Narrowband-internet of Things (NB-IoT) is a low power wide area network that contributes strongly to the revolution and expansion of the internet of things (IoT). Here, we aim at improving the performance and reliability of NB-IOT. Given than random access is one of the most influential characteristics of NB-IoT system performance, a detailed study of the NB-IOT random access was conducted, taking into account random access channel (NPRACH) periodicity, number of collisions, number of users, random access preamble repetitions and time taken for all system users to finalize a random access procedure. Simulation results have shown that appropriately choosing NPRACH periodicity values can efficiently achieve uplink channel optimization between its two signals NPRACH and NPUSCH with an acceptable number of collisions and a high number of delivered packets. Short periodicities (40ms and 80ms) show optimal results in reducing the number of collisions for both low and high traffic while all users win NPRACH and start to send data to the base station after approximately 2 second. However, short periodicities waste more uplink resources in random access, minimizing resources remaining for data transmission. Medium-length periodicities (such as 160ms and 320ms) show a promising performance that balances the two uplink physical channels. Our results demonstrate that doubling the number of users (from 40 to 80) is not a considerable factor in choosing NPRACH periodicity with different repetition values. We further showed how to maximize the system performance by selecting certain NPRACH periodicity value for every preamble repetition scheme.