Vijay K. (Illinois Institute of Technology, Lisle, USA) Gurbani & Xian-He (Illinois Institute of Technology, Darien, USA) Sun 
Architecting the Telecommunication Evolution [PDF ebook] 
Toward Converged Network Services

Service-oriented architecture (SOA) uses services as the baseline for developing new architectures and applications, as networks are built specifically to satisfy service requirements. Most services are currently handled over different networks, but newer services will soon require cross-network support. Architecting the Telecommunication Evolution