diff --git a/gtpv2/ie/ambr.go b/gtpv2/ie/ambr.go
index c9a730a3..6911cadb 100644
--- a/gtpv2/ie/ambr.go
+++ b/gtpv2/ie/ambr.go
@@ -11,9 +11,6 @@ import (
 
 // NewAggregateMaximumBitRate creates a new AggregateMaximumBitRate IE.
 func NewAggregateMaximumBitRate(up, down uint32) *IE {
-	// this is more efficient but removed for consistency with other structured IEs.
-	// return newUint64ValIE(AggregateMaximumBitRate, (uint64(up)<<32 | uint64(down)))
-
 	v := NewAggregateMaximumBitRateFields(up, down)
 	b, err := v.Marshal()
 	if err != nil {
diff --git a/gtpv2/ie/apn-restriction.go b/gtpv2/ie/apn-restriction.go
index f55e091c..98b21688 100644
--- a/gtpv2/ie/apn-restriction.go
+++ b/gtpv2/ie/apn-restriction.go
@@ -4,11 +4,9 @@
 
 package ie
 
-import "io"
-
 // NewAPNRestriction creates a new APNRestriction IE.
 func NewAPNRestriction(restriction uint8) *IE {
-	return newUint8ValIE(APNRestriction, restriction)
+	return NewUint8IE(APNRestriction, restriction)
 }
 
 // APNRestriction returns APNRestriction in uint8 if the type of IE matches.
@@ -17,11 +15,7 @@ func (i *IE) APNRestriction() (uint8, error) {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
 
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustAPNRestriction returns APNRestriction in uint8, ignoring errors.
@@ -30,3 +24,8 @@ func (i *IE) MustAPNRestriction() uint8 {
 	v, _ := i.APNRestriction()
 	return v
 }
+
+// RestrictionType returns RestrictionType in uint8 if the type of IE matches.
+func (i *IE) RestrictionType() (uint8, error) {
+	return i.APNRestriction()
+}
diff --git a/gtpv2/ie/apn.go b/gtpv2/ie/apn.go
index 520ed063..e49afbdb 100644
--- a/gtpv2/ie/apn.go
+++ b/gtpv2/ie/apn.go
@@ -4,22 +4,9 @@
 
 package ie
 
-import (
-	"strings"
-)
-
 // NewAccessPointName creates a new AccessPointName IE.
 func NewAccessPointName(apn string) *IE {
-	i := New(AccessPointName, 0x00, make([]byte, len(apn)+1))
-	var offset = 0
-	for _, label := range strings.Split(apn, ".") {
-		l := len(label)
-		i.Payload[offset] = uint8(l)
-		copy(i.Payload[offset+1:], label)
-		offset += l + 1
-	}
-
-	return i
+	return NewFQDNIE(AccessPointName, apn)
 }
 
 // AccessPointName returns AccessPointName in string if the type of IE matches.
@@ -27,25 +14,7 @@ func (i *IE) AccessPointName() (string, error) {
 	if i.Type != AccessPointName {
 		return "", &InvalidTypeError{Type: i.Type}
 	}
-
-	var (
-		apn    []string
-		offset int
-	)
-	max := len(i.Payload)
-	for {
-		if offset >= max {
-			break
-		}
-		l := int(i.Payload[offset])
-		if offset+l+1 > max {
-			break
-		}
-		apn = append(apn, string(i.Payload[offset+1:offset+l+1]))
-		offset += l + 1
-	}
-
-	return strings.Join(apn, "."), nil
+	return i.ValueAsFQDN()
 }
 
 // MustAccessPointName returns AccessPointName in string, ignoring errors.
diff --git a/gtpv2/ie/arp.go b/gtpv2/ie/arp.go
index a4c02380..0525692e 100644
--- a/gtpv2/ie/arp.go
+++ b/gtpv2/ie/arp.go
@@ -4,8 +4,6 @@
 
 package ie
 
-import "io"
-
 // NewAllocationRetensionPriority creates a new AllocationRetensionPriority IE.
 func NewAllocationRetensionPriority(pci, pl, pvi uint8) *IE {
 	i := New(AllocationRetensionPriority, 0x00, make([]byte, 1))
@@ -13,15 +11,12 @@ func NewAllocationRetensionPriority(pci, pl, pvi uint8) *IE {
 	return i
 }
 
+// AllocationRetensionPriority returns AllocationRetensionPriority in uint8 if the type of IE matches.
 func (i *IE) AllocationRetensionPriority() (uint8, error) {
 	if i.Type != AllocationRetensionPriority {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // HasPVI reports whether an IE has PVI bit.
diff --git a/gtpv2/ie/bearer-context.go b/gtpv2/ie/bearer-context.go
index be858b62..2834f69b 100644
--- a/gtpv2/ie/bearer-context.go
+++ b/gtpv2/ie/bearer-context.go
@@ -8,13 +8,7 @@ import "io"
 
 // NewBearerContext creates a new BearerContext IE.
 func NewBearerContext(ies ...*IE) *IE {
-	var omitted []*IE
-	for _, ie := range ies {
-		if ie != nil {
-			omitted = append(omitted, ie)
-		}
-	}
-	return newGroupedIE(BearerContext, omitted...)
+	return NewGroupedIE(BearerContext, ies...)
 }
 
 // NewBearerContextWithinCreateBearerRequest creates a new BearerContext used within CreateBearerRequest.
diff --git a/gtpv2/ie/bearer-flags.go b/gtpv2/ie/bearer-flags.go
index d5ea51ee..a8586807 100644
--- a/gtpv2/ie/bearer-flags.go
+++ b/gtpv2/ie/bearer-flags.go
@@ -4,11 +4,6 @@
 
 package ie
 
-import (
-	"fmt"
-	"io"
-)
-
 // NewBearerFlags creates a new BearerFlags IE.
 func NewBearerFlags(asi, vInd, vb, ppc uint8) *IE {
 	i := New(BearerFlags, 0x00, make([]byte, 1))
@@ -20,15 +15,11 @@ func NewBearerFlags(asi, vInd, vb, ppc uint8) *IE {
 func (i *IE) BearerFlags() (uint8, error) {
 	switch i.Type {
 	case BearerFlags:
-		if len(i.Payload) < 1 {
-			return 0, io.ErrUnexpectedEOF
-		}
-
-		return i.Payload[0], nil
+		return i.ValueAsUint8()
 	case BearerContext:
 		ies, err := i.BearerContext()
 		if err != nil {
-			return 0, fmt.Errorf("failed to retrieve BearerFlags: %w", err)
+			return 0, err
 		}
 
 		for _, child := range ies {
@@ -92,54 +83,38 @@ func (i *IE) HasASI() bool {
 // ActivityStatusIndicator reports whether the bearer context is preserved in
 // the CN without corresponding Radio Access Bearer established.
 func (i *IE) ActivityStatusIndicator() bool {
-	if len(i.Payload) < 1 {
-		return false
-	}
-	switch i.Type {
-	case BearerFlags:
-		return i.Payload[0]&0x08 == 1
-	default:
+	v, err := i.BearerFlags()
+	if err != nil {
 		return false
 	}
+	return v&0x08 == 1
 }
 
