Cell Relay Archive

["Erik Østlyngen" <eoestlyn@online.no>]

ARG- ZAPATA, GUILLERMO wrote:

> Dear Friends,
> If I had to built a Broadband backbone over Fiber , which would be the
> advantages of using SDH/SONET under ATM ?, why not use directly ATM over
> fiber?
> In fact , there are projects like Oxygen (worlwide submarine cable
> network) which directly uses ATM over fiber and if it is required (by
> the client) it transports SDH over its basic ATM network.
> Thankyou
>
> Ing. Guillermo Zapata
> IMPSAT
> Desarrollo Estratégico
> Phone: (54-1)362-4240
> Fax: (54-1)300-3189
> E-mail: gzapata@impsat.com.ar
> ARGENTINA

But you have not built your own broadband network, right? But you might want
to build an ATM network. Then you have to lease lines. These lines are SDH.

You might connect ATM nodes directly to the fiber if you have access to or
own them. But if you own fiber, what will you do with the rest of them? They
usually comes in pair of 96 or something. You only need one pair for ATM.

The nodes connected to the fiber run SDH themselves because these nodes are
built to normally map the ATM cells into SDH VC4, because that's what most
operators need most of the time.

If you are building your own network based on ATM nodes and fiber, you are
restricted to the limitation of reach of the node's laser beams. Then you
have to buy an ATM node for every 40 or 60 km even if you didn't have any
other need for it. Do you want to do that?

Well, you might use a repeater instead. But that would be an SDH repeater,
and then you had built a SDH network.

If you want to build an ATM network only, you will want to build on other
peoples existing infrastructure. If you are a large communications operator
you most probably have other networks than ATM. Those networks (like
telephone networks) would use SDH.

What it boils down to is economics.

Regards Erik Østlyngen