Cell Relay Archive

[dgriffin@gio.com.au]

I'm currently part of a team that is considering
options for a five site MAN ATM network
operating at 34Mbit or 155Mbit.  One transport
option is a private microwave system and the
other is telco provided fiber.  A typical 34Mbit
site looks like 6Mbit-10Mbit of CBR traffic with
the remaining 24Mbit as VBR-nrt.

The Telcos claim that fiber is the only viable
transport because of BER characteristics of
microwave.  Of course the Telcos charge ten
times as much for fiber as a private microwave
system would cost.

I quote one Telco's statement:

"The impact on ATM cell loss is significantly
worse on a microwave system.  A BER of  1x10(-8)
on optical fiber typically results in a Cell
Loss Rate of 5x10(-13).  The same BER for
microwave link results in a CLR of 1x10(-7) for
a 2 bit error burst improving to 1x10(-8)
for a 40 bit error burst.  Microwave radio
systems typically have 4 bit error bursts.  In
principle CLR should be confined to traffic
shaping, node congestion but not transmission
path.  This is an important factor in choosing
the optimum transmission medium for an ATM
network." (note:  The "2 bit error, 40 bit error
and 4 bit error" are exact quotes and not my
typos.)

Can anyone help me sort out if the above is
correct and what the heck it really means?  Any
comments, suggestions, or help would be most
appreciated.

Thanks for your time.

Cheers,
Dan

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