diff --git a/33128/r17/urn_3GPP_ns_li_3GPPX1Extensions.xsd b/33128/r17/urn_3GPP_ns_li_3GPPX1Extensions.xsd
index f3e6b851fb1b6f6285717d09a9a1024148f6c95a..a67f0136d08d14d8f63e17c1b67cf1966a92284f 100644
--- a/33128/r17/urn_3GPP_ns_li_3GPPX1Extensions.xsd
+++ b/33128/r17/urn_3GPP_ns_li_3GPPX1Extensions.xsd
@@ -28,11 +28,11 @@
       <xs:element name="PTCChatGroupID" type="PTCChatGroupID"></xs:element>
     </xs:choice>
   </xs:complexType>
-  
+
   <xs:simpleType name="MCPTTID">
     <xs:restriction base="xs:anyURI"></xs:restriction>
   </xs:simpleType>
-  
+
   <xs:simpleType name="InstanceIdentifierURN">
     <xs:restriction base="xs:anyURI"></xs:restriction>
   </xs:simpleType>
@@ -90,6 +90,7 @@
       <xs:element name="HeaderReporting" type="PDHRReportingExtensions"></xs:element>
       <xs:element name="SMSFExtensions" type="SMSFProvisioningExtensions"></xs:element>
       <xs:element name="IdentifierAssociation" type="IdentifierAssociationExtensions"></xs:element>
+      <xs:element name="SDP" type="SDP"></xs:element>
     </xs:choice>
   </xs:complexType>
 
@@ -276,7 +277,7 @@
       <xs:maxInclusive value="255"/>
     </xs:restriction>
   </xs:simpleType>
-  
+
   <xs:element name="RCSTargetIdentifierExtensions" type="RCSTargetIdentifierExtensions"></xs:element>
 
   <xs:complexType name="RCSTargetIdentifierExtensions">
@@ -295,4 +296,60 @@
     <xs:restriction base="xs:anyURI"></xs:restriction>
   </xs:simpleType>
 
-</xs:schema>
\ No newline at end of file
+  <xs:element name="IMST3TargetIdentifierExtensions" type="IMST3TargetIdentifierExtensions"></xs:element>
+
+  <xs:complexType name="IMST3TargetIdentifierExtensions">
+    <xs:sequence>
+      <xs:element name="IMST3TargetIdentifierExtension" type="IMST3TargetIdentifierExtension" minOccurs="1" maxOccurs="unbounded"></xs:element>
+    </xs:sequence>
+  </xs:complexType>
+
+  <xs:complexType name="IMST3TargetIdentifierExtension">
+    <xs:choice>
+      <xs:element name="H248ContextID" type="H248ContextID"></xs:element>
+      <xs:element name="PayloadDirectionAssignment" type="PayloadDirectionAssignment"></xs:element>
+      <xs:element name="TriggerScope" type="TriggerScope"></xs:element>
+    </xs:choice>
+  </xs:complexType>
+
+ <xs:simpleType name="PayloadDirectionAssignment">
+    <xs:restriction base="xs:string">
+      <xs:enumeration value="ToTarget"></xs:enumeration>
+      <xs:enumeration value="FromTarget"></xs:enumeration>
+      <xs:enumeration value="NotDetermined"></xs:enumeration>
+    </xs:restriction>
+  </xs:simpleType>
+
+  <xs:simpleType name="H248ContextID">
+    <xs:restriction base="xs:integer">
+      <xs:minInclusive value="1"></xs:minInclusive>
+      <xs:maxInclusive value="4294967293"></xs:maxInclusive>
+    </xs:restriction>
+  </xs:simpleType>
+
+  <xs:simpleType name="TriggerScope">
+    <xs:restriction base="xs:string">
+      <xs:enumeration value="Unidirectional"></xs:enumeration>
+      <xs:enumeration value="Bidirectional"></xs:enumeration>
+    </xs:restriction>
+  </xs:simpleType>
+
+  <xs:complexType name="SDP">
+    <xs:sequence>
+      <xs:element name="SDPData" type="SDPData" minOccurs="1" maxOccurs="unbounded"></xs:element>
+    </xs:sequence>
+  </xs:complexType>
+
+  <xs:complexType name="SDPData">
+    <xs:choice>
+      <xs:element name="LocalSDP" type="SDPInfo"></xs:element>
+      <xs:element name="RemoteSDP" type="SDPInfo"></xs:element>
+    </xs:choice>
+  </xs:complexType>
+
+  <xs:simpleType name="SDPInfo">
+    <xs:restriction base="xs:string">
+    </xs:restriction>
+  </xs:simpleType>
+
+</xs:schema>