[IP] WORTH READING more on worth reading "A Piece of the Action"
Begin forwarded message:
From: Louis Mamakos <louie@xxxxxxxxxxxx>
Date: January 22, 2006 8:58:21 PM EST
To: dave@xxxxxxxxxx
Subject: Re: [IP] more on worth reading "A Piece of the Action"
Dave,
As one of the perpetrator of PPPoE, I can say that "I was there" when
the protocol was conceived, and I can relate the reasons why. What
has happened subsequently, I take no credit/blame for.
At the time, I was at UUNET (er, MFS, not thats not right, WorldCom).
Well anyway, we though of ourselves as "UUNET" at the time before the
dark times came, but that's another story. I was working on a design
for a DSL product offering we wanted to roll out.
At the time, DSL for Internet was very much a new thing. Many
vendors where out there and many of them were trying to "add value"
by making their DSLAM and associated CPE device little baby brain-
damaged routers, and "IP aware". They mostly all did a pretty poor
job of it and it created more problems than it solved. In
particular, having DSLAM be an IP router means that your customers
all have related IP addresses, or at least routing policy and this
makes competitive equal access to the underlying DSL infrastructure
impossible.
Every wonder why there's little to no competition in choosing what
ISP you want to use on your cable plant? This is why -- it's because
the CATV IP service is tightly bound with the transport over the
medium. We didn't want that to happen again, and we really wanted
the DSL plant to know NOTHING about IP at all. Incidentally, this is
what will allow some DSL ISPs to offer IPv6 to their customers
sooner; the DSL plant doesn't even know.
Anyway, so we were casting about trying to figure out how to make
this work. Of the brain-damaged hardware we knew was deployed, and
there was a lot of it, pretty much all of it could be lobotomized and
just operate as in a dumb, simple, Ethernet bridge mode. That met
our need for L3 protocol insensitivity and enabled competitive access.
We wanted to enable competitive and wholesale opportunities for ISP
access here as well; UUNET had been tremendously successful building
a wholesale V.90 dial-up access network, and we wanted to enable that
same capability here. The key to making this work was enable the
ability to delegate the authentication for the customer wanting
access; with PPP we did this at UUNET by inventing the RADIUS proxy
and forwarding the authentication requests to our third-party
wholesale customers by a simple syntactic examination of the
principle name being authenticated (e.g., UU/louie or louie@xxxxxx or
louie@xxxxxxxx We never did UU!louie which would have been a great
inside joke!)
So, you could have competitive access at:
- the wire loop (being your own DSLAM)
- the logical connection to the CPE device (use their DSLAM, buy some
ATM or other backhaul)
- the customer (use someone else's router/session termination, bring
your own email, NNTP, news, etc.)
We then just looked for the obvious way of running PPP sessions over
Ethernet; figuring that PPP ran over every other damn thing. But
remarkably, there was no such thing, so we did an 80% solution in 20%
of the time and it appears to have addressed most of the
requirements. Ideally, we would have used something simple like L2TP
over Ethernet, but that didn't exist either, and it would have been
18 months getting through the working groups. I expected PPPoE to be
a proof-of-concept, with the L2TP crowd pickup up from there, but it
never happened.
Further, because of the way that PPPoE worked, you could share the
DSL span with multiple end-systems in the home, each connecting to a
different PPPoE session aggregator because of the discovery process.
We wanted to enable an AOL-like residential ISP on one PC and a very
different connection (work-at-home or something) on another PC, each
with their own PPPoE session. You could even connect multiple DSL
CPE devices, each with their OWN DSL span back to different PPPoE
session aggregators and have multiple sessions operable at the same
time using a single LAN at the customer premise. Of course, none of
this cool flexibility ever got used. Oh well.
Skip forward 5 or 6 years, and what did we learn:
- our believe that Path MTU discovery would be workable in the face
of the 1492 byte MTU failed due to zealous filtering of ICMP traffic
- not all of the competitive opportunities to hook into the DSL
infrastructure were taken advantage of. There are lots of reasons
for this, almost none of them technical
Control or choice? I guess it is a matter of perspective. When we
set out to do this, it was to enable options that were not (and are
still not) available on Cable TV-based Internet services. And those
limitations probably were not by accident, if I had to guess.
Today, I believe that cable operators have better control over
bandwidth, especially upstream bandwidth. If you think about the MAC
layer used on a cable TV plant for broadband data, the upstream
channel cannot be contention based; the CPE device is assigned
timeslots and thus a fixed upper bound on the bandwidth available.
Certainly there are session termination devices that can apply
traffic policers and shapers and other policies to traffic that would
apply equally to both cable and DSL. Of course, it's been a few
years since I've crawled around in that world of building networks so
the details may have changed.
Louis Mamakos
UUNET alumni
David Farber wrote:
Begin forwarded message:
From: Jeff Schult <jss@xxxxxxxx>
Date: January 17, 2006 3:22:07 PM EST
To: dave@xxxxxxxxxx
Subject: Re: [IP] more on worth reading "A Piece of the
Action" (was: Charging "content providers" ...)
Reply-To: Jeff Schult <jss@xxxxxxxx>
Dear Dave,
My own recollection from having worked at a telco or two on the
Internet side of things is that they had their eye on multiple
tiers of service almost from the moment that DSL became a
potential product -- and that this was a factor in the telcos all
(curiously?) opting to use and specify PPPoE rather than the
simpler cableco DHCP distribution.
Someone closer to the fray than I am now could perhaps shed more
light on this, but I suspect that the telcos have more control
over the deliver of metered bandwidth to individual customers than
do cablecos?
-jeff schult
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