This package implements a transaction layer for the SIP stack according to chapter 17 of RF2543 Bis 09. To implement transaction stateful components, you extend the SIPTransactionStack class and not the SIPStack class. To create a client transaction you create a transaction aware MessageChannel for the Hop returned from the router by calling Stack.createMessageChannel. A server transaction is created when an incoming request is fielded by the stack. It is passed to the application using the SIPServerRequest and SIPServerResponse interface. Acknowledgement: This package was contributed by Jeff Keyser.