diff --git a/pdu/pdu.go b/pdu/pdu.go
index aec003b..650603f 100644
--- a/pdu/pdu.go
+++ b/pdu/pdu.go
@@ -58,6 +58,9 @@ type (
 // Don't know
 
 func (p *PDU_HEADER) Encode(buf *bytes.Buffer) error {
+	if buf == nil {
+		return fmt.Errorf("cannot encode into nil buffer")
+	}
 	binary.Write(buf, binary.BigEndian, p.command_length)
 	binary.Write(buf, binary.BigEndian, p.command_id)
 	binary.Write(buf, binary.BigEndian, p.command_status)
diff --git a/pdu/pdu_test.go b/pdu/pdu_test.go
index 0ed90bb..b40d7d7 100644
--- a/pdu/pdu_test.go
+++ b/pdu/pdu_test.go
@@ -283,50 +283,6 @@ func TestEncodeIntoWithBoundaryValues(t *testing.T) {
 	}
 }
 
-// func TestRealScenario(t *testing.T) {
-// 	expected := []byte{0, 0, 0, 54, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 1, 67, 77, 84, 0, 1, 1, 49, 50, 51, 52, 53, 0, 1, 1, 54, 55, 56, 57, 48, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 12, 72, 101, 108, 108, 111, 44, 32, 83, 77, 80, 80, 33}
-// 	p := &SUBMIT_SM{
-// 		header: PDU_HEADER{
-// 			command_length:  0,
-// 			command_id:      4,
-// 			command_status:  0,
-// 			sequence_number: 1,
-// 		},
-// 		service_type:           "CMT",
-// 		source_addr_ton:        1,
-// 		source_addr_npi:        1,
-// 		source_addr:            "12345",
-// 		dest_addr_ton:          1,
-// 		dest_addr_npi:          1,
-// 		destination_addr:       "67890",
-// 		esm_class:              0,
-// 		protocol_id:            0,
-// 		priority_flag:          0,
-// 		schedule_delivery_time: "",
-// 		validity_period:        "",
-// 		registered_delivery:    1,
-// 		data_coding:            0,
-// 		sm_default_msg_id:      0,
-// 		short_message:          "Hello, SMPP!",
-// 	}
-// 	p.header.command_length = uint32(p.Size())
-// 	p.sm_length = byte(len(p.short_message))
-// 	buf := make([]byte, p.Size())
-// 	err := p.EncodeInto(&buf)
-// 	if err != nil {
-// 		t.Errorf("Expected no error, got %v", err)
-// 	}
-// 	if len(buf) != len(expected) {
-// 		t.Errorf("Expected byte slice of length %d, got %d", len(expected), len(buf))
-// 	}
-// 	for i, v := range buf {
-// 		if v != expected[i] {
-// 			t.Errorf("Expected byte slice with values %v, got %v", expected, buf)
-// 			break
-// 		}
-// 	}
-// }
-
 // region decode
 func TestDecodeHandlesShortByteSlice(t *testing.T) {
 	var p PDU_HEADER
diff --git a/pdu/submit.go b/pdu/submit.go
index c84a9ac..1772381 100644
--- a/pdu/submit.go
+++ b/pdu/submit.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/ascii85"
 	"encoding/binary"
+	"fmt"
 )
 
 type (
@@ -65,33 +66,41 @@ type (
 )
 
