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What does VoIP error "503 Service Unavailable" message mean?



The "Services Unavailable" error message has several potential triggers with Biamp VoIP devices. 


Status:  503 Service Unavailable


Proxy registration process

The "503 Service Unavailable" message being returned from the proxy during the registration process can be related to not having enough licenses available for the Biamp VoIP device to register. Some proxies require a license or multiple licenses for each endpoint. Or licenses are not required for the manufacturer's own devices but are required for 3rd party SIP endpoints like a Biamp VoIP device.


Competing VoIP devices

Another possible cause is two or more VoIP devices trying to register to a single extension on the proxy. Please note that Biamp devices require a unique extension for each line being used. Another indication that you may be experiencing this issue is one of the lines may successfully register, work intermittently but then drop unexpectedly.


Other possible causes

  • There can be a limit for the traffic which was made by the company that we sent the traffic. Or the route they sent may be working within limits.
  • Some operators return Sip 503 for calling the wrong number.
  • One of the possible reasons for this disconnect code may be the route being down or our numbers may be blocked by the other side.
  • A codec mismatch.  Either the Biamp or the far end is not able to negotiate a valid codec to use for the call.