engine running from a Windows terminal, is installed starting from 24 MB package). VISA keywords: # Resource-Any instrument in the system, including serial, and parallel ports # Session-You must open a VISA session to a resource to communicate with it, similar to a communication channel. # Instrument Descriptor-Exact name of a resource. The descriptor specifies the interface type (GPIB, VXI, ASRL), the address of the device (logical address or primary address), and the VISA session type (INSTR or Event). The VISA server: VISA Server runs on computers, controlling the instrumenta- tion work-benches (called by us "work-bench servers" in the generic multitier archi- tecture introduced before). It is needed in order to communicate with VISA-controlled instruments connected on a different machine in the same net- work or in case of communication with remote resources using Internet connec- tions (usually via HTTP protocol). VISA server is useful when devices need to be shared or when aggregating devices connected to different remote machines (see the case-studies below). By "VISA resources" they are meant, any kind of instruments or devices con- nected with the computer by GPIB, VXI, PXI, Serial (including USB), Parallel, or Ethernet interfaces. Building the Web service for remote VISA instrument access: The communication model proposed by this approach (Figure 12.39) contains the following elements: The client (can be any SOAP client) Web server (handles the HTTP communication) VISA server (handles the communication with the VISA compliant instruments) VISA instruments Tele-Measurement Services for m-Learning Standard PC Internet Web server VISA instruments Smart phone Figure 12.39 Communication model proposed for the Web service for remote VISA instrument access. On the Web server, we have an architectural solution (Figure 12.40) composed of three layers: Web Server Layer: This is the Web server responsible for the HTTP communica- tion with the client. The Web service SOAP requests and responses are sent using the H