The high costs of implementing a TTP come about mainly because traditional security solutions, which must be invoked where the protocol itself leaves off, involve high personnel costs. For more information on the necessity and security benefits of these traditional security solutions, especially personnel controls, when implementing TTP organizations, see this author's essay on group controls. The risks and costs borne by protocol users also come to be dominated by the unreliability of the TTP – the DNS and certificate authorities being two quite commom sources of unreliability and frustration with the Internet and PKIs respectively.