Delay Tolerant Networks (DTNs) challenge the operation of protocols used in terrestrial networks at the physical, medium access control (MAC), and transport layers of the protocol stack. Deep space, the most extreme DTN, is an environment where transmission reliability, accuracy, and timeliness may be more difficult to achieve than in terrestrial networks due to harsh and dynamic conditions. Transport protocols are being developed for use on the long- distance Interplanetary backbone, however, each has advantages and disadvantages in different scenarios. Future protocols developed must maximise link utilisation when connectivity exists, minimise communication attempts and wasted resource consumption when connectivity does not exist, and accommodate network congestion. Furthermore, performance should be achieved autonomously to minimise operating costs and optimise decision-making responses. Our approach, the Context-Aware Brokering (CAB) algorithm, is an autonomous middleware with context-aware capability which resides alongside any protocol stack between application and transport layers. It has capabilities to enable communication over both long- and short-distance links, and the version executed is optimised depending on the scenario. The CAB selects the most appropriate protocol for each transmission by comparing application requirements against environment constraints, intelligently configures it to maximise performance, and takes intermediary action when network dynamics compromise QoS levels. Its overall objective is allow transmission reliability, accuracy, latency, or sustainability QoS to be achieved, or enable a balance to be maintained between each, depending on the transmission scenario. Positive results are produced in a range of scenarios from an implementation of the CAB algorithm in ns-2.30. These are observed primarily when the CAB identifies environment constraints in relation to application requirements in advance of transmission beginning, and/or when the environment is dynamic and the CAB takes intermediary action to autonomously accommodate changes. A cost-benefit impact of the CAB architecture exists, and its positive impact on performance is most significant in dynamic environments which are long-distance and/or mobile when network conditions change in ways which are accommodated in the policy rules, and for applications without real-time and interactive transmission requirements. In a limited selection of scenarios, the CAB introduces overheads to the transmission without parallel improvements in performance. This is the case when pre-transmission assistance from the CAB is not required and the network remains stable until the transmission completes. Overhead costs are therefore incurred without any additional positive impacts from the CAB. The importance of deploying a CAB in all scenarios, however, is in the ability to exploit the potential of achieving a minimum level of service in the unpredictable and dynamic DTN.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:554285 |
| Date | January 2009 |
| Creators | Peoples, Cathryn |
| Publisher | University of Ulster |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0023 seconds