Cisco CAB-232MT= Fiche technique télécharger pdf (Page 25)

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Cisco 7100 Series VPN Router Installation and Configuration Guide

78-6341-03

Appendix C Cable Specifications

Cisco 7120-AT3, Cisco 7140-2AT3, Cisco 7120-AE3, Cisco 7140-2AE3, Cisco 7120-SMI3, and Cisco 7140-2MM3 Cables

Single-Mode Transmission

The single-mode signal source is an injection laser diode. Single-mode transmission is useful for longer

distances, because there is a single transmission path within the fiber and smear does not occur. In

addition, chromatic dispersion is also reduced because laser light is essentially monochromatic.

The receiver for single-mode intermediate reach (SMI) cannot be overloaded by the SMI transmitter and

does not require a minimum fiber cable length or loss. The maximum receive power for single-mode long

reach (SML) is –10 dBm, and the maximum transmit power is 0 dBm. The SML receiver can, therefore,

be overloaded when short lengths of fiber are used. Overloading the receiver will not damage the receiver

but can cause unreliable operation. To prevent overloading an SML receiver connected with short fiber

links, insert a minimum 10-dB attenuator on the link between any single-mode long-reach transmitter

and the receiver.

SONET Single-Mode Power Budget Example

The following example of a single-mode power budget assumes 2 buildings, 8 kilometers apart,

connected through a patch panel in an intervening building with a total of 12 connectors.

• Length of single-mode link = 8 km

• 12 connectors

Estimate the power budget as follows:

PM = PB – LL

PM = 16 dB – 8 km (0.5 dB/km) – 12 (0.5 dB)

PM = 16 dB – 4 dB – 6 dB

PM = 6 dB

The value of 6 dB indicates that this link would have sufficient power for transmission and is not in

excess of the maximum receiver input power.

Using Statistics to Estimate the Power Budget

Statistical models more accurately determine the power budget than the worst-case method. Determining

the link loss with statistical methods requires accurate knowledge of variations in the data link

components. Statistical power budget analysis is beyond the scope of this document. For further

information, refer to UNI Forum specifications, ITU-T standards, and your equipment specifications.

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Cisco CAB-232MT= Fiche technique Page 25