[VoiceOps] SIP return message on misdials - 487 or 500/503 or ?

Jay Hennigan jay at west.net
Mon Oct 5 11:51:41 EDT 2015

On 10/5/15 8:16 AM, Erick Bergquist wrote:
> Hello,
> Just trying to get idea of what is normal on what providers should
> return for a misdial, bad unknown number, etc.
> On one provider, I get a CANCEL and a 487 Request Terminated on mis-dials.
> On another provider, I get a 503 Service Unavailable and a 500
> Internal Service Error back.

It depends. CANCEL and 487 Request Terminated typically comes from the 
originator and means that you hung up before the call completed. Carrier 
was in post-dial delay and hadn't returned anything (yet).

503 means that the carrier can't or won't process the call. Could be a 
misdial where the number can't be parsed as in not enough or too many 
digits, prefix starts with 1 or 0, etc. Could also be that you tried to 
dial a valid number that the carrier doesn't handle, such as 
international, 900/976, etc. Could also mean that you didn't pay your 
bill or are coming from an IP address that isn't a customer of that 

For a number that is in the correct format but isn't in service, you 
might see 503 or also 404 or 604.

500 internal service error is usually a technical problem with the 
carrier and not a misdial.

Different carriers map ISDN/SS7 cause codes to SIP differently. See:


Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV

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