MANETs are important and integral part of next generation wireless networking. Real time multimedia communication over MANETs is challenging due to reasons like network topology changes, limitations of wireless links and demanding requirements of multimedia. Channel adaptivity is adopting applications to the dynamic and unpredictable network conditions. QoS adaptivity is adopting lower layers to multimedia application requirements. The novel cross layer context exchange approach called ConEx, presented in this paper improves the efficiency of this two-way information exchange. This paper focuses on adaptive multimedia applications over mobile ad hoc networks, which addresses the challenges of multimedia applications. ConEx uses publish-subscribe event notification system for vertical context exchange across layers of the mobile host and horizontal context exchange across the MANET. ConEx architecture and implementation issues are discussed in this paper.