Re: [Cerowrt-devel] trivial 6in4 fix(?)

[Sebastian Moeller <moeller0@gmx.de>]

Hi Toke,


On Jun 16, 2013, at 22:55 , Toke Høiland-Jørgensen <toke@toke.dk> wrote:

> Sebastian Moeller <moeller0@gmx.de> writes:
> 
>> As far as I can tell at least VDSL typically means VDSL2 and that
>> probably means PTM instead of ATM. In essence this means you do not
>> have to deal with ATMs 48 payload bytes per 53 byte cell transport
>> inefficiencies. So all you need to deal with is per packet overhead.
>> Then again I am sure you probably know that already. (Sidenote, as far
>> as I understand (so not very far) using ATM for DSL connections with
>> POTS service in the lower frequency range never made much sense at
>> all, the 5 byte ATM header typically was constant and by that just
>> ballast and the 48 byte quantization on the last mile never came with
>> any benefits, but I digress)
> 
> Right, thanks. So that means the overhead is constant per (ethernet)
> package?

	That is my interpretation, I am still waiting for vdxl deployment in my area so I have no actual hands-on experience yet. Honestly, I think the best thing to do is not so much assume ATM or lack of ATM, but simply measure it :) (while VDSL offers PTM, it can also operate over ATM if the telco wishes, so vdsl is technically not guaranteed to be free of ATM). If you collect a large quantity of pings to the nearest IP address ouside of your control for 16 to 113 byte ping sizes (say 100 packets at each size) you should be able to see a step profile in the RTTs for an ATM carrier (with two steps) and no steps (but rather a ramp) for no PTM. 

Best
	Sebastian

> 
> -Toke