Viporn Katekao. (2001) Distance learning : a case study of Ramkhamhaeng and Sukhothai Thammathirat Open Universities. National Institute of Development Administration,:ม.ป.ท.Viporn Katekao. 2001. Distance learning : a case study of Ramkhamhaeng and Sukhothai Thammathirat Open Universities. ม.ป.ท.:National Institute of Development Administration,;Viporn Katekao. Distance learning : a case study of Ramkhamhaeng and Sukhothai Thammathirat Open Universities. ม.ป.ท.:National Institute of Development Administration, 2001. Print.