diff --git a/internal/pkg/core/openolt_groupmgr.go b/internal/pkg/core/openolt_groupmgr.go
new file mode 100644
index 0000000..d14d24b
--- /dev/null
+++ b/internal/pkg/core/openolt_groupmgr.go
@@ -0,0 +1,350 @@
+/*
+ * Copyright 2020-present Open Networking Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+//Package core provides the utility for olt devices, flows, groups and statistics
+package core
+
+import (
+	"context"
+	"github.com/opencord/voltha-lib-go/v3/pkg/flows"
+	"github.com/opencord/voltha-lib-go/v3/pkg/log"
+	"github.com/opencord/voltha-openolt-adapter/internal/pkg/olterrors"
+	rsrcMgr "github.com/opencord/voltha-openolt-adapter/internal/pkg/resourcemanager"
+	ofp "github.com/opencord/voltha-protos/v3/go/openflow_13"
+	openoltpb2 "github.com/opencord/voltha-protos/v3/go/openolt"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+	"sync"
+)
+
+//QueueInfoBrief has information about gemPortID and service priority associated with Mcast group
+type QueueInfoBrief struct {
+	gemPortID       uint32
+	servicePriority uint32
+}
+
+//OpenOltGroupMgr creates the Structure of OpenOltGroupMgr obj
+type OpenOltGroupMgr struct {
+	deviceHandler                *DeviceHandler
+	resourceMgr                  *rsrcMgr.OpenOltResourceMgr
+	interfaceToMcastQueueMap     map[uint32]*QueueInfoBrief /*pon interface -> multicast queue map. Required to assign GEM to a bucket during group population*/
+	interfaceToMcastQueueMapLock sync.RWMutex
+}
+
+//////////////////////////////////////////////
+//            EXPORTED FUNCTIONS            //
+//////////////////////////////////////////////
+
+//NewGroupManager creates OpenOltGroupMgr object and initializes the parameters
+func NewGroupManager(ctx context.Context, dh *DeviceHandler, rMgr *rsrcMgr.OpenOltResourceMgr) *OpenOltGroupMgr {
+	logger.Infow(ctx, "initializing-flow-manager", log.Fields{"device-id": dh.device.Id})
+	var grpMgr OpenOltGroupMgr
+	grpMgr.deviceHandler = dh
+	grpMgr.resourceMgr = rMgr
+	grpMgr.interfaceToMcastQueueMap = make(map[uint32]*QueueInfoBrief)
+	grpMgr.interfaceToMcastQueueMapLock = sync.RWMutex{}
+	logger.Info(ctx, "initialization-of-group-manager-success")
+	return &grpMgr
+}
+
+// AddGroup add or update the group
+func (g *OpenOltGroupMgr) AddGroup(ctx context.Context, group *ofp.OfpGroupEntry) error {
+	logger.Infow(ctx, "add-group", log.Fields{"group": group})
+	if group == nil {
+		return olterrors.NewErrInvalidValue(log.Fields{"group": group}, nil)
+	}
+	groupToOlt := openoltpb2.Group{
+		GroupId: group.Desc.GroupId,
+		Command: openoltpb2.Group_SET_MEMBERS,
+		Action:  g.buildGroupAction(),
+	}
+	logger.Debugw(ctx, "sending-group-to-device", log.Fields{"groupToOlt": groupToOlt})
+	_, err := g.deviceHandler.Client.PerformGroupOperation(ctx, &groupToOlt)
+	if err != nil {
+		return olterrors.NewErrAdapter("add-group-operation-failed", log.Fields{"groupToOlt": groupToOlt}, err)
+	}
+	// group members not created yet. So let's store the group
+	if err := g.resourceMgr.AddFlowGroupToKVStore(ctx, group, true); err != nil {
+		return olterrors.NewErrPersistence("add", "flow-group", group.Desc.GroupId, log.Fields{"group": group}, err)
+	}
+	logger.Infow(ctx, "add-group-operation-performed-on-the-device-successfully ", log.Fields{"groupToOlt": groupToOlt})
+	return nil
+}
+
+// DeleteGroup deletes a group from the device
+func (g *OpenOltGroupMgr) DeleteGroup(ctx context.Context, group *ofp.OfpGroupEntry) error {
+	logger.Debugw(ctx, "delete-group", log.Fields{"group": group})
+	if group == nil {
+		logger.Error(ctx, "unable-to-delete-group--invalid-argument--group-is-nil")
+		return olterrors.NewErrInvalidValue(log.Fields{"group": group}, nil)
+	}
