What is a SIP response? Part 2

Common SIP responses in the service for Oki-Toki's internal and outsourced contact centers and the probable reasons for their occurrence.

What is a SIP response? Part 2

Part 2:
Reading the Codes

What is SIP Provider is easy to understand by reading our article. First part.

Common SIP Providers in Oki-Toki and the probable reasons for their occurrence (the rest are written here , but in general about everything – here ):

The article refers to products: Cloud Call Center

1. Why does the call fail with SIP 100?


Any IP phone, PBX and communication provider has its own limit on the duration of call processing: if the provider, after accepting the call for work (SIP 100), does not report anything about the progress of the call, then the call is forcibly terminated (in our case, after 10 seconds ). Typically, under operational conditions, it takes 0.1 – 3 seconds from SIP 100 to any other response. This is a practical rule. And 10 seconds is no longer ok, it requires investigation and participation of the telephony provider. Just imagine – you pressed the Call button on your mobile phone, and the beeps went only after 12-15 seconds. This cannot be considered the norm 🙂


2. SIP 403 – means forbidden (forbidden):


  • Call to a non-existent number;
  • The balance on the sip-telephony gateway that was used to make the call has run out;
  • You are trying to make a call in a direction that is blocked by the communication provider (for example, you called to another country, and the provider allows you to call only within the country);
  • SIP gateway registration is not active. In this case, the provider rejects our request to use the inactive gateway.


3. SIP 404 – number not found (Not found):


  • Call to a non-existent number (Alternatively, some providers may give such an error if, for example, you made a call through the prefix 7, and the provider recognizes numbers only with the prefix 8. This is solved by setting the sip- conversion gateway);
  • SIP gateway registration is not active. The provider rejects our request to use an inactive gateway.


4. SIP 480 – the subscriber is unavailable or the number is out of service


  • Most often means what it stands for. The device is out of network coverage, the number is not in service, and so on;
  • Some providers may mistakenly send us this response on beeps (where SIP 180/183 should be sent);
  • Something happened on the supplier’s side and he began to define all numbers as inactive.


EN What is a SIP Provider

5. SIP 503 – internal telephony server error (Internal server error)


  • SIP gateway registration is not active. In this case, the provider rejects our request to use the inactive gateway;
  • Perhaps the balance on the account of the used sip has run out.
  • Any other reason related to internal problems on the telephony server.


6. SIP 603 – All cards are busy (Decline)


  • Appears when you try to seize a provider’s line while all of its lines are already busy with other calls (or all lines are unavailable for any other reason).

As you can see, telephony providers describe the same situations with different codes. This is primarily due to the fact that the SIP standard describes the establishment of a connection and the problems associated with it, and not the errors associated with “business”.

In addition, discrepancies can also occur due to technical problems (different equipment settings , various implementations of the standard, etc.)

Therefore, we recommend that you collect some fresh examples in the form of a subscriber number and the exact time of the call and contact your supplier with them. If you are not satisfied with the answer, then please contact us, we will always be on your side.

How to make a report on SIP calls, see here.

Good luck!

Stanislav Luchkin

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