diff --git a/core/grpc_service.go b/core/grpc_service.go
index bc92483..d088e05 100644
--- a/core/grpc_service.go
+++ b/core/grpc_service.go
@@ -18,7 +18,6 @@
 
 import (
 	"net"
-	"strconv"
 
 	"gerrit.opencord.org/voltha-bbsim/common/logger"
 	"gerrit.opencord.org/voltha-bbsim/common/utils"
@@ -30,9 +29,11 @@
 	log "github.com/sirupsen/logrus"
 	"golang.org/x/net/context"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 )
 
-// gRPC Service
+// DisableOlt method sends OLT down indication
 func (s *Server) DisableOlt(c context.Context, empty *openolt.Empty) (*openolt.Empty, error) {
 	logger.Debug("OLT receives DisableOLT()")
 	if s.EnableServer != nil {
@@ -44,16 +45,26 @@
 	return new(openolt.Empty), nil
 }
 
+// ReenableOlt method sends OLT up indication for re-enabling OLT
 func (s *Server) ReenableOlt(c context.Context, empty *openolt.Empty) (*openolt.Empty, error) {
 	logger.Debug("OLT receives Reenable()")
+	if s.EnableServer != nil {
+		if err := sendOltIndUp(*s.EnableServer, s.Olt); err != nil {
+			logger.Error("Failed to send OLT UP indication for reenable OLT: %v", err)
+			return new(openolt.Empty), err
+		}
+		logger.Debug("Successfuly sent OLT UP indication")
+	}
 	return new(openolt.Empty), nil
 }
 
+// CollectStatistics method invoked by VOLTHA to get OLT statistics
 func (s *Server) CollectStatistics(c context.Context, empty *openolt.Empty) (*openolt.Empty, error) {
 	logger.Debug("OLT receives CollectStatistics()")
 	return new(openolt.Empty), nil
 }
 
+// GetDeviceInfo returns OLT info
 func (s *Server) GetDeviceInfo(c context.Context, empty *openolt.Empty) (*openolt.DeviceInfo, error) {
 	logger.Debug("OLT receives GetDeviceInfo()")
 	devinfo := new(openolt.DeviceInfo)
@@ -71,56 +82,88 @@
 	devinfo.GemportIdEnd = 65535
 	devinfo.FlowIdStart = 1
 	devinfo.FlowIdEnd = 16383
-	devinfo.DeviceSerialNumber = "BBSIMOLT00"+strconv.FormatInt(int64(s.Olt.ID), 10)
-
+	devinfo.DeviceSerialNumber = s.Olt.SerialNumber
 
 	return devinfo, nil
 }
 
+// ActivateOnu method handles ONU activation request from VOLTHA
 func (s *Server) ActivateOnu(c context.Context, onu *openolt.Onu) (*openolt.Empty, error) {
 	logger.Debug("OLT receives ActivateONU()")
-	result := device.ValidateONU(*onu, s.Onumap)
-	if result == true {
-		matched, error := getOnuBySN(s.Onumap, onu.SerialNumber)
-		if error != nil {
-			logger.Fatal("%s", error)
-		}
-		onuid := onu.OnuId
-		matched.OnuID = onuid
-		s.updateDevIntState(matched, device.ONU_ACTIVE)
-		logger.Debug("ONU IntfID: %d OnuID: %d activated succesufully.", onu.IntfId, onu.OnuId)
+
+	matched, err := getOnuBySN(s.Onumap, onu.SerialNumber)
+	if err != nil {
+		logger.Fatal("%s", err)
+		return new(openolt.Empty), status.Errorf(codes.NotFound, "ONU not found with serial number %v", onu.SerialNumber)
 	}
+	onuid := onu.OnuId
+	matched.OnuID = onuid
+	s.updateDevIntState(matched, device.ONU_ACTIVE)
+	logger.Debug("ONU IntfID: %d OnuID: %d activated succesufully.", onu.IntfId, onu.OnuId)
+
 	return new(openolt.Empty), nil
 }
 
+// CreateTconts method should handle Tcont creation
 func (s *Server) CreateTconts(c context.Context, tconts *openolt.Tconts) (*openolt.Empty, error) {
 	logger.Debug("OLT receives CreateTconts()")
 	return new(openolt.Empty), nil
 }
 
+// RemoveTconts method should handle t-cont removal
 func (s *Server) RemoveTconts(c context.Context, tconts *openolt.Tconts) (*openolt.Empty, error) {
 	logger.Debug("OLT receives RemoveTconts()")
 	return new(openolt.Empty), nil
 }
 
+// DeactivateOnu method should handle ONU deactivation
 func (s *Server) DeactivateOnu(c context.Context, onu *openolt.Onu) (*openolt.Empty, error) {
 	logger.Debug("OLT receives DeactivateONU()")
 	return new(openolt.Empty), nil
 }
 