+	groupToOlt := openoltpb2.Group{
+		GroupId: group.Desc.GroupId,
+	}
+	logger.Debugw(ctx, "deleting-group-from-device", log.Fields{"groupToOlt": groupToOlt})
+	_, err := g.deviceHandler.Client.DeleteGroup(ctx, &groupToOlt)
+	if err != nil {
+		logger.Errorw(ctx, "delete-group-failed-on-dev", log.Fields{"groupToOlt": groupToOlt, "err": err})
+		return olterrors.NewErrAdapter("delete-group-operation-failed", log.Fields{"groupToOlt": groupToOlt}, err)
+	}
+	//remove group from the store
+	if err := g.resourceMgr.RemoveFlowGroupFromKVStore(ctx, group.Desc.GroupId, false); err != nil {
+		return olterrors.NewErrPersistence("delete", "flow-group", group.Desc.GroupId, log.Fields{"group": group}, err)
+	}
+	logger.Debugw(ctx, "delete-group-operation-performed-on-the-device-successfully ", log.Fields{"groupToOlt": groupToOlt})
+	return nil
+}
+
+// ModifyGroup updates the group
+func (g *OpenOltGroupMgr) ModifyGroup(ctx context.Context, group *ofp.OfpGroupEntry) error {
+	logger.Infow(ctx, "modify-group", log.Fields{"group": group})
+	if group == nil || group.Desc == nil {
+		return olterrors.NewErrInvalidValue(log.Fields{"group": group}, nil)
+	}
+	newGroup := g.buildGroup(ctx, group.Desc.GroupId, group.Desc.Buckets)
+	//get existing members of the group
+	val, groupExists, err := g.getFlowGroupFromKVStore(ctx, group.Desc.GroupId, false)
+	if err != nil {
+		return olterrors.NewErrNotFound("flow-group-in-kv-store", log.Fields{"groupId": group.Desc.GroupId}, err)
+	}
+	var current *openoltpb2.Group // represents the group on the device
+	if groupExists {
+		// group already exists
+		current = g.buildGroup(ctx, group.Desc.GroupId, val.Desc.GetBuckets())
+		logger.Debugw(ctx, "modify-group--group exists",
+			log.Fields{
+				"group on the device": val,
+				"new":                 group})
+	} else {
+		current = g.buildGroup(ctx, group.Desc.GroupId, nil)
+	}
+	logger.Debugw(ctx, "modify-group--comparing-current-and-new",
+		log.Fields{
+			"group on the device": current,
+			"new":                 newGroup})
+	// get members to be added
+	membersToBeAdded := g.findDiff(current, newGroup)
+	// get members to be removed
+	membersToBeRemoved := g.findDiff(newGroup, current)
+	logger.Infow(ctx, "modify-group--differences found", log.Fields{
+		"membersToBeAdded":   membersToBeAdded,
+		"membersToBeRemoved": membersToBeRemoved,
+		"groupId":            group.Desc.GroupId})
+	groupToOlt := openoltpb2.Group{
+		GroupId: group.Desc.GroupId,
+	}
+	var errAdd, errRemoved error
+	if len(membersToBeAdded) > 0 {
+		groupToOlt.Command = openoltpb2.Group_ADD_MEMBERS
+		groupToOlt.Members = membersToBeAdded
+		//execute addMembers
+		errAdd = g.callGroupAddRemove(ctx, &groupToOlt)
+	}
+	if len(membersToBeRemoved) > 0 {
+		groupToOlt.Command = openoltpb2.Group_REMOVE_MEMBERS
+		groupToOlt.Members = membersToBeRemoved
+		//execute removeMembers
+		errRemoved = g.callGroupAddRemove(ctx, &groupToOlt)
+	}
+	//save the modified group
+	if errAdd == nil && errRemoved == nil {
+		if err := g.resourceMgr.AddFlowGroupToKVStore(ctx, group, false); err != nil {
+			return olterrors.NewErrPersistence("add", "flow-group", group.Desc.GroupId, log.Fields{"group": group}, err)
+		}
+		logger.Infow(ctx, "modify-group-was-success--storing-group",
+			log.Fields{
+				"group":         group,
+				"existingGroup": current})
+	} else {
+		logger.Warnw(ctx, "one-of-the-group-add/remove-operations-failed--cannot-save-group-modifications",
+			log.Fields{"group": group})
+		if errAdd != nil {
+			return errAdd
+		}
+		return errRemoved
+	}
+	return nil
+}
+
+//LoadInterfaceToMulticastQueueMap reads multicast queues per interface from the KV store
+//and put them into interfaceToMcastQueueMap.
