Synchronous or Asynchronous?

[NFI]

Hello,

I'm a bit confused about this whole synchronous/asychronous nature of ADSL over ATM. As ATM is, essentially, a packet based (albeit cell relay) data-link protocol, I can see how it might operate in asynchronous mode.

However, some sources I've read refer to ADSL being synchronous in nature, utilizing synchronised clocks at either end of the ATM Virtual Circuit.

Is this right? If so, is ATM being used as a synchronous protocol?

If anybody can explain this to me, I'd be very grateful,

Thanks,

Paul