One TTI duration corresponds to a number of consecutive symbols for one transmission in time domain. In the time domain, 5G NR will enable scalability to latencies much lower than what’s possible in today’s LTE networks. Today, LTE supports a fixed TTI of 1 ms. 5G frame structure is flexible.  This flexibility allows the air interface to optimize for lower latencies using shorter TTI (e.g., 100s of µs) or trading off for higherspectral efficiency for delay-tolerant use cases with a longer TTI

In addition to a scalable TTI, 5G NR will also support service-aware TTI multiplexing on the same
frequency that allows transmissions with different TTIs to start on integer symbol boundaries instead of a subframe boundary