Addressing OLTP Solutions with CICS: The Transaction Server ... - Ibm

• EPI
The EPI enables a non-CICS application program, running in the client
machine, to access the CICS for AIX region as if it was from a 3270 terminal.
As the EPI uses DCE RPC, DCE Base Services are required on the client
machine. With EPI you can have up to 15 concurrent logical terminals on
one client workstation. However, investment in programming the non-CICS
application is required to exploit the ability to serve several logical terminals
from a single EPI session.
With EPI, security is handled by DCE and can be controlled in the same way
as for cicsterm.
The EPI uses multiple threads when processing data to and from the CICS
for AIX region. cicsterm, however, communicates synchronously with
aixterm. Therefore, we believe that the EPI is more efficient than cicsterm or
cicsteld even after adding the overhead of a display manager such as X
Windows or Motif. The EPI provides a good opportunity to add a GUI front
end to existing applications. You have to consider the required
programming investment against the efficiency gain when using the EPI.
• cicsterm
cicsterm provides 3270 emulation for AIX terminals and is probably the most
straightforward way of accessing the CICS for AIX region. It runs as an AIX
process, on the server machine or on the desktop client machine. Running
cicsterm on the CICS for AIX server machine uses up to 40% of the server′s
processing and hence greatly undermines the server′s performance.
If DCE CDS is used, for successful connection the CICS Client for AIX client
machine must belong to the same DCE cell as the CICS for AIX server
machine. If DCE CDS is not in use, see 5.2.2, “Configuration without DCE
CDS and Security Services” on page 73.
For security, you can define the level of authentication used for RPCs
between the CICS for AIX region and the cicsterm. The higher the
authentication level used, for example, pkt_integ instead of none, the greater
the impact on performance. Therefore you have to balance between the
security requirements and an acceptable level of performance. To protect
from possible eavesdropping, you can encrypt the information flow across
the connection.
Each cicsterm process requires about 560 KB of real storage for its working
set and about 1.4 MB of virtual storage. Using these figures you can
estimate the number of cicsterm processes that a particular RISC
System/6000 machine can support or you can calculate the storage
requirements for a given number of cicsterm processes.
• cicsteld
CICS Client for AIX provides support for Telnet 3270 clients through the
cicsteld process. The cicsteld process that acts as a 3270 Telnet server has
to run on a machine located in the same DCE cell as the CICS for AIX server
machine. The Telnet 3270 client does not use DCE and hence is not required
to be in the same DCE cell as the server machine. A limitation of this
method is that you cannot encrypt, nor can you protect against
eavesdropping between the Telnet 3270 client and the cicsteld process.
cicsteld uses less processor power than cicsterm because the keystroke
handling and 3270 emulation costs are incurred by the machine running the
Telnet 3270 client. You can therefore potentially run the cicsteld process in
the same machine as the CICS for AIX region. However, for maximum
Chapter 4. Using CICS Clients 65