 // VSRVCC reports whether this bearer is an IMS video bearer and is candidate
 // for PS-to-CS vSRVCC handover.
 func (i *IE) VSRVCC() bool {
-	if len(i.Payload) < 1 {
-		return false
-	}
-	switch i.Type {
-	case BearerFlags:
-		return i.Payload[0]&0x04 == 1
-	default:
+	v, err := i.BearerFlags()
+	if err != nil {
 		return false
 	}
+	return v&0x04 == 1
 }
 
 // VoiceBearer reports whether a voice bearer when doing PS-to-CS (v)SRVCC handover.
 func (i *IE) VoiceBearer() bool {
-	if len(i.Payload) < 1 {
-		return false
-	}
-	switch i.Type {
-	case BearerFlags:
-		return i.Payload[0]&0x02 == 1
-	default:
+	v, err := i.BearerFlags()
+	if err != nil {
 		return false
 	}
+	return v&0x02 == 1
 }
 
 // ProhibitPayloadCompression reports whether an SGSN should attempt to
 // compress the payload of user data when the users asks for it to be compressed.
 func (i *IE) ProhibitPayloadCompression() bool {
-	if len(i.Payload) < 1 {
-		return false
-	}
-	switch i.Type {
-	case BearerFlags:
-		return i.Payload[0]&0x01 == 1
-	default:
+	v, err := i.BearerFlags()
+	if err != nil {
 		return false
 	}
+	return v&0x01 == 1
 }
diff --git a/gtpv2/ie/bearer-qos.go b/gtpv2/ie/bearer-qos.go
index ddc1e105..52f57b8c 100644
--- a/gtpv2/ie/bearer-qos.go
+++ b/gtpv2/ie/bearer-qos.go
@@ -134,10 +134,7 @@ func (i *IE) QCILabel() (uint8, error) {
 		}
 		return i.Payload[1], nil
 	case FlowQoS:
-		if len(i.Payload) < 1 {
-			return 0, io.ErrUnexpectedEOF
-		}
-		return i.Payload[0], nil
+		return i.ValueAsUint8()
 	default:
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
diff --git a/gtpv2/ie/cause.go b/gtpv2/ie/cause.go
index 65e15e98..a32fbbea 100644
--- a/gtpv2/ie/cause.go
+++ b/gtpv2/ie/cause.go
@@ -28,11 +28,7 @@ func NewCause(cause uint8, pce, bce, cs uint8, offendingIE *IE) *IE {
 func (i *IE) Cause() (uint8, error) {
 	switch i.Type {
 	case Cause:
-		if len(i.Payload) < 1 {
-			return 0, io.ErrUnexpectedEOF
-		}
-
-		return i.Payload[0], nil
+		return i.ValueAsUint8()
 	case BearerContext:
 		ies, err := i.BearerContext()
 		if err != nil {
diff --git a/gtpv2/ie/charging-characteristics.go b/gtpv2/ie/charging-characteristics.go
index 48a9f011..5eb5fbf0 100644
--- a/gtpv2/ie/charging-characteristics.go
+++ b/gtpv2/ie/charging-characteristics.go
@@ -4,14 +4,9 @@
 
 package ie
 
-import (
-	"encoding/binary"
-	"io"
-)
-
 // NewChargingCharacteristics creates a new ChargingCharacteristics IE.
 func NewChargingCharacteristics(chr uint16) *IE {
-	return newUint16ValIE(ChargingCharacteristics, chr)
+	return NewUint16IE(ChargingCharacteristics, chr)
 }
 
 // ChargingCharacteristics returns the ChargingCharacteristics value in uint16 if the type of IE matches.
@@ -19,11 +14,7 @@ func (i *IE) ChargingCharacteristics() (uint16, error) {
 	if i.Type != ChargingCharacteristics {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 2 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return binary.BigEndian.Uint16(i.Payload), nil
+	return i.ValueAsUint16()
 }
 
 // MustChargingCharacteristics returns ChargingCharacteristics in uint16, ignoring errors.
diff --git a/gtpv2/ie/charging-id.go b/gtpv2/ie/charging-id.go
index a018c48c..2942f4aa 100644
--- a/gtpv2/ie/charging-id.go
+++ b/gtpv2/ie/charging-id.go
@@ -4,30 +4,20 @@
 
 package ie
 
-import (
-	"encoding/binary"
-	"fmt"
-	"io"
-)
-
 // NewChargingID creates a new ChargingID IE.
 func NewChargingID(id uint32) *IE {
-	return newUint32ValIE(ChargingID, id)
+	return NewUint32IE(ChargingID, id)
 }
 
 // ChargingID returns the ChargingID value in uint32 if the type of IE matches.
 func (i *IE) ChargingID() (uint32, error) {
 	switch i.Type {
 	case ChargingID:
-		if len(i.Payload) < 4 {
-			return 0, io.ErrUnexpectedEOF
-		}
-
-		return binary.BigEndian.Uint32(i.Payload[:4]), nil
+		return i.ValueAsUint32()
 	case BearerContext:
 		ies, err := i.BearerContext()
 		if err != nil {
-			return 0, fmt.Errorf("failed to retrieve ChargingID: %w", err)
+			return 0, err
 		}
 
 		for _, child := range ies {
diff --git a/gtpv2/ie/cmi.go b/gtpv2/ie/cmi.go
index df3c3221..eb60c4dc 100644
--- a/gtpv2/ie/cmi.go
+++ b/gtpv2/ie/cmi.go
@@ -8,23 +8,19 @@ import "io"
 
 // NewCSGMembershipIndication creates a new CSGMembershipIndication IE.
 func NewCSGMembershipIndication(cmi uint8) *IE {
-	return newUint8ValIE(CSGMembershipIndication, cmi)
+	return NewUint8IE(CSGMembershipIndication, cmi)
 }
 
