Cell Relay Archive

[albert.e.manfredi@boeing.com]

In article <199803252236.RAA15571@jay.perf>,
  jbasrur@sahana.bellcore.com (33150-basrur) wrote:

> I am trying to compare IP/SONET vs IP/ATM/SONET approaches in a network
provider's core network.
>
> the absence of ATM creates a void in terms of QoS cappabilities. Is that
taken care of in some way
> by IP.? What is QoS based routing in IPv6.?
>
> IP/SONET is the preffered method because of its scalability, especially
given the rates at which
> SONET is capable of running. The bottleneck with ATM has been the
development of AAL chipsets that
> are capable of utilizing very high SONET rates. Am I right, or is there a
work around here.?

I would agree that ATM today cannot yet run at OC-192 rates (9.9 Gb/s), so in
a sense you might call that a bottleneck. But raw bitrate is not the only
consideration.

If you are only interested in IP (or regular data transfer), then of course
you can use SONET between IP routers, just as you can use T3, T1, or
fractional T1 lines between IP routers. SONET by itself is nothing more than
a pipe as far as the payload is concerned.

If you (a) want to have control of traffic across your network and (b) want
to mix in other types of traffic than simple packet-switched IP, then you'll
need more than just routers over SONET pipes, just as you would need more
than just routers over any other type of simple pipe. (Some people will tell
you that you could also get by with IP routers if you have enough excess
bandwidth throughout your network.)

> ATM provides circuit emulation services to carry DS1 type traffic. And ATM
cells are further
> embedded into SONET frames. Isnt this kind of redundant...increasing
overhead.?

"There's no such thing as a free lunch." The reasons for cells in ATM are to
support the types of channels that big fat IP packets would not permit.
Again, if all you care about is IP, I would have to agree that ATM is not so
compelling.

>  Isnt it better to just support DS1 type
> circuits on regular SONET Payload instead of carrying it inside ATM cells.?

What if you want to do high quality video teleconferencing? What about just
good quality voice telephony? Would you depend on a separate network for
that? Most people do, so they don't appreciate the limitations of IP as it is
today.

Bert
manfredi@arl.bnas.boeing.com

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