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libosmocore/lapd: Fixed handling of sequence errors at lapd_core.c 

If a sequence error is received, the N(R) variable must still be used to
acknowledge previously transmitted frames.

If there are two subsequent sequence errors received, ignore it. (Ignore
every second subsequent error.) This happens if our reply with the REJ is
too slow, so the remote gets a T200 timeout and sends another frame with
a sequence error. Test showed that replying with two subsequent REJ
messages could the remote L2 process to abort. Replying too slow shouldn't
happen, but may happen over serial link between BB and LAPD.
This commit is contained in:
Andreas Eversberg 2012-01-01 16:42:45 +01:00
parent c2b823faf0
commit 506a3443ba
1 changed files with 21 additions and 3 deletions
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24
src/shared/libosmocore/src/gsm/lapd_core.c
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@ -1497,14 +1497,32 @@ static int lapd_rx_i(struct msgb *msg, struct lapd_msg_ctx *lctx)
"V(R)=%u\n", ns, dl->v_recv);
/* discard data */
msgb_free(msg);
if (!dl->seq_err_cond) {
if (dl->seq_err_cond != 1) {
/* FIXME: help me understand what exactly todo here
dl->seq_err_cond = 1;
*/
dl->seq_err_cond = 1;
lapd_send_rej(lctx, lctx->p_f);
} else {
/* If there are two subsequent sequence errors received,
* ignore it. (Ignore every second subsequent error.)
* This happens if our reply with the REJ is too slow,
* so the remote gets a T200 timeout and sends another
* frame with a sequence error.
* Test showed that replying with two subsequent REJ
* messages could the remote L2 process to abort.
* Replying too slow shouldn't happen, but may happen
* over serial link between BB and LAPD.
*/
dl->seq_err_cond = 2;
}
return -EIO;
/* Even if N(s) sequence error, acknowledge to N(R)-1 */
/* 5.5.3.1: Acknowlege all transmitted frames up the N(R)-1 */
lapd_acknowledge(lctx); /* V(A) is also set here */
/* Send message, if possible due to acknowledged data */
lapd_send_i(lctx, __LINE__);
return 0;
}
dl->seq_err_cond = 0;