usbatm and AALx

Duncan Sands duncan.sands at
Sat Jun 18 18:04:57 EDT 2005

Hi baud123,

> We have a user that asks for AALx support

When I brought up the issue of supporting other AALs on the ATM mailing
list some time ago, Mitchell Blank's said:

"  2. The benefit of being able to globally support AAL's other than AAL0
and AAL5 is somewhat dubious.  For the simple AAL's (AAL1, AAL2) it's
probably simplest to let userland deal with them (and just have it speak
AAL0 to the kernel).  Implementing AAL3/4 in the core layer would have good
hack value but as far as I can see noone has been using it for years (AAL5
basically won that fight a *long* time ago) so it would be a lot of fairly
hard work that would probably never get used by anybody."

> Currently, we think that our driver eagle-usb support AAL5
> Class C - Connection-oriented data service: AAL5 protocol is often used to
> support this class of service which has variable bit rate and does not
> require bounded delay for delivery.
> As you may know we are implementing a replacement for ADI's chipset (eagle
> I, II, III) found in Sagem Fast 800 / Comtrend CT 350 / AT AR 215 and
> other modems, thanks to Matthieu Castet, based on usbatm. Hence the
> question : does usbatm provide support for other modes ? As defined :
> Class A - Constant Bit Rate (CBR) service: AAL1 supports a
> connection-oriented service in which the bit rate is constant
> Class B - Variable Bit Rate (VBR) service: AAL2 supports a
> connection-oriented service in which the bit rate is variable but requires
> a bounded delay for delivery
> from &
> We are going to check with ADI if they are willing to implement such
> protocols. Indeed, their latest chip supports those new modes :

What does supporting the mode mean exactly?

> Would it be worth it ?
> A priori, it provides a kind of QoS for telephony services for example.
> It may depend on BAS configuration on the ISP side as well ?
> Well, we are neither ATM nor ADSL specialist, any hint welcome ;-)

Neither am I for that matter!  Anyway, I've got nothing against adding
useful functionality.  However, is it really useful (see Mitchell Blank's
remark above)?  Also, if I implement something, how am I going to test it?



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