diff --git a/doc/ppp.txt b/doc/ppp.txt
index 68da58e3..8b0acdf0 100644
--- a/doc/ppp.txt
+++ b/doc/ppp.txt
@@ -183,17 +183,30 @@ static void status_cb(ppp_pcb *pcb, int err_code, void *ctx) {
 
 #include "netif/ppp/pppos.h"
 
+/*
+ * PPPoS serial output callback
+ *
+ * ppp_pcb, PPP control block
+ * data, buffer to write to serial port
+ * len, length of the data buffer
+ * ctx, optional user-provided callback context pointer
+ *
+ * Return value: len if write succeed
+ */
+static u32_t output_cb(ppp_pcb *pcb, u8_t *data, u32_t len, void *ctx) {
+  return uart_write(UART, data, len);
+}
+
 /*
  * Create a new PPPoS interface
  *
  * ppp_netif, netif to use for this PPP link, i.e. PPP IP interface
- * ppp_sio, handler to your SIO port (see include/lwip/sio.h)
+ * output_cb, PPPoS serial output callback
  * status_cb, PPP status callback, called on PPP status change (up, down, …)
  * ctx_cb, optional user-provided callback context pointer
  */
 ppp = pppos_create(&ppp_netif,
-       ppp_sio,
-       status_cb, ctx_cb);
+       output_cb, status_cb, ctx_cb);
 
 
 /*
@@ -304,7 +317,6 @@ ppp_free(ppp);
 3 PPPoS input path (raw API, IRQ safe API, TCPIP API)
 =====================================================
 
-PPPoS requires a serial I/O SIO port (see include/lwip/sio.h).
 Received data on serial port should be sent to lwIP using the pppos_input()
 function or the pppos_input_sys() function.
 
@@ -405,3 +417,5 @@ from previous lwIP version is pretty easy:
   unconditionally registering them, which is probably the wanted behavior in
   almost all cases. If you need it conditional contact us and we will made it
   conditional.
+
+* PPPoS now requires a serial output callback
diff --git a/src/api/pppapi.c b/src/api/pppapi.c
index 5b7940d1..e1122d77 100644
--- a/src/api/pppapi.c
+++ b/src/api/pppapi.c
@@ -127,7 +127,7 @@ pppapi_set_notify_phase_callback(ppp_pcb *pcb, ppp_notify_phase_cb_fn notify_pha
 static void
 pppapi_do_pppos_create(struct pppapi_msg_msg *msg)
 {
-  msg->ppp = pppos_create(msg->msg.serialcreate.pppif, msg->msg.serialcreate.fd,
+  msg->ppp = pppos_create(msg->msg.serialcreate.pppif, msg->msg.serialcreate.output_cb,
     msg->msg.serialcreate.link_status_cb, msg->msg.serialcreate.ctx_cb);
   TCPIP_PPPAPI_ACK(msg);
 }
@@ -137,13 +137,13 @@ pppapi_do_pppos_create(struct pppapi_msg_msg *msg)
  * tcpip_thread context.
  */
 ppp_pcb*
-pppapi_pppos_create(struct netif *pppif, sio_fd_t fd, ppp_link_status_cb_fn link_status_cb,
-                          void *ctx_cb)
+pppapi_pppos_create(struct netif *pppif, pppos_output_cb_fn output_cb,
+               ppp_link_status_cb_fn link_status_cb, void *ctx_cb)
 {
   struct pppapi_msg msg;
   msg.function = pppapi_do_pppos_create;
   msg.msg.msg.serialcreate.pppif = pppif;
-  msg.msg.msg.serialcreate.fd = fd;
+  msg.msg.msg.serialcreate.output_cb = output_cb;
   msg.msg.msg.serialcreate.link_status_cb = link_status_cb;
   msg.msg.msg.serialcreate.ctx_cb = ctx_cb;
   TCPIP_PPPAPI(&msg);
diff --git a/src/include/lwip/pppapi.h b/src/include/lwip/pppapi.h
index 270c5fc7..28c8a5fd 100644
--- a/src/include/lwip/pppapi.h
+++ b/src/include/lwip/pppapi.h
@@ -35,6 +35,9 @@
 #include "lwip/sys.h"
 #include "lwip/netif.h"
 #include "netif/ppp/ppp.h"
+#if PPPOS_SUPPORT
+#include "netif/ppp/pppos.h"
+#endif /* PPPOS_SUPPORT */
 
 #ifdef __cplusplus
 extern "C" {
@@ -60,7 +63,7 @@ struct pppapi_msg_msg {
 #if PPPOS_SUPPORT
     struct {
       struct netif *pppif;
-      sio_fd_t fd;
+      pppos_output_cb_fn output_cb;
       ppp_link_status_cb_fn link_status_cb;
       void *ctx_cb;
     } serialcreate;
@@ -119,7 +122,7 @@ void pppapi_set_auth(ppp_pcb *pcb, u8_t authtype, const char *user, const char *
 void pppapi_set_notify_phase_callback(ppp_pcb *pcb, ppp_notify_phase_cb_fn notify_phase_cb);
 #endif /* PPP_NOTIFY_PHASE */
 #if PPPOS_SUPPORT
-ppp_pcb *pppapi_pppos_create(struct netif *pppif, sio_fd_t fd, ppp_link_status_cb_fn link_status_cb, void *ctx_cb);
+ppp_pcb *pppapi_pppos_create(struct netif *pppif, pppos_output_cb_fn output_cb, ppp_link_status_cb_fn link_status_cb, void *ctx_cb);
 #endif /* PPPOS_SUPPORT */
 #if PPPOE_SUPPORT
 ppp_pcb *pppapi_pppoe_create(struct netif *pppif, struct netif *ethif, const char *service_name,
diff --git a/src/include/netif/ppp/pppos.h b/src/include/netif/ppp/pppos.h
index e1721395..39b2b7d0 100644
--- a/src/include/netif/ppp/pppos.h
+++ b/src/include/netif/ppp/pppos.h
@@ -55,6 +55,9 @@ enum {
   PDDATA       /* Process data byte. */
 };
 