 // CMI returns CMI in uint8 if the type of IE matches.
 func (i *IE) CMI() (uint8, error) {
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
 	switch i.Type {
 	case CSGMembershipIndication:
-		return i.Payload[0] & 0x01, nil
+		return i.ValueAsUint8()
 	case UserCSGInformation:
 		if len(i.Payload) < 8 {
 			return 0, io.ErrUnexpectedEOF
 		}
-		return i.Payload[7] & 0x01, nil
+		return i.Payload[7], nil
 	default:
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
diff --git a/gtpv2/ie/csg-id.go b/gtpv2/ie/csg-id.go
index 0e9fbf4f..b0e558a6 100644
--- a/gtpv2/ie/csg-id.go
+++ b/gtpv2/ie/csg-id.go
@@ -11,18 +11,14 @@ import (
 
 // NewCSGID creates a new CSGID IE.
 func NewCSGID(id uint32) *IE {
-	return newUint32ValIE(CSGID, id&0x7ffffff)
+	return NewUint32IE(CSGID, id&0x7ffffff)
 }
 
 // CSGID returns CSGID in uint32 if the type of IE matches.
 func (i *IE) CSGID() (uint32, error) {
-	if len(i.Payload) < 4 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
 	switch i.Type {
 	case CSGID:
-		return binary.BigEndian.Uint32(i.Payload[0:4]) & 0x7ffffff, nil
+		return i.ValueAsUint32()
 	case UserCSGInformation:
 		if len(i.Payload) < 7 {
 			return 0, io.ErrUnexpectedEOF
diff --git a/gtpv2/ie/delay-value.go b/gtpv2/ie/delay-value.go
index de0b531f..35b8a76f 100644
--- a/gtpv2/ie/delay-value.go
+++ b/gtpv2/ie/delay-value.go
@@ -11,10 +11,20 @@ import (
 
 // NewDelayValue creates a new DelayValue IE.
 func NewDelayValue(delay time.Duration) *IE {
-	return newUint8ValIE(DelayValue, uint8(delay.Seconds()*1000/50))
+	return NewUint8IE(DelayValue, uint8(delay.Seconds()*1000/50))
+}
+
+// NewDelayValueRaw creates a new DelayValue IE from a uint8 value.
+//
+// The value should be in multiples of 50ms or zero.
+func NewDelayValueRaw(delay uint8) *IE {
+	return NewUint8IE(DelayValue, delay)
 }
 
 // DelayValue returns DelayValue in time.Duration if the type of IE matches.
+//
+// The returned value is in time.Duration. To get the value in multiples of 50ms,
+// use ValueAsUint8 or access Payload field directly instead.
 func (i *IE) DelayValue() (time.Duration, error) {
 	if i.Type != DelayValue {
 		return 0, &InvalidTypeError{Type: i.Type}
diff --git a/gtpv2/ie/detach-type.go b/gtpv2/ie/detach-type.go
index e20f4ae7..ac83cda0 100644
--- a/gtpv2/ie/detach-type.go
+++ b/gtpv2/ie/detach-type.go
@@ -4,13 +4,9 @@
 
 package ie
 
-import (
-	"io"
-)
-
 // NewDetachType creates a new DetachType IE.
 func NewDetachType(dtype uint8) *IE {
-	return newUint8ValIE(DetachType, dtype)
+	return NewUint8IE(DetachType, dtype)
 }
 
 // DetachType returns DetachType in uint8 if the type of IE matches.
@@ -18,11 +14,7 @@ func (i *IE) DetachType() (uint8, error) {
 	if i.Type != DetachType {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustDetachType returns DetachType in uint8, ignoring errors.
diff --git a/gtpv2/ie/ebi.go b/gtpv2/ie/ebi.go
index 9fc35a78..4af88615 100644
--- a/gtpv2/ie/ebi.go
+++ b/gtpv2/ie/ebi.go
@@ -4,29 +4,20 @@
 
 package ie
 
-import (
-	"fmt"
-	"io"
-)
-
 // NewEPSBearerID creates a new EPSBearerID IE.
 func NewEPSBearerID(ebi uint8) *IE {
-	return newUint8ValIE(EPSBearerID, ebi&0x0f)
+	return NewUint8IE(EPSBearerID, ebi&0x0f)
 }
 
 // EPSBearerID returns EPSBearerID if the type of IE matches.
 func (i *IE) EPSBearerID() (uint8, error) {
 	switch i.Type {
 	case EPSBearerID:
-		if len(i.Payload) < 1 {
-			return 0, io.ErrUnexpectedEOF
-		}
-
-		return i.Payload[0], nil
+		return i.ValueAsUint8()
 	case BearerContext:
 		ies, err := i.BearerContext()
 		if err != nil {
-			return 0, fmt.Errorf("failed to retrieve EPSBearerID: %w", err)
+			return 0, err
 		}
 
 		for _, child := range ies {
diff --git a/gtpv2/ie/epc-timer.go b/gtpv2/ie/epc-timer.go
index fe83079e..13897e8d 100644
--- a/gtpv2/ie/epc-timer.go
+++ b/gtpv2/ie/epc-timer.go
@@ -11,7 +11,7 @@ import (
 	"time"
 )
 
-// NewEPCTimer creates a new Timer IE.
+// NewEPCTimer creates a new EPCTimer IE.
 func NewEPCTimer(duration time.Duration) *IE {
 	// 8.87 EPC Timer
 	// Timer unit
@@ -49,10 +49,18 @@ func NewEPCTimer(duration time.Duration) *IE {
 		value = 0
 	}
 
-	return newUint8ValIE(EPCTimer, unit+(value&0x1f))
+	return NewUint8IE(EPCTimer, unit+(value&0x1f))
+}
+
+// NewEPCTimerRaw creates a new EPCTimer IE from a uint8 value.
+func NewEPCTimerRaw(duration uint8) *IE {
+	return NewUint8IE(EPCTimer, duration)
 }
 
 // EPCTimer returns EPCTimer in time.Duration if the type of IE matches.
+//
+// The returned value is in time.Duration. To get the raw value as uint8,
+// use ValueAsUint8 or access Payload field directly instead.
 func (i *IE) EPCTimer() (time.Duration, error) {
 	return i.Timer()
 }
diff --git a/gtpv2/ie/fqdn.go b/gtpv2/ie/fqdn.go
index 95312b55..d20dcf00 100644
--- a/gtpv2/ie/fqdn.go
+++ b/gtpv2/ie/fqdn.go
@@ -4,22 +4,9 @@
 
 package ie
 
-import (
-	"strings"
-)
-
 // NewFullyQualifiedDomainName creates a new FullyQualifiedDomainName IE.
 func NewFullyQualifiedDomainName(fqdn string) *IE {
-	i := New(FullyQualifiedDomainName, 0x00, make([]byte, len(fqdn)+1))
-	var offset = 0
-	for _, label := range strings.Split(fqdn, ".") {
-		l := len(label)
-		i.Payload[offset] = uint8(l)
-		copy(i.Payload[offset+1:], label)
-		offset += l + 1
-	}
-
-	return i
+	return NewFQDNIE(FullyQualifiedDomainName, fqdn)
 }
 
