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NATM(4)			 BSD Kernel Interfaces Manual		       NATM(4)

NAME
     natm -- Native Mode ATM protocol layer

DESCRIPTION
     The BSD ATM software comes	with a native mode ATM protocol	layer which
     provides socket level access to AAL0 and AAL5 virtual circuits.  To en-
     able this protocol	layer, add
	   options NATM
	   device atm
     to	your kernel configuration file and re-make the kernel (do not forget
     to	do "make clean").

NATM API
     The NATM layer uses a struct sockaddr_natm	to specify a virtual circuit:

	   struct sockaddr_natm	{
	     uint8_t	   snatm_len;		   /* length */
	     uint8_t	   snatm_family;	   /* AF_NATM */
	     char	   snatm_if[IFNAMSIZ];	   /* interface	name */
	     uint16_t	   snatm_vci;		   /* vci */
	     uint8_t	   snatm_vpi;		   /* vpi */
	   };

     To	create an AAL5 connection to a virtual circuit with VPI	0, VCI 201 one
     would use the following:

	     struct sockaddr_natm snatm;
	     int s, r;
	     s = socket(AF_NATM, SOCK_STREAM, PROTO_NATMAAL5);
				  /* note: PROTO_NATMAAL0 is AAL0 */
	     if	(s < 0)	{ perror("socket"); exit(1); }
	     bzero(&snatm, sizeof(snatm));
	     snatm.snatm_len = sizeof(snatm);
	     snatm.snatm_family	= AF_NATM;
	     sprintf(snatm.snatm_if, "en0");
	     snatm.snatm_vci = 201;
	     snatm.snatm_vpi = 0;
	     r = connect(s, (struct sockaddr *)&snatm, sizeof(snatm));
	     if	(r < 0)	{ perror("connect"); exit(1); }
	     /*	s now connected	to ATM!	*/

     The socket() call simply creates an unconnected NATM socket.  The
     connect() call associates an unconnected NATM socket with a virtual cir-
     cuit and tells the	driver to enable that virtual circuit for receiving
     data.  After the connect()	call one can read() or write() to the socket
     to	perform	ATM I/O.

Internal NATM operation
     Internally, the NATM protocol layer keeps a list of all active virtual
     circuits on the system in natm_pcbs.  This	includes circuits currently
     being used	for IP to prevent NATM and IP from clashing over virtual cir-
     cuit usage.

     When a virtual circuit is enabled for receiving data, the NATM protocol
     layer passes the address of the protocol control block down to the	driver
     as	a receive "handle".  When inbound data arrives,	the driver passes the
     data back with the	appropriate receive handle.  The NATM layer uses this
     to	avoid the overhead of a	protocol control block lookup.	This allows us
     to	take advantage of the fact that	ATM has	already	demultiplexed the data
     for us.

SEE ALSO
     en(4), fatm(4), hatm(4), natmip(4), patm(4)

AUTHORS
     Chuck Cranor of Washington	University implemented the NATM	protocol layer
     along with	the EN ATM driver in 1996 for NetBSD.

CAVEATS
     The NATM protocol support is subject to change as the ATM protocols de-
     velop.  Users should not depend on	details	of the current implementation,
     but rather	the services exported.

BSD			       December	29, 1997			   BSD

NAME | DESCRIPTION | NATM API | Internal NATM operation | SEE ALSO | AUTHORS | CAVEATS

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