add dmtf verb

lib/utils/constants.json

@@ -4,6 +4,7 @@
     "Dequeue": "dequeue",
     "Dial": "dial",
     "Dialogflow": "dialogflow",
+    "Dtmf": "dtmf",
     "Enqueue": "enqueue",
     "Gather": "gather",
     "Hangup": "hangup",

lib/utils/place-outdial.js

@@ -108,11 +108,12 @@ class SingleDialer extends Emitter {
 
       this.ep = await ms.createEndpoint();
       this.logger.debug(`SingleDialer:exec - created endpoint ${this.ep.uuid}`);
-      let promiseStreamConnected;
+
+      let lastSdp;
       const connectStream = async(remoteSdp) => {
-        // wait for previous re-invite to complete, if any
-        if (promiseStreamConnected) await promiseStreamConnected.catch((err) => {});
-        return promiseStreamConnected = this.ep.modify(remoteSdp);
+        if (remoteSdp === lastSdp) return;
+        lastSdp = remoteSdp;
+        return this.ep.modify(remoteSdp);
       };
 
       Object.assign(opts, {