TVOICE – Troubleshooting of Endpoint Issues

TVOICE – Troubleshooting of Endpoint Issues

  • Noise – Silence, Clicking, Crackling, Crosstalk, Hissing Static, Buzz or Hum
  • Echo – Repeated (echoed) or Tunnel voice
  • Garbled – Robotic, Choppy, Underwater voice
  • Volume Distortion – Tinny sound, soft, fuzzy or muffled voice
  • One-Way Audio



  • Silence of Hissing – Typically caused by over-aggressive VAD (Service Parameters – Allow negation of VAD = FALSE)
  • Clicking – Clock slips or other digital TDM circuit errors
  • Crackling – Bad electrical connection or electrical interference (Physical)
  • Crosstalk – Signal leaking from one circuit to another – wires too close
  • Static – Codec mismatch which can be exacerbated by VAD


  • Listener Echo – Person listening hears talker twice (Too long of an echo tail or ECAN not effective) ECAN = ‘Echo Canceller’
  • Talker Echo – Person talking hears own voice (Too long of an echo tail of ECAN not effective)
  • Tunnel Voice – Echo problem, but very ‘tight’ echo (ECAN Issue)

Further reading on ECAN –


  • Choppy Voice – Packet loss of excessively delayed packets
  • Synthetic or Robotic Voice – Single packet loss or packet delay beyond the limit of the De-jitter buffer (ILBC, ISAC Codec)
  • Underwater Voice – G.729 Annex CODEC mismatch

Volume Distortion

  • Fuzzy Voice – Too much analog signal Gain
  • Muffled Voice – Overdriven signal (possibly hand over the handset mic – reduction Inside frequencies in the ‘key range’ – 440hz – 3.5Khz)
  • Soft Voice – Attenuated Signal (signal reduction in ‘volume’)
  • Tinny Voice – Overdriven signal (possibly hand over the handset mic – reduction Outside frequencies in the ‘key range’ – 440hz – 3.5Khz)

No Ringback or Other CPTones (Call Progress Tones)

PI: (Progress Indicators – Signals)

  • – 0 = No PI Included
  • – 1 = Call is not ISDN end to end, further call progress may be available in-band
  • – 2 = Destination address is non-ISDN
  • – 3 = Origination address is non-ISDN
  • – 8 = In-band information or appropriate pattern is now available


  • Setup, Alert, Progress, Connect, – (ISDN Messages)

PI’s from VoIP Dial-Peers in Setup msg are 0,1 or 3

PI’s from POTS Dial-Peers in Progress, Connect or Alert msgs are 1,2 or 8

Commands under dial-peers to enable PI:

(Mainly POTS with ISDN and VOIP and H.323)

progress_ind setup enable 3 - Old command
tone ringback alert-no-pi - New command

Further reading on PI:

One Way Audio

  • Take a look at the IP routing network infrastructure. 9/10 this is where the problem exists.
  • No return route is present on the network. (Possibly being dropped by an ACL)
  • Transcoding or MTP issue. Possibly the device is not allowed in a certain direction on the network.
  • Zero audio/dead air = Call is setup in CUCM, but perhaps an ACL is blocking UDP ports but allowing signalling only.
  • cRTP mismatch. Has to be enabled in both directions.