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It is known that, due to MANET characteristics, there is not a unique middleware solution that copes with all needed requirements. Several and different challenges arise when facing these requirements. In first place, efficient use of resources, such as memory, bandwidth and computational power, is needed. System scalability becomes crucial when a great amount of members join the network and try to intercommunicate. Other issues like quality of service, devices’ heterogeneity and security may also be considered when creating a middleware for ad hoc networks. Therefore, it seems that requirements may vary depending on the selected scenario for ad hoc networks.

Regarding mobile communication, during the last few years the reduction of the cost of portable devices has implied a growing utilization of mobile phones, handheld game consoles and pocket computers. In consequence, a new range of opportunities arise for collaborative working environments. However, bringing the features of collaborative systems to the mobile

ad-hoc (MANET) scenario is not trivial. Although flexibility and low cost establishment make these networks attractive for spontaneous collaboration, several management and communication problems emerge when traditional collaboration systems are moved towards the MANET environment. Topology awareness, node dynamicity, lack of central servers and

scarce resources are new elements that change the traditional rules in collaborative working environments.

Communication functionalities stand as one of the most important constraints since one-to-one and group communication are the key on which collaborative applications rely. Collaborative applications frequently need chat rooms, file sharing and e-mail messaging so synchronous and asynchronous message delivery seems necessary. Since using TCP as transport protocol seems to be ineffective in MANETs, lighter approaches using UDP seem to be the most suitable solution. However, these applications may need a reliable communication channel in order to ensure high packet delivery. Besides, although it is usually not mentioned,

an ordered channel is also necessary for delivering packets for most applications. Even though these assumptions may be too costly for large groups, this project’s scope is restricted to small, medium-sized groups, so providing these needs is feasible. We should not forget that communication efficiency plays a fundamental role in MANET communication due to the

multihop nature of the network. Achieving efficient group communication is one of the foundations of collaborative applications. On the other hand, group membership and management are also necessary in developing group-aware collaborative application.

Notification of online and joining/leaving members is useful for most collaboration systems, which usually user membership information to perform collective activities.

Regarding issues other than collaboration requirements, middleware approaches should be easy to deploy, extend and use. Usability and ease of application development turn middleware in a powerful tool to develop end-user applications. Current approaches tend to offer a restricted set of functionalities: publish a message under a certain topic, share a file or

retrieve information by using pattern-matching. These functionalities are in fact useful but may not be sufficient in order to develop more complex MANET applications in a fast and straightforward manner.

Taking all these considerations into account, the main directions we will take under the development of this project are the following:

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  The construction of a collaboration middleware provided with a full set of communication mechanisms and membership information.
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  The development of a plug-in framework which benefits from middleware services in order to build final applications in a rapid and simple manner.
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  The utilization of an application level multicast (ALM) protocol designed to enhance communication performance, which avoids using a specific MANET multicast.

With all these components, we state that AGORA offers a new ready-to-deploy solution for developing collaborative applications for MANETs in an easy and straightforward way. Since it is not restricted to offering just a single service like file-sharing or probabilistic multicast delivery, developers can use a full set of functionalities which fit the needs of each application.

As we will see hereafter, the collaboration middleware provides synchronous and reliable communication: communication channels, naming and publish/subscribe services. Besides, the topology-aware multicast protocol takes care of minimizing global communication, while the plug-in framework is in charge of reducing application development complexity.