 // FullyQualifiedDomainName returns FullyQualifiedDomainName in string if the type of IE matches.
@@ -27,25 +14,7 @@ func (i *IE) FullyQualifiedDomainName() (string, error) {
 	if i.Type != FullyQualifiedDomainName {
 		return "", &InvalidTypeError{Type: i.Type}
 	}
-
-	var (
-		fqdn   []string
-		offset int
-	)
-	max := len(i.Payload)
-	for {
-		if offset >= max {
-			break
-		}
-		l := int(i.Payload[offset])
-		if offset+l+1 > max {
-			break
-		}
-		fqdn = append(fqdn, string(i.Payload[offset+1:offset+l+1]))
-		offset += l + 1
-	}
-
-	return strings.Join(fqdn, "."), nil
+	return i.ValueAsFQDN()
 }
 
 // MustFullyQualifiedDomainName returns FullyQualifiedDomainName in string, ignoring errors.
diff --git a/gtpv2/ie/hop-counter.go b/gtpv2/ie/hop-counter.go
index eb572771..6b79cb61 100644
--- a/gtpv2/ie/hop-counter.go
+++ b/gtpv2/ie/hop-counter.go
@@ -4,11 +4,9 @@
 
 package ie
 
-import "io"
-
 // NewHopCounter creates a new HopCounter IE.
 func NewHopCounter(hop uint8) *IE {
-	return newUint8ValIE(HopCounter, hop)
+	return NewUint8IE(HopCounter, hop)
 }
 
 // HopCounter returns HopCounter in uint8 if the type of IE matches.
@@ -16,11 +14,7 @@ func (i *IE) HopCounter() (uint8, error) {
 	if i.Type != HopCounter {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustHopCounter returns HopCounter in uint8, ignoring errors.
diff --git a/gtpv2/ie/ie.go b/gtpv2/ie/ie.go
index fe2333a6..9e6bdd06 100644
--- a/gtpv2/ie/ie.go
+++ b/gtpv2/ie/ie.go
@@ -11,6 +11,8 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
+
+	"github.com/wmnsk/go-gtp/utils"
 )
 
 // IE definitions.
@@ -321,90 +323,6 @@ func (i *IE) String() string {
 	)
 }
 
-var grouped = []uint8{
-	BearerContext,
-	PDNConnection,
-	OverloadControlInformation,
-	LoadControlInformation,
-	RemoteUEContext,
-	SCEFPDNConnection,
-	V2XContext,
-	PC5QoSParameters,
-}
-
-// IsGrouped reports whether an IE is grouped type or not.
-func (i *IE) IsGrouped() bool {
-	for _, itype := range grouped {
-		if i.Type == itype {
-			return true
-		}
-	}
-	return false
-}
-
-// Add adds variable number of IEs to a IE if the IE is grouped type and update length.
-// Otherwise, this does nothing(no errors).
-func (i *IE) Add(ies ...*IE) {
-	if !i.IsGrouped() {
-		return
-	}
-
-	i.Payload = nil
-	i.ChildIEs = append(i.ChildIEs, ies...)
-	for _, ie := range i.ChildIEs {
-		serialized, err := ie.Marshal()
-		if err != nil {
-			continue
-		}
-		i.Payload = append(i.Payload, serialized...)
-	}
-	i.SetLength()
-}
-
-// Remove removes an IE looked up by type and instance.
-func (i *IE) Remove(typ, instance uint8) {
-	if !i.IsGrouped() {
-		return
-	}
-
-	i.Payload = nil
-	newChildren := make([]*IE, len(i.ChildIEs))
-	idx := 0
-	for _, ie := range i.ChildIEs {
-		if ie.Type == typ && ie.Instance() == instance {
-			newChildren = newChildren[:len(newChildren)-1]
-			continue
-		}
-		newChildren[idx] = ie
-		idx++
-
-		serialized, err := ie.Marshal()
-		if err != nil {
-			continue
-		}
-		i.Payload = append(i.Payload, serialized...)
-	}
-	i.ChildIEs = newChildren
-	i.SetLength()
-}
-
-// FindByType returns IE looked up by type and instance.
-//
-// The program may be slower when calling this method multiple times
-// because this ranges over a ChildIEs each time it is called.
-func (i *IE) FindByType(typ, instance uint8) (*IE, error) {
-	if !i.IsGrouped() {
-		return nil, ErrInvalidType
-	}
-
-	for _, ie := range i.ChildIEs {
-		if ie.Type == typ && ie.Instance() == instance {
-			return ie, nil
-		}
-	}
-	return nil, ErrIENotFound
-}
-
 // ParseMultiIEs decodes multiple IEs at a time.
 // This is easy and useful but slower than decoding one by one.
 // When you don't know the number of IEs, this is the only way to decode them.
@@ -426,46 +344,106 @@ func ParseMultiIEs(b []byte) ([]*IE, error) {
 	return ies, nil
 }
 
-func newUint8ValIE(t, v uint8) *IE {
+// NewUint8IE creates a new IE with uint8 value.
+func NewUint8IE(t, v uint8) *IE {
 	return New(t, 0x00, []byte{v})
 }
 
-func newUint16ValIE(t uint8, v uint16) *IE {
+// NewUint16IE creates a new IE with uint16 value.
+func NewUint16IE(t uint8, v uint16) *IE {
 	i := New(t, 0x00, make([]byte, 2))
 	binary.BigEndian.PutUint16(i.Payload, v)
 	return i
 }
 
-func newUint32ValIE(t uint8, v uint32) *IE {
+// NewUint32IE creates a new IE with uint32 value.
+func NewUint32IE(t uint8, v uint32) *IE {
 	i := New(t, 0x00, make([]byte, 4))
 	binary.BigEndian.PutUint32(i.Payload, v)
 	return i
 }
 
-// unused for now.
-// func newUint64ValIE(t uint8, v uint64) *IE {
-// 	i := New(t, 0x00, make([]byte, 8))
-// 	binary.BigEndian.PutUint64(i.Payload, v)
-// 	return i
-// }
+// NewUint64IE creates a new IE with uint64 value.
+func NewUint64IE(t uint8, v uint64) *IE {
+	i := New(t, 0x00, make([]byte, 8))
+	binary.BigEndian.PutUint64(i.Payload, v)
+	return i
+}
 
