Theory and Practice of Enhancing a Legacy Software System

Abstract

ion Models (HAMs) which represent hardware facilities in the HSS, and software for controlling, monitoring and managing signals between the HSS and SSS. A HAM is a state machine capturing the behaviour of a physical line or a trunk. The HSS represents, in software, the physical components of the real switch; hardware such as trunks and telephony terminals. The user of Desk interacts with these components through the HSS Graphical User Interface (GUI). The user can initiate calls, answer phones, and generally perform normal telephony actions. Hence the HSS can pass the user initiated signals, such as onhook and ohook, to the SSS through the TCP/IP link. Of course the HSS must also generate responses from the switching system such as ringing, dialtone, and ringtone. These responses originate from the SSS in response to the user-initiated signals, and again traverse the communications link. Note that the current state of a terminal is actually stored in the HAM situated in the SSS, the ...