CAAS Manual of Standards - Air Traffic Services Version 1.0: 1 October 2009

http://www.caas.gov.sg/caasWeb/export/sites/caas/en/Regulations_And_Guidelines/Rules_and_Regulations/Aerodrome_ANS/Air_Traffic_Services_Information_Circular/downloads/MOS_ATS_v1_09.pdf?__locale=en 
Standards for ATC