Thanks for all the comments. What I'm finding is that proving a negative is difficult, there's no trace of an ATM retransmission mechanism mentioned in any of the ITU documents, rfcs or SINs that I've looked at, other then G.INP (ITU G.998.4).
There's probably a reason why!
I'm finding lots of stuff that I'm not certain about, for example Wombat has just said that DSL is not ATM - but does it not carry ATM?
I think the best way to think of this is to separate ATM into two - one being the networks, protocols, routing, rules, specs; the other being the packets of data: cells of 53 bytes, made of 5 bytes of header and 48 bytes of payload.
At one time, BT's core network will have been based on ATM. The whole enchilada, including networks, protocols, routing, rules ... all to carry those 53 byte cells.
http://www2.bt.com/static/i/media/pdf/atm_vpn_dec05.pdf(In the days of poor QoS in the IP world, ATM was the telecomms solution for a converged network - small cells allowed low latency voice to coexist with high volume data; "ATM" as an overall concept is all about the routing & transmission of these small cells to keep voice working well).
But right on the access edge, the network hits the copper lines and ADSL. Here, the protocols and rules are all pure ADSL, not ATM. At this point, there is little need for the "big" network concepts, and every need for techniques to cope with long, dodgy copper lines. However, the data being carried, right down at the bottom level, remained in the form of little 53 byte packets, aka ATM cells.
The 5 bytes of header become a terrible overhead in there, given that most lines carry a single virtual circuit.
http://aa.net.uk/kb-broadband-how-atm.htmlSo we get to see that ADSL is carrying ATM cells, but it isn't actually performing any real function that we'd think of as a core ATM network function.
That's got me wondering, I always assumed that the modem recreated the ATM PVC from the DSL, then rebuilt PPP and in turn the Layer 3 packet from the ATM. However I'm not sure where I got that from, maybe just made the assumption because Cisco calls the DSL interface ATM (and the terminology itself of course, PPP over ATM).
Yup, it is indeed that way - at least when ATM mode is used in ADSL. There are also modes for SDH and PTM (which is more used in NGA). More information in the area here...
http://blog.farnz.org.uk/2010/02/on-pppoa-pppoe-atm-and-adsl.html