+func (g *OpenOltGroupMgr) LoadInterfaceToMulticastQueueMap(ctx context.Context) {
+	storedMulticastQueueMap, err := g.resourceMgr.GetMcastQueuePerInterfaceMap(ctx)
+	if err != nil {
+		logger.Error(ctx, "failed-to-get-pon-interface-to-multicast-queue-map")
+		return
+	}
+	for intf, queueInfo := range storedMulticastQueueMap {
+		q := QueueInfoBrief{
+			gemPortID:       queueInfo[0],
+			servicePriority: queueInfo[1],
+		}
+		g.interfaceToMcastQueueMap[intf] = &q
+	}
+}
+
+//GetInterfaceToMcastQueueMap gets the mcast queue mapped to to the PON interface
+func (g *OpenOltGroupMgr) GetInterfaceToMcastQueueMap(intfID uint32) (*QueueInfoBrief, bool) {
+	g.interfaceToMcastQueueMapLock.RLock()
+	defer g.interfaceToMcastQueueMapLock.RUnlock()
+	val, present := g.interfaceToMcastQueueMap[intfID]
+	return val, present
+}
+
+//UpdateInterfaceToMcastQueueMap updates the mcast queue information mapped to a given PON interface
+func (g *OpenOltGroupMgr) UpdateInterfaceToMcastQueueMap(intfID uint32, val *QueueInfoBrief) {
+	g.interfaceToMcastQueueMapLock.Lock()
+	defer g.interfaceToMcastQueueMapLock.Unlock()
+	g.interfaceToMcastQueueMap[intfID] = val
+}
+
+////////////////////////////////////////////////
+//      INTERNAL or UNEXPORTED FUNCTIONS      //
+////////////////////////////////////////////////
+//getFlowGroupFromKVStore fetches and returns flow group from the KV store. Returns (nil, false, error) if any problem occurs during
+//fetching the data. Returns (group, true, nil) if the group is fetched and returned successfully.
+//Returns (nil, false, nil) if the group does not exists in the KV store.
+func (g *OpenOltGroupMgr) getFlowGroupFromKVStore(ctx context.Context, groupID uint32, cached bool) (*ofp.OfpGroupEntry, bool, error) {
+	exists, groupInfo, err := g.resourceMgr.GetFlowGroupFromKVStore(ctx, groupID, cached)
+	if err != nil {
+		return nil, false, olterrors.NewErrNotFound("flow-group", log.Fields{"group-id": groupID}, err)
+	}
+	if exists {
+		return newGroup(groupInfo.GroupID, groupInfo.OutPorts), exists, nil
+	}
+	return nil, exists, nil
+}
+func newGroup(groupID uint32, outPorts []uint32) *ofp.OfpGroupEntry {
+	groupDesc := ofp.OfpGroupDesc{
+		Type:    ofp.OfpGroupType_OFPGT_ALL,
+		GroupId: groupID,
+	}
+	groupEntry := ofp.OfpGroupEntry{
+		Desc: &groupDesc,
+	}
+	for i := 0; i < len(outPorts); i++ {
+		var acts []*ofp.OfpAction
+		acts = append(acts, flows.Output(outPorts[i]))
+		bucket := ofp.OfpBucket{
+			Actions: acts,
+		}
+		groupDesc.Buckets = append(groupDesc.Buckets, &bucket)
+	}
+	return &groupEntry
+}
+
+//buildGroupAction creates and returns a group action
+func (g *OpenOltGroupMgr) buildGroupAction() *openoltpb2.Action {
+	var actionCmd openoltpb2.ActionCmd
+	var action openoltpb2.Action
+	action.Cmd = &actionCmd
+	//pop outer vlan
+	action.Cmd.RemoveOuterTag = true
+	return &action
+}
+
+//callGroupAddRemove performs add/remove buckets operation for the indicated group
+func (g *OpenOltGroupMgr) callGroupAddRemove(ctx context.Context, group *openoltpb2.Group) error {
+	if err := g.performGroupOperation(ctx, group); err != nil {
+		st, _ := status.FromError(err)
+		//ignore already exists error code
+		if st.Code() != codes.AlreadyExists {
