Cisco Systems ACIP-SM(=) manual ACIP Interface, SONET Distance Limitations, Power Budget

ACIP Description

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 SONET Maximum Fiber-Optic Transmission Distances

Transceiver Type	Maximum Distance between Stations1
Multimode	Up to 1.5 miles (3 kilometers)

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.

ATM Cable Interface Processor (ACIP) Installation and Configuration 5