Allow the number of terminals can simultaneously transmit data?

I have 21 ZB modules. A coordinator, the rest is a router. I try to let eight router were the other eight different router to send data. When the two group is the normal work, once again to join a group will not work. The amount of data of each group is 6kps

200kps / 6kps =33 groups This algorithm is correct?

Allow the number of groups to send data at the same time, in theory?

In theory and practice - this is radio, so only 1 node can ever send at one time.

The only way to have parallel data is to make sure your 8 XBee pairs are on 8 different frequencies (or channels). So you would have 8 coordinators and 8 routers, each linked 1-to-1.

Are you sure this is the correct technology? Ethernet radios can send many mbps on a single frequency.