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.
Individual communication services and tariffs
Individual communication services and tariffs is the regulatory protected ability for an identified user to obtain from a communication service provider, by a bilateral specific contract, a combination of the service and related content, at a specific price (called a tariff chosen by the user) corresponding to a user request specified with a service demand profile and some duration.