-func newStringIE(t uint8, v string) *IE {
+// NewStringIE creates a new IE with string value.
+func NewStringIE(t uint8, v string) *IE {
 	return New(t, 0x00, []byte(v))
 }
 
-func newGroupedIE(itype uint8, ies ...*IE) *IE {
-	i := New(itype, 0x00, make([]byte, 0))
-	i.ChildIEs = ies
-	for _, ie := range i.ChildIEs {
-		serialized, err := ie.Marshal()
-		if err != nil {
-			return nil
-		}
-		i.Payload = append(i.Payload, serialized...)
+// NewFQDNIE creates a new IE with FQDN value.
+func NewFQDNIE(t uint8, v string) *IE {
+	return New(t, 0x00, utils.EncodeFQDN(v))
+}
+
+// ValueAsUint8 returns the value of IE as uint8.
+func (i *IE) ValueAsUint8() (uint8, error) {
+	if i.IsGrouped() {
+		return 0, &InvalidTypeError{Type: i.Type}
+	}
+	if len(i.Payload) < 1 {
+		return 0, io.ErrUnexpectedEOF
 	}
-	i.SetLength()
 
-	return i
+	return i.Payload[0], nil
+}
+
+// ValueAsUint16 returns the value of IE as uint16.
+func (i *IE) ValueAsUint16() (uint16, error) {
+	if i.IsGrouped() {
+		return 0, &InvalidTypeError{Type: i.Type}
+	}
+	if len(i.Payload) < 2 {
+		return 0, io.ErrUnexpectedEOF
+	}
+
+	return binary.BigEndian.Uint16(i.Payload[0:2]), nil
+}
+
+// ValueAsUint32 returns the value of IE as uint32.
+func (i *IE) ValueAsUint32() (uint32, error) {
+	if i.IsGrouped() {
+		return 0, &InvalidTypeError{Type: i.Type}
+	}
+	if len(i.Payload) < 4 {
+		return 0, io.ErrUnexpectedEOF
+	}
+
+	return binary.BigEndian.Uint32(i.Payload[0:4]), nil
+}
+
+// ValueAsUint64 returns the value of IE as uint64.
+func (i *IE) ValueAsUint64() (uint64, error) {
+	if i.IsGrouped() {
+		return 0, &InvalidTypeError{Type: i.Type}
+	}
+	if len(i.Payload) < 8 {
+		return 0, io.ErrUnexpectedEOF
+	}
+
+	return binary.BigEndian.Uint64(i.Payload[0:8]), nil
+}
+
+// ValueAsString returns the value of IE as string.
+func (i *IE) ValueAsString() (string, error) {
+	if i.IsGrouped() {
+		return "", &InvalidTypeError{Type: i.Type}
+	}
+
+	return string(i.Payload), nil
+}
+
+// ValueAsFQDN returns the value of IE as string, decoded as FQDN.
+func (i *IE) ValueAsFQDN() (string, error) {
+	if i.IsGrouped() {
+		return "", &InvalidTypeError{Type: i.Type}
+	}
+
+	return utils.DecodeFQDN(i.Payload), nil
 }
 
 var ieTypeNameMap = map[uint8]string{
diff --git a/gtpv2/ie/ie_grouped.go b/gtpv2/ie/ie_grouped.go
new file mode 100644
index 00000000..0adae7e1
--- /dev/null
+++ b/gtpv2/ie/ie_grouped.go
@@ -0,0 +1,148 @@
+// Copyright 2019-2023 go-gtp authors. All rights reserved.
+// Use of this source code is governed by a MIT-style license that can be
+// found in the LICENSE file.
+
+package ie
+
+import "sync"
+
+// NewGroupedIE creates a new IE with the given IEs.
+//
+// The IEs with nil value will be ignored.
+func NewGroupedIE(itype uint8, ies ...*IE) *IE {
+	i := New(itype, 0x00, make([]byte, 0))
+	for _, ie := range ies {
+		if ie == nil {
+			continue
+		}
+
+		serialized, err := ie.Marshal()
+		if err != nil {
+			return nil
+		}
+
+		i.Payload = append(i.Payload, serialized...)
+		i.ChildIEs = append(i.ChildIEs, ie)
+	}
+	i.SetLength()
+
+	return i
+}
+
+// We're using map to avoid iterating over a list.
+// The value `true` is not actually used.
+// TODO: consider using a slice with utils in slices package introduced in Go 1.21.
+var (
+	mu                  sync.RWMutex
+	defaultGroupedIEMap = map[uint8]bool{
+		BearerContext:              true,
+		PDNConnection:              true,
+		OverloadControlInformation: true,
+		LoadControlInformation:     true,
+		RemoteUEContext:            true,
+		SCEFPDNConnection:          true,
+		V2XContext:                 true,
+		PC5QoSParameters:           true,
+	}
+	isGroupedFun = func(t uint8) bool {
+		mu.RLock()
+		defer mu.RUnlock()
+		_, ok := defaultGroupedIEMap[t]
+		return ok
+	}
+)
+
+// SetIsGroupedFun sets a function to check if an IE is of grouped type or not.
+func SetIsGroupedFun(fun func(t uint8) bool) {
+	mu.Lock()
+	defer mu.Unlock()
+	isGroupedFun = fun
+}
+
+// AddGroupedIEType adds IE type(s) to the defaultGroupedIEMap.
+// This is useful when you want to add new IE types to the defaultGroupedIEMap.
+//
+// See also SetIsGroupedFun().
+func AddGroupedIEType(ts ...uint8) {
+	mu.Lock()
+	defer mu.Unlock()
+	for _, t := range ts {
+		defaultGroupedIEMap[t] = true
+	}
+}
+
+// IsGrouped reports whether an IE is grouped type or not.
+//
+// By default, this package determines if an IE is grouped type or not by checking
+// if the IE type is in the defaultGroupedIEMap.
+// You can change this entire behavior by calling SetIsGroupedFun(), or you can add
+// new IE types to the defaultGroupedIEMap by calling AddGroupedIEType().
+func (i *IE) IsGrouped() bool {
+	return isGroupedFun(i.Type)
+}
+
+// Add adds variable number of IEs to a grouped IE and update length of it.
+// This does nothing if the type of the IE is not grouped (no errors).
+func (i *IE) Add(ies ...*IE) {
+	if !i.IsGrouped() {
+		return
+	}
+
+	for _, ie := range ies {
+		if ie == nil {
+			continue
+		}
+		i.ChildIEs = append(i.ChildIEs, ie)
+
+		serialized, err := ie.Marshal()
+		if err != nil {
+			continue
+		}
+		i.Payload = append(i.Payload, serialized...)
+	}
+	i.SetLength()
+}
+
+// Remove removes an IE looked up by type and instance.
+func (i *IE) Remove(typ, instance uint8) {
+	if !i.IsGrouped() {
+		return
+	}
+
+	i.Payload = nil
+	newChildren := make([]*IE, len(i.ChildIEs))
+	idx := 0
+	for _, ie := range i.ChildIEs {
+		if ie.Type == typ && ie.Instance() == instance {
+			newChildren = newChildren[:len(newChildren)-1]
+			continue
+		}
+		newChildren[idx] = ie
+		idx++
+
+		serialized, err := ie.Marshal()
+		if err != nil {
+			continue
+		}
+		i.Payload = append(i.Payload, serialized...)
+	}
+	i.ChildIEs = newChildren
+	i.SetLength()
+}
+
+// FindByType returns IE looked up by type and instance.
+//
+// The program may be slower when calling this method multiple times
+// because this ranges over a ChildIEs each time it is called.
+func (i *IE) FindByType(typ, instance uint8) (*IE, error) {
+	if !i.IsGrouped() {
+		return nil, ErrInvalidType
+	}
+
+	for _, ie := range i.ChildIEs {
+		if ie.Type == typ && ie.Instance() == instance {
+			return ie, nil
+		}
+	}
+	return nil, ErrIENotFound
+}
diff --git a/gtpv2/ie/ie_test.go b/gtpv2/ie/ie_test.go
index d67b2f5b..f2f40209 100644
--- a/gtpv2/ie/ie_test.go
+++ b/gtpv2/ie/ie_test.go
@@ -727,6 +727,7 @@ func TestIEAddRemove(t *testing.T) {
 		ie.NewMSISDN("819012345678"),
 	)
 	i.Add(ie.NewAccessPointName("foo.example"))
+	i.Add(nil) // ignored
 
