Contention resolution using z/OS® Communications Server

Starting with z/OS® 1.2, IBM® implemented contention resolution in z/OS® Communications Server , including VTAM®. However, the original implementation in z/OS® 1.2, 1.3, and 1.4 did not precisely match the emerging standard. Consequently, HATS might have difficulty communicating with these original releases of z/OS® Communications Server. To address the problem, IBM® issued patches (PTFs) and published an informational APAR (technical note) listing the recommended patches.

Ask your z Systems administrator to refer to APAR II13135, entitled Common Telnet Problems Under z/OS®. APAR II13135 lists the recommended PTFs that enable HATS to take advantage of contention resolution. For example, for z/OS® 1.4, the APARs PQ71574 and PQ72265 apply, and are corrected by PTF UQ76065. Without the proper fixes, HATS might experience random hangs. HATS developers observed this problem as a clocked screen in the HATS Toolkit terminal window (a screen frozen with a clock icon displayed at the bottom).

If your z Systems administrator cannot immediately install the II13135 patches, use the negotiateCResolution setting described in Related HATS settings and specify a value of false. This setting with a value of false causes HATS to skip contention resolution negotiation, reverting to the earlier TN3270E specification. Disabling contention resolution can degrade HATS performance by lengthening 3270 response time, but otherwise has no negative consequences.

This contention resolution negotiation problem does not occur when HATS connects through a front end 3270 communications gateway instead of directly to the affected z/OS® host system. These gateways might or might not support contention resolution, or might require additional service to be applied to support contention resolution.