|The NOMAD Session Manager (NSM) is a resource management program that dramatically improves response time and performance for interactive NOMAD users. This breakthrough in technology allows multiple NOMAD users and applications to run in a single address space - outside the confines of TSO. As such, it extends the range of applications that can be developed and efficiently run far forward into the production arena. The NOMAD Session Manager provides a reliable, ready-to-use solution for delivering efficient, production-level applications at a fraction of the development cost of traditional methods.
NOMAD's extensive functionality remains the same when used under the NOMAD Session Manager. Existing NOMAD applications generally need no modification to run under NSM.
All NOMAD interfaces are available from within the Session Manager, providing full access to DB2, Teradata, IDMS and IMS files. With NOMAD's interface to DB2, all NOMAD's facilities for application development and reporting are available to DB2 users, without the slow response time of TSO.
NOMAD and the Transaction Processing Environment
To design a product that would allow it to support production-level applications, Select Business Solutions looked at the evolution of currently successful production environments, such as CICS. Production system needs were previously satisfied by providing an alternative to TSO, with its single-user address space bottleneck and high swap-time overhead. The one-address-space-per-user limitations had to be overcome and replaced by a more transaction-oriented, multi-user address space approach (see Figure 1).
A transaction processing environment is structured to perform as much set-up processing as possible before the actual transaction arrives. Anything the transaction program needs during its execution should be made available with absolute minimum delay. This allows the transaction to complete its work, present the result to the user and release its resources as quickly as possible.
Given the extremely dynamic nature of NOMAD and the ad hoc nature of conversational NOMAD requests, adopting transaction processing philosophies in a number of areas without compromising its basic function was an exciting challenge, one that resulted in dramatic performance improvements for NOMAD users.
NOMAD Session Manager
The Three Basics
The primary requirement for a non-TSO, multiple-user NOMAD is a Terminal Driver capable of managing multiple terminal sessions associated with a single application, and capable of interfacing directly with VTAM as a VTAM application. The next step is an address-space-level NOMAD that can create, delete and manage the multiple NOMAD sessions that correspond to these terminal sessions, as well as manage resources common to and shared by all the sessions. The final step is single-user NOMAD, enhanced to take advantage of the multiple-user environment.
The NOMAD Session Manager product is composed of three such pieces. The first is the VTAM Terminal Driver, or VTD. The VTD executes as a VTAM Authorized Path Application, and employs a multi-tasking architecture to provide an access path between its "application" and VTAM.
The second is NOMAD/SM, which plays the part of VTD's "application." The NOMAD/SM exchanges information with the VTD concerning logons and logoffs, and ATTACHes a NOMAD subtask (or session) for each NOMAD user. The NOMAD/SM also performs global memory management for the sessions, as well as dataset allocation management.
The third piece is NOMAD code, augmented to recognize and take advantage of the NSM environment .
A Logon Rotor facility monitors NSM region populations and routes new logons to new regions when region capacity limits are reached. These capacity limits for both number of users per region and number of regions are controlled by the NSM site.
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The spectrum of transaction-type applications is extremely wide. At the low end are the relatively long and infrequently used applications, such as ad-hoc queries, where performance is generally a secondary consideration to the time it takes in design and i implementation. On the high end are short and frequently used applications, such as automated teller transactions, where performance is extremely critical.
With the Session Manager, NOMAD is a proven solution for developing mid-range, transaction processing applications where the resource requirements are such that response is almost completely a function of I/O delay (file + paging).
By eliminating unnecessary I/O delays, NOMAD under the NSM is competitive with any other transaction-processing environment for mid-range applications, relative to response time. In addition, the NOMAD application development environment dramatically reduces application design and implementation time over that currently required by transaction processing environments such as CICS.
Compare the programmer time required to code a simple query application between CICS and NOMAD. The procedural code for a simple NOMAD Window application might take 10 or 20 lines. By contrast, the equivalent CICS program is considerably more complex. Typically, a CICS transaction requires one or two weeks of effort. The corresponding NOMAD activity can be completed in an hour by an application developer whose experience is much less than the CICS programmer.
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NOMAD Session Manager
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