see: http://www.livingston.com/Tech/Appnotes/app.serial-port-error.shtml
Port Error Counters
The PortMaster keeps count of errors detected on its ports which are useful
when
debugging a problem or when trying to detect a problem. Below are sample
screen
shots of some PortMaster ports with links to definitions of the various
errors.
Sample synchronous port output
Command> show w1
----------------------- Current Status - Port W1 ---------------------------
Status: ESTABLISHED
Input: 915287284 Abort Errors: 56/1
Output: 3214289999 CRC Errors: 27
Pending: 0 Overrun Errors: 0
TX Errors: 0 Frame Errors: 15
Modem Status: DCD+ CTS+
Sample asynchronous port output
Command> show s10
----------------------- Current Status - Port S10 --------------------------
Status: ESTABLISHED
Input: 1392900 Parity Errors: 0
Output: 453743 Framing Errors: 0
Pending: 0 Overrun Errors: 0
Modem Status: DCD+ CTS+
Abort Errors
An abort error means that a connection did not establish on the synchronous
port
and it is trying again. Each time it tries again it increments the error
count by one.
When you see a slash in the Abort Error (Abort Errors: 56/1) count the first
number represents framing errors, the second number represents device errors.
Framing Errors count is incremented when:
The receiver chip reports a framing error
The receiver chip reports an abort
Device Errors count is incremented when:
When frame size is 0.
When frame size is greater than the maximum size of a PPP frame.
When frames overlap each other
CRC Errors
Means the data received did not pass a verification routine.
Cyclical Redundancy Check - Is a check on the data to make sure that it has
arrived ok. The checking mechanism is a hashing algorithm. The CRC hashes the
large set of all possible binary numbers onto the smaller set of all
possible CRC
codes. Hashing by nature loses data so at least two different blocks must
produce
identical CRC. So CRC is very good at detecting changes in data blocks caused
by typical erros occurring during serial transmission (Which is what
Portmasters
use it for) but a clever programmer could slip a virus through one that was
being
used to scan disk files for virus (Which the Portmaster does NOT do).
Overrun Errors
If a character is received sent to the buffer to be processed before the
previous
character has been read by the processor the previous character is
destroyed or
overwritten. Basically someone is force-feeding characters to a port
greater than
the port speed.
Frame Errors
Basically, the frame was munged in transit. Almost always caused by a hardware
failure in a line or modem, etc.
A frame is considered invalid if it does not terminate with at least 1 STOP
bit. If a
framing error occurs the counter is incremented, and the portmaster
automatically
attempts to resynchronize by assuming that the incorrect STOP bit was
actually the
start bit for the next character. A new character is then constructed
beginning with
this new START bit.
On synchronous ports the "Frame errors" is sometimes followed by two numbers
separated by a slash.
Frame Errors: small packets/large packets
Large packets count is incremented when receive character counter
overflow (packet too big - drop it).
Small error count is incremented when a short frame is received.
Troubleshooting Framing Errors
What to watch for?
See if the framing errors are rising constantly or just sometimes.
You need to know if your framing errors are incrementing at a constant
rate
or if your framing errors are ocurring all at once. If they are
incrementing at
a constant rate, by how much? How quickly? If they happen all at once and
are not on the rise then they were probably caused by a single event.
Unplugging a serial cable from the PortMaster can result in a jump of
framing errors.
Determine if the framing errors are limited to one port
If you notice a particular port has numerous framing errors on the
rise then
swap the serial cable, device (modem, CSU/DSU), phone wire with that of
another port. If the problem follows the port then check the
Livingston. If
the problem follows the line then begin swapping cables, modems, etc to
narrow down the source of the framing errors.
What to do?
Make sure your power cables are perpindicular to your data cables.
Electricity passing through a cable generates a magnetic field. The
electro-magnetic fields generated by the power cables can disrupt
information passing through the data cables. By running your power cables
perpendicular to your data cables you minimized the contact with the
electro-magnetic fields.
Check your serial cables
The cable (and possibly connectors and adapters) between the PortMaster
and (modem or CSU/DSU) should be shielded to minimize noise from other
serial cables and power connectors.
Try swapping the cable and/or adapters. Sometimes a cable will have a
short. Usually serial cables come bad in batches since they are all
manufactured at the same time. When swapping cables try to use store
bought cables to prevent human error. Be especially suspicious of DB25 to
RJ45 connects as these often have problems.
Have your lines tested for noise
Analog, ISDN, T1, etc lines are all susceptable to noise at the telephone
company. This is OFTEN the cause of many framing errors and the noise
test is generally free. Noise can come and go so you will want to see
when
the framing errors are occuring.
Check the enviornment
Other devices can cause noise as well that can result in framing
errors. Be
sure to keep your data cables away from monitors, magnets, old color
TV's, arc welders and low flying UFOs.
Verify Modem/CSU/DSU
Modems and CSU/DSU's can also cause framing errors if they are
defective or misconfigured.
Verify Phone Wire and block
Check the wiring in your building, in the block and from the block to the
modem. If this is wired poorly, or you have bare copper running or
ordinary
phone wiring running for a few feet will make you susecpable to framing
errors.
--- jstorms@livingston.com Diplomacy: The art of saying good doggie while seaching for a big rock.