Problem statement:This study aims to discuss several issues on session initiation protocol security and threats. An in-depth investigation related to SIP with the intention to categorize the wide variety of SIP security issues. Approach: Related papers to the infrastructure of SIP security were analyzed. Some of the identified issues are: Social threats, eavesdropping, delaying, modification of media session, service abuse threats, physical access threats and denied services threats. Results and Conclusion: A useful categorization of SIP security issues has been done. The vulnerabilities of existing SIP infrastructure and possible remedies are discussed. It is confirmed that, message attacks are the most dominant category of SIP attacks.

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This work proposes context aware handover algorithms for mobile positioning systems. The algorithms perform handover among positioning systems based on important contextual factors related to position determination with efficient use of battery. The proposed solution is implemented in the form of an Android application named Locate@nav6. The performance of the proposed solution was tested in selected experimental areas. The handover performance was compared with other existing location applications. The proposed solution performed correct handover among positioning systems in 95 percent of cases studied while two other applications performed correct handover in only 50 percent of cases studied. Battery usage of the proposed solution is less than one third of the battery usage of two other applications. The analysis of the positioning error of the applications demonstrated that, the proposed solution is able to reduce positioning error indirectly by handing over the task of positioning to an appropriate positioning system. This kept the average error of positioning below 42.1 meters for Locate@nav6 while the average error for two other applications namely Google Latitude and Malaysia maps was between 92.7 and 171.13 meters.Keywords handover among mobile positioning systems, power efficient mobile positioning, switching between indoor and outdoor positioning systemsComputer Science • 15 (2) 2014 http://dx