Time Division Duplex is a technology used in communications where the uplink and the downlink use the same frequency. The uplink and downlink are separated in time. Users get one or more time slots assigned for the uplink and the downlink respectively. TDD makes it possible to dynamically allocate more bandwidth to downstream traffic if necessary. This makes TDD very bandwidth efficient in cases where the traffic flow is asymmetric.
In order to cater for the time needed by the data to travel from the source to the destination, a guard time is needed between the time slots assigned to the uplink and the downlink. For the same reason, the distance between the user and the network may not be too big in a wireless network. Another disadvantage of TDD is that it introduces some delay within the network.