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

for OS/2 system. When the client process is started on the client, flows that start
the initialization transaction (CCIN) are sent to the server. This transaction is
responsible for performing an autoinstall of the appropriate CD entry for the
CICS Client for OS/2 system. After the CCIN has run, all further requests are the
ECI, EPI, or cicsterm request, depending on the type of client.
4.5.1.1 TCP/IP Connection
The CICS for AIX region must have a listener definition (LD) entry defined as an
additional method to listen for incoming requests from the CICS Client for OS/2
across the TCP/IP network. The Protocol attribute in the LD entry should be set
to TCP. The cicsip listener process is started at region startup. It listens on a
TCP/IP port. The standard default port number is 1435. If you choose to use a
nonstandard port, you must add an entry to the /etc/services file.
The CD model used by CCIN for autoinstall must have the ConnectionType
attribute set to cics_tcp for the CICS family TCP/IP support.
The optimum number of connections simultaneously active through a single port
is about 200, and the maximum is about 450 connections. Each time a CICS
Client for OS/2 connects to the CICS for AIX server, a thread is started in cicsip
and a connection is established. If you need more than 450 connections, there
are two choices:
• Add a new adapter card to the machine
This increases the adapter bandwidth. The port address is the same for all
of the client systems, but the server Internet address is different. Two LDs
are configured—one to listen exclusively on one network adapter and one to
listen on the other. The TCPAddress attribute in the LD is used to specify
the server Internet address.
• Use a second port
The Internet address of the CICS for AIX server machine remains the same,
but the port address is different. The TCPAddress attribute in the LD is left
blank, and port addresses are explicitly defined.
If your CICS for AIX server machine manages many TCP/IP connections, it may
run out of space in the mbuf pool (an area of memory allocated by TCP/IP when
AIX is initialized). You can check the size by noting the value of thewall in the
output of the no -a command. The default size of thewall is 2 MB, which
supports up to about 800 CICS family TCP/IP connections. If you have to support
more than 800 connections, you have to increase the value of thewall
accordingly.
4.5.1.2 SNA Connection
The CICS for AIX region must have an LD entry defined as an additional method
to listen for incoming requests from the CICS Client for OS/2 across the SNA
network. The Protocol attribute in the LD entry should be set to SNA. The cicssl
listener process is started at region startup. The CD model used by CCIN for
autoinstalling the client must have the ConnectionType attribute set to local_sna.
The initial planning effort lies in the tailoring of the supported SNA product that
provides the underlying SNA services to be used by the CICS for AIX region.
IBM SNA Server for AIX Version 3.1 is an example of a supported SNA product.
For more detail refer to CICS on Open Systems Intercommunication Guide,
SC33-1564-01, and SNA Server for AIX: Planning and Performance Guide,
SC31-8220.
Chapter 4. Using CICS Clients 61