Bug 1465

The problem seems to be still here, see https://groups.google.com/forum/#!topic/ns-3-users/q_ktE2vZdds

Moreover, I double checked and on my computer the network *seems* to be formed, but no packets are actually exchanged.
Checking the cap files, the ARP request arrives at the intended node, but it doesn't reply.

(In reply to Tommaso Pecorella from comment #1)
> The problem seems to be still here, see
> https://groups.google.com/forum/#!topic/ns-3-users/q_ktE2vZdds
> 
> Moreover, I double checked and on my computer the network *seems* to be
> formed, but no packets are actually exchanged.
> Checking the cap files, the ARP request arrives at the intended node, but it
> doesn't reply.


I think it is due to the problem reported in bug 737, which was marked invalid a while back but which I think probably ought to be reopened and fixed based on Kirill's patch there or something similar.

The problem is that the relaying nodes do not defer and backoff; they immediately forward, causing a repeatable ARP collision on a grid topology.  The ARP eventually fails.

(In reply to Tom Henderson from comment #2)
> (In reply to Tommaso Pecorella from comment #1)
> > The problem seems to be still here, see
> > https://groups.google.com/forum/#!topic/ns-3-users/q_ktE2vZdds
> > 
> > Moreover, I double checked and on my computer the network *seems* to be
> > formed, but no packets are actually exchanged.
> > Checking the cap files, the ARP request arrives at the intended node, but it
> > doesn't reply.
> 
> 
> I think it is due to the problem reported in bug 737, which was marked
> invalid a while back but which I think probably ought to be reopened and
> fixed based on Kirill's patch there or something similar.
> 
> The problem is that the relaying nodes do not defer and backoff; they
> immediately forward, causing a repeatable ARP collision on a grid topology. 
> The ARP eventually fails.

Sadly it's not that easy. ARP request is received correctly, but ARP reply can't be delivered because the node can't find a route to the originator.
Basically it's a bug in HWMP.

Another interesting fact. Beacons gave a duration of 60 us. Path req. have ZERO duration

I must correct myself. It *is* a collision issue, but it's not ARP. The colliding packets are path requests.

I Still have no idea how to fix it for good. I tried adding some jitter but no luck.
As a side note, HWMP uses random variables but no stream assignments(if I'm right).


(In reply to Tommaso Pecorella from comment #3)
> (In reply to Tom Henderson from comment #2)
> > (In reply to Tommaso Pecorella from comment #1)
> > > The problem seems to be still here, see
> > > https://groups.google.com/forum/#!topic/ns-3-users/q_ktE2vZdds
> > > 
> > > Moreover, I double checked and on my computer the network *seems* to be
> > > formed, but no packets are actually exchanged.
> > > Checking the cap files, the ARP request arrives at the intended node, but it
> > > doesn't reply.
> > 
> > 
> > I think it is due to the problem reported in bug 737, which was marked
> > invalid a while back but which I think probably ought to be reopened and
> > fixed based on Kirill's patch there or something similar.
> > 
> > The problem is that the relaying nodes do not defer and backoff; they
> > immediately forward, causing a repeatable ARP collision on a grid topology. 
> > The ARP eventually fails.
> 
> Sadly it's not that easy. ARP request is received correctly, but ARP reply
> can't be delivered because the node can't find a route to the originator.
> Basically it's a bug in HWMP.

(In reply to Tom Henderson from comment #2)
> (In reply to Tommaso Pecorella from comment #1)
> > The problem seems to be still here, see
> > https://groups.google.com/forum/#!topic/ns-3-users/q_ktE2vZdds
> > 
> > Moreover, I double checked and on my computer the network *seems* to be
> > formed, but no packets are actually exchanged.
> > Checking the cap files, the ARP request arrives at the intended node, but it
> > doesn't reply.
> 
> 
> I think it is due to the problem reported in bug 737, which was marked
> invalid a while back but which I think probably ought to be reopened and
> fixed based on Kirill's patch there or something similar.
> 
> The problem is that the relaying nodes do not defer and backoff; they
> immediately forward, causing a repeatable ARP collision on a grid topology. 
> The ARP eventually fails.

the patch to bug 2369 (changeset 12345:a94d790ef6e5) changed the behavior so that backoff occurs if the request for access arrives during AIFS interval, but allows immediate access if the medium has been idle for time >= AIFS.  See discussion and documentation in bug 2369.

This behavior solves the grid configuration issue (because backoff will now be invoked upon relaying a frame), so am marking this as resolved fixed.

*** Bug 1605 has been marked as a duplicate of this bug. ***