Billing systems are called to supervise financial mutual relations of the subscriber system of hosting service with hosting company in a real time mode. As the competence of these systems usually includes duties:

• To expose accounts on payment of the rendered services;
• To write off and charge means for the personal account of the subscriber according to accounts and payment assignments;
• To activate additional services or to change their list or volume.

Billing systems usually work with three participants of process of financial mutual relations:

• Client;
• Hosting sevice provider;
• The bank structure serving payments of the hosting company.

Proceeding from purpose and the basic functions billing systems - it is obvious, that the enhanced attention of developers of the given systems should be given safety and reliability of their functioning. In fact, any failure in systems of such class or not authorized intervention in their work can lead to serious financial losses. Therefore, usually developers include in systems of this class algorithms of multistage authorization, support of safe reports of data exchange (for example - SSL) and other technologies, called to provide safety of monetary transactions.

Hosting service provider can try to develop such system independently. In this case it is necessary for it to learn and accept requirements of the bank which has given to it the Internet merchant account, to make testing the developed system by the foreign company and to pass certification of this system in bank.

In most cases hosting service providers introduce at themselves the decisions developed by the foreign specialized companies and certificated on use by a lot of dear banks. In this case service to the provider the ready decision is necessary to introduce a hosting only at itself, following instructions of developers and experts of the chosen bank-partner.

Hosting provider can and order a writing of such system of the foreign specialized company, having assigned on it duties on testing and certifice this product. Such decision used in case service of the given provider is in something unique, or those the way of interaction between the provider and its clients is innovative.

Within the limits of given clause we shall not analyze concrete billing the decision of various manufacturers. We shall stop only on some prominent aspects. Generally:

• Well proved system of the known manufacturer having a plenty of successful introductions - is more preferable than the system developed by programmers of the Hosting Service Provider;
• The system of billing developed to order at the known manufacturer is more preferable as himself programming than billing and successful introduction of well proved system.

But, as well as from any rule, from this there are exceptions. And we know examples when talented commands of programmers-enthusiasts created improbably reliable, stable and convenient decisions become subsequently by successful commercial products.