Installation guide

Making External Connections to Cisco 4000 Series Routers 4-99
Network Connection Considerations
ATM SONET Distance Limitations
The SONET specification for fiber-optic transmission defines two types of fiber: single
mode and multimode. Single-mode fiber is capable of higher bandwidth and greater cable
run distances than multimode fiber.
The typical maximum distances for single-mode and multimode transmissions, as defined
by SONET, are in Table 4-10. If the distance between two connected stations is greater than
these maximum distances, significant signal loss can result, making transmission
unreliable.
Table 4-10 SONET Maximum Fiber-Optic Transmission Distances
Power Budget
To design an efficient optical data link, you must evaluate the power budget. The power
budget is the amount of light available to overcome attenuation in the optical link and to
exceed the minimum power that the receiver requires to operate within its specifications.
Proper operation of an optical data link depends on modulated light reaching the receiver
with enough power to be correctly demodulated.
Attenuation, caused by the passive media components (cables, cable splices, and
connectors), is common to both multimode and single-mode transmission.
The following variables reduce the power of the signal (light) transmitted to the receiver in
multimode transmission:
• Chromatic dispersion (spreading of the signal in time because of the different speeds of
light wavelengths)
• Modal dispersion (spreading of the signal in time because of the different propagation
modes in the fiber)
1. This table gives typical results. You should use the power budget calculations to
determine the actual distances.
Transceiver Type Maximum Distance between Stations
1
Single-mode Up to 9 miles (15 kilometers)
Multimode Up to 1.5 miles (3 kilometers)