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This list of frequently asked questions on
3780 BSC/RJE emulation is derived from one
company's nearly fifteen years experience
selling and supporting RJE emulation products.
Where appropriate, embedded links have been
included to take you outside the www.3780-emulation.com
site to other resources for more detailed
information.
| Q: |
I know what IBM 3270 emulation is. How is
3780 emulation different from 3270 emulation? |
| A: |
It is easy to be confused when talking about
the various IBM terminals and emulators that
bring the functionality of these terminals
to the PC. Although they may both use the
same underlying bisync protocol, IBM 3270
emulation and 3780 emulation are as different
as night and day. A 3270 terminal was an
interactive display station and keyboard
often with an attached Model 3287 printer.
Such terminals are designed for an operator
to make queries and enter data interactively.
A 3780 terminal is designed to transmit and
receive data in large batches -- originally
via punch cards and printed output, now via
disk files. One key clue to the fundamental
differences between the two types of terminals
is that the Model 3780 terminal did not even
have a keyboard. |
| Q: |
We've been told to get a 3780 emulator and
we don't understand why. |
| A: |
That seems to happen a lot. Need for 3780
connectivity often sneaks up on some organizations
-- particularly banks, credit unions, automobile
parts manufacturers, and suppliers to large
retailers (e.g., Wal*Mart, Target, Best Buy).
Often purchasing agents in these organizations
are sent blindly out onto the Internet to
locate something vaguely referred to as a
"3780 emulator." Obviously 3780
connectivity is not cutting edge technology
and therefore most people have never heard
of it, but it is still frequently used in
many specific business-to-business communications
applications -- most of which have been in
place for many years. In a great many of
these situations 3780 emulation is the best,
or even the only way, to move vital data
from point A to point B -- that's why you've
been asked to obtain a 3780 emulation package. |
| Q: |
How is bisync different from async communications? |
| A: |
Although both bisync (binary synchronous)
and async (asynchronous) are used to send
data over modems, the similarity stops there.
Bisync is a specific form of synchronous
communications, so the real question is what
is the difference between synchronous and
asynchronous communications?
Asynchronous communications sends each data
byte individually; synchronous communications
establishes a timing pattern between the transmitter and receiver and
then data streams from one to the other without
the overhead of start and stop bits -- and usually without a parity bit -- which
are required by, and add overhead to, asynchronous
communications.
Almost all computers sold today
have asynchronous
communications capability. They
are called
by different names: COM ports,
serial ports,
and TTY ports. Almost no computers
have built-in
synchronous ports -- that's why
the purchase
of a synchronous communications
product,
like a 3780 emulator, almost
always involves
acquiring both hardware and software.
Synchronous
communications is most commonly
used in connectivity
with IBM mainframes. See the glossary and links on that page for more details
on synchronous vs. asynchronous communications. |
| Q: |
What is RJE and how does it relate to file
transfer? |
| A: |
RJE is an acronym for Remote Job Entry. In
the early days of computing submitting jobs
(i.e., programs and data) to a mainframe
computer was typically done by transmitting
punch cards from an RJE terminal. The mainframe
would process the job, usually taking its
own sweet time in doing so, and the results
would eventually come to the terminal in
the form of output printed to the printer
and/or punched out onto a new set of cards.
Back then disk storage was extremely expensive
and therefore "data files" as we
know them today did not exist outside of
the mainframe. But as computers got smaller
and their cost came down, there was an increasing
need to move data files more from one computer
to another. The 3780 RJE protocol was already
in place and lent itself perfectly to performing
file transfers -- so, in a sense, 3780 RJE
communications was reborn as a file transfer
mechanism between a wide variety of computer
platforms. It is still used for that purpose
today, particularly between PCs and mainframes. |
| Q: |
Bisync is such an old technology. Isn't 3780
emulation going away? |
| A: |
Well, yes and no. Yes, in the sense that
eventually the need for bisync connectivity
will disappear. But, no in the sense that
it has been around for a long time and there
is so huge an investment in a bisync infrastructure,
especially in the financial and business-to-business
sectors, that the phasing out of such a reliable
system is often prohibitively expensive.
