stimation of the interface implementation efforts can be used in order to estimate the size of the organization in both cases. If a specific portion of staff is devoted to interface implementation efforts in the company's R&D, the size of the R&D department(s) and consequently the total size of the organization can be estimated. All protocols max (E) Only IETF protocols Fig. 1 Efforts devoted to interface implementation by a mediation software company O. Mazhelis and P. Tyrväinen Assuming that 5-10% of personnel are dealing with interface implementation and maintenance, it is possible to infer that: In the first case, the organization is likely to have a few hundreds of employees. In the second case, the size of the organization is estimated to be a few dozens of employees (assuming that all protocols are to be developed within two years). Therefore, only relatively large vendors are capable of serving the incumbent operators, due to large efforts required. On the other hand, it is much easier for new software vendors (especially those with highly limited resources) to serve new operators, which require only IETF interfaces to be implemented. As a result, a significant number of newcomers are likely to compete for the market of such new operators. Thus, higher interface implementation efforts represent a threshold for the vendors entering the market of incumbent operators thereby effectively disabling the entries by small commencing vendors. Thus the high required vendors size is a real market entry barrier to new entrants in the OSS/BSS software market if also legacy network interfaces need to be supported. In a longer run, such a threshold can be assumed to reduce the number of software vendors in the market, causing a delay in the vertical disintegration of the market. The above analysis suggests that a market polarization scenario illustrated in Fig. 2 is likely, as long as a fraction of the customers in the market require a large number of complex interfaces to be supported, while the other customers request