..., IMHO, you really need PPP.
We run PPP on all non-frame-or-smds and less-than-DS3 links so that
the customer (or ourselves, if it came to it) could switch to non-
Cisco gear instantly.But we usually leave most cisco-cisco high-speed links at HDLC.
My impression is that HDLC was the same efficiency - or moderately
more so - than PPP.
There are about three flavors of HDLC encapsulation, one of which
is cisco and because of that the others don't matter. There is precious
little difference between all the flavors of HDLC and PPP, they all
carry the old OUI/Ethertype/etc overhead. And the efficiencies of all
are the same compared to SMDS or ATM.
For what do feel that one *really* needs PPP?
Well, that's it -- I don't assume that the whole world is cisco,
but I'm a bit naive. Of course there are other hooks in PPP that
are useful, since PPP, like BGP, is a Swiss Army knife protocol, but
again since the whole world is cisco, let BGP figure everything out
and run HDLC. You don't really need PPP in an all cisco backbone.
But I like PPP because cisco still doesn't document their HDLC line
protocol. 
(Go ahead, try to find it online or ask someone on
one of the tech support lists to find it for you.
--Kent
I'm kidding. Of course I love everything about cisco, since as Dave
O'Leary has told me for a long time "Sooner or later everyone ends
up working for cisco" and he seems to be right.
(Go ahead, try to find it online or ask someone on