The Public Switched Telephone Network - The public switched telephone network (PSTN) is the international network of circuit-switched telephones. Learn more about PSTN at HowStuffWorks. x
Black Belt Certification. The IASSC Certified Lean Six Sigma Black Belt (ICBB) is a professional who is well versed in the Lean Six Sigma Methodology, who leads improvement projects, typically in a full-time role. A Lean Six Sigma Black Belt possesses a thorough understanding of all aspects within the phases of D-M-A-I-C.
The black belt is commonly the highest belt color used and denotes a degree of competence. It is often associated with a teaching grade though frequently not the highest grade or the expert of public perception. It is also a relatively recent invention (dating from the late 19th century) rather than an ancient custom.