diff --git a/schema/cord-service-volt.yang b/schema/cord-service-volt.yang
new file mode 100644
index 0000000..3073366
--- /dev/null
+++ b/schema/cord-service-volt.yang
@@ -0,0 +1,167 @@
+module cord-service-volt {
+  namespace "urn:onlab:cord:service:volt";
+  prefix volt;
+  yang-version 1.1;
+
+  import ietf-yang-types { prefix yang; }
+  import xos-core { prefix xos; }
+
+  organization
+   "Open Networking Lab (CORD) / Corenova Technologies";
+
+  contact
+    "Larry Peterson <llp@onlab.us>
+     Peter K. Lee <peter@corenova.com>";
+
+  revision 2016-09-09 {
+    description "Initial revision.";
+  }
+
+  identity volt-service { base xos:service; }
+
+  feature onos-app-olt {
+    description "System facility to configure VLAN tags on the OLT.";
+  }
+  feature onos-app-aaa {
+    description "System facility to broker authentication between CPE and Radius server.";
+  }
+
+  typedef bandwidth {
+    type xos:bandwidth;
+    default 1000000000; // VOLT bandwidth default is 1Gbps
+  }
+  typedef subscriber-flow {
+    type leafref {
+      path "/volt:service/volt:provider/volt:port/volt:id";
+    }
+  }
+
+  grouping devices-list {
+    grouping olt-device {
+      description
+        "This grouping describes an OLT device which contains ODN link attachments.";
+    
+      leaf name {
+        description "name of OLT device";
+        type string {
+          length 1..254;
+        }
+      }
+      leaf mac { type yang:mac-address; mandatory true; }
+
+      container uplink {
+        description "Uplink description of the OLT device.";
+        leaf network { type yang:uuid; }
+        leaf tag {
+          if-feature onos-app-olt;
+          type xos:vlan;
+          description
+            "Represents S-Tag for instructing OLT to associate a VLAN tag for
+             traffic originating from OLT device.";
+        }
+      }
+    
+      list link {
+        description
+          "Each link represents an ONU/ONT (Optical Network Termination) endpoint
+           connection.";
+
+        key serial;
+        unique tag;
+      
+        leaf mac    { type yang:mac-address; mandatory true; }
+        leaf serial { type string; mandatory true; }
+        leaf active { type boolean; default false; }
+        leaf tag {
+          if-feature onos-app-olt;
+          type xos:vlan;
+          description
+            "Represents C-Tag for instructing ONT to add/remove vlan tag for
+             traffic within OLT device.";
+        }
+      }
+    }
+    list device {
+      description
+        "Each entry represents an OLT device.";
+      key mac;
+      //unique 'uplink/tag';
+      uses olt-device;
+    }
+  }
+  grouping provider {
+    description
+      "This grouping represents a VOLT agent/provider which manages multiple
+       OLT devices. The VOLT agent provides aggregate abstraction of
+       the entire PON as a sigle switch to the controller. Each port
+       entry of the agent represents each ONU/ONT endpoint as a
+       separate openflow port.";
+
+    uses devices-list {
+      description
+        "Each entry represents an OLT device managed by the agent.";
+    }
+    list port {
+      description
+        "Each entry represents an ONU/ONT endpoint connected across OLT devices.";
+      key id;
+      leaf id {
+        description "OpenFlow Port ID";
+        type yang:uuid;
+        mandatory true;
+      }
+      leaf link {
+        type leafref {
+          path '../../device/link/serial';
+        }
+        mandatory true;
+      }
+    }
+    container radius {
+      if-feature onos-app-aaa;
+      // configuration for how to broker authentication requests
+    }
+  }
+  grouping subscriber {
+    description
+      "This grouping represents a VOLT service subscriber along with
+       references to ONU/ONT access endpoints used by the subscriber.";
+    
+    list tag {
+      description
+        "Each entry represents a unique combination of the OLT uplink VLAN
+         (outer tag) and the ONU/ONT link VLAN (inner tag) connecting
+         into the fabric for the subscriber.";
+      
+      key 'outer inner';
+      leaf outer {
+        type leafref {
+          path "/volt:service/volt:provider/volt:device/volt:uplink/volt:tag";
+        }
+      }
+      leaf inner {
+        type leafref {
+          path "/volt:service/volt:provider/volt:device/volt:link/volt:tag";
+        }
+      }
+    }
+    leaf-list flows {
+      description
+        "Each entry represents a unique openflow port ID that the subscriber
+         uses to connect into the fabric from the VOLT service.";
+      config false;
+      type subscriber-flow;
+    }
+  }
+
+  /*
