diff --git a/include/patty/ax25.h b/include/patty/ax25.h
index fc82de8..87f5623 100644
--- a/include/patty/ax25.h
+++ b/include/patty/ax25.h
@@ -29,8 +29,15 @@ enum patty_ax25_sock_status {
     PATTY_AX25_SOCK_ESTABLISHED
 };
 
+enum patty_ax25_sock_mode {
+    PATTY_AX25_SOCK_DM,
+    PATTY_AX25_SOCK_SABM,
+    PATTY_AX25_SOCK_SABME
+};
+
 typedef struct _patty_ax25_sock {
     enum patty_ax25_sock_status status;
+    enum patty_ax25_sock_mode   mode;
 
     time_t timer_ack;
     time_t timer_response;
diff --git a/include/patty/ax25/frame.h b/include/patty/ax25/frame.h
index 7e93bf5..bd62e4a 100644
--- a/include/patty/ax25/frame.h
+++ b/include/patty/ax25/frame.h
@@ -19,11 +19,16 @@ enum patty_ax25_frame_cr {
     PATTY_AX25_FRAME_RESPONSE
 };
 
+enum patty_ax25_frame_format {
+    PATTY_AX25_FRAME_NORMAL   = 0,
+    PATTY_AX25_FRAME_EXTENDED = 1
+};
+
 typedef struct _patty_ax25_frame {
     patty_ax25_address dest;
     patty_ax25_address src;
     patty_ax25_address repeaters[8];
-    
+
     int hops;
     int repeated;
 
@@ -31,8 +36,8 @@ typedef struct _patty_ax25_frame {
     enum patty_ax25_frame_type type;
     enum patty_ax25_frame_cr   cr;
 
-    uint8_t control;
-    uint8_t proto;
+    uint16_t control;
+    uint8_t  proto;
 
     void * payload;
     size_t payloadsz;
@@ -40,6 +45,7 @@ typedef struct _patty_ax25_frame {
     size_t size;
 } patty_ax25_frame;
 
-int patty_ax25_frame_decode(patty_ax25_frame *frame, void *data, size_t len);
+int patty_ax25_frame_decode(patty_ax25_frame *frame,
+    void *data, size_t len, enum patty_ax25_frame_format format);
 
 #endif /* _PATTY_AX25_FRAME_H */
diff --git a/src/ax25.c b/src/ax25.c
index a7ccc71..ff0ab4a 100644
--- a/src/ax25.c
+++ b/src/ax25.c
@@ -77,6 +77,7 @@ static void sock_init(patty_ax25_sock *sock) {
     memset(sock, '\0', sizeof(*sock));
 
     sock->status   = PATTY_AX25_SOCK_OPEN;
+    sock->mode     = PATTY_AX25_SOCK_DM;
     sock->n_maxlen = PATTY_AX25_FRAME_DEFAULT_MAXLEN;
     sock->n_window = PATTY_AX25_FRAME_DEFAULT_WINDOW;
 }
diff --git a/src/frame.c b/src/frame.c
index ad149a1..9d5b61e 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -3,7 +3,7 @@
 
 #include <patty/ax25.h>
 
-static ssize_t frame_decode_station(patty_ax25_address *address, void *data, off_t offset) {
+static ssize_t frame_decode_station(patty_ax25_address *address, void *data, off_t offset, enum patty_ax25_frame_format format) {
     int i, space = 0;
     uint8_t ssid = ((uint8_t *)data + offset)[6];
 
@@ -59,7 +59,7 @@ error:
     return -1;
 }
 
-static ssize_t frame_decode_hops(patty_ax25_frame *frame, void *data, off_t start) {
+static ssize_t frame_decode_hops(patty_ax25_frame *frame, void *data, off_t start, enum patty_ax25_frame_format format) {
     ssize_t decoded;
       off_t offset = start;
 
@@ -70,7 +70,7 @@ static ssize_t frame_decode_hops(patty_ax25_frame *frame, void *data, off_t star
      * frame.
      */
     for (i=0; i<PATTY_AX25_MAX_HOPS; i++) {
-        if ((decoded = frame_decode_station(&frame->repeaters[i], data, offset)) < 0) {
+        if ((decoded = frame_decode_station(&frame->repeaters[i], data, offset, format)) < 0) {
             goto error;
         } else {
             offset += decoded;
@@ -101,11 +101,11 @@ error:
     return -1;
 }
 
-static ssize_t frame_decode_address(patty_ax25_frame *frame, void *data, off_t start) {
+static ssize_t frame_decode_address(patty_ax25_frame *frame, void *data, off_t start, enum patty_ax25_frame_format format) {
       off_t offset = start;
     ssize_t decoded;
 
-    if ((decoded = frame_decode_station(&frame->dest, data, offset)) < 0) {
+    if ((decoded = frame_decode_station(&frame->dest, data, offset, format)) < 0) {
         goto error;
     } else {
         offset += decoded;
@@ -115,7 +115,7 @@ static ssize_t frame_decode_address(patty_ax25_frame *frame, void *data, off_t s
      * It would be considered erroneous if the destination address did have the
      * extension bit set to 1.
      */
-    if ((decoded = frame_decode_station(&frame->src, data, offset)) < 0) {
+    if ((decoded = frame_decode_station(&frame->src, data, offset, format)) < 0) {
         goto error;
     } else {
         offset += decoded;
@@ -140,7 +140,7 @@ static ssize_t frame_decode_address(patty_ax25_frame *frame, void *data, off_t s
      * decoding repeater addresses.
      */
     if (!frame->src.last) {
-        if ((decoded = frame_decode_hops(frame, data, offset)) < 0) {
+        if ((decoded = frame_decode_hops(frame, data, offset, format)) < 0) {
             goto error;
         } else {
             offset += decoded;
@@ -153,7 +153,7 @@ error:
     return -1;
 }
 
-static ssize_t frame_decode_payload(patty_ax25_frame *frame, void *data, off_t offset) {
+static ssize_t frame_decode_payload(patty_ax25_frame *frame, void *data, off_t offset, enum patty_ax25_frame_format format) {
     uint8_t control = ((uint8_t *)data + offset)[0];
      size_t decoded = 0;
 
@@ -204,7 +204,7 @@ error:
     return -1;
 }
 
-int patty_ax25_frame_decode(patty_ax25_frame *frame, void *data, size_t size) {
+int patty_ax25_frame_decode(patty_ax25_frame *frame, void *data, size_t size, enum patty_ax25_frame_format format) {
     ssize_t decoded;
       off_t offset = 0;
 
@@ -215,7 +215,7 @@ int patty_ax25_frame_decode(patty_ax25_frame *frame, void *data, size_t size) {
     /*
      * First, decode the variable-length Address field.
      */
-    if ((decoded = frame_decode_address(frame, data, offset)) < 0) {
+    if ((decoded = frame_decode_address(frame, data, offset, format)) < 0) {
         goto error_decode;
     } else {
         offset += decoded;
@@ -225,7 +225,7 @@ int patty_ax25_frame_decode(patty_ax25_frame *frame, void *data, size_t size) {
      * Now, decode the remaining Control Field, optional Protocol Identifier
      * field, and payload that may follow.
      */
-    if ((decoded = frame_decode_payload(frame, data, offset)) < 0) {
+    if ((decoded = frame_decode_payload(frame, data, offset, format)) < 0) {
         goto error_decode;
     } else {
         offset += decoded;