Hi Lotte,
I guess when the messages become stale, they could be deleted from the
queue...as there would be no point sending them. We would have to note at
what time they were put in the queue, and use the corresponding timeouts -
- for a queued RREQ, there's no point sending it if the time for an
expected RREP has been reached, because AODVv2 itself would create a new
RREQ and add it to the queue.
- for a queued RREP, there's no point sending it if the time for an
expected RREP has been reached, because receivers of this delayed RREP
would ignore it. (Although, since RREP_Gen doesnt know when the RREQ was
generated, it might still send this with a delay that means RREQ_Gen would
ignore it)
- for a queued RREP_Ack there's no point sending if the time for an
expected RREP_Ack has been reached, as RREP_Gen would ignore it (again, we
dont know exactly when that timer expires on RREP_Gen so we might allow
this RREP_Ack to be sent with enough delay that it would get ignored)
- for a queued RERR, the only time it would be pointless to send is if
the reported route was re-established before the RERR was sent. In that
case the new route should have a greater seqnum and this route from the
RERR would be ignored by a receiver. For further optimisation, its possible
that when a route is installed you could go through any queued RERRs to see
if they still need sending.
Is that all really implementation detail though, would it cause
interoperability issues? Is it enough to say "you should limit the rate of
message generation, aiming for a maximum of CONTROL_TRAFFIC_LIMIT, and (to
help you out) here are the priorities...whether you want to discard
messages or queue them in priority order, whether you only take action when
the limit is reached, or when its close to being reached, that's up to
you."..? I suppose if some routers decided to discard messages rather than
queue them, it would affect protocol operation, but so would the huge
amount of messages being flooded across the network which caused it to
reach the limit anyway.
When the control message limit is reached, we want to give the network a
chance to recover, so if some messages were dropped and only the important
ones (e.g. RREPs and RREP_Acks) sent, then we are relying on RREQ retries
at a later point to deal with the fact we discarded some RREQs in that
period. I think thats why RREQ ended up lower down in the priorities,
because we know there are retries.
Kind regards,
Vicky.
On Fri, Mar 18, 2016 at 7:11 PM, Lotte Steenbrink <
lotte.steenbrink@xxxxxxxxxxxx> wrote:
Hi all,
Am 10.03.2016 um 15:48 schrieb John Dowdell <john.dowdell486@xxxxxxxxx>:
<snip>
(It’s not clear to me how this priority works. Do the messages just get
dropped when tsome threshold for max number of messages is reached? Is
there some queuing method because if their isn’t I don’t see how
priority would work at all, as the choices are drop or send. This whole
section seems out of place as we have’t talked about generating messages.
I’d suggest moving or removing JWD)
This is a good point. In order to be clear, we need to say that there is
a queue of messages and then use the priority mechanism to discard
low-priority queued messages. Or, perhaps better, we can say that messages
are not sent more frequently than one message per (1 /
CONTROL_TRAFFIC_LIMIT)th of a second, and then the queue is reordered based
on priority.
Any objections? If not I'll craft some text that says that.
Thanks. I think it represents a nice improvement.
+1
Quick followup to that one:
I changed the text to:
To avoid congestion, each AODVv2 router's rate of message generation
SHOULD be limited (CONTROL_TRAFFIC_LIMIT) and administratively
configurable. Messages SHOULD NOT be sent more frequently than one message
per (1 / CONTROL_TRAFFIC_LIMIT)th of a second. If this threshold is
reached, messages MUST be sent based on their priority:
* Highest priority SHOULD be given to RREP_Ack messages. This allows links
between routers to be confirmed as bidirectional and
avoids undesired blacklisting of next hop routers.
* Second priority SHOULD be given to RERR messages for undeliverable IP
packets. This avoids repeated forwarding of packets over broken routes that
are still in use by other routers.
* Third priority SHOULD be given to RREP messages in order that RREQs do
not time out.
* Fourth priority should be given to RREQ messages.
* Fifth priority should be given to RERR messages for newly invalidated
routes.
* Lowest priority SHOULD be given to RERR messages generated in response
to RREP messages which cannot be regenerated. In this case the route
request will be retried at a later point.
, but I don’t think I got the beginning quite right. What I’m stumbling
over is the „reordering based on priority“ thing:
if we’re doing something like:
while CONTROL_TRAFFIC_LIMIT reached:
reorder(queue)
send(queue.getHighestPrio())
we might *only* send RREP_Acks and RREPs, while other message types are
never sent. This might als mean that (then stale) RREP_Acks are sent, while
fresh RREQs are discarded?
Additionally, note that I’ve reworded the bullet points to improve clarity
and conciseness. I hope I preserved their meaning! (any comments very
welcome)
Also, while I understand Justin’s point that it is confusing to talk about
message sending before message generation, but it follows the general
structure of the document and I don’t really see where else this paragraph
belongs.
Cheers,
Lotte
