+#define PPP_HDRLEN 4 /* octets for standard ppp header */
+#define PPP_FCSLEN 2 /* octets for FCS */
+
+#define PPP_ADDRESS(cp) ((cp)[0])
+#define PPP_CONTROL(cp) ((cp)[1])
+#define PPP_PROTOCOL(cp) (((cp)[2] << 8) + (cp)[3])
+
+#define PPP_ALLSTATIONS 0xff /* All-Stations broadcast address */
+#define PPP_UI 0x03 /* Unnumbered Information */
+#define PPP_FLAG 0x7e /* Flag Sequence */
+#define PPP_ESCAPE 0x7d /* Asynchronous Control Escape */
+#define PPP_TRANS 0x20 /* Asynchronous transparency modifier */
+
+/*
+ * Protocol field values.
+ */
+#define PPP_IP 0x21 /* Internet Protocol */
+#define PPP_XNS 0x25 /* Xerox NS */
+#define PPP_VJC_COMP 0x2d /* VJ compressed TCP */
+#define PPP_VJC_UNCOMP 0x2f /* VJ uncompressed TCP */
+#define PPP_COMP 0xfd /* compressed packet */
+#define PPP_LCP 0xc021 /* Link Control Protocol */
+#define PPP_CCP 0x80fd /* Compression Control Protocol */
+
+/*
+ * Important FCS values.
+ */
+#define PPP_INITFCS 0xffff /* Initial FCS value */
+#define PPP_GOODFCS 0xf0b8 /* Good final FCS value */
+#define PPP_FCS(fcs, c) (((fcs) >> 8) ^ fcstab[((fcs) ^ (c)) & 0xff])
+
+/*
+ * Packet sizes
+ */
+#define PPP_MTU 1500 /* Default MTU (size of Info field) */
+#define PPP_MRU 1500 /* Default MRU (max receive unit) */
+#define PPP_MAXMRU 65000 /* Largest MRU we allow */
+