Adjusting the number of transmissions in SNA transaction flows (MSGINTEG, and ONEWTE)

Within CICS®, the MSGINTEG option can be used to control the communication requests and responses that are exchanged between the terminals in a network and the VTAM® and NCP communications programs.

Effects

One of the options in Systems Network Architecture (SNA) is whether the messages exchanged between CICS and a terminal are to be in definite or exception response mode. Definite response mode requires both the terminal and CICS to provide acknowledgment of receipt of messages from each other on a one-to-one basis.

SNA also ensures message delivery through synchronous data link control (SDLC), so definite response is not normally required. Specifying message integrity (MSGINTEG) causes the sessions for which it is specified to operate in definite response mode.

In other cases, the session between CICS and a terminal operates in exception response mode, and this is the normal case.

In SNA, transactions are defined within brackets. A begin bracket (BB) command defines the start of a transaction, and an end bracket (EB) command defines the end of that transaction. Unless CICS knows ahead of time that a message is the last of a transaction, it must send an EB separate from the last message if a transaction terminates. The EB is an SNA command, and can be sent with the message, eliminating one required transmission to the terminal.

Specifying the ONEWTE option for a transaction implies that only one output message is to be sent to the terminal by that transaction, and allows CICS to send the EB along with that message. Only one output message is allowed if ONEWTE is specified and, if a second message is sent, the transaction is abended.

The second way to allow CICS to send the EB with a terminal message is to code the LAST option on the last terminal control or basic mapping support SEND command in a program. Multiple SEND commands can be used, but the LAST option must be coded for the final SEND in a program.

The third (and most common) way is to issue SEND without WAIT as the final terminal communication. The message is then sent as part of task termination.

You have the following options:

Where useful

The above options can be used in all CICS systems that use VTAM.

Limitations

The MSGINTEG option causes additional transmissions to the terminal. Transactions remain in CICS for a longer period, and tie up virtual storage and access to resources (primarily enqueues). MSGINTEG is required if the transaction must know that the message was delivered.

When MSGINTEG is specified, the TIOA remains in storage until the response is received from the terminal. This option can increase the virtual storage requirements for the CICS region because of the longer duration of the storage needs.

How implemented

With resource definition online (RDO) using the CEDA transaction, protection can be specified in the PROFILE definition by means of the MSGINTEG, and ONEWTE options. The MSGINTEG option is used with SNA LUs only. See the CICS Resource Definition Guide for more information about defining a PROFILE.

How monitored

You can monitor the use of the above options from a VTAM trace by examining the exchanges between terminals and CICS and, in particular, by examining the contents of the request/response header (RH).

Related tasks
Networking and VTAM: improving performance
Setting the size of the terminal input/output area (TYPETERM IOAREALEN or TCT TIOAL)
Setting the size of receive-any input areas (RAMAX)
Setting the size of the receive-any pool (RAPOOL)
Using the MVS high performance option (HPO) with VTAM
Using SNA chaining to segment large messages (TYPETERM RECEIVESIZE, BUILDCHAIN, and SENDSIZE)
Limiting the number of concurrent logon/logoff requests (OPNDLIM)
Adjusting the terminal scan delay (ICVTSD)
Compressing output terminal data streams
Tuning automatic installation of terminals
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