typedef struct PPP	PPP;typedef struct Pstate	Pstate;typedef struct Lcpmsg	Lcpmsg;typedef struct Lcpopt	Lcpopt;typedef struct Qualpkt	Qualpkt;typedef struct Qualstats Qualstats;typedef struct Tcpc	Tcpc; typedef uchar Ipaddr[IPaddrlen]; enum{	HDLC_frame=	0x7e,	HDLC_esc=	0x7d, 	/* PPP frame fields */	PPP_addr=	0xff,	PPP_ctl=	0x3,	PPP_initfcs=	0xffff,	PPP_goodfcs=	0xf0b8, 	/* PPP phases */	Pdead=		0,		Plink,				/* doing LCP */	Pauth,				/* doing chap */	Pnet,				/* doing IPCP, CCP */	Pterm,				/* closing down */ 	/* PPP protocol types */	Pip=		0x21,		/* internet */	Pvjctcp=	0x2d,		/* compressing van jacobson tcp */	Pvjutcp=	0x2f,		/* uncompressing van jacobson tcp */	Pcdata=		0xfd,		/* compressed datagram */	Pipcp=		0x8021,		/* ip control */	Pecp=		0x8053,		/* encryption control */	Pccp=		0x80fd,		/* compressed datagram control */	Plcp=		0xc021,		/* link control */	Ppap=		0xc023,		/* password auth. protocol */	Plqm=		0xc025,		/* link quality monitoring */	Pchap=		0xc223,		/* challenge/response */ 	/* LCP codes */	Lconfreq=	1,	Lconfack=	2,	Lconfnak=	3,	Lconfrej=	4,	Ltermreq=	5,	Ltermack=	6,	Lcoderej=	7,	Lprotorej=	8,	Lechoreq=	9,	Lechoack=	10,	Ldiscard=	11, 	/* Lcp configure options */	Omtu=		1,	Octlmap=	2,	Oauth=		3,	Oquality=	4,	Omagic=		5,	Opc=		7,	Oac=		8,	Obad=		12,		/* for testing */ 	/* authentication protocols */	APmd5=		5, 	/* lcp flags */	Fmtu=		1<<Omtu,	Fctlmap=	1<<Octlmap,	Fauth=		1<<Oauth,	Fquality=	1<<Oquality,	Fmagic=		1<<Omagic,	Fpc=		1<<Opc,	Fac=		1<<Oac,	Fbad=		1<<Obad, 	/* Chap codes */	Cchallenge=	1,	Cresponse=	2,	Csuccess=	3,	Cfailure=	4, 	/* Pap codes */	Cpapreq=		1,	Cpapack=		2,	Cpapnak=		3, 	/* link states */	Sclosed=		0,	Sclosing,	Sreqsent,	Sackrcvd,	Sacksent,	Sopened, 	/* ccp configure options */	Ocoui=		0,	/* proprietary compression */	Ocstac=		17,	/* stac electronics LZS */	Ocmppc=		18,	/* microsoft ppc */ 	/* ccp flags */	Fcoui=		1<<Ocoui,	Fcstac=		1<<Ocstac,	Fcmppc=		1<<Ocmppc, 	/* ecp configure options */	Oeoui=		0,	/* proprietary compression */	Oedese=		1,	/* DES */ 	/* ecp flags */	Feoui=		1<<Oeoui,	Fedese=		1<<Oedese, 	/* ipcp configure options */	Oipaddrs=	1,	Oipcompress=	2,	Oipaddr=	3,	Oipdns=		129,	Oipwins=	130,	Oipdns2=	131,	Oipwins2=	132, 	/* ipcp flags */	Fipaddrs=	1<<Oipaddrs,	Fipcompress=	1<<Oipcompress,	Fipaddr=	1<<Oipaddr, 	Period=		3*1000,	/* period of retransmit process (in ms) */	Timeout=	10,	/* xmit timeout (in Periods) */ 	MAX_STATES	= 16,		/* van jacobson compression states */	Defmtu=		1450,		/* default that we will ask for */	Minmtu=		128,		/* minimum that we will accept */	Maxmtu=		2000,		/* maximum that we will accept */};  struct Pstate{	int	proto;		/* protocol type */	int	timeout;		/* for current state */	int	rxtimeout;	/* for current retransmit */	ulong	flags;		/* options received */	uchar	id;		/* id of current message */	uchar	confid;		/* id of current config message */	uchar	termid;		/* id of current termination message */	uchar	rcvdconfid;	/* id of last conf message received */	uchar	state;		/* PPP link state */	ulong	optmask;		/* which options to request */	int	echoack;	/* recieved echo ack */	int	echotimeout;	/* echo timeout */}; struct Qualstats{	ulong	reports;	ulong	packets;	ulong	bytes;	ulong	discards;	ulong	errors;}; struct PPP{	QLock; 	Chan*	dchan;			/* serial line */	Chan*	cchan;			/* serial line control */	int		framing;	/* non-zero to use framing characters */	Ipaddr	local;	int		localfrozen;	Ipaddr	remote;	int		remotefrozen; 	int	pppup;	Fs	*f;		/* file system we belong to */	Ipifc*	ifc;	Proc*	readp;			/* reading process */	Proc*	timep;			/* timer process */	Block*	inbuf;			/* input buffer */	Block*	outbuf;			/* output buffer */	QLock	outlock;		/*  and its lock */ 	ulong	magic;			/* magic number to detect loop backs */	ulong	rctlmap;		/* map of chars to ignore in rcvr */	ulong	xctlmap;		/* map of chars to excape in xmit */	int		phase;		/* PPP phase */	Pstate*	lcp;			/* lcp state */	Pstate*	ipcp;			/* ipcp state */	char	secret[256];		/* md5 key */	char	chapname[256];		/* chap system name */	Tcpc*	ctcp;	ulong		mtu;		/* maximum xmit size */	ulong		mru;		/* maximum recv size */ 	int	baud;	int	usepap;	/* authentication is PAP in every sense, not CHAP */	int	papid;	int	usechap; 	/* rfc */	int	usedns;	Ipaddr	dns1;	Ipaddr	dns2; 	/* link quality monitoring */	int		period;		/* lqm period */	int		timeout;	/* time to next lqm packet */	Qualstats	in;		/* local */	Qualstats	out;	Qualstats	pin;		/* peer */	Qualstats	pout;	Qualstats	sin;		/* saved */}; PPP*		pppopen(PPP*, char*, Ipaddr, Ipaddr, int, int, char*, char*);Block*	pppread(PPP*);int		pppwrite(PPP*, Block*);void		pppclose(PPP*); struct Lcpmsg{	uchar	code;	uchar	id;	uchar	len[2];	uchar	data[1];}; struct Lcpopt{	uchar	type;	uchar	len;	uchar	data[1];}; struct Qualpkt{	uchar	magic[4]; 	uchar	lastoutreports[4];	uchar	lastoutpackets[4];	uchar	lastoutbytes[4];	uchar	peerinreports[4];	uchar	peerinpackets[4];	uchar	peerindiscards[4];	uchar	peerinerrors[4];	uchar	peerinbytes[4];	uchar	peeroutreports[4];	uchar	peeroutpackets[4];	uchar	peeroutbytes[4];}; ushort	compress(Tcpc*, Block*, Fs*);Tcpc*	compress_init(Tcpc*);int		compress_negotiate(Tcpc*, uchar*);ushort	tcpcompress(Tcpc*, Block*, Fs*);Block*	tcpuncompress(Tcpc*, Block*, ushort, Fs*);