On 2020-11-24 12:43, David Laight wrote:
From: Martin Schiller
Sent: 24 November 2020 09:36
1. DTE interface changes immediately to LAPB_STATE_1 and start sending
SABM(E).
2. DCE interface sends N2-times DM and changes to LAPB_STATE_1
afterwards if there is no response in the meantime.
Seems reasonable.
It is 35 years since I wrote LAPB and I can't exactly remember
what we did.
If I stole a copy of the code it's on a QIC-150 tape cartridge!
I really don't remember having a DTE/DCE option.
It is likely that LAPB came up sending DM (response without F)
until level3 requested the link come up when it would send
N2 SABM+P hoping to get a UA+F.
It would then send DM-F until a retry request was made.
We certainly had several different types of crossover connectors
for DTE-DTE working.
David
The support for DTE/DCE was already in the LAPB code and I made it
configurable from userspace (at least for hdlc interfaces) with this
commit:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=f362e5fe0f1f
For Layer3 (X.25) I will add it with an addional patch (you already
commented on that) on a next step.
The described behaviour above is my interpretation of point 2.4.4.1 of
the "ITU-T Recommendation X.25 (10/96) aka "Blue Book" [1].
[1] https://www.itu.int/rec/T-REC-X.25-199610-I/
Signed-off-by: Martin Schiller <ms@xxxxxxxxxx>
---
net/lapb/lapb_timer.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/net/lapb/lapb_timer.c b/net/lapb/lapb_timer.c
index 8f5b17001a07..baa247fe4ed0 100644
--- a/net/lapb/lapb_timer.c
+++ b/net/lapb/lapb_timer.c
@@ -85,11 +85,18 @@ static void lapb_t1timer_expiry(struct timer_list
*t)
switch (lapb->state) {
/*
- * If we are a DCE, keep going DM .. DM .. DM
+ * If we are a DCE, send DM up to N2 times, then switch to
+ * STATE_1 and send SABM(E).
*/
case LAPB_STATE_0:
- if (lapb->mode & LAPB_DCE)
+ if (lapb->mode & LAPB_DCE &&
+ lapb->n2count != lapb->n2) {
+ lapb->n2count++;
lapb_send_control(lapb, LAPB_DM, LAPB_POLLOFF, LAPB_RESPONSE);
+ } else {
+ lapb->state = LAPB_STATE_1;
+ lapb_establish_data_link(lapb);
+ }
break;
/*
--
2.20.1
-
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