Is there a need for a common protocol to prevent trafficking in human being?

 yes , and there is a legal instrument to tackle human trafficking  :

The Protocol to Prevent, Suppress and Punish Trafficking in Persons, especially Women and Children, was adopted by the United Nations General Assembly in 2000 and entered into force on 25 December 2003.

The Trafficking Protocol, which supplements the United Nations Convention against Transnational Organized Crime, is the only international legal instrument addressing human trafficking as a crime and falls under the jurisdiction of the United Nations Office on Drugs and Crime (UNODC)