The same thing has been said about the COBOL programming language -- it was supposed
to disappear years ago but so much of the
software in the mainframe world is written
in COBOL that it is simply too expensive
to do away with it. There are no new large
scale bisync systems being installed today,
but until existing systems are phased out,
which may take another ten years or more,
there will continue to be a need for 3780
emulation. |
| Q: |
Why are 3780 emulation products so expensive? |
| A: |
A basic 3780 emulation package for Windows
PC is likely to cost between US $1,000 and
US $2,000 including both emulation software
and hardware (a sync adapter and/or synchronous
capable modem. With some companies technical
support may cost extra. Often the purchasers
of 3780 emulation suffer from "sticker
shock" when prices in this range are
first mentioned. However, when you understand
that your organization will never be called
upon to install 3780 emulation on everyone's
desktop, and that specialized knowledge is
required to produce, maintain, and support
a product that is not sold in huge quantities,
the higher price is easier to justify and
to accept. |
| Q: |
Why can't I use the modem that came with
my PC? |
| A: |
This is one of the most frequently asked
questions. The modems that comes as standard
equipment in PCs are asynchronous modems.
3780 RJE emulation requires the use of a
modem that can operate in synchronous mode. Originally the modems used with 3780
terminals were only synchronous -- namely
the Bell 201C (2400 bps) and the Bell 208B
(4800 bps). Nowadays many modems are capable
of both synchronous and asynchronous operation
(i.e., Hayes Optima, 3Com Courier) but these
are higher priced products than the relatively
inexpensive Win-modems that come preinstalled
in PCs. |
| Q: |
Why do I need to put an adapter in my PC? |
| A: |
It is not always a requirement to put an
adapter in your PC in order to use a 3780
emulation product. There are other solutions
such as using a specific modem which incorporates
a feature named AutoSync (see Q & A on
that subject for more information.) But the
general answer to this question is that PCs
do not come with hardware that supports synchronous
communication protocols such as bisync used
by a 3780 emulator. (The built-in COM port
of your PC is asynchronous only.) So it is
necessary to either add a synchronous port
by the addition of an adapter or provide
a way to do an asynchronous - synchronous
conversion (e.g., AutoSync) to support 3780
RJE emulation on a given PC. |
| Q: |
What is AutoSync? |
| A: |
AutoSync is a feature built into Hayes Optima Business Modems. When AutoSync is enabled, the Optima modem
performs an "on the fly" asynchronous
to synchronous conversion of data being sent
by the modem and a synchronous to asynchronous
conversion of data received by the modem.
In effect, then, the Optima modem permits
a connection to a synchronous remote system
via a built-in asynchronous COM port. |
| Q: |
When I load the 3780 emulator that my company
purchased, it doesn't seem to do anything
-- even after I dial out. What am I missing? |
| A: |
A 3780 RJE communications session is not
interactive like other terminal connections
such as 3270 or Telnet. There is not going to be a sign on screen
or prompts for an operator to send a user
ID and password. RJE by definition is a batch
process which entails sending and receiving
files rather than character oriented interaction
with a user. Even after a physical connection
has been established, most RJE mainframe
computers wait for the terminal to send something
-- usually commands and/or data to run a
particular program. Therefore, if you do
not have things set up for your emulation
product to send anything, the connection
may remain idle. For this reason, 3780 emulation
products are typically script driven in order
to automatically send commands and/or data
to the mainframe. |
| Q: |
What's the difference between 2780 and 3780
emulation? |
| A: |
There were two distinct bisync RJE terminals
made and sold by IBM. The Model 2780 terminal
came first. The Model 3780 terminal was a
later model and incorporated numerous improvements.
The most notable of these improvements was
a refinement of the bisync protocol. Functionally
a 2780 and 3780 terminal did the same job,
but the 3780 terminal was more dependable
and more efficient. Most modern 3780 emulation
packages support both the 2780 and 3780 variants
of the bisync protocol, but the 3780 variant
is used almost exclusively today. |
| Q: |
How is 3780 BSC/RJE emulation different from
3770 SNA/RJE emulation? |
| A: |
Fundamentally 3770 SNA/RJE and 3780 BSC/RJE terminals were designed
to do the same job: namely, submit batch
jobs from a remote location to an IBM mainframe
computer. (Oddly the 3780 terminal came before
the 3770 family.) 3780 BSC/RJE uses the bisync protocol while
a 3770 RJE terminal uses the SDLC protocol (or other protocol supported by IBM's SNA network). These protocols are mutually exclusive
and therefore 3780 and 3770 terminals are
not interchangeable. |
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Introduction to IBM 3780 BSC/RJE Communications
Who Uses 3780 BSC/RJE Communications Today?
What Did 3780/2780 BSC/RJE Terminals Look
Like?
What is the Bisync Protocol?
3780 BSC/RJE Communications Frequently Asked Questions
3780 BSC/RJE Communications Glossary
Things to Consider When Purchasing 3780 BSC/RJE Emulation
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