+   * Configuration data
+   */
+  container service {
+    uses xos:service {
+      refine kind { default volt-service; }
+      augment "provider"   { uses volt:provider; }
+      augment "subscriber" { uses volt:subscriber; }
+    }
+  }
+}
diff --git a/schema/cord-service-vsg.yang b/schema/cord-service-vsg.yang
new file mode 100644
index 0000000..aeae976
--- /dev/null
+++ b/schema/cord-service-vsg.yang
@@ -0,0 +1,148 @@
+module cord-service-vsg {
+  namespace "urn:onlab:cord:service:volt";
+  prefix volt;
+  yang-version 1.1;
+
+  import ietf-yang-types { prefix yang; }
+  import xos-core { prefix xos; }
+  import cord-service-volt { prefix volt; }
+
+  organization
+   "Open Networking Lab (CORD) / Corenova Technologies";
+
+  contact
+    "Larry Peterson <llp@onlab.us>
+     Peter K. Lee <peter@corenova.com>";
+
+  revision 2016-09-09 {
+    description "Initial revision.";
+  }
+
+  identity vsg-service { base xos:service; }
+
+  typedef subscriber-flow {
+    type leafref {
+      path "/vsg:service/vsg:provider/vsg:port/vsg:id";
+    }
+  }
+
+  grouping provider {
+    description
+      "This grouping represents a VSG agent/provider which manages multiple
+       VSG gateways. The VSG agent provides agregate abstraction of
+       the entire NFaaS as a single switch to the controller. Each
+       port entry of the agent represents each VSG endpoint as a
+       separate openflow port.";
+
+    list gateway {
+      description
+        "Each entry represents a VSG instance managed by the agent.";
+
+      leaf id { type yang:uuid; }
+      container services {
+        description
+          "Contains various services provided by the gateway.";
+        container cdn {
+          if-feature cdn;
+        }
+        container firewall {
+          if-feature firewall;
+          leaf-list rules { type string; }
+        }
+        container url-filter {
+          if-feature url-filter;
+          leaf level {
+            type enumeration {
+              enum "PG";
+              // others...
+            }
+          }
+          leaf-list rules { type string; }
+        }
+        container uverse {
+          if-feature uverse;
+        }
+      }
+    }
+    list port {
+      description
+        "Each entry represents a VSG endpoint connected across VSG gateways.";
+      key id;
+      leaf id {
+        description "OpenFlow Port ID";
+        type yang:uuid;
+        mandatory true;
+      }
+      leaf link {
+        type leafref {
+          path '../../gateway/id';
+        }
+        mandatory true;
+      }
+    }
+  }
+  grouping subscriber {
+    description
+      "This grouping represents a VSG service subscriber along with
+       reference to fabric flows used by the subscriber.";
+
+    leaf status {
+      type enumeration {
+        enum "enabled" {
+          description "Enabled";
+          value 1;
+        }
+        enum "suspended" {
+          description "Suspended";
+        }
+        enum "delinquent" {
+          description "Delinquent";
+        }
+        enum "violation" {
+          description "Copyright Violation";
+        }
+      }
+      default enabled;
+    }
+    leaf demo { type boolean; default false; }
+    leaf uplink-speed   { type volt:bandwidth; }
+    leaf downlink-speed { type volt:bandwidth; }
+    
+    list tag {
+      description
+        "Each entry represents a unique openflow port ID that the subscriber
+         connects to the VSG service from the fabric.";
+      
+      key flow;
+      leaf flow {
+        type union {
+          type volt:subscriber-flow;
+          type vsg:subscriber-flow {
+            description "can be an output flow from the VSG service.";
+          }
+          type yang:uuid {
+            description "supports a generic openflow port ID";
+          }
+        }
+      }
+    }
+    leaf-list flows {
+      description
+        "Each entry represents a unique openflow port ID that the subscriber
+         uses to connect into the fabric from the VSG service.";
+      config false;
+      type subscriber-flow;
+    }
+  }
+  
+  /*
+   * Configuration data
+   */
+  container service {
+    uses xos:service {
+      refine kind { default vsg-service; }
+      augment "provider"   { uses vsg:provider; }
+      augment "subscriber" { uses vsg:subscriber; }
+    }
+  }
+}
diff --git a/schema/cord-subscriber.yang b/schema/cord-subscriber.yang
index 7fa098e..86fa0e8 100644
--- a/schema/cord-subscriber.yang
+++ b/schema/cord-subscriber.yang
@@ -1,5 +1,4 @@
 module cord-subscriber {
-  
   namespace "urn:onlab:cord:subscriber";
   prefix csub;
   yang-version 1.1;
@@ -13,7 +12,7 @@
   
