[ndnSIM] How to prevent packet drops in ndnSIM 1.0?

[Al Dab]

Hi Alex,

That's a fair point. At this stage, however, I control the queue overflows
by making sure that total number of generated interests during my entire
simulation time will not exceed the capacity of individual queues. Also, I
keep the interests rate fairly low---consumer nodes will request on average
1 interest per sec. While keeping the interest rate fixed, the channel
delay, however, is going to be my independent variable which I'd like to be
able to set to different values ranging between 1-500ms and still not get
packet timeouts/drops.

With the previously described configurations, a 500ms channel delay makes
the majority of interests timed out (i.e., #TimedOutInterests almost
matches #InInterests, even though #DropInterests is fairly low---strange?).
Also, on data packets #DropData almost matches #InData and I barely receive
any data on the consumers side. I suspect all such drops are purely due to
timeouts which presumably could be avoided if packets time-to-live is set
sufficiently high. Isn't that right?

Thanks,
Ali

P.S. -- The topology I use is a binary tree of height 6, consumers as
leaves and the sole provider as root.

On Sat, Feb 28, 2015 at 3:21 PM, Alex Afanasyev <
alexander.afanasyev at ucla.edu> wrote:

> Hi Ali,
>
> No matter how big queue you set, if the rate with which you send packets
> exceed the capacity of the link, you will get data or interest packet to be
> dropped and interests will timeout.
>
> To prevent losses, you just need to make sure your topology matches the
> application demand.
>
> —
> Alex
>
> On Feb 28, 2015, at 11:10 AM, Al Dab <ali090385 at gmail.com> wrote:
>
> Hi,
>
> I am performing some simulations on ndnSIM 1.0 and for some of my
> measurements I'd like to completely eliminate interest/data drops or at
> least make them as close to zero as possible. My understanding is that most
> packet drops happen due to a timeout or a queue overflow. For the interest
> part, I have tried to increase the lifetime of the interest packets,
> MaxPitEntryLifetime and also the queue size as follows:
>
> ndn::AppHelper consumerHelper ("ns3::ndn::ConsumerZipfMandelbrot"); // to
> be installed on all consumers
> consumerHelper.SetAttribute ("LifeTime", StringValue ("9999s"));
> ...
> Config::Set ("/NodeList/<nodeID>/$ns3::ndn::Pit/MaxPitEntryLifetime",
> TimeValue (Seconds (9999))); // for all nodeID's
> ...
> Config::SetDefault ("ns3::DropTailQueue::MaxPackets", StringValue
> ("9999"));
>
> Still, I am getting some interest and data drops. These drops are measured
> through L3AggregateTracer and tend to increase by increasing the channel
> delay using the following command:
>
> Config::SetDefault ("ns3::PointToPointChannel::Delay", StringValue
> ("500ms"));
>
> I am wondering what other settings can lead to packet drops, both on
> interests and data and what is the most efficient way of preventing such
> drops?
>
> Thanks,
> Ali
>
>
>
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