One Way or No Way Voice on Calls

Most common causes of One Way/No Way Voice

  • Faulty curly cord or receiver
  • Phone is plugged into the wrong router
  • SIP ALG Active on Router/Firewall
  • Blocked RTP Ports on Router/Firewall
  • Codec Negotiation Failure

Faulty curly cord or receiver

Swap the curly cord and receiver with a known working handset.

  • If the fault stays with the original handset, the curly cord and receiver are not at fault
  • If the fault moves to the known working handset, move the receiver back to the original handset
  • If the fault moves back, the problem is the receiver. If not, the fault is the curly cord

Phone is plugged into the wrong router

It is common for customers to have multiple networks for voice and data. Voice routers will often be specifically configured for VoIP whilst Data routers have no need for this. If a phone is accidentally plugged into the wrong router, they will experience issues.

  • Cross check the LAN side IP address of the non-working phone with a working phone. This should identify the phone on a different network
  • Resolve by returning the phone to the appropriate VoIP router

SIP ALG Active on Router/Firewall

SIP ALG is active in most commercial routers. By design, it inspects SIP packets and if necessary, modify them to assist VoIP traffic. In actuality, it can interfere with VoIP traffic, often causing call drops, one way voice or registration based issues. SIP ALG should be disabled in all circumstances.

Any router provided by Inclarity will have SIP ALG disabled. 
Any router not provided by Inclarity will need to be referred to the router maintainer to disable. Inclarity cannot provide assistance on unsupported routers

Blocked RTP Ports on Router/Firewall

VoIP uses specific network ports to pass traffic back and forth to set up, continue and tear down the call. In the event of any ports being blocked, the call will experience difficulties. Please refer to the Network Advisory Document at the bottom of this page for the full list of ports.

Codec Negotiation Failure

In most instances, Inclarity can negotiate with a codec offering on an inbound call. All phones are able to accept a selection of codecs with a minimum 3 configured per handset. However, in some circumstances, it's possible that the inbound codec offering will not match the available or accepted codecs. Should this be the case, Inclarity Technical Support will be able to identify this and offer best alternatives.

All other circumstances

In the event that these checks do not resolve the problem, please log a ticket with Inclarity Customer Services. The following pieces of information are mandatory for investigation:

  • Customer and Site name
  • Checks completed so far
  • A minimum of 2 call examples containing the following information:
  •  - Callers number
  •  - Number they dialled
  •  - The agent who answered the call
  •  - Time and Date of the call
  •  - Fault Symptom
  • Technical Contact Name and Number


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