diff --git a/src/include/netif/ppp/ppp_impl.h b/src/include/netif/ppp/ppp_impl.h
index fb5f0393..cde5dcfd 100644
--- a/src/include/netif/ppp/ppp_impl.h
+++ b/src/include/netif/ppp/ppp_impl.h
@@ -157,6 +157,12 @@ struct link_callbacks {
   err_t (*write)(ppp_pcb *pcb, void *ctx, struct pbuf *p);
   /* Send a packet from lwIP core (IPv4 or IPv6) */
   err_t (*netif_output)(ppp_pcb *pcb, void *ctx, struct pbuf *p, u_short protocol);
+  /* configure the transmit-side characteristics of the PPP interface */
+  void (*send_config)(ppp_pcb *pcb, void *ctx, u32_t accm);
+  /* confire the receive-side characteristics of the PPP interface */
+  void (*recv_config)(ppp_pcb *pcb, void *ctx, u32_t accm);
+  /* configure TCP header compression */
+  void (*vj_config)(ppp_pcb *pcb, void *ctx, int vjcomp, int cidcomp, int maxcid);
 };
 
 /*
diff --git a/src/include/netif/ppp/pppos.h b/src/include/netif/ppp/pppos.h
index 3c1298ac..9e9727f6 100644
--- a/src/include/netif/ppp/pppos.h
+++ b/src/include/netif/ppp/pppos.h
@@ -102,10 +102,7 @@ void pppos_input(ppp_pcb *ppp, u_char* data, int len);
  *
  * You may use them if you REALLY know what you are doing.
  */
-void pppos_accm_out_config(pppos_pcb *pppos, u32_t accm);
-void pppos_accm_in_config(pppos_pcb *pppos, u32_t accm);
 sio_fd_t pppos_get_fd(pppos_pcb *pppos);
-void pppos_vjc_config(pppos_pcb *pppos, int vjcomp, int cidcomp, int maxcid);
 int pppos_vjc_comp(pppos_pcb *pppos, struct pbuf *pb);
 int pppos_vjc_uncomp(pppos_pcb *pppos, struct pbuf *pb);
 
diff --git a/src/netif/ppp/ppp.c b/src/netif/ppp/ppp.c
index 76cab5d7..c305aaec 100644
--- a/src/netif/ppp/ppp.c
+++ b/src/netif/ppp/ppp.c
@@ -872,11 +872,9 @@ int ppp_send_config(ppp_pcb *pcb, int mtu, u32_t accm, int pcomp, int accomp) {
   pcb->pcomp = pcomp;
   pcb->accomp = accomp;
 
-#if PPPOS_SUPPORT
-  pppos_accm_out_config((pppos_pcb*)pcb->link_ctx_cb, accm);
-#else /* PPPOS_SUPPORT */
-  LWIP_UNUSED_ARG(accm);
-#endif /* PPPOS_SUPPORT */
+  if (pcb->link_cb->send_config) {
+    pcb->link_cb->send_config(pcb, pcb->link_ctx_cb, accm);
+  }
 
   PPPDEBUG(LOG_INFO, ("ppp_send_config[%d]\n", pcb->num) );
   return 0;
@@ -891,11 +889,9 @@ int ppp_recv_config(ppp_pcb *pcb, int mru, u32_t accm, int pcomp, int accomp) {
   LWIP_UNUSED_ARG(pcomp);
   LWIP_UNUSED_ARG(mru);
 
-#if PPPOS_SUPPORT
-  pppos_accm_in_config((pppos_pcb*)pcb->link_ctx_cb, accm);
-#else /* PPPOS_SUPPORT */
-  LWIP_UNUSED_ARG(accm);
-#endif /* PPPOS_SUPPORT */
+  if (pcb->link_cb->recv_config) {
+    pcb->link_cb->recv_config(pcb, pcb->link_ctx_cb, accm);
+  }
 
   PPPDEBUG(LOG_INFO, ("ppp_recv_config[%d]\n", pcb->num));
   return 0;
@@ -1128,14 +1124,9 @@ int cifproxyarp(ppp_pcb *pcb, u32_t his_adr) {
  * sifvjcomp - config tcp header compression
  */
 int sifvjcomp(ppp_pcb *pcb, int vjcomp, int cidcomp, int maxcid) {
-#if VJ_SUPPORT
-  pppos_vjc_config((pppos_pcb*)pcb->link_ctx_cb, vjcomp, cidcomp, maxcid);
-#else /* VJ_SUPPORT */
-  LWIP_UNUSED_ARG(pcb);
-  LWIP_UNUSED_ARG(vjcomp);
-  LWIP_UNUSED_ARG(cidcomp);
-  LWIP_UNUSED_ARG(maxcid);
-#endif /* VJ_SUPPORT */
+  if (pcb->link_cb->vj_config) {
+    pcb->link_cb->vj_config(pcb, pcb->link_ctx_cb, vjcomp, cidcomp, maxcid);
+  }
   return 0;
 }
 
diff --git a/src/netif/ppp/pppoe.c b/src/netif/ppp/pppoe.c
index 0caa005a..6f79c03e 100644
--- a/src/netif/ppp/pppoe.c
+++ b/src/netif/ppp/pppoe.c
@@ -153,7 +153,10 @@ static const struct link_callbacks pppoe_callbacks = {
   pppoe_disconnect,
   pppoe_destroy,
   pppoe_link_write_callback,
-  pppoe_link_netif_output_callback
+  pppoe_link_netif_output_callback,
+  NULL,
+  NULL,
+  NULL
 };
 
