APA (7th ed.) Citation

Held, G., & Friend, G. E. (1994). Understanding data communications (4th ed.). Jemma.

Chicago Style (17th ed.) Citation

Held, Gilbert, and George E. Friend. Understanding Data Communications. 4th ed. Rizal: Jemma, 1994.

MLA (9th ed.) Citation

Held, Gilbert, and George E. Friend. Understanding Data Communications. 4th ed. Jemma, 1994.