One
of the side effects of introducing TCP/IP
for VSE and TN3270 into
an SNA network is the loss of VTAM printing capability. For decades,
users have been able to use green-screen 327x terminals with 328x
print support. However, when the green-screen is replaced with
TN3270, the user loses the 328x functionality. The General Print
Server (GPS) restores and enhances this function in a TN3270 environment,
without requiring you to change any of
your applications.
 GPS
Function
The idea behind GPS is simple: intercept the data streams that
were intended for VTAM printers, process the data and then use
the LPR/LPD protocol to cause that data to print on any TCP/IP-capable
printer anywhere in the TCP/IP network. For printers that are directly
attached to the network, GPS implements the HP Jetdirect Sockets
protocol to allow it to communicate directly to the printer. For
other printers, GPS uses the standard LPR/LPD function within TCP/IP
for VSE, so you have the
advantage of being compatible with a wide variety of network operating
systems and network-based printers.
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GPS
Definition and Method of Operation
Each GPS Daemon identifies itself to VTAM as a logical unit with
the characteristics of a locally attached 3287 printer. Either
GPS or an application then initiates a BIND to establish communication.
Once connected, the GPS daemon receives data from the application
through VTAM, just like a physical printer. Each buffer is reformatted
with ASA carriage control and is written to a staging member in
a library. At some predetermined point, based on the amount of
data or idle time, the accumulated data is either passes to the
standard TCP/IP LPR client or is queued for transmission using
the HP Jetdirect protocol. A TCP connection with the remote host,
running either a Line Printer Daemon or HP Jetdirect Software is
established and the data is sent. The LPD then physically prints
the file or disposes of it in some predetermined manner.
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Why
not just implement TN3270E?
TCP/IP for VSE does not include a TN3270E Daemon. We’ve
chosen to implement the 328x printer function using GPS for the
following reasons:
• TN3270E requires the user to specify their LU name. Many
of our customers are using the VTAM LU name for security purposes
and by allowing the TN3270 clients to specify their own LU name,
any installation-specified security could be circumvented.
• GPS is far more flexible than TN3270 printer support. GPS allows
328x print output to be sent to any TCP/IP printers.
• TN3270 requires someone to log on to the mainframe to establish
a printer connection. With GPS, as long as the printer and/or
the associated Line Printer is available, printing occurs with
no manual intervention.
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Summary
The General Print Sever for VSE restores
and augments the 328x print function that is critical to many VSE
environments. GPS is an optional product that is included with
your TCP/IP for VSE distribution.
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