GGSN/PGW to LNS recommendations

Hi !

I'm looking for a GGSN/PGW implementation that would act as a LAC, to
re-encapsulate PPP sessions into L2TP tunnels to some LNS already
deployed for traditional IP-ADSL collects.

I found that feature available in Cisco ASR5000 but couldn't yet find
any other.

Would you have any pointer or references ?

Thanks !