On Tuesday 28 February 2006 11:32, Tomas Vilda wrote:
>
> I can see what is going on E1 D channel, it's what both sides sends to each
> other.
Fine.
> Because there is not much comments on visdn source code I can't figure out,
> how to open lapd socket to netdev
Ok, let's do one step a time. I recently restructured the sockets model to be
even more generic and versatile.
Each socket represents a DLC. A DLC (Data Link Connection) is a virtual
channel between a (the, in your case) TE and the NT.
A DLC is identified by the pari SAPI and TEI which comprise the DLCI (DLC
Identifier).
The SAPI is the application identifier, 0 for q.931, 16 for X.25...
The TEI is the TE identifier, it may be dynamic in point-to-multipoint buses
or fixed to 0 in point-to-point interfaces (PRIs are P2P).
So, limiting ourselves to P2P interfaces you need at least a socket bound to
DLC 0/0 (SAPI=0, TEI=0), the steps are:
Create a socket:
s = socket(PF_LAPD, SOCK_SEQPACKET, 0); /* 0 = SAPI 0 */
Bind it to the interface:
#include <linux/lapd.h>
char intf[] = "visdn0";
setsockopt(s, SOL_LAPD, SO_BINDTODEVICE, intf, strlen(intf));
Bind it to the TEI 0:
struct sockaddr_lapd sal;
sal.sal_family = AF_LAPD;
sal.sal_tei = 0;
bind(s, (struct sockaddr *)&sal, sizeof(sal);
Now begin a select/poll loop on the socket and read the frames with recvmsg(2)
You may want to set the socket non-blocking as the whole q.921/q.931 is
asynchronous:
int oldflags;
oldflags = fcntl(s, F_GETFL, 0);
fcntl(s, F_SETFL, oldflags | O_NONBLOCK);
Note that U-frames will be received and transmitted with the MSG_OOB flag.
Looking at tests/traffic.c should be helpful understanding the sockets model.
End of lesson 1
Ciao :)
--
Daniele Orlandi
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