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Knowledgebase: Important & Helpful Info
How Outbound Calling Works
Posted by Wayne Landt, Last modified by Wayne Landt on 07 May 2024 09:05 AM
How Outbound Calling Works

This article explains how outbound calling works. It is a detailed and technical article, but it is very valuable to anyone who needs to understand the process and how to best troubleshoot outbound calling issues with RingLogix Customer Support.

1. When a customer places an outbound call their equipment, referred to in this article as the CPE or “Customer Premise Equipment”, will send the RingLogix Voice Network a SIP INVITE.


2. Based on the type of service and authentication method, one of the following will occur.

  • For a Hosted PBX service, SIP Trunk or T38 fax line using digest authentication (username and password based):
    • The voice switch will respond with a challenge in the form of a 487 Rejected response.
    • The CPE should then resend the INVITE with an additional “Authorization” header that contains the service credentials.
  • For a SIP Trunk or T38 fax service using IP based authentication:
    • The voice switch will attempt match the customers public IP to an account on the system.
    • If this step fails, the call will get rejected and the caller will hear an “Invalid Account Number” error message.

3. Upon successful SIP authentication, the voice switch will proceed to get further authorization from the real-time billing engine. The following is verified during this check.

  • Customer Status: Open/Closed/Suspended
  • Available Credit Limit
  • Available Call Paths
  • Outbound Tariff Matching
  • Rate Lookup
  • Free Minute Bundle Check
  • Dial Permission: Allowed/Blocked
  • Maximum Call Duration
If this step fails, the system will typically play an error message for the reason causing the billing rejection.


4. After a successful billing check, our SBC will then continue to route the call to a Termination Carrier.

  • RingLogix may have as many as 10-20 termination carriers at any given time for any given destination.
  • Carriers are attempted in the order listed within our routing policies.
  • Which carrier is used is highly dependent on the combination of the Callers Caller ID and the LRN of the destination.
  • Although a call may be sent to carrier X, that carrier may not be able to process the call at that time. If so, our SBC will immediately attempt to route the call to another carrier.

5. Once the call connects, the SBC will instruct the real-time billing engine to start the accounting process. Upon either party ending the call, the accounting will stop, and the customer’s billing records are immediately updated.


Note: Outbound carrier routing is a simple operation that can sometimes get tricky. Particularly when troubleshooting an isolated (even when reoccurring) outbound calling issue.

Because not every carrier is always used in the same order for every call attempt, even to the same destination, and because several carriers may reciprocate traffic within each other with no pattern or consistency, it is probable that several calls to the same destination could at different times for different reasons traverse different carriers. Fun