Classical IP and LAN/MAC Emulation approaches compaired.

The IETF scheme defines an encapsulation and an address resolution
mechanism. The encapsulation could be applied to a lot of LAN protocols
but the address resolution mechanism is specifically defined (only) for IP.
Further, the IETF has not (yet) defined a multicast capability. So, those
protocols which require multicast definitely cannot adapt the IETF scheme for
their own use.

The purpose behind the ATM Forum's LAN-Emulation effort is to allow
existing applications (i.e., layer-3 and above protocol stacks) to
run *with no changes* over ATM. Thus, the mapping for all protocols
is already defined. In a PC environment, such applications tend to
run over an NDIS/ODI/etc. interface. The LAN-Emulation effort aims
to be able to be implementable underneath the NDIS/ODI-type interface.

In contrast to LAN-Emulation, the IETF's scheme will allow IP to make
better use of ATM capabilities (e.g., the larger MTU sizes), and for
unicast traffic will be more efficient than having the additional
LAN-Emulation layer. However, the Classical draft suggests that IP
multicast (e.g., the MBONE) will have to be tunnelled over ATM; I
suspect this will be less efficient than LAN-Emulation.

For better or worse, I think both are going to be used. So, vendors
may have to do both. The worse part is extra drivers (or extra
code in one driver that does both). The better part is that all existing
LAN applications can use one (LAN Emulation), and over time (as their mapping
to ATM is fully defined) can transition to use the other (IETF Scheme).

I would summarize LAN-Emulation as follows:

The advantage of LAN-Emulation is that the applications don't know
they're running over ATM. The disadvantage of LAN-Emulation is also
that the applications don't know they're running over ATM.