Merge pull request #15 from RADAR-CNS/external_time

Added external time source for the pRMT application

common/application/application_external_time.avsc

@@ -0,0 +1,14 @@
+{
+  "namespace": "org.radarcns.application",
+  "type": "record",
+  "name": "ApplicationExternalTime",
+  "doc": "Timestamp from an external source.",
+  "fields": [
+    {"name": "time", "type": "double", "doc": "device timestamp in UTC (s)"},
+    {"name": "timeReceived", "type": "double", "doc": "device receiver timestamp in UTC (s)"},
+    {"name": "externalTime", "type": "double", "doc": "timestamp in UTC according to an external source (s)", "default": "NaN"},
+    {"name": "host", "type": ["null", "string"], "doc": "hostname or IP address that time was polled from", "default": null},
+	{"name": "protocol", "type": {"name": "ExternalTimeProtocol", "type": "enum", "symbols": ["SNTP", "NTP"], "doc": "SNTP (Simple Network Time Protocol) synchronizes with a single server once, NTP (Network Time Protocol) may synchronize with multiple servers and derive some continuous measures."}, "doc": "protocol for external time synchronization", "default": "SNTP"},
+    {"name": "delay", "type": "double", "doc": "delay between sending and receiving a message from the host (s). The lower this delay, the more precise the external timestamp is expected to be.", "default": "NaN"}
+  ]
+}