Cambium PMP systems use Time Division Duplexing (TDD) - one channel alternately transmits and receives - rather than using one channel for transmitting and a second channel for receiving. To accomplish TDD, the AP must provide sync to its SMs – it must keep them in sync. Furthermore, co-located APs must be synced together - an unsynchronized AP that transmits during the receive cycle of a co-located AP can prevent that second AP from being able to decode the signals from its SMs. In addition, across a geographical area, APs that can “hear” each other benefit from using a common sync to further reduce self-interference within the network.