8
Mode Conditioning Patch Cord for 1000BASE-LX
The following information applies to installations in which multimode
fiber-optic cables are connected to a 1000BASE-LX module.
Unlike 1000BASE-SX, which connects to only multimode fiber-optic
cabling, 1000BASE-LX can use either single-mode or multimode cable.
Multimode cable has a design characteristic called “Differential Mode
Delay”, which requires that the transmission signals be “conditioned” to
compensate for the cable design and thus prevent resulting transmission
errors. Since 1000BASE-SX is designed to operate only with multimode
cable, 1000BASE-SX modules provide that conditioning internally.
1000BASE-LX modules, since they are designed to operate with both single-
mode and multimode cable, do not provide the transmission conditioning
internally. Thus, under certain circumstances, depending on the cable used
and the length of the cable run, an external
Mode Conditioning Patch
Cord
may need to be installed between the 1000BASE-LX module and the
multimode network cable to provide the transmission conditioning.
If you experience a high number of transmission errors on the 1000BASE-
LX ports, usually CRC or FCS errors, you may need to install one of these
patch cords between the 1000BASE-LX port in your switch and your multi-
mode fiber-optic network cabling,
and between the 1000BASE-LX trans-
mission device and the network cabling at the other end of the multimode
fiber-optic cable run. A patch cord must be installed at both ends.
The patch cord consists of a short length of single-mode fiber cable coupled
to graded-index multimode fiber cable on the transmit side, and only
multimode cable on the receive side. The section of single-mode fiber is
connected in such a way that it minimizes the effects of the differential mode
delay in the multimode cable.
N o t e
Most of the time, if you are using good quality graded-index multimode fiber
cable that adheres to the standards listed on page 4, there should not be a
need to use mode conditioning patch cords in your network. This is espe-
cially true if the fiber runs in your network are relatively short.
If you are using
single-mode
fiber optic cabling in your network, there is no
need to use mode conditioning patch cords. Connect the single-mode
network cable directly to the 1000BASE-LX module.