+// DeleteOnu handles ONU deletion request from VOLTHA
 func (s *Server) DeleteOnu(c context.Context, onu *openolt.Onu) (*openolt.Empty, error) {
 	logger.Debug("OLT receives DeleteONU()")
+	Onu, err := s.GetOnuByID(onu.OnuId, onu.IntfId)
+	if err != nil {
+		return new(openolt.Empty), err
+	}
+
+	// Mark ONU internal state as ONU_FREE and reset onuID
+	Onu.InternalState = device.ONU_FREE
+	Onu.OnuID = 0
+
 	return new(openolt.Empty), nil
 }
 
+// OmciMsgOut receives OMCI messages from voltha
 func (s *Server) OmciMsgOut(c context.Context, msg *openolt.OmciMsg) (*openolt.Empty, error) {
 	logger.Debug("OLT %d receives OmciMsgOut to IF %v (ONU-ID: %v) pkt:%x.", s.Olt.ID, msg.IntfId, msg.OnuId, msg.Pkt)
+	// Get ONU state
+	onu, err := s.GetOnuByID(msg.OnuId, msg.IntfId)
+	if err != nil {
+		logger.Error("ONU not found intfID %d, onuID %d", msg.IntfId, msg.OnuId)
+		return new(openolt.Empty), err
+	}
+	state := onu.GetIntState()
+	logger.Debug("ONU-ID: %v, ONU state: %d", msg.OnuId, state)
+
+	// If ONU is ONU_INACTIVE or ONU_FREE do not send omci response
+	if state == device.ONU_INACTIVE || state == device.ONU_FREE {
+		logger.Info("ONU (IF %v ONU-ID: %v) is not ACTIVE, so not processing OmciMsg", msg.IntfId, msg.OnuId)
+		return new(openolt.Empty), nil
+	}
 	s.omciOut <- *msg
 	return new(openolt.Empty), nil
 }
 
 func (s *Server) OnuPacketOut(c context.Context, packet *openolt.OnuPacket) (*openolt.Empty, error) {
-	onu, _ := s.GetOnuByID(packet.OnuId, packet.IntfId)
+	onu, err := s.GetOnuByID(packet.OnuId, packet.IntfId)
+	if err != nil {
+		logger.Error("Failed in OnuPacketOut, %v", err)
+		return new(openolt.Empty), err
+	}
 	utils.LoggerWithOnu(onu).Debugf("OLT %d receives OnuPacketOut () to IF-ID:%d ONU-ID %d.", s.Olt.ID, packet.IntfId, packet.OnuId)
 	onuid := packet.OnuId
 	intfid := packet.IntfId
@@ -141,6 +184,7 @@
 	return new(openolt.Empty), nil
 }
 
+// FlowAdd method should handle flows addition to datapath for OLT and ONU
 func (s *Server) FlowAdd(c context.Context, flow *openolt.Flow) (*openolt.Empty, error) {
 	logger.Debug("OLT %d receives FlowAdd() IntfID:%d OnuID:%d EType:%x GemPortID:%d", s.Olt.ID, flow.AccessIntfId, flow.OnuId, flow.Classifier.EthType, flow.GemportId)
 	onu, err := s.GetOnuByID(uint32(flow.OnuId), uint32(flow.AccessIntfId))
@@ -166,6 +210,7 @@
 	return new(openolt.Empty), nil
 }
 
+// FlowRemove should handle flow deletion from datapath
 func (s *Server) FlowRemove(c context.Context, flow *openolt.Flow) (*openolt.Empty, error) {
 	onu, _ := s.GetOnuByID(uint32(flow.OnuId), uint32(flow.AccessIntfId))
 
@@ -194,6 +239,7 @@
 	return new(openolt.Empty), nil
 }
 
+// Reboot method handles reboot of OLT
 func (s *Server) Reboot(c context.Context, empty *openolt.Empty) (*openolt.Empty, error) {
 	logger.Debug("OLT %d receives Reboot ().", s.Olt.ID)
 	// Initialize OLT & Env
@@ -202,6 +248,7 @@
 	return new(openolt.Empty), nil
 }
 
+// EnableIndication starts sending indications for OLT and ONU
 func (s *Server) EnableIndication(empty *openolt.Empty, stream openolt.Openolt_EnableIndicationServer) error {
 	logger.Debug("OLT receives EnableInd.")
 	defer func() {
@@ -214,6 +261,7 @@
 	return nil
 }
 
+// NewGrpcServer starts openolt gRPC server
 func NewGrpcServer(addrport string) (l net.Listener, g *grpc.Server, e error) {
 	logger.Debug("Listening %s ...", addrport)
 	g = grpc.NewServer()