f areas is the key for correct site re-engineering. Site Re-engineering Works In this phase, the planners' recommendations are implemented on the field. Sometimes, the site needs to be reconfigured (in the case of re-azimuthing, for example). In this case radio parameters and adjacency network definitions may change. Results Qualification Qualifying results are always a crucial part of any optimisation process. This qualification consists of checking whether the optimisation actions helped achieve the objective or not. It is also the phase where the process can be launched again in order to propose better solutions. Frequency Planning Review Spectral efficiency is the key word in TDMA based networks. The frequency resource is rare and expen- sive, SO it should be efficiently used. Frequency planning is an operation that is necessary each time it becomes difficult to find new frequencies for integrating new sites. In fact, while being optimised, the network still continues to expand with the addition of new sites. Therefore the frequency plan review, even though part of the planning process, also belongs to the optimisation phase. Frequency planning aptitude is a mandatory skill for good network optimisers. It is based on well-established procedures. However, field knowledge is also required, especially for manual tunings. Process Frequency plan implementation is a serious task that involves several departments. For instance, the NWP team is in charge of producing the radio parameters, the NMS team will implement the new database while the implementation team will be available on sensitive sites to intervene quickly where problems occur. Success in the implementation of a frequency plan on a multivendor area is a challenging issue. Good communication is very important in such a case. One efficient solution may be to use frequency band segmentation. Each vendor is allocated a separate frequency band that will not interfere with the others. Frequency Planning in the Optimisation Phase Establishing a good frequency p