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testing) are the same for Inline testing. The speed/duplex indicated
is the result of the two devices negotiating to a common speed and
duplex. This is termed the "negotiated speed". Speed and Duplex
are important considerations because two LAN devices will not to
communicate unless they both are operating at the same speed and
duplex.For more detailed information about Data and Link pulses
see Appendix B.
Negotiating the speed between two LAN devices. When all de-
vices were 10 Base-T, half duplex, two LAN devices linked together
operated at 10 MB/s, half duplex. Today's devices offer a
mixture of speed and duplex across 10 MB/s, 100 MB/s
and 1000 MB/s. Their capabilities range from being fixed
at one speed and duplex to handling all speeds and
duplexes. To determine the speed of a link, a negotia-
tion may take place between the two LAN devices. The
negotiation normally consists of a mixture of link pulses
and data packets sent between the two devices. As an example,
presume unit A (a 100 MB/s, full duplex device) is connected to a
unit B capable of 100 MB/s and 1000 MB/s, full or half duplex. If typi-
cal, unit A will negotiate with unit B and unit B will reconfigure itself
for 100 MB/s, full duplex communication.
Displaying the DATA packet and LINK pulse activity of the
connected device(s). The DATA and LINK LEDs provide
and easy way to identify the device type (does a device
LINK
appear to be a hub/switch or a PC) but beyond that, as you
become more familiar with the operation of your network devices,
you will find the ability to differentiate between data and link pulses
to be very helpful. See Appendix B for further details about data and
link pulses.
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Keeping in mind the above, the following applies:
If the TVR1000 is connected to only one LAN device, it will
●
display all of the device's speed and duplex capability.
If the TVR1000 is placed inline between two LAN devices, it
●
will display the negotiated speed and duplex of the devices.
If 1000 MB/s equipment is communicating at 100 MB/s, the causes
could be:
The other LAN device is a 100 Base-T.
●
There is a "Cable Fault." A cable fault is when a wiring pair
●
is inverted (e.g. pair 1,2 is wired 2,1).
One or both LAN ports is capable of 1000 MB/s but has
●
been programmed to 100 MB/s (slowing down the link).
Important: If testing a PC, reboot the computer after a LAN device is
connected. Some PCs will select their speed/duplex after detecting
the speed/duplex of the connected device.
Cable Fault Indication. The "three jacks" are constantly testing
a connected cable for inverted pairs (e.g. pair 1,2 is wired 2,1). In-
verted pairs, although rare, can slow and even stop communication.
The TVR1000 indicates the presence of inverted pairs by lighting the
DATA/LINK LEDs red (normally green). For an example of testing for
inverted pairs see section VI, example 6.
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