The Universal Mobile Telecommunications System (UMTS) offers panoply of 3G services that require a high protection of the transmitted information. In the present paper, we are interested by network access security, especially the protection of the data integrity and the provisioning of data encryption. A special interest will be given to the second set of 3GPP cryptographic algorithms UEA2/UIA2 based on the SNOW 3G algorithm. This set was, in fact, a subject only of few research works in comparison with the first one based on KASUMI algorithm. A closer look is taken at both the encryption algorithm UEA2 and the integrity algorithm UIA2 operations. The different operation modes of the algorithm SNOW 3G will be presented as well. A study of the time and space complexity of three algorithms has been carried out