Cabletron Systems 100BASE-FX, Cabling Manual

Page: 59 / 192

10BASE-F (Multimode) 5-5
Ethernet Network Requirements
Attenuation
Multimode fiber optic cables must be tested for attenuation with a fiber optic
attenuation test set. The test set must be configured to determine attenuation of
the cable at a wavelength of 850 nm. The attenuation test will confirm or deny that
the cable falls within an acceptable level. The acceptable level of attenuation for a
cable is dependent upon the type of multimode fiber optic cable being tested. The
acceptable levels of attenuation for the types of multimode fiber optic cabling
supported by Cabletron Systems products are listed in Table 5-1 below:
Insertion Loss
The 10BASE-F specification allows for a total dB loss of 10 dB or less between any
two stations or devices connected by fiber optic cabling. When calculating
insertion loss, you must consider and count any loss introduced by fiber optic
splices, barrel connectors, distribution boxes or other cable management devices.
The typical dB loss for a splice or a connector is less than 1 dB. The loss statistics
for any fiber optic cable management hardware should be available from the
manufacturer.
Delay
As fiber optic cabling is often used to make connections between Ethernet
repeaters or hubs, the 10BASE-F specification allows a multimode fiber optic link
to be configured such that the total propagation delay for the link is less than or
equal to 25.6
µ
s one-way. Keep in mind, however, that propagation delay must be
calculated for the entire network. If there are more stations than the one
connected by your fiber optic link, you must also calculate the propagation delay
for the longest of those station links.
If there is any signal path whose total one-way propagation delay exceeds 25.6
µ
s,
the Ethernet network is out of specifications, and error conditions may result. To
eliminate propagation delay problems, incorporate some form of segmentation,
such as bridging or routing, into the network to separate the problem signal paths
from one another.
Table 5-1. Multimode Fiber Optic Attenuation Limits
Cable Type
Maximum
Attenuation
50/125
µ
m 13.0 dB
62.5/125
µ
m 16.0 dB
100/140
µ
m 19.0 dB