diff --git a/Immocaster/Immobilienscout/Immobilienscout.php b/Immocaster/Immobilienscout/Immobilienscout.php
index 95ab5d1..8c99063 100755
--- a/Immocaster/Immobilienscout/Immobilienscout.php
+++ b/Immocaster/Immobilienscout/Immobilienscout.php
@@ -341,8 +341,9 @@ protected function createAttachmentBody($sMimeBoundary,$aArgs)
 		$sBody .= 'xmlns:ns3="http://rest.immobilienscout24.de/schema/platform/gis/1.0" xmlns:xlink="http://www.w3.org/1999/xlink" ';
 		$sBody .= 'xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">' . $sBreak;
 		$sBody .= '<title>'.$aArgs['title'].'</title>' . $sBreak;
+		$sBody .= '<externalId>'.$aArgs['externalId'].'</externalId>' . $sBreak;
+		$sBody .= '<externalCheckSum>'.$aArgs['externalCheckSum'].'</externalCheckSum>' . $sBreak;
 		if( $aArgs['type']==='Picture' || $aArgs['type']==='PDFDocument') {
-			$sBody .= '<externalId>'.$aArgs['externalId'].'</externalId>' . $sBreak;
 			$sBody .= '<floorplan>'.$aArgs['floorplan'].'</floorplan>' . $sBreak;
 		}
 		if( $aArgs['type']==='Picture') {
diff --git a/Immocaster/Immobilienscout/Rest.php b/Immocaster/Immobilienscout/Rest.php
index 4c98f9b..50b7258 100755
--- a/Immocaster/Immobilienscout/Rest.php
+++ b/Immocaster/Immobilienscout/Rest.php
@@ -817,6 +817,7 @@ private function _exportObjectAttachment($aArgs)
 		if(!isset($aArgs['titlePicture'])){ $aArgs['titlePicture'] = 'false'; }
 		if(!isset($aArgs['type'])){ $aArgs['type'] = ''; }
 		if(!isset($aArgs['externalId'])){ $aArgs['externalId'] = ''; }
+        if(!isset($aArgs['externalCheckSum'])){ $aArgs['externalCheckSum'] = ''; }
 		$oToken = null;
 		$sSecret = null;
 		$aHeader = array();
@@ -853,6 +854,7 @@ private function _exportObjectAttachment($aArgs)
 		$req->unset_parameter('url');
 		$req->unset_parameter('type');
 		$req->unset_parameter('externalId');
+        $req->unset_parameter('externalCheckSum');
 		return parent::getContent(
 			$req,
 			$sSecret,
diff --git a/Immocaster/Sdk.php b/Immocaster/Sdk.php
index c777318..d820051 100755
--- a/Immocaster/Sdk.php
+++ b/Immocaster/Sdk.php
@@ -9,17 +9,17 @@
  * @author     Norman Braun (medienopfer98.de)
  * @link       http://www.immobilienscout24.de
  */
- 
+
 class Immocaster_Sdk
 {
-	
+
     /**
      * Version and Application
 	 *
      * @var string
      */
 	 private $_sImmocasterApplication = 'SDK';
-	 private $_sImmocasterVersion = '1_1_x';	
+	 private $_sImmocasterVersion = '1_1_x';
 
     /**
      * Service Objekt
@@ -27,14 +27,14 @@ class Immocaster_Sdk
      * @var mixed
      */
 	 private $_oService = false;
-	 
+
     /**
      * Singleton Instanzen
      *
      * @var array
      */
 	static private $_instances = array();
-	
+
     /**
      * Singleton Pattern für die Erstellung
 	 * der Instanzen von Immocaster_Sdk.
@@ -55,7 +55,7 @@ static public function getInstance($sName,$sKey='',$sSecret='',$sService='immobi
 		}
 		return self::$_instances[$sName];
 	}
-	
+
     /**
      * Abhängige Dateien laden und Verbindung
 	 * zu einem Service aufbauen.
@@ -92,7 +92,7 @@ protected function __construct($sKey,$sSecret,$sService,$sAuth,$sProtocol)
 		echo sprintf(IMMOCASTER_SDK_LANG_CANNOT_CONNECT_SERVICE,$sService,$sAuth.'/'.$sProtocol);
 		return false;
 	}
-	
+
     /**
      * Aufgerufene Methode in den jeweiligen
 	 * Service weiterleiten und dort aufrufen.
@@ -110,7 +110,7 @@ public function __call($method,$args)
 		echo IMMOCASTER_SDK_LANG_NO_SERVICE_FOUND;
 		return false;
 	}
-	
+
 	/**
      * Haupt-URL zum Service ändern.
 	 *
@@ -126,7 +126,7 @@ public function setRequestUrl($sUrl=false)
 		echo IMMOCASTER_SDK_LANG_NO_SERVICE_FOR_CHANGE_URL;
 		return false;
 	}
-	
+
 	/**
      * Datenspeicherung Datenbank
 	 * initialisieren (für 3-legged-oauth).
@@ -148,5 +148,5 @@ public function setDataStorage($aConnection,$sSessionNamespace=null,$sTableName=
 		require_once(dirname(__FILE__).'/Data/'.$sFileName.'.php');
 		return call_user_func(array('Immocaster_Data_'.$sFileName,'getInstance'),$aConnection,$sTableName);
 	}
-	
-}
\ No newline at end of file
+
+}
diff --git a/README.txt b/README.txt
index 7b380f1..cfc48f0 100755
--- a/README.txt
+++ b/README.txt
@@ -1,4 +1,4 @@
-Immocaster PHP SDK v1.1.80
+Immocaster PHP SDK v1.1.81
 ==========================
 Author:     Norman Braun (http://www.medienopfer98.de)
 Copyright:  Immobilien Scout GmbH
@@ -9,6 +9,9 @@ Das PHP SDK von ImmobilienScout24 steht unter der FreeBSD Lizenz zur Verfügung
 History
 =======
 
+SDK Version 1.1.81
+- externalCheckSum für effizientere Synchronisierung von Attachments verfügbar.
+
 SDK Version 1.1.80
 - Erlaubt die Verwendung eines eigenen Proxys. Vielen Dank, webbird!
 
diff --git a/index.php b/index.php
index 3ea8a3f..4268fc4 100755
--- a/index.php
+++ b/index.php
@@ -353,7 +353,8 @@
   'type' => 'ATTACHMENTTYPE', // Picture, PDFDocument or Link
   'file' => 'LOCATION', // file path OR URL
   //'url' => 'URL',
-  'externalId' => 'EXTERNALID'); // optional
+  'externalId' => 'EXTERNALID', // optional
+  'externalCheckSum' => 'CHECKSUM'); // optional
 $res = $oImmocaster->exportObjectAttachment($aParameter);
 echo '<div class="codebox"><textarea>'.$res.'</textarea></div>';
 */