 	added := ie.NewBearerContext(
 		ie.NewIMSI("123451234567890").WithInstance(1),
diff --git a/gtpv2/ie/integer-number.go b/gtpv2/ie/integer-number.go
index b85872ec..259e2c24 100644
--- a/gtpv2/ie/integer-number.go
+++ b/gtpv2/ie/integer-number.go
@@ -4,28 +4,16 @@
 
 package ie
 
-import (
-	"encoding/binary"
-	"io"
-)
-
 // NewIntegerNumber creates a new IntegerNumber IE.
-func NewIntegerNumber(port uint16) *IE {
-	return newUint16ValIE(IntegerNumber, port)
+func NewIntegerNumber(num uint16) *IE {
+	return NewUint16IE(IntegerNumber, num)
 }
 
 // IntegerNumber returns IntegerNumber in uint16 if the type of IE matches.
 func (i *IE) IntegerNumber() (uint16, error) {
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
 	switch i.Type {
 	case IntegerNumber:
-		if len(i.Payload) < 2 {
-			return 0, io.ErrUnexpectedEOF
-		}
-		return binary.BigEndian.Uint16(i.Payload[0:2]), nil
+		return i.ValueAsUint16()
 	default:
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
diff --git a/gtpv2/ie/ldn.go b/gtpv2/ie/ldn.go
index a532f1e9..dbaf08d0 100644
--- a/gtpv2/ie/ldn.go
+++ b/gtpv2/ie/ldn.go
@@ -4,11 +4,9 @@
 
 package ie
 
-import "io"
-
 // NewLocalDistinguishedName creates a new LocalDistinguishedName IE.
 func NewLocalDistinguishedName(name string) *IE {
-	return newStringIE(LocalDistinguishedName, name)
+	return NewStringIE(LocalDistinguishedName, name)
 }
 
 // LocalDistinguishedName returns LocalDistinguishedName in string if the type of IE matches.
@@ -16,11 +14,7 @@ func (i *IE) LocalDistinguishedName() (string, error) {
 	if i.Type != LocalDistinguishedName {
 		return "", &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return "", io.ErrUnexpectedEOF
-	}
-
-	return string(i.Payload), nil
+	return i.ValueAsString()
 }
 
 // MustLocalDistinguishedName returns LocalDistinguishedName in string, ignoring errors.
diff --git a/gtpv2/ie/mbms-flags.go b/gtpv2/ie/mbms-flags.go
index 3aaf5ed5..1af2f876 100644
--- a/gtpv2/ie/mbms-flags.go
+++ b/gtpv2/ie/mbms-flags.go
@@ -4,8 +4,6 @@
 
 package ie
 
-import "io"
-
 // NewMBMSFlags creates a new MBMSFlags IE.
 func NewMBMSFlags(lmri, msri uint8) *IE {
 	i := New(MBMSFlags, 0x00, make([]byte, 1))
@@ -18,11 +16,7 @@ func (i *IE) MBMSFlags() (uint8, error) {
 	if i.Type != MBMSFlags {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustMBMSFlags returns MBMSFlags in uint8, ignoring errors.
@@ -55,27 +49,19 @@ func (i *IE) HasLMRI() bool {
 // LocalMBMSBearerContextRelease reports whether the MBMS Session Stop Request
 // message is used to release the MBMS Bearer Context locally in the MME/SGSN.
 func (i *IE) LocalMBMSBearerContextRelease() bool {
-	if len(i.Payload) < 1 {
-		return false
-	}
-	switch i.Type {
-	case MBMSFlags:
-		return i.Payload[0]&0x02 == 1
-	default:
+	v, err := i.MBMSFlags()
+	if err != nil {
 		return false
 	}
+	return v&0x02 == 1
 }
 
 // MBMSSessionReEstablishment reports whether the MBMS Session Start Request
 // message is used to re-establish an MBMS session.
 func (i *IE) MBMSSessionReEstablishment() bool {
-	if len(i.Payload) < 1 {
-		return false
-	}
-	switch i.Type {
-	case MBMSFlags:
-		return i.Payload[0]&0x01 == 1
-	default:
+	v, err := i.MBMSFlags()
+	if err != nil {
 		return false
 	}
+	return v&0x01 == 1
 }
diff --git a/gtpv2/ie/node-features.go b/gtpv2/ie/node-features.go
index eb2ceb32..9a8f3110 100644
--- a/gtpv2/ie/node-features.go
+++ b/gtpv2/ie/node-features.go
@@ -4,13 +4,9 @@
 
 package ie
 
-import (
-	"io"
-)
-
 // NewNodeFeatures creates a new NodeFeatures IE.
 func NewNodeFeatures(flags uint8) *IE {
-	return newUint8ValIE(NodeFeatures, flags)
+	return NewUint8IE(NodeFeatures, flags)
 }
 
