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NOMAD
Session Manager |
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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 .
Logon Rotor
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.
Explore NOMAD MVS Session Manager:
Summary
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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