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Gemini

Gemini is an Application Server responsible for twinning VoIP clients with a mobile phone hosted on a native circuit-switched network.

Gemini routes terminating calls to any VoIP clients and the native device, with the exception of a VoIP client running on the native device (so it is not alerted twice by the same call).

It is implemented as a transaction-stateful but otherwise entirely-stateless AS, and builds on top of the AS infrastructure provided by Sprout.

Building Gemini

Gemini is integrated into the Application Server framework provided by Sprout, and can be run on the Sprout nodes or as a standalone node. It is built as part of the Sprout build.

Gemini Configuration

Gemini is configured in the subscriber's IFCs, and is registered as a general terminating AS for INVITE and SUBSCRIBE requests. It has an optional "twin-prefix" parameter - this specifies the prefix to apply to the user part of URIs to route to the mobile twin. The application server name should be set to mobile-twinned @ the cluster of nodes running the Gemini application servers (which will be the Sprout cluster, or a standalone application server cluster).

An example IFC is:

<InitialFilterCriteria>
  <TriggerPoint>
  <ConditionTypeCNF>0</ConditionTypeCNF>
  <SPT>
    <ConditionNegated>0</ConditionNegated>
    <Group>0</Group>
    <SessionCase>1</SessionCase>
    <Extension></Extension>
  </SPT>
  <SPT>
    <ConditionNegated>0</ConditionNegated>
    <Group>0</Group>
    <Method>INVITE</Method>
    <Extension></Extension>
  </SPT>
  </TriggerPoint>
  <ApplicationServer><ServerName>sip:mobile-twinned@gemini.cw-ngv.com;twin-prefix=123</ServerName>
    <DefaultHandling>0</DefaultHandling>
  </ApplicationServer>
</InitialFilterCriteria>

This is triggered if the request is a terminating INVITE for a registered subscriber. The application server is gemini.cw-ngv.com, and the prefix that will be applied to the callee's URI to generate the mobile number is 123.

To enable Gemini on a Sprout node or a standalone server, simply install the Gemini plugin and restart the sprout process.

Scalability

Multiple Gemini nodes can be deployed using NAPTR/SRV load-balancing. Gemini is transaction-stateful but otherwise entirely stateless, so no clustering is required.