 	No ADLS is one out of a family of xDSLs (digital subscriber lines). As far as I know SDSL does not use ATM, VDSL1 might use ATM and all ADSL variants use ATM.
>> and where ethernet fits into the scheme of things.
> 	Ethernet is also a link layer, one that does typically not show quantization as ATM does, selecting the ethernet link layer allows to still specify an overhead, and that is somewhat useful for VDSL (since VDSL often still uses PPPoE).

... and ...

>> - (I believe) Only two “protocols” (above) require “link layer adaptation": PPPoE (DSL/ADSL) and PPPoATM (PPP over ATM). All the others seem to be some variation on Ethernet. (Please correct me if I’m wrong.) 
> 	Well for PPPoATM I agree, but PPPoE is also used with VDSL which uses PTM in stead of ATM and has no quantization issues, but still profits from setting the overhead correctly so needs the link layer adaptation as well. Now, as far as I know PPPoATM is quite rare so I have no idea of how to deal with the common case automagically.

So basically, if I understand what you’re saying, it’s a big mess. :-)

Even though my desires conflict, I still hold out for the two goals of "working well enough for random people” and “providing a platform for research”. 

I hunger for the first, because we want people to be able to use CeroWrt right away and not be scared off. (Rich’s Rule of Trial Software: Each hurdle that you place in someone’s way reduces the potential audience by half. :-) I am hopeful that we can find default settings that are “good enough” for all link layers so that new people can see an improvement with CeroWrt. I am also mindful that the features will likely wind up in OpenWrt unchanged; it’s worth struggling a bit with the GUI so that we minimize the folklore and misinformation surrounding its use.

The tester in me also is rooting for the second goal. We need to be able to test and tweak the entire queueing system. Making some of it accessible via the GUI will make it easier to experiment, but of course, limits the kinds of changes that could be made. (The lua scripts, though, do give a lot of flexibility.)

On to more concrete ideas:

- From what you’ve said, I don’t have much hope for doing it automagically. But maybe we can provide clues to help the customer do to the right thing. Perhaps the first dropdown could be “Link Layer Adjustments (used on DSL or ATM)” with options for “None/ADSL/SDSL/VDSL over PTM/VDSL over ATM/PPPoATM” and maybe others. CeroWrt could automatically set the proper link layer adaptations for each. We could also include a link to the wiki for a flow chart for setting each of these cases, especially the questions they should ask their ISP.

- Would it be possible to keep from mentioning tc_stab in the GUI? 



PS That was a nice discussion of the (wackiness of) ATM framing.
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