DC/UCF Concepts › External User Sessions › External Request Elements

External Request Elements

External request elements (EREs) are control blocks used with SVC communications to maintain the link between an external user session and the DC/UCF system servicing its requests.

Each external request unit takes up one ERE. The ERE is dedicated to that request unit from the time the first service request is issued until all services for the user session are terminated.

EREs in a UCF Session

A UCF session requires the use of an ERE only while screen images are being transferred between the front-end and back-end systems. At other times, such as while the back-end task is executing or while the front-end system is waiting on a terminal interrupt, the UCF session does not hold an ERE. Therefore several UCF sessions can share a relatively small number of EREs.

Number of Available EREs

The number of EREs available is specified using the MAXIMUM ERUS parameter of the SYSTEM statement. When determining the value for this parameter considers the following:

• The value should be at least as high as the number of concurrent external sessions you wish to support.
• Allow for UCF requirements by increasing the number by an amount that is between 10% and 20% of the number of UCF terminals defined in the system generation.
• If all EREs are in use, a program or UCF front-end attempting to initiate a session receives a 1473 error status.