The Use of OO-Modelling Principles (OOM) and UML Notation to Define Signalling Requirements Raphael J. Schumacher, Rapporteur Q.8/11 Swisscom AG, Switzerland.
Why SIP-I? A Switching Core Protocol Recommendation for GSM ...
3 g americas_sip-i_white_paper_august_2007-final
Lower Layer Q and X Protocol[1]