Subject: [manet] AODV - UU 0.8.1(last but one node in a chain doesn't forward the route reply until source retransmits for route request again)

From: "Xavi Mantecón (UPCNet)"<[email-masked]>
Date: Wed, 08 Dec 2004 20:59:17 +0100

Hi to all,
 
I'm making some test with AODV-UU 0.8.1 (I've tried 0.9v but the problem 
persists). I've made a test with 5 laptops (running Fedora 2, kernel 
2.6.9 and IPW2100 v1.01 driver for Intel Centrino).

They are working well without AODV and static routes (good RTTS, 
bandwith, delays...)

Laptops are all in the same subnet (192.178.7.x) and out of range as 
desired to make the test:

192.168.7.2 <-> 192.168.7.3 <->192.168.7.4 <->192.168.7.5 <->192.168.7.6

This is,

7.2 only sees 7.3
7.3 only sees 7.2 and 7.4
7.4 only sees 7.3 and 7.5
7.5 only sees 7.4 and 7.6
7.6 only sees 7.5

(it has been made using iptables, filtering by MAC address)

I'm testing now Round Trip Time. I ping from 7.2 to 7.3, 7.4, 7.5 and 
7.6, and compare the results of the first ping (which includes AODV 
RouteRequest and Route Reply).

When I ping 7.2 to 7.3, I get a 4ms value for the first ping and 2 ms 
for the following ones. That's ok (first ping includes rreq and rrep, it 
adds 2 ms).

But when I ping 7.4, the result for the first RTT is 300ms !!, the 
following ones are ok (about 4ms). Route taken by the pings is ok but 
(7.2->7.3>7.4)

If I ping 7.5, the first RTT is about 500 ms !!, the following ones are 
ok (about 6ms). Route taken is good again.

And the same for all the other cases.... it goes on.

I've made captures with Ethereal. It seems that there's always the same 
error.

*******************************************************************************
This is what's happening:

Let's see what happens with 2 jumps, pinging from 7.2 tp 7.4

7.2             7.3         7.4         7.5

send rreq ->
               fw rreq ->

                          <-  rrep
                *
retx rreq ->
             <- fw rrep

(*) -> there should be a forwarded rrep from 7.4 to 7.3, but it's not here!

Then the route it's stablished and communication begins.

It seems that the last but one (or penultimate?) doesn't forward the 
first reply, until the source retransmits for rreq again (this is why 
RTT for the first pings times are bigger than they should be, 
retransmission time is added to the first time).

*****************************************************************************************

Let's see what happens with 3 jumps, pinging from 7.2 tp 7.5

7.2             7.3         7.4         7.5

send rreq ->
               fw rreq ->
                           fw rreq  ->
                                    <-  rrep
                            *
retx rreq ->
               fw rreq ->
                        <- fw rrep
             <- fw rrep

and it begins to transmit data. It's the same than before. The last but 
one only forwards the reply when he receives the second rreq.

*****************************************************************************************

This happens about 99% times. In 1% cases the last but one forwards the 
first reply, and times are what they should be.

Iptables is configured correctly, so I can assure that packets go 
through desired route. And there are cases where the things works like 
they should (1% cases, but it works!!)

Does someone know what's happening? Someone has made this test and has 
get the desired values for the first RTT (stablish route + RTT).

Thanks in advance. I'm waiting for you responses. Kind regards,

Xavi M (UPC student)

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---

From: Erik Nordström <[email-masked]>
Date: Fri, 10 Dec 2004 14:56:16 +0100

The delay is probably caused by the expanding ring search. The first 
RREQ only reaches the first neighbor (if using link layer feedback) and 
then the route discovery on the source node needs to timeout before a 
new RREQ with a higher TTL is sent. This goes on as the ring expands... 
However, the delays you mention still seem a bit long. Try using 
"--no-expanding-ring" when starting AODV-UU and see what happens.

Erik

Xavi Mantecón (UPCNet) wrote:

> Hi to all,
>
> I'm making some test with AODV-UU 0.8.1 (I've tried 0.9v but the 
> problem persists). I've made a test with 5 laptops (running Fedora 2, 
> kernel 2.6.9 and IPW2100 v1.01 driver for Intel Centrino).
>
> for the following ones. That's ok (first ping includes rreq and rrep, 
> it adds 2 ms).
>
> If I ping 7.5, the first RTT is about 500 ms !!, the following ones 
> are ok (about 6ms). Route taken is good again.
>
> I've made captures with Ethereal. It seems that there's always the 
> same error.
>
>
>
> and it begins to transmit data. It's the same than before. The last 
> but one only forwards the reply when he receives the second rreq.
>
>
> This happens about 99% times. In 1% cases the last but one forwards 
> the first reply, and times are what they should be.
>