TCP/IP settings for IMS Connect

You can choose different TCP/IP values to maximize your environment settings for IMS Connect.

The z/OS® Communications Server configuration settings for TCP/IP are located in the z/OS PROFILE.TCPIP data set.

The following TCP/IP parameter values affect IMS Connect:

TCPNODELAY=ENABLE
  • Data is transmitted by TCP/IP per client SEND.
  • TCP/IP waits one millisecond per transmission.
  • Multiple client TCP/IP SENDS can result in multiple TCP/IP transmissions.
TCPNODELAY=DISABLE
  • Data is collected by TCP/IP from client TCP/IP SENDS, before transmission.
  • TCP/IP waits until the buffer is full before transmission.
  • Multiple client SENDS results in 1 to n TCP/IP transmissions to IMS Connect.
SO_LINGER=Y, VALUE=0
  • Immediate return to client code.
  • A client request to close the socket can bypass data sent with a previous client TCP/IP SEND request, but may result in the loss of the client SEND data.
SO_LINGER=N
  • Immediate return to client code.
  • A client request to close the socket can bypass data sent with a previous client TCP/IP SEND request, but may result in the loss of the client SEND data.
SO_LINGER=Y, VALUE=10
  • Return to client code when an ACK is received from the host, or wait for 10 seconds before sending close.
  • Socket close will not bypass data sent.
DELAYACK
DELAYACK is used to minimize non-data transmissions from the host. If DELAYACK is used, the z/OS TCP/IP waits 200 milliseconds before sending an ACK to the remote server TCP/IP. However, if the ACK is appended to the data being sent from IMS Connect, there is no delay.

If your client application performs a single SEND followed by a READ, DELAYACK is recommended.

DELAYACK can be set on the TCP/IP "Port Statement" or on the "Gateway Statement."

NODELAYACK
NODELAYACK is used to allow non-data transmissions from the host to flow without data. If NODELAYACK is used, the z/OS TCP/IP immediately sends an ACK to the remote server TCP/IP. The ACK is not appended to the data being sent from IMS Connect.

If the client code sends one SEND followed by a READ to the host with a NODELAYACK setting, an ACK is sent separately.

If the client code sends two or more SENDs followed by a READ to the host, the host TCP/IP will send an ACK immediately to the data received. This will allow the next SEND of data from the client to flow.

NODELAYACK is recommended if your client application sends more than one SEND followed by a READ.

NODELAYACK can be set on the TCP/IP "Port Statement" or on the "Gateway Statement."

SOMAXCONN

The SOMAXCONN statement can be used in conjunction with the TCPIPQ parameter of the TCPIP statement in the IMS Connect HWSCFGxx member of the IMS.PROCLIB data set. The SOMAXCONN statement in PROFILE.TCPIP controls the TCP/IP queue depth for listening sockets at the LPAR level. You can use the TCPIPQ parameter to override the value of SOMAXCONN for an instance of IMS Connect. The value of TCPIPQ is used only if it is lower than the value of SOMAXCONN for the host LPAR.

Recommendation: Because the default value of SOMAXCONN (10) is lower than the minimum value of TCPIPQ (50), use the TCPIPQ parameter only when the value for SOMAXCONN is modified to be greater than 50.