This package implements the main protocol abstractions that are defined by the SIP RFC 3261. These include the following main ones:

- SIPServerTransaction -- an implementation of the Server Transaction State Machine (Chapter 17 of RFC 3261).
- SIPClientTransaction -- an implementation of the Client Transction State Machine (Chapter 17 of RFC 3261).
- SIPDialog -- an implementation of the SIP Dialog ( Chapter 11 of RFC 3261 ).

SIPTransactionStack is the container that holds references to these protocol objects.