diff --git a/features/cellular/framework/API/CellularNetwork.h b/features/cellular/framework/API/CellularNetwork.h
index c3f3855e04..8f81e66110 100644
--- a/features/cellular/framework/API/CellularNetwork.h
+++ b/features/cellular/framework/API/CellularNetwork.h
@@ -228,7 +228,7 @@ public:
      */
     virtual nsapi_error_t get_attach(AttachStatus &status) = 0;
 
-    /** Request detach from a network.
+    /** Request detach and deregister from a network.
      *
      *  @return         NSAPI_ERROR_OK on success
      *                  NSAPI_ERROR_DEVICE_ERROR on failure
diff --git a/features/cellular/framework/AT/ATHandler.cpp b/features/cellular/framework/AT/ATHandler.cpp
index 840bf5cfff..d12a46ab44 100644
--- a/features/cellular/framework/AT/ATHandler.cpp
+++ b/features/cellular/framework/AT/ATHandler.cpp
@@ -69,7 +69,6 @@ ATHandler::ATHandler(FileHandle *fh, EventQueue &queue, int timeout, const char
     _previous_at_timeout(timeout),
     _at_send_delay(send_delay),
     _last_response_stop(0),
-    _fh_sigio_set(false),
     _processing(false),
     _ref_count(1),
     _is_fh_usable(true),
@@ -106,9 +105,7 @@ ATHandler::ATHandler(FileHandle *fh, EventQueue &queue, int timeout, const char
     set_tag(&_info_stop, CRLF);
     set_tag(&_elem_stop, ")");
 
-    _fileHandle->set_blocking(false);
-
-    set_filehandle_sigio();
+    set_file_handle(fh);
 }
 
 void ATHandler::set_debug(bool debug_on)
@@ -151,6 +148,8 @@ FileHandle *ATHandler::get_file_handle()
 void ATHandler::set_file_handle(FileHandle *fh)
 {
     _fileHandle = fh;
+    _fileHandle->set_blocking(false);
+    set_filehandle_sigio();
 }
 
 void ATHandler::set_is_filehandle_usable(bool usable)
@@ -309,11 +308,7 @@ void ATHandler::process_oob()
 
 void ATHandler::set_filehandle_sigio()
 {
-    if (_fh_sigio_set) {
-        return;
-    }
     _fileHandle->sigio(mbed::Callback<void()>(this, &ATHandler::event));
-    _fh_sigio_set = true;
 }
 
 void ATHandler::reset_buffer()
@@ -1207,3 +1202,26 @@ void ATHandler::debug_print(char *p, int len)
     }
 #endif // MBED_CONF_CELLULAR_DEBUG_AT
 }
+
+bool ATHandler::sync(int timeout_ms)
+{
+    tr_debug("AT sync");
+    // poll for 10 seconds
+    for (int i = 0; i < 10; i++) {
+        lock();
+        set_at_timeout(timeout_ms, false);
+        // For sync use an AT command that is supported by all modems and likely not used frequently,
+        // especially a common response like OK could be response to previous request.
+        cmd_start("AT+CMEE?");
+        cmd_stop();
+        resp_start("+CMEE:");
+        resp_stop();
+        restore_at_timeout();
+        unlock();
+        if (!_last_err) {
+            return true;
+        }
+    }
+    tr_error("AT sync failed");
+    return false;
+}
diff --git a/features/cellular/framework/AT/ATHandler.h b/features/cellular/framework/AT/ATHandler.h
index 1e9952a4f7..3fbcdc8e10 100644
--- a/features/cellular/framework/AT/ATHandler.h
+++ b/features/cellular/framework/AT/ATHandler.h
@@ -181,6 +181,13 @@ public:
      */
     void set_is_filehandle_usable(bool usable);
 
+    /** Synchronize AT command and response handling to modem.
+     *
+     *  @param timeout_ms ATHandler timeout when trying to sync. Will be restored when function returns.
+     *  @return true is synchronization was successful, false in case of failure
+     */
+    bool sync(int timeout_ms);
+
 protected:
     void event();
 #ifdef AT_HANDLER_MUTEX
@@ -211,8 +218,6 @@ private:
     uint16_t _at_send_delay;
     uint64_t _last_response_stop;
 
