On the occasion of the 20 th anniversary of the establishment of diplomatic ties between Vietnam and the Republic of Korea (RoK) (December 22), President Truong Tan Sang, Prime Minister Nguyen Tan Dung and the National Assembly Chairman Nguyen Sinh Hung on Dec 21 exchanged greetings to their RoK counterparts, including President Lee Myung Bak, Prime Minister Kim Hwang Sik and Speaker of the National Assembly Kang Chang Hee.-VNA