Akbar Arabi, Ali (14 September 2007). Comprehensive Glossary of Telecom Abbreviations and Acronyms. AUERBACH. p. 19. ISBN 978-1-4200-5866-6. 978-1-4200-5866-6
Williams, Jack (2007-11-30). The Illustrated Dictionary of Mass Communications. Lotus Press. p. 173. ISBN 978-81-89093-46-4. 978-81-89093-46-4
Williams, Jack (2007-11-30). The Illustrated Dictionary of Mass Communications. Lotus Press. pp. 15–16. ISBN 978-81-89093-46-4. 978-81-89093-46-4