-    bool _fh_sigio_set;
-
     bool _processing;
     int32_t _ref_count;
     bool _is_fh_usable;
diff --git a/features/cellular/framework/AT/AT_CellularContext.cpp b/features/cellular/framework/AT/AT_CellularContext.cpp
index cd201ced17..7ac30d13ba 100644
--- a/features/cellular/framework/AT/AT_CellularContext.cpp
+++ b/features/cellular/framework/AT/AT_CellularContext.cpp
@@ -28,6 +28,7 @@
 #define DEVICE_TIMEOUT 5 * 60 * 1000 // 5 minutes
 
 #if NSAPI_PPP_AVAILABLE
+#define AT_SYNC_TIMEOUT 1000 // 1 second timeout
 #include "nsapi_ppp.h"
 #endif
 
@@ -555,6 +556,8 @@ void AT_CellularContext::do_connect()
             tr_error("Failed to open data channel!");
             call_network_cb(NSAPI_STATUS_DISCONNECTED);
             _is_connected = false;
+        } else {
+            _is_context_activated = true;
         }
     }
 #else
@@ -627,13 +630,17 @@ nsapi_error_t AT_CellularContext::disconnect()
     _at.lock();
     _at.set_file_handle(_at.get_file_handle());
     _at.set_is_filehandle_usable(true);
-    //_at.sync(); // consume extra characters after ppp disconnect, also it may take a while until modem listens AT commands
+    if (!_at.sync(AT_SYNC_TIMEOUT)) { // consume extra characters after ppp disconnect, also it may take a while until modem listens AT commands
+        tr_error("AT sync failed after PPP Disconnect");
+    }
     _at.unlock();
 #endif // NSAPI_PPP_AVAILABLE
     _at.lock();
 
     // deactivate a context only if we have activated
     if (_is_context_activated) {
+        // CGACT and CGATT commands might take up to 3 minutes to respond.
+        _at.set_at_timeout(180 * 1000);
         _is_context_active = false;
         size_t active_contexts_count = 0;
         _at.cmd_start("AT+CGACT?");
@@ -659,16 +666,26 @@ nsapi_error_t AT_CellularContext::disconnect()
         // 3GPP TS 27.007:
         // For EPS, if an attempt is made to disconnect the last PDN connection, then the MT responds with ERROR
         if (_is_context_active && (rat < CellularNetwork::RAT_E_UTRAN || active_contexts_count > 1)) {
+            _at.clear_error();
             _at.cmd_start("AT+CGACT=0,");
             _at.write_int(_cid);
             _at.cmd_stop_read_resp();
         }
+
+        if (_new_context_set) {
+            _at.clear_error();
+            _at.cmd_start("AT+CGDCONT=");
+            _at.write_int(_cid);
+            _at.cmd_stop_read_resp();
+        }
+        _at.clear_error();
+        _at.cmd_start("AT+CGATT=0");
+        _at.cmd_stop_read_resp();
+        _at.restore_at_timeout();
     }
 
-    if (!_at.get_last_error()) {
-        _is_connected = false;
-        call_network_cb(NSAPI_STATUS_DISCONNECTED);
-    }
+    _is_connected = false;
+    call_network_cb(NSAPI_STATUS_DISCONNECTED);
 
     return _at.unlock_return_error();
 }
diff --git a/features/cellular/framework/AT/AT_CellularNetwork.cpp b/features/cellular/framework/AT/AT_CellularNetwork.cpp
index dcb1480482..9a421e3f46 100644
--- a/features/cellular/framework/AT/AT_CellularNetwork.cpp
+++ b/features/cellular/framework/AT/AT_CellularNetwork.cpp
@@ -350,6 +350,9 @@ nsapi_error_t AT_CellularNetwork::detach()
     _at.cmd_start("AT+CGATT=0");
     _at.cmd_stop_read_resp();
 
+    _at.cmd_start("AT+COPS=2");
+    _at.cmd_stop_read_resp();
+
     call_network_cb(NSAPI_STATUS_DISCONNECTED);
 
     return _at.unlock_return_error();