Cisco ATM Cable Interface Processor ACIP-SM(=) Manuale di installazione e configurazione - Pagina 5
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ACIP Interface
The ACIP's ATM interface is full duplex. You must use the appropriate ATM interface cable to
connect the ACIP with external ATM equipment. (Refer to the section "ACIP Cables, PLIM, and
Connections," on page 7, for descriptions of ATM cables and connectors.) The ACIP provides an
interface to ATM switching fabrics for transmitting and receiving data at rates of up to 155 Mbps
bidirectionally; the actual rate is determined by the PLIM. The ACIP supports a PLIM that connects
to the following physical layer: SONET/SDH 155 Mbps, multimode fiber optic—STS-3C (or
STM-1).
SONET Distance Limitations
The SONET specification for fiber-optic transmission defines two types of fiber: single mode and
multimode; however, the ACIP supports multimode fiber only. Modes can be thought of as bundles
of light rays entering the fiber at a particular angle. Multimode fiber allows multiple modes of light
to propagate through the fiber. Because multiple modes of light propagating through the fiber travel
different distances depending on the entry angles, causing them to arrive at the destination at
different times (a phenomenon called modal dispersion), single-mode fiber is capable of higher
bandwidth and greater cable run distances than multimode fiber.
The typical maximum distances for multimode transmissions, as defined by SONET, are in Table 1.
If the distance between two connected stations is greater than these maximum distances, significant
signal loss can result, making transmission unreliable.
Table 1
Transceiver Type
Multimode
1. Table 1 gives typical results. You should use the power budget calculations to
determine the actual distances.
Power Budget
To design an efficient optical data link, 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)
Attenuation is significantly lower for optical fiber than for other media. For multimode transmission,
chromatic and modal dispersion reduce the available power of the system by the combined
dispersion penalty (dB). The power lost over the data link is the sum of the component, dispersion,
and modal losses.
Table 2 lists the factors of attenuation and dispersion limit for typical fiber-optic cable.
SONET Maximum Fiber-Optic Transmission Distances
Maximum Distance between Stations
Up to 1.5 miles (3 kilometers)
ATM Cable Interface Processor (ACIP) Installation and Configuration
1
ACIP Description
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