 // NodeFeatures returns NodeFeatures in uint8 if the type of IE matches.
@@ -18,12 +14,7 @@ func (i *IE) NodeFeatures() (uint8, error) {
 	if i.Type != NodeFeatures {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustNodeFeatures returns NodeFeatures in uint8 if the type of IE matches.
diff --git a/gtpv2/ie/node-type.go b/gtpv2/ie/node-type.go
index 1ce4c5ae..ab39a106 100644
--- a/gtpv2/ie/node-type.go
+++ b/gtpv2/ie/node-type.go
@@ -4,11 +4,9 @@
 
 package ie
 
-import "io"
-
 // NewNodeType creates a new NodeType IE.
 func NewNodeType(nodeType uint8) *IE {
-	return newUint8ValIE(NodeType, nodeType)
+	return NewUint8IE(NodeType, nodeType)
 }
 
 // NodeType returns NodeType in uint8 if the type of IE matches.
@@ -16,11 +14,7 @@ func (i *IE) NodeType() (uint8, error) {
 	if i.Type != NodeType {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustNodeType returns NodeType in uint8, ignoring errors.
diff --git a/gtpv2/ie/p-tmsi.go b/gtpv2/ie/p-tmsi.go
index 48bcb459..f23ab824 100644
--- a/gtpv2/ie/p-tmsi.go
+++ b/gtpv2/ie/p-tmsi.go
@@ -4,14 +4,9 @@
 
 package ie
 
-import (
-	"encoding/binary"
-	"io"
-)
-
 // NewPacketTMSI creates a new PacketTMSI IE.
 func NewPacketTMSI(ptmsi uint32) *IE {
-	return newUint32ValIE(PacketTMSI, ptmsi)
+	return NewUint32IE(PacketTMSI, ptmsi)
 }
 
 // PacketTMSI returns PacketTMSI value in uint32 if type matches.
@@ -19,11 +14,7 @@ func (i *IE) PacketTMSI() (uint32, error) {
 	if i.Type != PacketTMSI {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 4 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return binary.BigEndian.Uint32(i.Payload), nil
+	return i.ValueAsUint32()
 }
 
 // MustPacketTMSI returns PacketTMSI in uint32, ignoring errors.
diff --git a/gtpv2/ie/pdn-type.go b/gtpv2/ie/pdn-type.go
index db9da962..06b7133b 100644
--- a/gtpv2/ie/pdn-type.go
+++ b/gtpv2/ie/pdn-type.go
@@ -4,22 +4,16 @@
 
 package ie
 
-import "io"
-
 // NewPDNType creates a new PDNType IE.
 func NewPDNType(pdn uint8) *IE {
-	return newUint8ValIE(PDNType, pdn)
+	return NewUint8IE(PDNType, pdn)
 }
 
 // PDNType returns the PDNType value in uint8 if the type of IE matches.
 func (i *IE) PDNType() (uint8, error) {
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
 	switch i.Type {
 	case PDNType, PDNAddressAllocation:
-		return i.Payload[0], nil
+		return i.ValueAsUint8()
 	default:
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
diff --git a/gtpv2/ie/port-number.go b/gtpv2/ie/port-number.go
index 0592e566..3fb9aab5 100644
--- a/gtpv2/ie/port-number.go
+++ b/gtpv2/ie/port-number.go
@@ -4,28 +4,16 @@
 
 package ie
 
-import (
-	"encoding/binary"
-	"io"
-)
-
 // NewPortNumber creates a new PortNumber IE.
 func NewPortNumber(port uint16) *IE {
-	return newUint16ValIE(PortNumber, port)
+	return NewUint16IE(PortNumber, port)
 }
 
 // PortNumber returns PortNumber in uint16 if the type of IE matches.
 func (i *IE) PortNumber() (uint16, error) {
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
 	switch i.Type {
 	case PortNumber:
-		if len(i.Payload) < 2 {
-			return 0, io.ErrUnexpectedEOF
-		}
-		return binary.BigEndian.Uint16(i.Payload[0:2]), nil
+		return i.ValueAsUint16()
 	default:
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
diff --git a/gtpv2/ie/pti.go b/gtpv2/ie/pti.go
index a3d2fd1d..e647c161 100644
--- a/gtpv2/ie/pti.go
+++ b/gtpv2/ie/pti.go
@@ -4,11 +4,9 @@
 
 package ie
 
-import "io"
-
 // NewProcedureTransactionID creates a new ProcedureTransactionID IE.
 func NewProcedureTransactionID(pti uint8) *IE {
-	return newUint8ValIE(ProcedureTransactionID, pti)
+	return NewUint8IE(ProcedureTransactionID, pti)
 }
 
 // ProcedureTransactionID returns ProcedureTransactionID in uint8 if the type of IE matches.
@@ -16,11 +14,7 @@ func (i *IE) ProcedureTransactionID() (uint8, error) {
 	if i.Type != ProcedureTransactionID {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustProcedureTransactionID returns ProcedureTransactionID in uint8, ignoring errors.
diff --git a/gtpv2/ie/rat-type.go b/gtpv2/ie/rat-type.go
index 0b70d767..237203ef 100644
--- a/gtpv2/ie/rat-type.go
+++ b/gtpv2/ie/rat-type.go
@@ -4,22 +4,16 @@
 
 package ie
 
-import "io"
-
 // NewRATType creates a new RATType IE.
 func NewRATType(rat uint8) *IE {
-	return newUint8ValIE(RATType, rat)
+	return NewUint8IE(RATType, rat)
 }
 
 // RATType returns RATType in uint8 if the type of IE matches.
 func (i *IE) RATType() (uint8, error) {
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
 	switch i.Type {
 	case RATType:
-		return i.Payload[0], nil
+		return i.ValueAsUint8()
 	default:
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
diff --git a/gtpv2/ie/recovery.go b/gtpv2/ie/recovery.go
index cf09e4a7..55f09ce6 100644
--- a/gtpv2/ie/recovery.go
+++ b/gtpv2/ie/recovery.go
@@ -4,11 +4,9 @@
 
 package ie
 
-import "io"
-
 // NewRecovery creates a new Recovery IE.
 func NewRecovery(recovery uint8) *IE {
-	return newUint8ValIE(Recovery, recovery)
+	return NewUint8IE(Recovery, recovery)
 }
 
