A disturbing trend has developed among SNA users who are considering
TCP/IP-centric intranet solutions as the basis for their next-generation
corporate networks.
Rather than taking a systematic top-down approach, starting with the
applications in use and working down toward the networking infrastructure
required to support these and future applications, some enterprises are
focusing entirely on the TCP/IP-centric intranet architecture with little
regard for the legacy applications that still need to be sustained.
Once these users have determined the structure and composition of the
intranet that theoretically meets the needs of their new applications, they
then try to force-fit the SNA/ APPN requirements into the intranet
architecture - more or less as an afterthought. Instead of envisaging a
tightly integrated, SNA-capable intranet that innovatively utilizes some of
the new SNA Web technology, such as browser-based access, enterprises are
resorting to separate circuits for the SNA traffic or using Data Link
Switching (DLSw) to graft the existing SNA network onto the intranet.
The rationale for not devoting too much attention to SNA vis--vis the
new intranet is obvious. SNA is now legacy and passe and, in time, will
indubitably be surpassed by TCP/IP, even though the conversion may not
happen for another five years or more. So the SNA requirements are deemed
to be somewhat unimportant compared to the value of building
high-bandwidth, multimedia-capable intranets with secure interfaces to the
Internet. But this attitude is wrong and counter-productive.
Intranet-centric reengineering represents the first real opportunity
most SNA shops have had in the past 10 years or more to streamline their
SNA operation and replace obsolete equipment. Dont abdicate this golden
opportunity to reconstitute your SNA infrastructure using all of the new,
but proven, intranet-related technologies at your disposal. You can now
realize cost-effective, secure SNA-capable intranets that fully support all
existing mainframe and Application System/400-resident SNA applications and
that are not based on parallel circuits or entirely on DLSw.
DLSw is one technique you can use to build SNA-capable intranets.
However, it is an option you should consider only if you're stuck with
having to support old, SNA-only devices such as a 3274 or compatible. If
you are dealing with machines or devices that support TCP/IP as well as
SNA, such as the AS/400, you should evaluate the possibility of cutting
over to TCP/IP using tn5250, browser-based access and File Transfer
Protocol, rather than maintaining existing SNA data flows through DLSw.
Likewise, there are options other than DLSw for transporting SNA
traffic from a remote SNA LAN gateway across the TCP/IP intranet to the
data center, consider other options. In most cases, you can eliminate the
remote SNA LAN gateway and use tn3270, browser-based access or the 3270
datastream encapsulated in TCP/IP to transport data to the data center.
This saves you money by eliminating the remote gateways and restricts the
traffic flowing across the intranet to TCP/IP - as opposed to having SNA
encapsulated within TCP/IP.
Even 3x74 control units present multiple options for reducing costs,
upgrading terminals and updating the hostile 3270 user interfaces of most
SNA applications. If you're using 3x74s purely as SNA LAN gateways or to
support nonprogrammable 3270 terminal used only to access SNA applications,
now is your chance to finally get rid of this 20-year-old technology.
Many enterprises persevere with old 3270 terminals because PCs,
despite their ever-increasing affordability, are still just a tad too
expensive. But now network computers and browser-based access provide a new
and compelling option at a price comparable to that of a terminal,
especially if one considers the maintenance costs.
Browser-based access currently is hindered by lack of comprehensive
printer support. However, solid printer support should be available from
multiple vendors this summer.
While DLSw, browser-based access, and tn3270- and tn5250-based SNA
access are the most productive and relevant techniques for achieving
SNA-capable intranets, other options are available, as well. These include
IBM's AnyNet protocol conversion software, which converts SNA data to
TCP/IP, and Desktop DLSw, which encapsulates 3270 and 5250 data in TCP/IP
packets at the source. This is useful for certain mobile user applications.
Intranet-centric network reengineering is the best opportunity we have
had in more than a decade to throw out the old and bring in the new when it
comes to SNA networking. Don't waste it. Evaluate all of the new and
exciting technology at your disposal, rather than just forging ahead with
parallel circuits or DLSw.
Gurug‚ is an independent consultant specializing in internetworking
and IBM network architectures. He can be reached at (603) 878-1303 or via
the Internet at aguruge@mcimail.com.
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