diff --git a/include/config.h b/include/config.h
index db4eda5..0b3fa44 100644
--- a/include/config.h
+++ b/include/config.h
@@ -6,9 +6,12 @@
 
 #define UDT_VERSION 4
 
+#define MIN_DATA_SIZE (8 * sizeof(uint32_t))
 #define MAX_DATA_SIZE 1024
 #define MAX_PACKET_SIZE (4 * sizeof(uint32_t) + MAX_DATA_SIZE)
 
+#define MAX_LOSS_SIZE 100
+
 /* comment the following definition to turn off debuf */
 #define DEBUG 1
 
diff --git a/include/losslist.h b/include/losslist.h
new file mode 100644
index 0000000..6a312c5
--- /dev/null
+++ b/include/losslist.h
@@ -0,0 +1,7 @@
+#ifndef LOSSLIST_H_OFAY39Z2
+#define LOSSLIST_H_OFAY39Z2
+
+int     loss_list_add       (uint32_t);
+int     loss_list_remove    (uint32_t);
+
+#endif /* end of include guard: LOSSLIST_H_OFAY39Z2 */
diff --git a/include/packet.h b/include/packet.h
index 0c4b0c7..788938a 100644
--- a/include/packet.h
+++ b/include/packet.h
@@ -33,6 +33,12 @@
 #define packet_get_type(PACKET) \
     ((PACKET).header._head0 & PACKET_MASK_TYPE)
 
+#define packet_get_seqnum(PACKET) \
+    ((PACKET).header._head0 & PACKET_MASK_SEQ)
+
+#define packet_get_order(PACKET) \
+    ((PACKET).header._head1 & 0x20000000)
+
 #define packet_clear_header(PACKET) \
     ((PACKET).header._head0 &= 0x00000000); \
     ((PACKET).header._head1 &= 0x00000000); \
diff --git a/src/losslist.c b/src/losslist.c
new file mode 100644
index 0000000..ba39a0d
--- /dev/null
+++ b/src/losslist.c
@@ -0,0 +1,43 @@
+#include <inttypes.h>
+
+#include "losslist.h"
+#include "config.h"
+
+static uint32_t loss_list[MAX_LOSS_SIZE];
+static int last = 0;
+
+int loss_list_getindex(uint32_t);
+
+/* TODO: Optimize this to not use O(n) time */
+
+int loss_list_add(uint32_t seqnum)
+{
+    if (last >= MAX_LOSS_SIZE) return -1;
+    if (loss_list_getindex(seqnum) == -1) return -1;
+
+    loss_list[last] = seqnum;
+    last++;
+    return 0;
+}
+
+int loss_list_remove(uint32_t seqnum)
+{
+    int i;
+    i = loss_list_getindex(seqnum);
+    if (i == -1) return -1;
+
+    for (; i < MAX_LOSS_SIZE - 1; ++i) {
+        loss_list[i] = loss_list[i + 1];
+    }
+
+    last--;
+    return 0;
+}
+
+int loss_list_getindex(uint32_t seqnum)
+{
+    for (int i = 0; i < MAX_LOSS_SIZE; ++i) {
+        if (loss_list[i] == seqnum) return i;
+    }
+    return -1;
+}
diff --git a/src/packet.c b/src/packet.c
index e1e63ea..e686258 100644
--- a/src/packet.c
+++ b/src/packet.c
@@ -9,6 +9,9 @@
 #include "util.h"
 
 extern conn_t connection;
+int last_packet = 0;
+
+#define loss_list_add(NUM)
 
 void packet_deserialize(packet_t *packet)
 {
@@ -128,16 +131,47 @@ void packet_parse(packet_t packet)
 
         if (packet.header._head1 & 0x80000000 &&
             packet.header._head1 & 0x40000000)      /* solo packet */
+        {
+            console_log_mod("%x: solo\n", packet_get_seqnum(packet));
             recv_buffer_write(packet.data, PACKET_DATA_SIZE);
-
-        else if (packet.header._head1 & 0x40000000) /* last packet */
-            recv_buffer_write(packet.data, PACKET_DATA_SIZE);
+        }
 
         else if (packet.header._head1 & 0x80000000) /* first packet */
+        {
+            console_log_mod("%x: first\n", packet_get_seqnum(packet));
+            if (packet_get_order(packet))
+                last_packet = packet_get_seqnum(packet);
             recv_buffer_write(packet.data, -1);
+        }
 
         else                                        /* middle packet */
-            recv_buffer_write(packet.data, -1);
+        {
+            if (packet_get_order(packet)) {
+                uint32_t seqnum = packet_get_seqnum(packet);
+                if (seqnum == last_packet + 1) {
+                    console_log_mod("%x: correct\n", seqnum);
+
+                    if (packet.header._head1 & 0x40000000) /* last packet */
+                        recv_buffer_write(packet.data, PACKET_DATA_SIZE);
+                    else
+                        recv_buffer_write(packet.data, -1);
+
+                    last_packet++;
+                } else {
+                    console_log_mod("%x: loss\n", seqnum);
+                    uint32_t num = last_packet;
+                    while (num < seqnum) {
+                        packet_clear_header(packet);
+                        packet_set_ctrl(packet);
+                        packet_set_type(packet, PACKET_TYPE_NAK);
+                        packet_new(&packet, (char *) &num, sizeof(uint32_t));
+                        send_packet_buffer_write(&packet);
+                        loss_list_add(num);
+                        num++;
+                    }
+                }
+            }
+        }
     }
     return;
 }