diff --git a/storage-xray-udp/RATIONALE.md b/storage-xray-udp/RATIONALE.md
new file mode 100644
index 00000000..11ff3691
--- /dev/null
+++ b/storage-xray-udp/RATIONALE.md
@@ -0,0 +1,2 @@
+# storage-xray-udp rationale
+
diff --git a/storage-xray-udp/README.md b/storage-xray-udp/README.md
index 9794a74b..3add520b 100644
--- a/storage-xray-udp/README.md
+++ b/storage-xray-udp/README.md
@@ -4,3 +4,17 @@ Encoding and wire protocol for sending Zipkin spans to AWS X-Ray.
 
 See [reporter-xray-udp](../reporter-xray-udp) for instructions on setting up
 X-Ray reporting for an application.
+
+## Overview
+This storage module performs three activites:
+ 1. Receives incoming zipkin spans
+ 2. Encodes received zipkin spans to X-Ray compatible segments
+ 3. Forwards the encoded X-Ray segments to a X-Ray daemon endpoint
+
+The encoder is implemented by `zipkin2.storage.xray_udp.UDPMessageEncoder` class.
+
+### Field Mappings
+
+| Name | Source | Destination | Mandatory | Transformation | Reference |
+|------|--------|-------------|-----------|----------------|-----------|
+| Origin | `span.tags['aws.origin']` | `segment.origin` | No | Simple value mapped | [**Segment fields**](https://docs.aws.amazon.com/xray/latest/devguide/xray-api-segmentdocuments.html#api-segmentdocuments-fields) > **Optional Segment Fields** > `origin` |
\ No newline at end of file
diff --git a/storage-xray-udp/src/main/java/zipkin2/storage/xray_udp/UDPMessageEncoder.java b/storage-xray-udp/src/main/java/zipkin2/storage/xray_udp/UDPMessageEncoder.java
index de705734..f367153f 100644
--- a/storage-xray-udp/src/main/java/zipkin2/storage/xray_udp/UDPMessageEncoder.java
+++ b/storage-xray-udp/src/main/java/zipkin2/storage/xray_udp/UDPMessageEncoder.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 The OpenZipkin Authors
+ * Copyright 2016-2020 The OpenZipkin Authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
@@ -110,6 +110,8 @@ static void writeJson(Span span, Buffer buffer) throws IOException {
     // aws.ec2 section
     String ec2AvailabilityZone = null,
         ec2InstanceId = null;
+    // aws.origin section
+    String xrayOrigin = null;
     // cause section
     String causeWorkingDirectory = null, causeExceptions = null;
     boolean http = false, sql = false, aws = false, cause = false;
@@ -185,6 +187,9 @@ static void writeJson(Span span, Buffer buffer) throws IOException {
           case "aws.ec2.instance_id":
             ec2InstanceId = entry.getValue();
             continue;
+          case "aws.origin":
+            xrayOrigin = entry.getValue();
+            continue;
         }
       }
 
@@ -273,6 +278,7 @@ static void writeJson(Span span, Buffer buffer) throws IOException {
         writer.endObject();
       }
       writer.endObject();
+      if (xrayOrigin != null) writer.name("origin").value(xrayOrigin);
     }
 
     if (cause) {
diff --git a/storage-xray-udp/src/test/java/zipkin2/storage/xray_udp/UDPMessageEncoderTest.java b/storage-xray-udp/src/test/java/zipkin2/storage/xray_udp/UDPMessageEncoderTest.java
index 1b2910cb..bd37b308 100644
--- a/storage-xray-udp/src/test/java/zipkin2/storage/xray_udp/UDPMessageEncoderTest.java
+++ b/storage-xray-udp/src/test/java/zipkin2/storage/xray_udp/UDPMessageEncoderTest.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 The OpenZipkin Authors
+ * Copyright 2016-2020 The OpenZipkin Authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
@@ -43,6 +43,30 @@ public void writeJson_server_isSegment() throws Exception {
             "{\"trace_id\":\"1-12345678-90abcdef1234567890abcdef\",\"id\":\"1234567890abcdef\"}");
   }
 
+  @Test
+  public void writeJson_origin_no_default() throws Exception {
+    Span span =
+        serverSpan
+            .toBuilder()
+            .build();
+
+    String json = writeJson(span);
+    assertThat(readString(json, "origin")).isNull();
+  }
+
+  @Test
+  public void writeJson_origin_custom() throws Exception {
+    Span span =
+        serverSpan
+            .toBuilder()
+            .putTag("aws.origin", "AWS::EC2::Instance")
+            .build();
+
+    String json = writeJson(span);
+    assertThat(readString(json, "origin")).isEqualTo("AWS::EC2::Instance");
+    assertThat(readString(json, "annotations.aws_origin")).isNull();
+  }
+
   @Test
   public void writeJson_server_localEndpointIsName() throws Exception {
     Span span =