Due to the inherent complexity of nowadays Air Traffic Management (ATM) system, standard methods looking at an event as a linear sequence of failures might become inappropriate. For this purpose, adopting a systemic perspective, the... more
Due to the inherent complexity of nowadays Air Traffic Management (ATM) system, standard methods looking at an event as a linear sequence of failures might become inappropriate. For this purpose, adopting a systemic perspective, the Functional Resonance Analysis Method (FRAM) originally developed by Hollnagel, helps in identifying nonlinear combinations of events and interrelationships. This paper aims to enhance the strength of FRAM-based accident analyses, discussing the Resilience Analysis Matrix (RAM), a user-friendly tool that supports the analyst during the analysis, in order to reduce the complexity of representation of FRAM. The RAM offers a two-dimensional representation which systematically highlights the connections among couplings, and thus even the highly connected group of couplings. As an illustrative case study, this paper develops a systemic accident analysis for the runway incursion happened in February 1991 at LAX airport, involving SkyWest Flight 5569 and USAir F...
UMTS was envisaged as a "universal" mobile telecommunications system with multiple access options and full IP packet support. However, 3GPP Rel99 is a single access technology, and its core is still switch centric. Rel4 further optimises... more
UMTS was envisaged as a "universal" mobile telecommunications system with multiple access options and full IP packet support. However, 3GPP Rel99 is a single access technology, and its core is still switch centric. Rel4 further optimises the air interface. Rel5 first adds an IP multimedia core network sub-system (IMS) adjunct to the UMTS packet switched (PS) GPRS CN bearer. This adds basic PS call control trial capabilities. Rel6 will provide full UMTS packet call control (CC) capabilities (e.g.: security, emergency & QoS support). The Rel5/6 standards employ the text based call control protocol: SIP. Text based protocols are easier to develop than bit-wise presentations and likely to be more expediently taken to market. However, initial indications as to the delays associated with packet call control using SIP have concerned operators about the viability of IP-based services over a UMTS air interface. This has led UMTS vendors/operators to invest in the standardization of ways to wireless enable the efficient use of SIP with such measures as protocol compression. This paper explains GSM, UMTS circuit switched call control and SIP call control as applied to UMTS and then compares and contrasts the relative performance of both schemes using results derived from a UMTS system simulator called the Framework for Radio Architecture Modelling (FRAM).