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 -----------------------------------------------------------------------