portability; (d) obligation to provide subscribers listed in public directories with information; (e) transfer of usage rights at the initiative of the rights-holder, and conditions applicable to the transfer; (f) charges for usage rights; and (g) obligations under relevant international agreements relating to number usage. (4) Specific conditions relating to the use and effective management of radio-frequency spectrum that may be attached to information and communications licences where justified and with due respect for the principle of proportionality, include(a) designation of the service or type of network or technology for which spectrum usage rights have been granted, including, where applicable, exclusive use of a frequency for the transmission of content or specific audiovisual services; (b) effective and efficient use of frequencies, including, where appropriate, requirements in regard to coverage; (c) technical and operational conditions necessary to avoid harmful interference and limit exposure of the public to electromagnetic fields, where those conditions differ from those laid down in this Act; (d) transfer of radio-frequency spectrum usage rights at the initiative of the rightsholder, and conditions applicable to the transfer; (e) fees for the use of spectrum; (f) commitments made during the competitive or comparative selection process by the 56