North American Network Operators Group

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Re: ATM over T1

  • From: John L Lee
  • Date: Wed Dec 01 21:10:53 2004


My assumption from your discussion is that you are transporting ATM cell traffic over T1 circuits. If you are transporting T1 TDM traffic over ATM than
that is a different matter. T1 over ATM cells need to be terminated and have the ATM cells stripped reconstruct the ESF frame of T1 and then you can run
it over "standard" T1/DS3/T3 infrastructure.

Having done ATM over T1 in a previous life, usually the framing for an ATM T1 is ESF. As long as you are muxing on a straight 28 T1's on a T3/DS3 over fiber or that keeps channelized T1s for your ATM circuits you are fine. SBC and Verizon both have tarriffed services for ATM over T1, T3, OC-3c and OC12c the last time I worked with them. If memory serves We used HEC encoding on the DS3 based ATM circuits but for standard M13 mux i do not know if it will be C, hec or PLCP encoding.

What is the payload that you are transporting over the ATM cells? TDM traffic such as voice, IP over ATM, IP over Frame Over ATM, video over ATM
or native ATM cells? You will get some additional propagation delay and jitter whether you just transport the bits or terminate the circuits and forward the
data streams or PDUs.

One issue that I would research on the device that you are terminating the T1 with ATM payload into is whether the interface uses the ESF signalling channel
at all?

John Lee
(ISDN - It Suites Dennis's Needs)

Greg Boehnlein wrote:
	This is my first post to the NANOG list, so please.. be gentle! ;)

I am looking at consolidating several different POPs in a specific city 
that include a mixture of Point to Point and ATM T1 circuits. My goal is 
to shut down all of the physical infrastructure in that city, cross 
connecting all of the circuits onto a Muxed DS3 and backhaul them into a 
larger Metro POP.
	This is pretty simple for the standard DS1 and PRI circuits, but 
the ATM T1 connections have me wondering. I do not have a great deal of 
experience with ATM, and although we have a couple of T1 ATM 
interconnetions in our primary Metro POP, I am questioning wether it is 
truly possible to cross connect the ATM T1 interconnects to Verizon and 
SBC onto a standard M13T mux, backhaul them into my Metro POP and then 
hand them off to appropriate ATM interfaces.
	I've gotten conflicting answers from various sources, so I figured 
that I would ask here, as most likely there is someone here who can give a 
cogent answer as to why or why not.

So, can I cross connect several ATM T1s onto a DS3 mux and break them out 
on the other side? Or do I need some sort of intelligent MUX that 
understands ATM?