 // Recovery returns Recovery value if the type of IE matches.
@@ -16,10 +14,7 @@ func (i *IE) Recovery() (uint8, error) {
 	if i.Type != Recovery {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustRecovery returns Recovery in uint8, ignoring errors.
diff --git a/gtpv2/ie/rfsp-index.go b/gtpv2/ie/rfsp-index.go
index 389ab3e2..5fae6b18 100644
--- a/gtpv2/ie/rfsp-index.go
+++ b/gtpv2/ie/rfsp-index.go
@@ -4,11 +4,9 @@
 
 package ie
 
-import "io"
-
 // NewRFSPIndex creates a new RFSPIndex IE.
 func NewRFSPIndex(idx uint8) *IE {
-	return newUint8ValIE(RFSPIndex, idx)
+	return NewUint8IE(RFSPIndex, idx)
 }
 
 // RFSPIndex returns RFSPIndex in uint8 if the type of IE matches.
@@ -16,11 +14,7 @@ func (i *IE) RFSPIndex() (uint8, error) {
 	if i.Type != RFSPIndex {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustRFSPIndex returns RFSPIndex in uint8, ignoring errors.
diff --git a/gtpv2/ie/selection-mode.go b/gtpv2/ie/selection-mode.go
index 658c58c9..7e9f7864 100644
--- a/gtpv2/ie/selection-mode.go
+++ b/gtpv2/ie/selection-mode.go
@@ -4,14 +4,9 @@
 
 package ie
 
-import "io"
-
 // NewSelectionMode creates a new SelectionMode IE.
-//
-// Note that exactly one of the parameters should be set to true.
-// Otherwise, you'll get the unexpected result.
 func NewSelectionMode(mode uint8) *IE {
-	return newUint8ValIE(SelectionMode, mode)
+	return NewUint8IE(SelectionMode, mode)
 }
 
 // SelectionMode returns SelectionMode value if the type of IE matches.
@@ -19,11 +14,7 @@ func (i *IE) SelectionMode() (uint8, error) {
 	if i.Type != SelectionMode {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustSelectionMode returns SelectionMode in uint8, ignoring errors.
diff --git a/gtpv2/ie/service-indicator.go b/gtpv2/ie/service-indicator.go
index 6d3e2fd8..71460b6c 100644
--- a/gtpv2/ie/service-indicator.go
+++ b/gtpv2/ie/service-indicator.go
@@ -4,11 +4,9 @@
 
 package ie
 
-import "io"
-
 // NewServiceIndicator creates a new ServiceIndicator IE.
 func NewServiceIndicator(ind uint8) *IE {
-	return newUint8ValIE(ServiceIndicator, ind)
+	return NewUint8IE(ServiceIndicator, ind)
 }
 
 // ServiceIndicator returns ServiceIndicator in uint8 if the type of IE matches.
@@ -16,11 +14,7 @@ func (i *IE) ServiceIndicator() (uint8, error) {
 	if i.Type != ServiceIndicator {
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
-	if len(i.Payload) < 1 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	return i.Payload[0], nil
+	return i.ValueAsUint8()
 }
 
 // MustServiceIndicator returns ServiceIndicator in uint8, ignoring errors.
diff --git a/gtpv2/ie/tmsi.go b/gtpv2/ie/tmsi.go
index 7bd7da1e..6b07c395 100644
--- a/gtpv2/ie/tmsi.go
+++ b/gtpv2/ie/tmsi.go
@@ -4,25 +4,16 @@
 
 package ie
 
-import (
-	"encoding/binary"
-	"io"
-)
-
 // NewTMSI creates a new TMSI IE.
 func NewTMSI(tmsi uint32) *IE {
-	return newUint32ValIE(TMSI, tmsi)
+	return NewUint32IE(TMSI, tmsi)
 }
 
 // TMSI returns TMSI in uint32 if the type of IE matches.
 func (i *IE) TMSI() (uint32, error) {
-	if len(i.Payload) < 4 {
-		return 0, io.ErrUnexpectedEOF
-	}
-
 	switch i.Type {
 	case TMSI:
-		return binary.BigEndian.Uint32(i.Payload), nil
+		return i.ValueAsUint32()
 	default:
 		return 0, &InvalidTypeError{Type: i.Type}
 	}
diff --git a/gtpv2/ie/uli-timestamp.go b/gtpv2/ie/uli-timestamp.go
index 6e873f85..911de400 100644
--- a/gtpv2/ie/uli-timestamp.go
+++ b/gtpv2/ie/uli-timestamp.go
@@ -13,7 +13,7 @@ import (
 // NewULITimestamp creates a new ULITimestamp IE.
 func NewULITimestamp(ts time.Time) *IE {
 	u64sec := uint64(ts.Sub(time.Date(1900, time.January, 1, 0, 0, 0, 0, time.UTC))) / 1000000000
-	return newUint32ValIE(ULITimestamp, uint32(u64sec))
+	return NewUint32IE(ULITimestamp, uint32(u64sec))
 }
 
 // Timestamp returns Timestamp in time.Time if the type of IE matches.
diff --git a/utils/utils.go b/utils/utils.go
index 1221d961..9f4fd390 100644
--- a/utils/utils.go
+++ b/utils/utils.go
@@ -8,6 +8,7 @@ package utils
 import (
 	"encoding/binary"
 	"encoding/hex"
+	"strings"
 )
 
 // StrToSwappedBytes returns swapped bits from a byte.
@@ -142,3 +143,42 @@ func ParseECI(eci uint32) (enbID uint32, cellID uint8, err error) {
 	enbID = binary.BigEndian.Uint32([]byte{0, buf[0], buf[1], buf[2]})
 	return
 }
+
+// EncodeFQDN encodes the given string as the Name Syntax defined
+// in RFC 2181, RFC 1035 and RFC 1123.
+func EncodeFQDN(fqdn string) []byte {
+	b := make([]byte, len(fqdn)+1)
+
+	var offset = 0
+	for _, label := range strings.Split(fqdn, ".") {
+		l := len(label)
+		b[offset] = uint8(l)
+		copy(b[offset+1:], label)
+		offset += l + 1
+	}
+
+	return b
+}
+
+// DecodeFQDN decodes the given Name Syntax-encoded []byte as a string.
+func DecodeFQDN(b []byte) string {
+	var (
+		fqdn   []string
+		offset int
+	)
+
+	max := len(b)
+	for {
+		if offset >= max {
+			break
+		}
+		l := int(b[offset])
+		if offset+l+1 > max {
+			break
+		}
+		fqdn = append(fqdn, string(b[offset+1:offset+l+1]))
+		offset += l + 1
+	}
+
+	return strings.Join(fqdn, ".")
+}