 ronments (like the LabVIEW Runtime, required to run remote VIs) on the client system. Because Web services are accessed using standard SOAP protocol using the HTTP as transport protocol, which is allowed in most firewall configurations, any computer connected to internet can be used to access the provided Web services. The communication with the instruments is based on VISA standard, and for this implementation we will use the VISA libraries provided by National Instruments. The VISA standard is endorsed by over 35 of the largest instrumentation com- panies in the industry including Tektronix, Hewlett-Packard, and National Instruments, and due to this wide acceptance, VISA unifies the industry to make instrumentation software interoperable and reusable. 12.3.2.1 Remote Instruments' Aggregation with VISA In 1993, National Instruments joined with several companies involved in the instrument industry like GenRad, Racal Instruments, Tektronix, and Wavetek to form the VXI plug&play Systems Alliance. One of the goals of this alliance was to ensure multivendor interoperability for VXI [VME (Versa-Module Eurocard) eXtended for Instrumentation] systems and to reduce the software development time for an operational system. This was meant to develop a new standard for instrument drivers, soft front panels, and I/O interface software. The term VXI plug&play has come to indicate the conformity of hardware and software to these standards. VISA (Virtual Instrument Standard Architecture) is the VXI plug&play I/O software language that is the basis for the software standardization efforts of the VXI plug&play Systems Alliance. VISA is a standard defined by Hewlett- Packard/Agilent Technologies and National Instruments for communicating with instruments regardless of the interface. Tele-Measurement Services for m-Learning Session-orientation of VISA (based on interrupts' servicing) encouraged us to use the virtual instrumentation software-like NI LabVIEW-together with NI Measurement and Automation Explorer (MAX) in order to integ