+			return olterrors.NewErrGroupOp("groupAddRemove", group.GroupId, log.Fields{"status": st}, err)
+		}
+	}
+	return nil
+}
+
+//findDiff compares group members and finds members which only exists in groups2
+func (g *OpenOltGroupMgr) findDiff(group1 *openoltpb2.Group, group2 *openoltpb2.Group) []*openoltpb2.GroupMember {
+	var members []*openoltpb2.GroupMember
+	for _, bucket := range group2.Members {
+		if !g.contains(group1.Members, bucket) {
+			// bucket does not exist and must be added
+			members = append(members, bucket)
+		}
+	}
+	return members
+}
+
+//contains returns true if the members list contains the given member; false otherwise
+func (g *OpenOltGroupMgr) contains(members []*openoltpb2.GroupMember, member *openoltpb2.GroupMember) bool {
+	for _, groupMember := range members {
+		if groupMember.InterfaceId == member.InterfaceId {
+			return true
+		}
+	}
+	return false
+}
+
+//performGroupOperation call performGroupOperation operation of openolt proto
+func (g *OpenOltGroupMgr) performGroupOperation(ctx context.Context, group *openoltpb2.Group) error {
+	logger.Debugw(ctx, "sending-group-to-device",
+		log.Fields{
+			"groupToOlt": group,
+			"command":    group.Command})
+	_, err := g.deviceHandler.Client.PerformGroupOperation(log.WithSpanFromContext(context.Background(), ctx), group)
+	if err != nil {
+		return olterrors.NewErrAdapter("group-operation-failed", log.Fields{"groupToOlt": group}, err)
+	}
+	return nil
+}
+
+//buildGroup build openoltpb2.Group from given group id and bucket list
+func (g *OpenOltGroupMgr) buildGroup(ctx context.Context, groupID uint32, buckets []*ofp.OfpBucket) *openoltpb2.Group {
+	group := openoltpb2.Group{
+		GroupId: groupID}
+	// create members of the group
+	for _, ofBucket := range buckets {
+		member := g.buildMember(ctx, ofBucket)
+		if member != nil && !g.contains(group.Members, member) {
+			group.Members = append(group.Members, member)
+		}
+	}
+	return &group
+}
+
+//buildMember builds openoltpb2.GroupMember from an OpenFlow bucket
+func (g *OpenOltGroupMgr) buildMember(ctx context.Context, ofBucket *ofp.OfpBucket) *openoltpb2.GroupMember {
+	var outPort uint32
+	outPortFound := false
+	for _, ofAction := range ofBucket.Actions {
+		if ofAction.Type == ofp.OfpActionType_OFPAT_OUTPUT {
+			outPort = ofAction.GetOutput().Port
+			outPortFound = true
+		}
+	}
+	if !outPortFound {
+		logger.Debugw(ctx, "bucket-skipped-since-no-out-port-found-in-it", log.Fields{"ofBucket": ofBucket})
+		return nil
+	}
+	interfaceID := IntfIDFromUniPortNum(outPort)
+	logger.Debugw(ctx, "got-associated-interface-id-of-the-port",
+		log.Fields{
+			"portNumber:":  outPort,
+			"interfaceId:": interfaceID})
+	g.interfaceToMcastQueueMapLock.RLock()
+	defer g.interfaceToMcastQueueMapLock.RUnlock()
+	if groupInfo, ok := g.interfaceToMcastQueueMap[interfaceID]; ok {
+		member := openoltpb2.GroupMember{
+			InterfaceId:   interfaceID,
+			InterfaceType: openoltpb2.GroupMember_PON,
+			GemPortId:     groupInfo.gemPortID,
+			Priority:      groupInfo.servicePriority,
+		}
+		//add member to the group
+		return &member
+	}
+	logger.Warnf(ctx, "bucket-skipped-since-interface-2-gem-mapping-cannot-be-found", log.Fields{"ofBucket": ofBucket})
+	return nil
+}