XCOM Windows to z/OS "XCOMN0780E TcpIp 505: Unexpected ... data in Xprprcv"

Products

• XCOM Data Transport
• XCOM Data Transport - Windows
• XCOM Data Transport - z/OS

Issue/Introduction

An normal (unsecure) XCOM transfer from Windows to z/OS gives error:
XCOMN0297E Error requesting header confirmation: XCOMN0780E TcpIp  505: Unexpected 128 bytes of residual data in Xprprcv

The XCOM for Windows servers are running under Amazon Web Services (AWS).

Environment

XCOM™ Data Transport® for Windows
XCOM™ Data Transport® for z/OS

Cause

The problem was due to reaching the TCP socket connection limit on z/OS due to some strange network activity from XCOM clients where connections to the unsecure port 8044 were not being closed on z/OS even thought they were being closed by the client.

Resolution

Restarting the XCOM started task (STC) resolved the problem.