freebsd-skq/share/man/man4/natm.4

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.\" $FreeBSD$
.\"
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.Dd December 29, 1997
.Dt NATM 4
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.Os
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.Sh NAME
.Nm natm
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.Nd Native Mode ATM protocol layer
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.Sh DESCRIPTION
The
.Bx
ATM software comes with a
.Em native mode ATM protocol layer
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which provides socket level access to AAL0 and AAL5 virtual circuits.
To enable this protocol layer, add
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.Dl options NATM
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to your kernel configuration file and re-make the kernel (do not forget
to do
.Dq make clean ) .
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.Sh NATM API
The NATM layer uses a
.Vt struct sockaddr_natm
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to specify a virtual circuit:
.Bd -literal -offset indent
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 */
};
.Ed
.Pp
To create an AAL5 connection to a virtual circuit with VPI 0, VCI 201
one would use the following:
.Bd -literal -offset indent
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));
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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! */
.Ed
.Pp
The
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.Fn socket
call simply creates an unconnected NATM socket.
The
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.Fn 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
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.Fn connect
call one can
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.Fn read
or
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.Fn write
to the socket to perform ATM I/O.
.Sh Internal NATM operation
Internally, the NATM protocol layer keeps a list of all active virtual
circuits on the system in
.Dv natm_pcbs .
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This includes circuits currently being used for IP to prevent NATM and
IP from clashing over virtual circuit usage.
.Pp
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
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.Dq 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
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advantage of the fact that ATM has already demultiplexed the data for
us.
.Sh CAVEATS
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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
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the services exported.
.Sh SEE ALSO
.Xr en 4 ,
.Xr fatm 4 ,
.Xr hatm 4 ,
.Xr natmip 4 ,
.Xr patm 4
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.Sh AUTHORS
.An Chuck Cranor
of Washington University implemented the NATM protocol layer
along with the EN ATM driver in 1996 for
.Nx .