MADAMA: QoS Adaptation Support

Mobile Agent-based Distributed Architecture for Multimedia Applications

QoS Provision in MADAMA is based on the implementation of a set of mobile lower-level services, provided by agents that are distributed over the paths between the source and the targets of the video stream.

MADAMA VoD permits users to require a QoS level for any multimedia stream, and allows to manage and adjust the requested quality during service provision, to respond to dynamic modifications of network resource availability. The service is realized by coordinating two different types of MADAMA management agents:

the QoS Negotiators (QoSNs) that define and grant a specific level of quality for the service;

the Admission Controllers (ACs) that manage the resources to be engaged by local intermediate nodes.

ACs have been realized by tailoring already implemented agents for general-purpose monitoring.
ACs are present on every node of the network; this assumption is not severe because they are implemented by mobile agents that can move and be installed whenever they are needed. Each AC manages locally available resources and keeps track of resources currently committed to already accepted streams. The stream flow specifications are recorded in a local table of <receiving host, bandwidth, delay, loss> tuples. Any tuple represents the statistics of VoD traffic between the local and the receiving host: the first time, it contains values computed in a short sample time; then, it is updated by monitoring real traffic of current VoD sessions. ACs are in charge of answering to reservation requests from QoSNs.

The VoD service requires the coordination of a set of QoSN agents located at least at the source, at the target, and at some of the intermediate nodes. These QoSN agents maintain session state, by recording user preferences and flow specifications for a video stream, and they can also move from node to node when in need. QoSNs evaluate the feasibility of meeting these requirements against the local AC database and exploit a subset of communication facility to perform the negotiation phase for the definition of the achievable QoS.
After the negotiation phase, during multimedia streaming, any QoSN is in charge of receiving packets from the previous QoSN and of forwarding them to the next QoSN. When multiple video streams interest the same network node, one QoSN can handle all of them.

 
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