Load Multiplier offers a JSON based proxy / back-to-back agent. Using Load Multiplier proprietary client, you can simulate JSON clients. Now you have JSON proxy, JSON clients and you can test an end to end call flow. Please refer below diagram.

A Simple JSON Call Flow
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Typically, it is used to test a third party server like Turn Server. Using JSON call flows media parameters, ICE candidates etc are exchanged between two different peers (JSON clients). In the process these JSON clients does ICE resolutions, ICE connectivity check etc and enable users to test STUN / TURN server for functionality, load and performance.

This complete setup JSON client and proxy provides a stand alone independent testbed to test Turn Server. However it can be used in other scenarios as an enabler to test various kinds of other scenarios as well.