Tariff
A tariff is called an optimal tariff if it's set to maximize the welfare of the country imposing the tariff. It is a tariff derived by the intersection between the "trade indifference curve" of that country and the offer curve of another country. In this case, the welfare of the other country grows worse simultaneously, thus the policy is a kind of "beggar thy neighbor policy". If the offer curve of the other country is a line through the origin point, the original country is in the "condition of a small country", so any tariff worsens the welfare of the original country.
Telecommunications tariff
At a minimum, tariffs imposed must cover the cost of providing the service to the consumer. The consumer may be the final user or an intermediary such as a service provider. If a telecommunications operator cannot recover its costs, it will make a loss and the company will go bankrupt. Tariffs must also be used to cover maintenance, additional research and other indirect costs associated with providing the service. However, telecommunications service providers must be careful not to over-price each service, as prices have a direct influence on demand for that service (see supply and demand). Such an operator must constantly balance the need to provide cheaper rates, especially if there is strong competition, with the cost of maintaining the service at an optimum quality that is acceptable to the customer. If an operator charges too much, it risks alienating its customers, resulting in a loss of traffic and therefore revenue; if they charge too little, they will have insufficient capital to maintain the network's quality of Service. Over time this will result in customer attrition.