Re: [ns] Questions about Application Data

[Haobo Yu <haoboy@packetdesign.com>]

You were using a UDP agent, right? By default the UDP agent does not know
how to handle application data (it should, but it wasn't there). You can
either derive a simple UDP agent that implements a send(int, AppData*) and
a recv() that handles AppData. E.g., something like this:

void HttpInvalAgent::recv(Packet *pkt, Handler*)
{
        if (app_ == 0) 
                return;
        app_->process_data(pkt->datalen(), pkt->userdata());
        Packet::free(pkt);
}

void HttpInvalAgent::send(int realsize, AppData* data)
{
        Packet *pkt = allocpkt(data->size());
        pkt->setdata(data);
        Agent::send(pkt, 0);
}

It should be included in the udp agent. I'll add it there sometime later,
perhaps this week. Thanks for the Q that reminds me.

- Haobo

On Fri, 16 Feb 2001, Ken Sedgwick wrote:

> Greetings,
> 
> I'm trying to construct a simulation of a system of interconnected
> application-level programs.  I need to pass application data between
> the simulated entities in this model.
> 
> So far I have created a subclass of Application, and have provided
> a send method which attempts to create and send some application
> data:
>     PacketData * pdatap = new PacketData(nbytes);
>     memcpy(pdatap->data(), datap, nbytes);
>     agent_->send(nbytes, pdatap);
> 
> When I run the simulator, I get the following error:
>     "Agent::sendmsg(int, AppData*, const char*) not implemented"
> 
> I discovered the following comment in agent.cc where the
> indicated routine is defined:
> /*
>  * Place holders for sending application data
>  */
> 
> What is my best plan of attack here?  Should I implement the needed
> routines in agent.cc?  Is this hard for some reason?
> 
> I noticed other simulations with application level data seem to
> avoid passing the data in the "payload" of the packets.  Is an
> "out-of-band" mechanism for communicating the application data
> a better way to go?
> 
> Many, many thanks in advance.
> 
> Ken
> 
> Ken Sedgwick
> Zodiac Networks
> ken@zodiacnetworks.com
> 
>