 /*
diff --git a/src/netif/ppp/pppol2tp.c b/src/netif/ppp/pppol2tp.c
index 7c920ad2..493a4133 100644
--- a/src/netif/ppp/pppol2tp.c
+++ b/src/netif/ppp/pppol2tp.c
@@ -102,7 +102,10 @@ static const struct link_callbacks pppol2tp_callbacks = {
   pppol2tp_disconnect,
   pppol2tp_destroy,
   pppol2tp_link_write_callback,
-  pppol2tp_link_netif_output_callback
+  pppol2tp_link_netif_output_callback,
+  NULL,
+  NULL,
+  NULL
 };
 
 
diff --git a/src/netif/ppp/pppos.c b/src/netif/ppp/pppos.c
index 4709766e..1406eea7 100644
--- a/src/netif/ppp/pppos.c
+++ b/src/netif/ppp/pppos.c
@@ -87,6 +87,11 @@ static err_t pppos_link_netif_output_callback(ppp_pcb *ppp, void *ctx, struct pb
 static err_t pppos_connect(ppp_pcb *ppp, void *ctx);
 static void pppos_disconnect(ppp_pcb *ppp, void *ctx);
 static err_t pppos_destroy(ppp_pcb *ppp, void *ctx);
+static void pppos_send_config(ppp_pcb *ppp, void *ctx, u32_t accm);
+static void pppos_recv_config(ppp_pcb *ppp, void *ctx, u32_t accm);
+#if VJ_SUPPORT
+static void pppos_vjc_config(ppp_pcb *ppp, void *ctx, int vjcomp, int cidcomp, int maxcid);
+#endif /* VJ_SUPPORT */
 
 /* Prototypes for procedures local to this file. */
 #if PPP_INPROC_MULTITHREADED
@@ -103,7 +108,14 @@ static const struct link_callbacks pppos_callbacks = {
   pppos_disconnect,
   pppos_destroy,
   pppos_link_write_callback,
-  pppos_link_netif_output_callback
+  pppos_link_netif_output_callback,
+  pppos_send_config,
+  pppos_recv_config,
+#if VJ_SUPPORT
+  pppos_vjc_config
+#else /* VJ_SUPPORT */
+  NULL
+#endif /* VJ_SUPPORT */
 };
 
 /* PPP's Asynchronous-Control-Character-Map.  The mask array is used
@@ -760,34 +772,30 @@ drop:
 }
 #endif /* PPP_INPROC_MULTITHREADED */
 
-void
-pppos_accm_out_config(pppos_pcb *pppos, u32_t accm)
+static void
+pppos_send_config(ppp_pcb *ppp, void *ctx, u32_t accm)
 {
   int i;
-
-  if (!pppos_exist(pppos)) {
-    return;
-  }
+  pppos_pcb *pppos = (pppos_pcb *)ctx;
+  LWIP_UNUSED_ARG(ppp);
 
   /* Load the ACCM bits for the 32 control codes. */
   for (i = 0; i < 32/8; i++) {
     pppos->out_accm[i] = (u_char)((accm >> (8 * i)) & 0xFF);
   }
 
-  PPPDEBUG(LOG_INFO, ("pppos_accm_out_config[%d]: in_accm=%X %X %X %X\n",
+  PPPDEBUG(LOG_INFO, ("pppos_send_config[%d]: in_accm=%X %X %X %X\n",
             pppos->ppp->num,
             pppos->out_accm[0], pppos->out_accm[1], pppos->out_accm[2], pppos->out_accm[3]));
 }
 
-void
-pppos_accm_in_config(pppos_pcb *pppos, u32_t accm)
+static void
+pppos_recv_config(ppp_pcb *ppp, void *ctx, u32_t accm)
 {
   int i;
+  pppos_pcb *pppos = (pppos_pcb *)ctx;
   SYS_ARCH_DECL_PROTECT(lev);
-
-  if (!pppos_exist(pppos)) {
-    return;
-  }
+  LWIP_UNUSED_ARG(ppp);
 
   /* Load the ACCM bits for the 32 control codes. */
   SYS_ARCH_PROTECT(lev);
@@ -796,7 +804,7 @@ pppos_accm_in_config(pppos_pcb *pppos, u32_t accm)
   }
   SYS_ARCH_UNPROTECT(lev);
 
-  PPPDEBUG(LOG_INFO, ("pppos_accm_in_config[%d]: in_accm=%X %X %X %X\n",
+  PPPDEBUG(LOG_INFO, ("pppos_recv_config[%d]: in_accm=%X %X %X %X\n",
             pppos->ppp->num,
             pppos->in_accm[0], pppos->in_accm[1], pppos->in_accm[2], pppos->in_accm[3]));
 }
@@ -811,16 +819,11 @@ pppos_get_fd(pppos_pcb *pppos)
 }
 
 #if VJ_SUPPORT
-void
-pppos_vjc_config(pppos_pcb *pppos, int vjcomp, int cidcomp, int maxcid)
+static void
+pppos_vjc_config(ppp_pcb *ppp, void *ctx, int vjcomp, int cidcomp, int maxcid)
 {
-  ppp_pcb *ppp;
+  pppos_pcb *pppos = (pppos_pcb *)ctx;
 
-  if (!pppos_exist(pppos)) {
-    return;
-  }
-
-  ppp = pppos->ppp;
   ppp->vj_enabled = vjcomp;
   pppos->vj_comp.compressSlot = cidcomp;
   pppos->vj_comp.maxSlotIndex = maxcid;