Once two client's sessions are linked you can then retrieve the sessions using getLinkedSession.
private void sendByeToServer(SipServletRequest clientBye) throws ServletException, IOException { B2buaHelper b2buaHelper = clientBye.getB2buaHelper(); SipSession serverSession = b2buaHelper.getLinkedSession(clientBye.getSession()); SipServletRequest serverBye = serverSession.createRequest("BYE"); logger.info("Sending BYE request.\n" + serverBye); serverBye.send(); }