No Subject

[Haobo Yu <haoboy@ISI.EDU>]

The following way to do it is rather involved, and it requires
modification of UDP agent and deriving your own cbr class from
CBR_Traffic. If you do not follow things below, wait a couple of weeks and
I'll set up a web page as how to pass app-level data in ns. 

Basically, there are 3 steps and you need the AppData stuff:

(1) Derive a class from AppData (defined in ns-process.h) which contains,
say, sequence number. In this derived class, you should define method
pack() and a constructor so that it "marshalls" data into/from a packet.

class MyData : public AppData {
private: 
	int num_; // my number
public:
        // used to extract data from a byte stream
        struct hdr : AppData::hdr {
                int num_;
        };
public:
        MyData(int d) : AppData(MYDATA) {
                num_ = d;
        }
        MyData(char *b) : AppData(b) {
                hdr* h = (hdr *)b;
                num_ = h->num_;
        }

        inline int& num() { return num_; }
        virtual int size() const { return hdrlen(); }
        virtual int hdrlen() const { return sizeof(hdr); }

        virtual void pack(char* buf) const {
                AppData::pack(buf);
                ((hdr*)buf)->num_ = num_;
        }
};

(2) Remember to put MYDATA in the enum AppDataType in ns-process.h

(3) Derive your own cbr class from CBR_Traffic in cbr_traffic.cc, override
its timeout() function (defined in trafgen.cc) to pass your own data into
a packet:

* construct send(appdata, size_) construct your own AppData:

void MyCBR::timeout()
{
        if (! running_)
                return;

//-----
        /* send a packet */
        // send(size_);
	// Construct our own appdata, assuming the number magicall appears
	// as NUM_
	MyData data(NUM_);
	// Instead of send(size_), call send(size_, data)
	send(size_, &data);
//-----
        /* figure out when to send the next one */
        nextPkttime_ = next_interval(size_);
        /* schedule it */
        if (nextPkttime_ > 0)
                timer_.resched(nextPkttime_);
}

void MyCBR::process_data(int size, char *data)
{
	if (data == NULL)
		return;
	if (AppData::type(data) != MYDATA)
		// ERROR
		abort();
	AppData d(data);
	// Process your number here...
}

* Modify UDP agent to pack your own number into packets and pass your own 
data to your own CBR:

- Copy UdpAgent::sendmsg(int, const char*) to UdpAgent::send(int size,
const AppData *data). Then change the two allocpkt() to
allocpkt(data->size()), and add the following line before the two
"target_->recv(p)":
	data->pack((char *)pkt->accessdata());

- Add: 

UdpAgent::recv(Packet *pkt, Handler *)
{
        if (app_ == 0) 
                return;
        hdr_inval *ih = (hdr_inval *)pkt->access(off_inv_);
        ((MyCBR*)app_)->process_data(ih->size(),(char*)pkt->accessdata());
        Packet::free(pkt);
}

That's about it.

- Haobo

> Subject: cbr packets
> 
> Hi,
> How to put a number in a CBR packet at the source, and read this number
> at the receiver?
> 
> Arnaud.
> - -- 
> - ----------------------------------------------------------------------
> Arnaud Legout
> 
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