ks. The regulation regarding mobile ultra-broadband access which is coming with 5G and beyond should be targeted to support the innovation of services and application in par- allel with existing enhanced services (e.g. ultra-broadband access to the Internet for use of OTT services via mobile network with very high bitrates). Network neutrality also influences mobile ultra-broadband, including the mobile operators, service providers, and customers. However, network neutrality may have a certain negative effect on inno- vation capabilities of mobile operators, which have to invest in mobile ultra-broadband access and core networks, but it has a positive effect on OTT services and applications for which mobile broadband is used in practice. Mobile operators also enjoy increased revenues due to higher usage statistics of mobile users via ultra-broadband access of OTT services. In that manner network neutrality has a positive effect on mobile opera- tors' revenues from broadband access, which brings higher revenues than mobile voice in the second part of the 2010s, and such a trend will continue. However, when there are stricter network neutrality rules, it may limit the pos- sibility for quality differentiation, thus reducing the motivation of mobile network operators to invest in new technologies (e.g. 5G in the 2020s, or 6G, expected in the 2030s) and to improve the return on their investment in new technolo- gies. Nevertheless, strict network neutrality fosters innovations from OTT service providers. References Generally, it will be nearly impossible for regulation to determine the point of optimal performance for network neutrality regulation which gives the highest investment-innovation incentives, which may be referred to as a zone of acceptable performance or "workable" zone between lower and upper bounds of regulatory intensity [23]. However, it is almost impossible to find the workable zone in advance, especially considering the new emerging services which have stricter QoS requirements. Besides the network 