Telos Zephyr Xstream User Manual page 292

13.6.3 Audio Difficulties
Condition: ISDN Connecting OK, But No Audio
What is the state of the LOCK LEDs?
Check the LOCK LED. On means OK, connected and receiving valid data. If not
illuminated, try cycling through receive modes to see if you can "find" the mode at the
other end.
What happens when you call yourself?
Try calling yourself, from one ISDN line to the other (assuming you have both available).
Use a 56 kbps rate first, as this is the most universal. Set Rcv mode to L3 Stereo and Xmt
to L3 Dual or L3 Stereo) Audio should work in both directions. This confirms that the
Zephyr is OK, and that the problem lies somewhere downstream, probably in the Telco's
connection facilities either between its own central office switching equipment or to the
long‐distance carrier you are trying to use.
What happens to your local audio when you try an ISDN loopback?
If successful, this eliminates over 70% of the Xstream circuitry as the culprit. Remaining
suspects would be primarily the ISDN card, or the V.35 card (if relevant to your
problem). Remember, Xmt and Rcv modes must be compatible.
Are the coding modes set properly?
The Xmt (transmit) and Rcv (receive) modes and the bitrate must be set in conjunction
with those of the unit at the other end. The Bit Rate and Sample Rate setting must also
match.
What happens if you try a different long distance carrier for the call?
What happens if you try the call at 56 vs 64 (or vice versa)?
What happens if you try reversing the direction of the call?
What happens if you try placing a local call as a long distance call?
Since most of the network uses separate transmit and receive paths, it is entirely
possible to have a path in one direction but not the other. The above tests may force
you through the network via a different path.
If local calls are ok, but long distance calls fail with all three major long distance carriers,
then it is likely there is a trunk problem between your local CO and the tandem switch.
Condition: No Audio In Both Directions
Does the Zephyr Xstream's loopback isolate the problem?
See above for tips on using the loopback modes.
On the other hand, if you can't receive distant audio, but get a delayed version of your
own transmitted signal, it's possible that one of the Xstreams was left in the loopback
mode. We've also run across situations were a piece of the Telco's network gear was
left in loopback mode.
Section 13: Deep Tech Information and Troubleshooting
USER'S MANUAL
280