6 ARTICLE 5A Security and robustness of networks 41B Member States shall individually and collectively endeavour to ensure the security and robustness of international telecommunication networks in order to achieve effective use thereof and avoidance of technical harm thereto, as well as the harmonious development of international telecommunication services offered to the public. ARTICLE 5B Unsolicited bulk electronic communications 41C Member States should endeavour to take necessary measures to prevent the propagation of unsolicited bulk electronic communications and minimize its impact on international telecommunication services. Member States are encouraged to cooperate in that sense. ARTICLE 6 Charging and accounting 42A International telecommunication arrangements 42B 6.1 Subject to applicable national law, the terms and conditions for international telecommunication service arrangements may be established through commercial agreements or through accounting-rate principles established pursuant to national regulation. 42C 6.1.1 Member States shall endeavour to encourage investments in international telecommunication networks and promote competitive wholesale pricing for traffic carried on such telecommunication networks. 42D Accounting-rate principles 42DA Terms and conditions 42E 6.2 The following provisions may apply where the terms and conditions of international telecommunication service arrangements are established through accounting-rate principles, established pursuant to national regulation. These provisions do not apply to arrangements established through commercial agreements. 42F 6.2.1 For each applicable service in a given relation, authorized operating agencies shall, by mutual agreement, establish and revise accounting rates to be applied between them, in accordance with the provisions of Appendix 1 and taking into account the relevant ITU-T Recommendations.