Telco Bridges FreeSBC partner solutions

Telco Bridges FreeSBC

TelcoBridges designs and manufactures carrier grade session border controllers and VoIP media gateways. Their FreeSBC is a feature-rich, high-performance, easy-to-use virtual Session Border Controller that’s free to use, with paid PRO-edition options that add features and include support.

TransNexus software products are tightly integrated with Telco Bridges FreeSBC. For example, our software products use the SIP X-OTG field, which contains the source NAP identified by the FreeSBC. This enables more granular control over call handling.

Integration framework

TransNexus software uses standard SIP messaging to integrate with Telco Bridges FreeSBC solution. Either ClearIP or NexOSS is set up as a SIP trunk and is placed at the top of the routing table.

When a SIP INVITE, either inbound or outbound, arrives at the Telco Bridges FreeSBC, it sends the invite to the TransNexus software as if it were an actual SIP destination for call completion.

The TransNexus software performs the services configured for the call and returns a SIP message to the Telco Bridges FreeSBC according to the result of the services. Here are a few illustrative examples of typical SIP message communications:

ServicesResultReply (configurable)FreeSBC action
outbound fraud analysisno fraud foundSIP 404 Not Foundroute call using static route
outbound fraud analysisfraud detectedSIP 603 Declinedo not route call, return decline to source
outbound routing and fraud analysisno fraud foundSIP 302 Moved Temporarilyroute call using Contact header
inbound robocall preventionnot a robocallSIP 404 Not Foundroute call using static route
inbound robocall prevention with blockingrobocall detectedSIP 603 Declinedo not route call, return decline to source
inbound robocall prevention with diversionrobocall detectedSIP 302 Moved Temporarilyroute call to CAPTCHA gateway for call screening
SHAKEN authenticationauthenticated, attested and signedSIP 302 Moved Temporarily with Identity headercopy Identity header, route call using static route
SHAKEN verificationidentity header and certificate are validatedSIP 302 Moved Temporarily with verstatcopy verstat, route call using static route

Call handling

Select tabs to view call flows for various call handling scenarios:

Block the call

SIP ladder – block the call

If a TransNexus service determines that the call should be blocked, then it returns a SIP 603 Decline message to the FreeSBC.

Diversion call flow

Divert the call to CAPTCHA

If you have scenarios where a call might be bad but you’d prefer a less severe alternative to call blocking, you can set up the software to divert the call instead. The default diversion is to the TransNexus CAPTCHA gateway. Here are the steps:

  1. The call arrives at the TelcoBridges FreeSBC.
  2. The FreeSBC routes the call to the TransNexus software for services.
  3. If the TransNexus software determines the call should be diverted, it replies to the FreeSBC with a SIP 302 Moved Temporarily. The FreeSBC routes the call to the CAPTCHA gateway.
  4. The CAPTCHA gateway answers the call and prompts the caller to enter a random two-digit code. If the code is not entered correctly, the CAPTCHA gateway ends the call with a BYE.
  5. If the code is entered correctly, the CAPTCHA gateway sends a SIP REFER back to the FreeSBC.
  6. The FreeSBC receives the SIP REFER from the CAPTCHA gateway and sends an INVITE to the called party to complete the call. It also sends an INVITE to the calling party to enable audio codec renegotiation with the called party.

Alternative diversion destinations can be set up. For example, some customers have set up diversion to voicemail.

Route the call using static route

SIP ladder – send the call with static route

If there is no fraud detected and TransNexus software is not set up to perform routing services, then the software will return a SIP 404 Not Found to have the FreeSBC route the call using static route.

Route the call using Contact header

SIP ladder – send the call with using routes from TransNexus

TransNexus software can provide a list of routes for the FreeSBC to use. The list of routes can either be set up as static routes or generated in the TransNexus software using jurisdictional least cost routing.

If there is no fraud detected and TransNexus software is set up to do routing, then the software will return a SIP 302 Moved Temporarily with a list of routes in preference order for the FreeSBC to use.

Similar call flow for both authentication and verification

SHAKEN call flow

TransNexus software can provide SHAKEN authentication, verification, and certificate management services.

Authentication

If SHAKEN authentication is requested, then the TransNexus Authentication Service (AS) will use policy controls to determine the attestation level to use, create a SIP Identity header and insert it into a SIP 302 response to the SBC. The FreeSBC will copy the Identity header from the response into the outbound INVITE using a header manipulation rule.

If AS policies determine that the call should be blocked, then the AS will return a SIP 603 Decline.

Verification

If a call has a SHAKEN SIP Header and verification is requested, then the TransNexus Verification Service (VS) will use information in the SIP Header to fetch certificate information from Certificate Repositories for the Certificate Authority and the originating service provider that signed the call. The VS will validate the certificates and use the public key to verify that the call information has not be tampered with or replayed.

For call termination, the VS will generate a SIP 302 with verstat information in the P-Asserted-Identity field. The FreeSBC will copy the verstat information into the terminating INVITE using a header manipulation rule. Depending on the handset, this verstat information may be used to display information to the user about the verification results.

If VS policies determine that the call should be blocked or diverted, then the VS will return either a SIP 603 Decline or SIP 302 Moved Temporarily respectively.

Contact us

Please contact us for more information, assistance and guidance in connecting your TelcoBridges FreeSBC to TransNexus software products.

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