Subject: Re: [manet] marginal utility of retransmitting pkt after retrytimeout

From: "Alvin C Valera Alvin" <[email-masked]>
Date: Sat, 17 Aug 2002 09:43:06 +0800

Hi Jim,

Here is the summary of the simulation results:

Packet Salvaging Off:
(1) AODV - Packet salvaging is in the code but not used. Turning local
repair on (and therefore packet salvaging) can increase packet delivery
by 2-3% when there are 10 and 20 sources. At 30 and 40 sources, local
repair somehow *adversely* affects the performance, lowering the packet
delivery by 4-6%.
 
(2) DSR - Drop by 8-10% in packet delivery ratio at 10 sources. The drop
increases as the traffic or number of sources increases.

Link Layer Feedback Off:
(1) AODV - Packet delivery drops by 25-30%. The drop goes down to around
10% when there are 30 or more sources.

(2) DSR - Packet delivery drops by 65-70% at 10 and 20 sources. The drop
goes down to around 30% when there are 30 or more sources.

I think the better performance of AODV can be attributed to its periodic
"hello" broadcast to ascertain link status. Hence even when the link
layer does not provide a quick feedback, the network layer will know,
albeit a little bit later, that the link is down. On the other hand, the
ns implementation of DSR relies heavily on the link layer feedback to
ascertain link status.

Best regards,
Alvin 

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From: "Alvin C Valera Alvin" <[email-masked]>
Date: Mon, 19 Aug 2002 10:03:31 +0800

Hi Frank,

You're right that by default, periodic "hello" messages are turned off.
But when you disable link layer feedback, it is turned on. The code is:

if(strncasecmp(argv[1], "start", 2) == 0) {
   btimer.handle((Event*) 0);
#ifndef AODV_LINK_LAYER_DETECTION
   htimer.handle((Event*) 0);
   ntimer.handle((Event*) 0);
#endif
   rtimer.handle((Event*) 0);
   return TCL_OK;
}

Note that when we do not define AODV_LINK_LAYER_DETECTION, the
htimer.handle() and ntimer.handle() are compiled. htimer is the hello
timer and ntimer is the neighbor timeout timer.

Best regards,
Alvin

>>> "Zhenqiang(Frank) Ye" <[email-masked]> 08/19/02 03:06 AM >>>

> "hello" broadcast to ascertain link status. Hence even when the link

Are you sure the "hello" function is ON in AODV implementation of ns-2?

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From: "Alvin C Valera Alvin" <[email-masked]>
Date: Mon, 19 Aug 2002 10:03:31 +0800

Hi Frank,

Best regards,
Alvin