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 cir

cuits. To
enable this protocol layer, add

options NATM

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 vir

tual circuit:

struct sockaddr_natm {

u_int8_t snatm_len; /* length */
u_int8_t snatm_family; /* AF_NATM */
char snatm_if[IFNAMSIZ]; /* interface

name */
u_int16_t snatm_vci; /* vci */
u_int8_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, size

of(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 ac

tive 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.

CAVEATS

The NATM protocol support is subject to change as the ATM

protocols
develop. Users should not depend on details of the current

implementation, but rather the services exported.

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.

BSD December 29, 1997

BSD