ATM networks have emerged as viable transport technologies within the last few years. However, they do not yet have the stability and maturity of well-established networks such as X.25. Any new X.25 product can be tested and measured against steady components using validated Means of Testing (MoT) before it is introduced on the market. This is far from being the case with ATM. There is no Reference Implementation (RI) yet. In addition, many of the protocols that comprise ATM, such as the signalling protocols, are quite complex, which makes the validation of a new design or product that much more important.