;version&#39;] &lt; 72)
              ? &quot;plan-b&quot;
              : &quot;unified-plan&quot;;
    }
    Map&lt;String, dynamic&gt; pcConstraints = {
      &quot;mandatory&quot;: {},
      &quot;optional&quot;: [
        {&quot;DtlsSrtpKeyAgreement&quot;: true}
      ]
    };
    if (this.ipv6Support) {
      pcConstraints[&#39;optional&#39;].add({&quot;googIPv6&quot;: true});
    }
    &#47;&#47; Any custom constraint to add?
    if (callbacks.rtcConstraints != null) {
      Janus.debug(&quot;Adding 