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1 - 8 ONline Ethernet 10BASE-T Module User’s Guide
The Off position sets the Squelch level to low. When the Squelch level is set
to low, the ports are able to receive weaker signals. Note that Low Squelch
mode does not conform to the 10BASE-T standard. If you change the
module's Squelch level to low, you must change the 10BASE-T Transceiver
Squelch level to low also. Refer to the ONline Ethernet 10BASE-T
Transceiver Installation Guide for information on setting the transceiver
Squelch level.
On unshielded twisted pair cable, setting the Squelch level to low increases
the achievable link distance by approximately 25% to 50%, but with the
added risk of losing packets to impulse noise. Do not use Low Squelch
mode if your network should experience too many illegally short packets
(runts). This problem will occur if there is significant external noise around
the link.
Setting the Squelch level to low in conjunction with shielded twisted pair
wiring increases the achievable link distance without sacrificing noise
immunity. Thus, there is no real drawback in using Low Squelch on shielded
twisted pair.
To gain the extended link distance achieved by using Low Squelch mode,
you must use qualified data grade shielded twisted pair cable or qualified
high performance unshielded cable. IBM Type 1 shielded cable (with an
appropriate RJ45 to Type 1 connector), among others, meets this
requirement. If you are unsure of the grade of twisted pair cable to use, set
the Squelch level to high, or call 3Com for a list of qualified cables to use in
extended distance applications.
Channel Select Switch Settings
The ONline Ethernet 10BASE-T Module is equipped with the technology to
work with the ONline System Concentrator's unique TriChannel™
architecture. This feature allows you to assign the module to any of three
channels (or none) on the ONline System Concentrator backplane. Refer to
Chapter 1 in the ONline System Concentrator Installation and Operation
Guide for a complete discussion of ONline's TriChannel architecture.
The channel select switch settings (switches 2 and 3) on dip switch SW3 let
you select a channel. Switches 2 and 3 are factory set to On, therefore, the