diff --git a/src/consumer.cpp b/src/consumer.cpp
index 545acea..301828b 100644
--- a/src/consumer.cpp
+++ b/src/consumer.cpp
@@ -92,10 +92,34 @@
   NDN_LOG_TRACE("m_iblt: " << std::hash<std::string>{}(m_iblt.toUri()));
 
   State state(data.getContent());
+  std::vector<MissingDataInfo> updates;
+  std::vector<ndn::Name> availableSubscriptions;
 
-  NDN_LOG_DEBUG("Content: " << state);
+  for (const auto& content : state.getContent()) {
+    ndn::Name prefix = content.getPrefix(-1);
+    uint64_t seq = content.get(content.size()-1).toNumber();
+    if (m_prefixes.find(prefix) == m_prefixes.end()) {
+      // In case this the first prefix ever received via hello data,
+      // add it to the available subscriptions
+      availableSubscriptions.push_back(prefix);
+    }
+    else if (seq > m_prefixes[prefix]) {
+      // Else this is not the first time we have seen this prefix,
+      // we must let application know that there is missing data
+      // (scenario: application nack triggers another hello interest)
+      updates.push_back(MissingDataInfo{prefix, m_prefixes[prefix] + 1, seq});
+      m_prefixes[prefix] = seq;
+    }
+  }
 
-  m_onReceiveHelloData(state.getContent());
+  NDN_LOG_DEBUG("Hello Data:  " << state);
+
+  m_onReceiveHelloData(availableSubscriptions);
+
+  if (!updates.empty()) {
+    NDN_LOG_DEBUG("Updating application with missed updates");
+    m_onUpdate(updates);
+  }
 }
 
 void
@@ -140,8 +164,8 @@
   m_iblt = syncDataName.getSubName(syncDataName.size()-1, 1);
 
   if (data.getContentType() == ndn::tlv::ContentType_Nack) {
-    NDN_LOG_DEBUG("Received application Nack from producer, renew sync interest");
-    sendSyncInterest();
+    NDN_LOG_DEBUG("Received application Nack from producer, send hello again");
+    sendHelloInterest();
     return;
   }
 
diff --git a/src/consumer.hpp b/src/consumer.hpp
index 47825a9..9b30d8d 100644
--- a/src/consumer.hpp
+++ b/src/consumer.hpp
@@ -46,11 +46,17 @@
  * @brief Consumer logic to subscribe to producer's data
  *
  * Application needs to call sendHelloInterest to get the subscription list
- * in ReceiveHelloCallback. It can then add the desired names using addSubscription.
+ * in psync::ReceiveHelloCallback. It can then add the desired names using addSubscription.
  * Finally application will call sendSyncInterest. If the application adds something
  * later to the subscription list then it may call sendSyncInterest again for
  * sending the next sync interest with updated IBF immediately to reduce any delay in sync data.
  * Whenever there is new data UpdateCallback will be called to notify the application.
+ *
+ * If consumer wakes up after a long time to sync, producer may not decode the differences
+ * with its old IBF successfully and send an application nack. Upon receiving the nack,
+ * consumer will send a hello again and inform the application via psync::ReceiveHelloCallback
+ * and psync::UpdateCallback.
+ *
  * Currently, fetching of the data needs to be handled by the application.
  */
 class Consumer
@@ -97,6 +103,7 @@
    * @brief Add prefix to subscription list
    *
    * @param prefix prefix to be added to the list
+   * @return true if prefix is added, false if it is already present
    */
   bool
   addSubscription(const ndn::Name& prefix);
diff --git a/src/partial-producer.cpp b/src/partial-producer.cpp
index 73fb677..d8d98a5 100644
--- a/src/partial-producer.cpp
+++ b/src/partial-producer.cpp
@@ -79,8 +79,8 @@
 
   State state;
 
-  for (const auto& p : m_prefixes) {
-    state.addContent(p.first);
+  for (const auto& prefix : m_prefixes) {
+    state.addContent(ndn::Name(prefix.first).appendNumber(prefix.second));
   }
   NDN_LOG_DEBUG("sending content p: " << state);