Chapter 10: Troubleshooting
local loopback using a short DS3 cable, since connectors and cables are a much more likely
source of problems. Local loopback can also often result in LAN equipment attached to the
converter to immediately disable the LAN port as a flood-prevention measure.
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FEAC Loopback Requests
: All intermediate equipment on the DS3 path and the converter
must be in C-Bit mode for a FEAC request to be forwarded and acted upon.
Alternatives to Loopback
Loopback is not typically the best way to diagnose or confirm a DS3 connection. Here are some
alternatives:
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Web Management
: User-friendly status messages will appear at the top of the converter's web
management status page. Errors are highlighted in orange. Sophisticated error detection
status, such as frame-slip, is only available through this interface mechanism.
•
SNMP Management
: 24 hours of historical DS3 operational data is maintained in the standard
DS3 MIB-variable of the converter and can be accessed via any common SNMP client
program.
•
Circuit ID
: For units/paths configured as a C-Bit-framed DS3, the incoming DS3 circuit ID of
the remote sender is shown at the top of the web management status screen and details the
remote equipment type, geographical location, IP address, location in rack, and whatever text
the operator wishes to configure in the web management configuration settings of the remote
unit. This confirms that a valid, framed receive DS3 signal from the correct remote equipment
is being received.
•
Alarm Signals
: Standard telco alarm signals are shown in orange at the top of the web
management status screen and indicate: loss of signal, loss of framing, remote loss of signal, in
loopback mode. Some alarms are also available through the standard DS3 MIB-variables.
•
Bit Errors
: Both bit error rate and individual C-bit/P-bit and line-code error counts are shown
at the top of the web management status screen to indicate a flaky link, even if alarm signals
are OK. The error counts are also available through the standard DS3 MIB-variables. For a
sophisticated user, these counts indicate where in the path the error is occurring.
•
Packet Audit
: The ingress/egress of every packet as it passes through the converter (or is
dropped due to an error condition) is detailed at the top of the web management status screen.
The “Clear Statistics” button zeros the values and allows a quick determination of where a link
is failing – whether configuration or physical.
•
Clock Frequency
: High accuracy ingress/egress clock frequency statistics are shown at the
bottom of the web management status screen.
•
SFP Optical LAN
: Receive and transmit power levels, alarms, warnings and temperature of
SFP optical modules in the SFP LAN port of the converter are displayed at the bottom of the
web management status screen. Finisar SFP transceivers are recommended as one source
capable of reporting detailed operating statistics.
Initiating Loopback
Warning: Any of the following can cause loss of communication with the local or remote converter.
•
FEAC Code Initiation
: A converter that is configured for DS3 C-Bit framing will respond to
FEAC loopback commands that it receives from the incoming DS3 line. FEAC loopback
requests can be generated by a carrier's intermediate DS3 equipment or by commanding the
source converter to send a FEAC loopback request via an SNMP command as detailed below.
•
SNMP Direct Initiation
: First, write-access to the DS3 MIB, using VACM settings, must be
enabled as described below. RFC3896 details the DS3 MIB configuration and status values
available. The SNMP requests are issued by commonly available text or GUI SNMP-client
programs which send requests to the converter's internal SNMP agent. An SNMP request can
set the local converter's dsx3LoopbackConfig variable to dsx3LineLoop. The following
sample SNMP command might be used to set DS3 Port 2 into remote loopback:
▪
snmpset -v 1 -c public <ip-address-of-unit> .1.3.6.1.2.1.10.30.5.1.9.6 i 3
(.6 is DS3 Port 2; .5 is DS3 Port 1, matching SNMP MIB-variable interface ID values)
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