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Date: Wed, 24 Dec 2008 17:29:05 +0000
From: Bruce Simpson <bms@incunabulum.net>
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To: Robert Watson <rwatson@FreeBSD.org>
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Cc: Qing Li <qingli@freebsd.org>, Hartmut Brandt <hartmut.brandt@dlr.de>,
	freebsd-current@freebsd.org, "Li, Qing" <qing.li@bluecoat.com>,
	freebsd-net@freebsd.org
Subject: Re: NATM hardware available
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Bruce Simpson wrote:
> Robert Watson wrote:
>> ...
>> Do we have any of the necessary software parts to do simulated ATM 
>> hardware similar to what if_tap does for Ethernet?  Using the VIMAGE 
>> stuff and virtual ATM hardware might open up the door to a more 
>> accessible development and test environment.  I did the NATM locking 
>> work essentially "blind" due to a lack of test environment locally, 
>> which seemed to work out, but a software test system would go a long 
>> way.
>
> Loopback would be possible, sure, but you are probably only going to 
> be able to simulate looped-back PVCs.
> Fortunately, the ITU G.DMT mandated use of ATM for xDSL generally only 
> uses PVCs.

P.S. You can probably cut corners for the job, by only marshaling the 
whole packet payloads for NATM across the loopback boundary.

There is little point in simulating the 53 byte cell 
segmentation-and-reassembly unless you love masochism.

Of course, NATM makes the job somewhat easier, by giving you some 
equivalent knobs -- stuff stashed in NATM socket state usually winds up 
in the cell headers.