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
     enable 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 circuit
     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 circuit 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 develop.  Users should not depend on details of the current implementa-
     tion, but rather the services exported.

BSD
								 December 29, 1997							       BSD