Generating random arrivals via Poisson process c++

There is something I didn't understand. I use the sample given from the cpp reference to generate numbers:

const int nrolls = 10; // number of experiments

std::default_random_engine generator;
std::poisson_distribution<int> distribution(4.1);

for (int i=0; i<nrolls; ++i){
int number = distribution(generator);
cout<<number<<" "<<endl;
}

(original code: http://ift.tt/15YoFeV )

This outputs: 2 3 1 4 3 4 4 3 2 3 and so on... First of all what those numbers mean? I mean do I have to sum them to create timing? For example: 2, (2+3)=5, (5+1)=6, (6+4)=10,..., and so on..

Secondly, my real question is, I need to produce both random arrivals for network packets and the size of packets. I mean, when the packets come and if packets come, what are the size of packets? How can I do that? I need something like that: http://ift.tt/1tALJLW