Accton Technology 12i, 12mi SNMP manual Power Budget for Common Guage Fiber Optics

Fast EtherHub 3500 System User’s Guide

Note: To determine the power loss incurred by intervening devices and specific cable type, inquire with the manufacturer. The power budget depends on the gauge of cable as shown below.

Gauge of Fiber Cable

50/125 mm

62.5/125 mm

Power Budget

9.2dB 13 dB

Table 2.2 Power Budget for Common Guage Fiber Optics

For a sample calculation, assume the following values:

∙cable gauge - 62.5/125 mm, which means a 13 dB power budget,

∙2 patch panels along the path, each with 1.5 dB power loss,

∙1 splice with 1 dB power loss, and

∙inherent power loss in the cable is 4 dB/km

The maximum cable length is therefore: m = 13 dB - 4 dB = 2.25 km

4dB/km

ΙWhen the 100BASE-FX link is set for the full-duplex communications (i.e., a dedicated connection), cable length should not exceed 2 kilometers. However, when the link is set for half-duplex communications (i.e., a shared collision domain), cable length should not exceed 412 meters (IEEE 802.3u).

Note: Even though your calculations for power loss may indicate a longer permissible length based on signal strength (as seen in the preceeding example), we advise remaining within the recommended limits.

Maximum Segment Length - In contrast to cascading devices through repeater ports, cascading through the SmartExtender Module breaks up the collision domain. The number of devices that can be cascaded is therefore theoretically unlimited. However, in practice, the length of a cascade (even one passing through switching ports, as implemented in the extender modules) may be limited by the time-out requirements of the particular applications running over the network. Considering these delay factors, the IEEE 802.1D standard (i.e., RFC for MAC bridges) recommends restricting the number of interconnection devices between any two nodes to seven.

Installing the System 2-9