+/* PPPoS serial output callback function prototype */
+typedef u32_t (*pppos_output_cb_fn)(ppp_pcb *pcb, u8_t *data, u32_t len, void *ctx);
+
 /*
  * Extended asyncmap - allows any character to be escaped.
  */
@@ -67,7 +70,7 @@ typedef struct pppos_pcb_s pppos_pcb;
 struct pppos_pcb_s {
   /* -- below are data that will NOT be cleared between two sessions */
   ppp_pcb *ppp;                    /* PPP PCB */
-  sio_fd_t fd;                     /* File device ID of port. */
+  pppos_output_cb_fn output_cb;    /* PPP serial output callback */
 
   /* -- below are data that will be cleared between two sessions
    *
@@ -92,7 +95,7 @@ struct pppos_pcb_s {
 };
 
 /* Create a new PPPoS session. */
-ppp_pcb *pppos_create(struct netif *pppif, sio_fd_t fd,
+ppp_pcb *pppos_create(struct netif *pppif, pppos_output_cb_fn output_cb,
        ppp_link_status_cb_fn link_status_cb, void *ctx_cb);
 
 #if !NO_SYS && !PPP_INPROC_IRQ_SAFE
diff --git a/src/netif/ppp/pppos.c b/src/netif/ppp/pppos.c
index 07a2dade..4e78e5f9 100644
--- a/src/netif/ppp/pppos.c
+++ b/src/netif/ppp/pppos.c
@@ -44,7 +44,6 @@
 #include "lwip/snmp_mib2.h"
 #include "lwip/tcpip.h"
 #include "lwip/api.h"
-#include "lwip/sio.h"
 #include "lwip/ip4.h" /* for ip4_input() */
 
 #include "netif/ppp/ppp_impl.h"
@@ -170,7 +169,7 @@ ppp_get_fcs(u8_t byte)
  *
  * Return 0 on success, an error code on failure.
  */
-ppp_pcb *pppos_create(struct netif *pppif, sio_fd_t fd,
+ppp_pcb *pppos_create(struct netif *pppif, pppos_output_cb_fn output_cb,
        ppp_link_status_cb_fn link_status_cb, void *ctx_cb)
 {
   pppos_pcb *pppos;
@@ -188,7 +187,7 @@ ppp_pcb *pppos_create(struct netif *pppif, sio_fd_t fd,
   }
 
   pppos->ppp = ppp;
-  pppos->fd = fd;
+  pppos->output_cb = output_cb;
   ppp_link_set_callbacks(ppp, &pppos_callbacks, pppos);
   return ppp;
 }
@@ -786,21 +785,10 @@ pppos_recv_config(ppp_pcb *ppp, void *ctx, u32_t accm, int pcomp, int accomp)
 static err_t
 pppos_ioctl(ppp_pcb *pcb, void *ctx, int cmd, void *arg)
 {
-  pppos_pcb *pppos = (pppos_pcb *)ctx;
   LWIP_UNUSED_ARG(pcb);
-
-  switch(cmd) {
-    case PPPCTLG_FD:            /* Get the fd associated with the ppp */
-      if (!arg) {
-        goto fail;
-      }
-      *(sio_fd_t *)arg = pppos->fd;
-      return ERR_OK;
-
-    default: ;
-  }
-
-fail:
+  LWIP_UNUSED_ARG(ctx);
+  LWIP_UNUSED_ARG(cmd);
+  LWIP_UNUSED_ARG(arg);
   return ERR_VAL;
 }
 
@@ -858,7 +846,7 @@ pppos_output_append(pppos_pcb *pppos, err_t err, struct pbuf *nb, u8_t c, u8_t a
    * Sure we don't quite fill the buffer if the character doesn't
    * get escaped but is one character worth complicating this? */
   if ((PBUF_POOL_BUFSIZE - nb->len) < 2) {
-    u32_t l = sio_write(pppos->fd, (u8_t*)nb->payload, nb->len);
+    u32_t l = pppos->output_cb(pppos->ppp, (u8_t*)nb->payload, nb->len, pppos->ppp->ctx_cb);
     if (l != nb->len) {
       return ERR_IF;
     }
@@ -884,9 +872,7 @@ pppos_output_append(pppos_pcb *pppos, err_t err, struct pbuf *nb, u8_t c, u8_t a
 static err_t
 pppos_output_last(pppos_pcb *pppos, err_t err, struct pbuf *nb, u16_t *fcs)
 {
-#if MIB2_STATS
   ppp_pcb *ppp = pppos->ppp;
-#endif /* MIB2_STATS */
 
   /* Add FCS and trailing flag. */
   err = pppos_output_append(pppos, err,  nb, ~(*fcs) & 0xFF, 1, NULL);
@@ -899,7 +885,7 @@ pppos_output_last(pppos_pcb *pppos, err_t err, struct pbuf *nb, u16_t *fcs)
 
   /* Send remaining buffer if not empty */
   if (nb->len > 0) {
-    u32_t l = sio_write(pppos->fd, (u8_t*)nb->payload, nb->len);
+    u32_t l = pppos->output_cb(ppp, (u8_t*)nb->payload, nb->len, ppp->ctx_cb);
     if (l != nb->len) {
       err = ERR_IF;
       goto failed;