Installation Instructions

Table Of Contents

fiber systems have an associated maximum dispersion power penalty (DPP

max

) specification, which

applies to G.652 (dispersion unshifted) single mode fiber and the rated transceiver reach. The actual

power penalty that you must use is

DPP

budget

= [link length(km) / transceiver maximum reach (km)] * DPP

max

For example, if an 80 km transceiver is specified as having DPP < 3 dB, and if the actual link length

will be 40 km, DPP

budget

is one-half the maximum, or 1.5 dB.

Link operating margins are sometimes allocated for impairments such as aging, thermal, or other

environmental effects. Because of the potentially large number of factors that can degrade

performance, you can usually rely on statistics to represent these factors as a single margin value,

in dB, to cover all effects. Margin is life and design dependent, but is typically 3.5 to 4.5 dB,

minimum. Whether you require additional margin depends on the details, such as whether actual or

specified transmitter power and receiver sensitivity are used. Avaya specifications represent worst-

case values.

The sum of margin, dispersion power penalty, and passive cable plant losses must be less than the

available power budget. Alternatively, if you calculate available power margin as the difference

between the available budget and the sum of losses and dispersion, the margin can be more or less

than required, which determines whether additional consideration is needed. If the power budget is

exceeded or margin is insufficient, you can either use a transceiver rated for longer distance

operation, or calculate budget and losses using actual values rather than specified limit values.

Either method can improve the link budget by 4 to 5 dB or more.