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Re: [nanog] Re: Microsoft offering xDSL
From: vaananen () NASBPD01BS ntc nokia com (Vaananen Pasi NTC/Boston)
Date: Fri, 23 Jan 1998 13:35:34 -0500



We are part of the Bell Atlantic ADSL trial in Northern VA - basically BA
has 6 CO's with terminating ADSL modems. This is aggregated onto a FDDI
ring between each CO on cisco's. One of the CO's has a port into the BA
SMDS cloud which is the interconnect with participating ISP's who also
have a port on the SMDS cloud. So basically, packetize the data as early
as possible to get the 20x plus economies of scale vs hauling channelized
circuits.

Hmm... as we are developing equipment for something like this,
I would like to get the opinion of the real peoples (read ISPs)of the Cisco
 - Microsoft - Alcatel... etc. network architecture for the xDSL services (they are mainly talking of ADSL, but who 
cares).

Basic idea is that the telco has xDSL links to subscribers and you are
supposed to run ATM over that link. So the access network is "simple
ATM network", with VP (or VC) connections from individual subscribers to
your favorite ISP's or company network. PPP / L2TP over the ATM are the
protocols of choice to run on top of ATM.

I can see some problems with this, here are my favorite ones:

1.)

If you are supposed to be ISP and get handled over the traffic of
say 100k active users nicely encapsulated in PPP or L2TP, where are you
going to terminate these PPP sessions ? (I am sure it's possible to
construct "massive PPP terminator", but is it necessary ???)

2.)

The idea seems to be that ordinary consumers suddenly need n Mbits/s
(n=2-6) to home, one use for this (in addition to connecting to web
server which is attached with T1 and serving  500 other customers at
same time) is to "be able to access content like video".

If this kind of bandwith becomes available for the ordinary customers,
what's going to happen for backbone (answer is nothing, it should be
something) ?  Certainly things like multicasting would be required to
deliver set of high bandwith services like video to subscribers.

Problem with the "simple ATM access network" then becomes that if you
are delivering your video nicely packed onto IP packets, you would like
to duplicate as late as possible, which means in access network, instead
of at the end of the PPP session (ISP).

Pasi

Ps. Sorry for non-operational posting, but there is not better place
to reach the ISPs in states than NANOG list.

 -----------------------------------------------------------------------
Pasi Vaananen, Senior Systems Engineer      pasi.vaananen () ntc nokia com
Nokia Telecommunications, Network Systems, IP Networking
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