[ndnSIM] OnInterest/OnData functions : access to an output queue

[Alex Afanasyev]

Quick thing. Don't forget to check that netDeviceFace returned by DynamicCast is no 0, otherwise you'll get in trouble with segfaults.

As for the queue. There are two options.  ns-3 style and c++-style.

(1) ns-3 style
==============
ns-3 allows you to access to many internal variables using so called attributes, without accessing implementation class.  For netdevice example, you can access to queue using the following:

PointerValue txQueueAttribute;
nd->GetAttribute ("TxQueue", txQueueAttribute); 
/** // or this, more safer way
 * bool ok = nd->GetAttributeFailSafe ("TxQueue", txQueueAttribute);
 * if (!ok) { /* something wrong */ }
**/

Ptr<Queue> txQueue = txQueueAttribute.Get<Queue> ();
if (txQueue == 0) { /*something wrong*/ }

...

(2) c++ style
Alternative and more C++ way is to make another dynamic cast on NetDevice object:

Ptr<PointToPointNetDevice> p2pNd = DynamicCast<PointToPointNetDevice> (nd);
...
and do the rest. 

The small disadvantage of the second approach is that it requires exact knowledge of the class you're casting to, that is, you need to include "point-to-point-net-device.h" header.


---
Alex

On Dec 12, 2012, at 2:43 PM, Natalya Rozhnova <natalya.rozhnova at lip6.fr> wrote:

> Hi Alex!
>  
> Thanks for your reply!
> That's what I thought to do, but one thing was disturbing me.
> I tried so this :
> Ptr<NetDeviceFace> netDeviceFace = DynamicCast<NetDeviceFace> (inFace);
> Ptr<NetDevice> nd = netDeviceFace->GetNetDevice ();
>  
> Then, I presume to use the function GetQueue() which is in PointToPointNetDevice class and not virtual function of base NetDevice object.
>  So I'm just confused how to get the p2p device after getting the NetDevice object...
>  
> Thanks,
> Natalya
>  
> 13.12.2012, 04:55, "Alex Afanasyev" <alexander.afanasyev at ucla.edu>:
>> Hi, Natalya!
>> 
>> It is easy, but would take a couple of steps. 
>> 
>> First, you need to figure out what from which type of face you have received a packet (as it could be an application face, which doesn't have a queue).  This could be done using DynamicCast call, like in https://github.com/NDN-Routing/ndnSIM/blob/master/model/ndn-l3-protocol.cc#L229.
>> 
>> Second, you will need to get netdevice pointer from the NetDeviceFace using GetNetDevice method (http://ndnsim.net/doxygen/classns3_1_1ndn_1_1_net_device_face.html#ae5ee510df5ba24c4a1aa94343302bb46).
>> 
>> Finally, you can access queue and other NetDevice attributes in a standard NS-3 way.
>> 
>> ---
>> Alex
>> 
>> On Dec 12, 2012, at 1:46 PM, Natalya Rozhnova <natalya.rozhnova at lip6.fr> wrote:
>> 
>>  Hi everyone,
>> 
>>  I'm trying to access to the output queue from m_forwardingStrategy::OnInterest(...) and OnData(...) functions. I need to access to the output queue installed on the interface from where the router just received a packet.
>>  Like:
>>  +-----+
>>  | R     |->out
>>  |        |
>>  +-----+<-in
>> 
>>  What I'm actually trying to do is : when the router receives an Interest (or Data) packet on the Interface "in", I'd like to access to the queue instaled on interface "out" and to put there some values.
>>  How I could access to this queue correctly?
>> 
>>  Thanks in advance!
>>  Best,
>>  Natalya
>>  
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