Very Long Baseline Interferometry (VLBI) has a very important role in geodesy as it provides important products such as all five Earth Orientation Parameters (EOP) and it is the only space geodetic technique that contributes to the International Celestial Reference Frame (ICRF). At the beginning of the VLBI analysis, it is needed to do the resolution of the ambiguities for S/X band multiband delays and the calculation of the ionospheric calibration. In the past, these two pre-processing steps were performed by other software packages such as Solve/nuSolve, and the Vienna VLBI and Satellite Software (VieVS) always used external results. For the Vienna VLBI Analysis Center it is important that the ambiguity resolution and ionospheric calibration can be calculated in VieVS in order to be independent of the external results in the vgosDB. The first part of the thesis deals with a new approach of the ambiguity resolution based on multiband-singleband delay differences. Using triangle delay closures, the ambiguities per baseline can be calculated with a network of all stations. The approach was successfully tested with S/X band sessions of the Continuous Very Long Baseline Interferometry Campaign 2017 (CONT17) and has shown that VLBI sessions with clock breaks can also be solved. There have been individual observations in CONT17 Sessions that still require an ambiguity correction after this automated solution, these can be solved manually in VieVS. Performing an ambiguity resolution exclusively manually is not recommended, as it is very time consuming and can only be done with practice. Furthermore, all the necessary steps required for software implementation of the new automatic ambiguity resolution approach in VieVS were worked out. In the second part of the thesis, the calculation of the ionospheric calibration was described in more detail. The topic is particularly relevant because over time, the methods for calculating the effective frequencies and ionospheric calibration have changed significantly which leads to inconsistencies in the vgosDB files. Here it could be shown that the calculated solution of the ionospheric contribution for CONT17 can deviate from the vgosDB up to 100 ps. The following effect of the difference in the station coordinates was up to 1 mm. Together with the Vienna VLBI Analysis Center, it was possible to implement the updated calculation for the ionospheric calibration in VieVS so that the values can be calculated on the fly instead of using external results.