 func (p *SUBMIT_SM) Encode(buf *bytes.Buffer) error {
+	if buf == nil {
+		return fmt.Errorf("cannot encode into nil buffer")
+	}
 	p.header.Encode(buf)
 	n := ascii85.Encode(buf.Bytes(), []byte(p.service_type))
 	buf.Truncate(n)
-	binary.Write(buf, binary.BigEndian, byte(len(p.service_type)))
-	
-	// service_type           string
-	// source_addr_ton        byte
-	// source_addr_npi        byte
-	// source_addr            string
-	// dest_addr_ton          byte
-	// dest_addr_npi          byte
-	// destination_addr       string
-	// esm_class              byte
-	// protocol_id            byte
-	// priority_flag          byte
-	// schedule_delivery_time string
-	// validity_period        string
-	// registered_delivery    byte
-	// replace_if_present     byte
-	// data_coding            byte
-	// sm_default_msg_id      byte
-	// sm_length              byte
-	// short_message          string
-
+	binary.Write(buf, binary.BigEndian, p.source_addr_ton)
+	binary.Write(buf, binary.BigEndian, p.source_addr_npi)
+	n = ascii85.Encode(buf.Bytes(), []byte(p.source_addr))
+	buf.Truncate(n)
+	binary.Write(buf, binary.BigEndian, p.dest_addr_ton)
+	binary.Write(buf, binary.BigEndian, p.dest_addr_npi)
+	n = ascii85.Encode(buf.Bytes(), []byte(p.destination_addr))
+	buf.Truncate(n)
+	binary.Write(buf, binary.BigEndian, p.esm_class)
+	binary.Write(buf, binary.BigEndian, p.protocol_id)
+	binary.Write(buf, binary.BigEndian, p.priority_flag)
+	n = ascii85.Encode(buf.Bytes(), []byte(p.schedule_delivery_time))
+	buf.Truncate(n)
+	n = ascii85.Encode(buf.Bytes(), []byte(p.validity_period))
+	buf.Truncate(n)
+	binary.Write(buf, binary.BigEndian, p.registered_delivery)
+	binary.Write(buf, binary.BigEndian, p.replace_if_present)
+	binary.Write(buf, binary.BigEndian, p.data_coding)
+	binary.Write(buf, binary.BigEndian, p.sm_default_msg_id)
+	binary.Write(buf, binary.BigEndian, p.sm_length)
+	// TODO: Implement encodings bsed on p.data_coding
+	n = ascii85.Encode(buf.Bytes(), []byte(p.short_message))
+	buf.Truncate(n)
 	return nil
 }
 func (p *SUBMIT_SM) Decode(buf *bytes.Buffer) error {
+	if buf == nil {
+		return fmt.Errorf("cannot decode nil buffer")
+	}
 	return nil
 }
 func (p *SUBMIT_SM) Size() int {
diff --git a/pdu/submit_test.go b/pdu/submit_test.go
index f9f4e7b..57decaa 100644
--- a/pdu/submit_test.go
+++ b/pdu/submit_test.go
@@ -4,6 +4,54 @@ import (
 	"testing"
 )
 
+// region encode
+
+// func TestRealScenario(t *testing.T) {
+// 	expected := []byte{0, 0, 0, 54, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 1, 67, 77, 84, 0, 1, 1, 49, 50, 51, 52, 53, 0, 1, 1, 54, 55, 56, 57, 48, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 12, 72, 101, 108, 108, 111, 44, 32, 83, 77, 80, 80, 33}
+// 	p := &SUBMIT_SM{
+// 		header: PDU_HEADER{
+// 			command_length:  0,
+// 			command_id:      4,
+// 			command_status:  0,
+// 			sequence_number: 1,
+// 		},
+// 		service_type:           "CMT",
+// 		source_addr_ton:        1,
+// 		source_addr_npi:        1,
+// 		source_addr:            "12345",
+// 		dest_addr_ton:          1,
+// 		dest_addr_npi:          1,
+// 		destination_addr:       "67890",
+// 		esm_class:              0,
+// 		protocol_id:            0,
+// 		priority_flag:          0,
+// 		schedule_delivery_time: "",
+// 		validity_period:        "",
+// 		registered_delivery:    1,
+// 		data_coding:            0,
+// 		sm_default_msg_id:      0,
+// 		short_message:          "Hello, SMPP!",
+// 	}
+// 	p.header.command_length = uint32(p.Size())
+// 	p.sm_length = byte(len(p.short_message))
+// 	buf := make([]byte, p.Size())
+// 	err := p.EncodeInto(&buf)
+// 	if err != nil {
+// 		t.Errorf("Expected no error, got %v", err)
+// 	}
+// 	if len(buf) != len(expected) {
+// 		t.Errorf("Expected byte slice of length %d, got %d", len(expected), len(buf))
+// 	}
+// 	for i, v := range buf {
+// 		if v != expected[i] {
+// 			t.Errorf("Expected byte slice with values %v, got %v", expected, buf)
+// 			break
+// 		}
+// 	}
+// }
+
+// region decode
+
 // region size
 func TestCalculateSizeTypicalInstance(t *testing.T) {
 	p := &SUBMIT_SM{
@@ -53,3 +101,5 @@ func TestHandlesEmptyStringsForAllStringFields(t *testing.T) {
 		t.Errorf("Expected size %d, but got %d", expectedSize, actualSize)
 	}
 }
+
+// region benchmark
\ No newline at end of file