The Physical Layer Statistics screen shows SONET STS-3c and SDH STM-1 error statistics. These statistics are used to track down problems with the physical connection, and are more useful in a WAN environment.
To access Physical Layer statistics, first access the ATM Port Statistics screen, as described in "ATM Port Statistics", and then select the PHYSICAL button.
An example of the Physical Layer Statistics screen is shown in Figure 9-5, and the statistics are described in the following text.
Port Identifies the currently selected port.
OCD State Shows the Out of Cell Delineation (OCD) state. The OCD State is set to Fail when seven consecutive cells have had Header Error Control violations. This implies that the cell has been corrupted and that there is probably a hardware problem with the ATM Module or ATM Switch.
The OCD State is only set to OK when six good cells are received by the ATM Module followed by approximately 10 seconds of good signal from the ATM fiber optic cable.
Figure 9-5 Physical Layer Statistics
Current Sample Specifies the number of seconds elapsed within the current sampling period.
SONET/SDH counters are accumulated over a period of 15 minutes (900 seconds). At the end of the 15 minute sampling period, the software stores the results of the current sampling period, and resets the values shown on the screen to zero.
The results of the previous 96 sampling periods can be accessed through the SONET MIB using a MIB Browser.
Physical Layer statistics are broken down into the following layers:
Physical Layer errors are measured in units called Seconds: each Second is a second in time.
In the following statistics a second is considered errored if it contains a Coding Violation.
A coding violation occurs when the parity check in the SONET or SDH frame indicates that the cell payload has been corrupted.
A second is considered severely errored if it contains 16 coding violations for a path or section, or 32 coding violations for a line counter.
A second is unavailable if 10 continuous severely errored seconds are seen at the ATM interface.
A second becomes available again, when 10 consecutive seconds are received that are not severely errored.
The following statistics are available:
Errored Seconds (Near) The number of errored seconds at the ATM Module end of the connection.
Errored Seconds (Far) The number of seconds at the ATM Switch end of the connection.
Severe Errored Sec (Near) The number of severely errored seconds at the ATM Module end of the connection.
Severe Errored Sec (Far) The number of severely errored seconds at the ATM Switch end of the connection.
Coding Violations (Near) The number of coding violations that have occurred at the ATM Module end of the connection.
Coding Violations (Far) The number of coding violations that have occurred at the ATM Switch end of the physical connection.
Unavailable Seconds (Near) The number of seconds that were unavailable at the ATM interface on the ATM Module.
Unavailable Seconds (Far) The number of seconds that were unavailable at the ATM interface on the ATM Switch.
This section describes how to use the physical layer statistics to track and resolve problems.
If no values are shown on the screen, the problem probably lies with the ATM Switch rather than the ATM Module. Follow the troubleshooting information in the user guide that accompanies your ATM Switch.
High values usually indicate that the SONET standards are incompatible, or that there is a fault on the cable. Use the following troubleshooting suggestions to try and resolve the problem:
1 . Check that the ports at both end of the link are enabled.
2 . Check that the cable is securely connected to the port at both ends of the link.
3 . Check each end of the cable to ensure that each of the fiber connectors is correctly connected. If you have connectors that can be reversed, you may need to reverse the TX and RX cable connectors at one end of the link.
4 . Make sure that the cable does not exceed the cable length or other technical specifications. Check the cable against the technical specification given in .
5 . Remove any obstructions and straighten out any kinks in the cable.
6 . If you suspect that the fiber optic connector is dirty, refer to "Cleaning Dirty Fiber Optic Connectors".
7 . If you suspect that the fiber optic cable is not working, replace the cable with a cable known to be working, and check the Link Status LED.
8 . Check that the cable has not been accidently plugged into an FDDI connector at one end of the connection.
9 . Check that the ATM Module and ATM Switch are using compatible transmit clocking options.
10 . Check that the Line Rate settings on the two devices are compatible.
11 . If there is still a problem, contact your repair center for advice. For more details, refer to "Support from 3Com".
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