Figure 1: Rendezvous in CRNs: if there is no hatched rectangle of a PU on a particular channel, it means that this PU is not active on this channel; for example, there is no PU’s activity on Channel 3 (Ch3). CR1, not being in the range of any of PUs, can use all four channels. CR3 can sporadically use Channel 1 due to the PU1 activity there. CR2 has two available channels (1, 3), while the availability in Channels 2 and 4 is limited to spectrum holes of PU2 and PU3. Hence, CRs have an asymmetric channel occupancy knowledge. In a 16 slots of long time period, CR1 user can meet CR2 user on Channel 1 in slot 0 and on Channel 3 in slot 5. However, they cannot communicate on Channel 4 in slot 9, nor on Channel 2 in slot 12, due to the PU2 and PU3 activities there (CR2 cannot transmit).