APA (7th ed.) Citation

(1989). Digital private branch exchanges (PBXs): Tutorial. IEEE Computer Soc. Pr.

Chicago Style (17th ed.) Citation

Digital Private Branch Exchanges (PBXs): Tutorial. Washington, D.C: IEEE Computer Soc. Pr, 1989.

MLA (9th ed.) Citation

Digital Private Branch Exchanges (PBXs): Tutorial. IEEE Computer Soc. Pr, 1989.