NS3000/iX Operations and Maintenance Reference Manual (36922-90039)

Appendix A 185
LINKCONTROL Command
NS 3000/iX LAN Link Statistics
The reflectometer field, for a thick LAN cable, is calculated in the
following manner:
The ThickLAN velocity of propagation = .77c
Where c (the speed of light) = 3x10 E8
The bandwidth of a LAN = 10Mb/sec.
Before determining the level of cable fault isolation, you must first
determine how many meters of the cable are covered per bit time. You
then divide .77c by 10Mb/sec. This translates into:
7x10E-2) x (3x10E8)
__________________ = 231 meters
10E6 b/sec)
Therefore, in order to pinpoint a fault in a thick LAN cable by the value
of this field, multiply the field value by 231 meters.
The accuracy of the reflectometer field is plus or minus 1/2 bit time, or
115m. Using this calculation, the location of the cable fault is
determined by the following formula:
(value of field x 231 meters) +\- 115m
Since the maximum length of a cable is 500m, the value of this field
would be 0, 1 or 2, and would pinpoint a cable fault to 1 of 3 sections of
cable.
If this value were to be used for isolating a cable fault in a ThinLAN
cable, the value 0.65 would be substituted for .77c in the calculation
above. (The ThinLAN velocity of propagation is .65c).
Transmits >1 retry. The Transmits >1 retry field indicates the
number of frames that collided more than one, but fewer than 16 times,
before being transmitted successfully onto the link. If the frame was not
transmitted successfully (more than 16 attempts were made without
success), then the card aborts transmission of this frame, and it counts
the event as a retry error (see the Transmits 16 collision field).
CRC errors. The CRC errors field specifies the number of cyclic
redundancy check (CRC) errors that were seen on the link. A CRC error
indicates that the frame was checked using CRC-32 frame-checking,
but that the value obtained by the CRC did not match the CRC value
contained within the packet.
Normally there will be an equal number of alignment errors. If
alignment errors occur frequently, one of the following may be the
cause:
• A LAN card is not listening to the link before transmitting.
• A repeater that is performing poorly.
• A section of LAN coax which contains an impedance.
• The driver level of a MAU is set too low.