Inbound Bridge

The purpose of the Inbound Bridge is to allow OnSIP customers to incorporate inbound DID service from third party providers which do NOT support SIP transfers, RFC 3515, yet provide some valuable services (such as international DIDs) that OnSIP does not currently supply.


Background Information:

SIP, the protocol that OnSIP has built its VoIP infrastructure on, is an application layer protocol that has been designed to standardize the control signaling for sessions which transport multimedia across the internet. OnSIP is open and flexible enough to work out of the box with any other SIP provider that has implemented the following set of SIP RFCs:

  • RFC 2833 - RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals
  • RFC 3261 - SIP: Session Initiation Protocol
  • RFC 3263 - Session Initiation Protocol (SIP): Locating SIP Servers
  • RFC 3515 - The Session Initiation Protocol (SIP) Refer Method
  • RFC 4961 - Symmetric RTP / RTP Control Protocol (RTCP)

Ask your provider if they support the RFCs listed above.

OnSIP will work out of the box with any VoIP provider who supports this minimum set of standards. These standards compliant providers may be tied into your OnSIP PBX for FREE simply using SIP addresses. However, some providers who offer a "SIP" service simply implement the minimum requirements for internet telephony and call it SIP compliant. These providers, however do not support basic features like transfers, because they have not implemented the RFC defining such functionality. Here is where the purpose of the Inbound Bridge comes in.

Using the Inbound Bridge, OnSIP customers may use inbound DID service from third party providers that do not implement all of the required standards to be fully interoperable with OnSIP. The provider must still implement RFC 3261, 3263, 4961, and 2833 for DTMF, however our Inbound Bridge will handle transfers internally, allowing inbound calls from this provider to work seamlessly.


Creating an Inbound Bridge:

Creating a working Inbound Bridge will require first setting up the bridge in your OnSIP Hosted PBX, then setting up your third-party provider to send calls to the Inbound Bridge.


  1. Go to Administrators, click on "Inbound Call Settings." Then, click "Inbound Bridge" > "Add Inbound Bridge".
  1. Enter a descriptive name for the bridge.
  1. Choose the user to bill calls against and to report CDRs under. All calls made through the Inbound Bridge will generate a CDR at $0.005/minute (requires purchasing PSTN credits).
  1. Select the destination to forward calls to.
  1. Click "Save and Exit".


Next Steps:

Now that you have created your Inbound Bridge, you will need to get its SIP address in order to configure your third-party provider properly. Open the Inbound Bridge details by clicking the name of the bridge in the application list on the "Inbound Bridge" page. Under SIP address, note the address for this bridge.


In the example above the SIP address is ''. This is the address that you will need to give to your third-party provider.

Once you have configured your provider to route calls to this address, any customer calling the DID provisioned to you by your third-party provider should be directed into your OnSIP PBX just as if OnSIP had provisioned the number.

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