   description
    "This module contains CORD Subscriber model representing its
-    relationship to features, services, and devices.
+    relationship to features and services.
 
     Copyright (c) 2016 ON.LAB and the persons identified as authors of
     the code.  All rights reserved.
diff --git a/schema/xos-core.yang b/schema/xos-core.yang
index 44a702c..1137c28 100644
--- a/schema/xos-core.yang
+++ b/schema/xos-core.yang
@@ -35,8 +35,8 @@
   }
   
   identity kind;
-  identity generic    { base kind; }
-  identity subscriber { base kind; }
+  identity generic { base kind; }
+  identity service { base kind; }
 
   typedef unique-identifier {
     description "defines valid formats for external reference id";
@@ -46,14 +46,23 @@
       type inet:uri;
     }
   }
+  typedef bandwidth {
+    type uint32 {
+      range 1000000..max; // should be at least 1 Mbps?  
+    }
+    units 'bps';
+  }
+  typedef vlan {
+    type uint16 { range 0..4095; }
+  }
 
-  grouping xos-attribute {
+  grouping attribute-pair {
     leaf name  { type string { length 0..128; } }
     leaf value { type string; }
     // don't need pointer back to service
   }
 
-  grouping xos-sync-record {
+  grouping sync-record {
     description "Synchronizer-specific properties for model records";
     
     leaf created { type yang:date-and-time; }
@@ -100,25 +109,18 @@
     }
   }
   
-  grouping xos-base {
+  grouping base-common {
     leaf id {
       type unique-identifier;
       mandatory true;
     }
-    leaf kind {
-      type identityref {
-        base kind;
-      }
-      default generic;
-    }
     leaf name {
       type string {
         length 0..255;
       }
     }
-    
     list attribute {
-      uses xos-attribute;
+      uses attribute-pair;
       key name;
       status deprecated;
       reference "XOS: service-specific-attribute";
@@ -129,15 +131,14 @@
       mandatory true;
       status deprecated;
     }
-
     container record {
       if-feature synchronizer;
-      uses xos-sync-record;
+      uses sync-record;
     }
   }
 
   grouping tenant-root {
-    uses xos-base {
+    uses base-common {
       refine 'name' {
         description "Specify name of the TenantRoot";
       }
@@ -167,11 +168,17 @@
   }
 
   grouping service {
-    uses xos-base {
+    uses base-common {
       refine 'name' {
         description "Name of the Service";
       }
     }
+    leaf kind {
+      type identityref {
+        base kind;
+      }
+      default generic;
+    }
     leaf description {
       type string {
         length 0..254;
@@ -197,6 +204,22 @@
       leaf public  { type string { length 0..1024; } }
       leaf private { type string { length 0..1024; } }
     }
+    list provider {
+      description
+        "Each entry represents a provider of the service. Each unique service
+         should augment this block with service specific attributes.";
+      key id;
+      uses xos:provider;
+    }
+    list subscriber {
+      description
+        "Each entry represents a subscriber of the service. Each unique service
+         should augment this block with service specific attributes.";
+      key id;
+      uses xos:subscriber;
+      notification subscriber-added;
+      notification subscriber-deleted;
+    }
     
     // TOOD: need to better understand relationship between Service and Slice
     action scale {
@@ -207,7 +230,7 @@
   }
 
   grouping tenancy {
-    uses xos-base;
+    uses base-common;
 
     choice provider {
       description "only one type of provider node is valid.";