Also important was ALOHAnet's use of the outgoing hub channel to broadcast packets directly to all clients on a second shared frequency, using an address in each packet to allow selective receipt at each client node. Two frequencies were used so that a device could both receive acknowledgments regardless of transmissions. The Aloha network introduced the mechanism of randomized multiple access, which resolved device transmission collisions by transmitting a package immediately if no acknowledgement is present, and if no acknowledgment was received, the transmission was repeated after a random waiting time.