Small file transfers are working and large file transfers are failing with XCOM

Products

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

Issue/Introduction

You may, all of the sudden, encounter a situation in which large files can no longer be transferred, but small files transfer successfully. No changes have been made to your XCOM parameters and such large file transfers were successfully being transferred previously. 

Environment

• XCOM™ Data Transport® for z/OS
• XCOM™ Data Transport® for Windows
• XCOM™ Data Transport® for UNIX/Linux PC

Cause

Changes in configuration and/or network problems.

Resolution

Here are some pointers to check: 

1. Make sure that none of the XCOM parameters have changed in your SYSIN01, CONFIG(XCOMDFLT) member, or Destination member.
2. Check with the XCOM administrator on the remote system for any changes that may have been done on their side.
3. Make sure to check with your local and remote Network Administrators in case changes have been made to the network involved with the transfers.
4. Usually, this type of scenario can occur not only by changes that were made, but because there may be a faulty piece of hardware as well. The fact that smaller file transfers are successful and larger file transfers are not, can lead us to believe that something can be wrong within the network. Here are some helpful things to do to debug this scenario:
   1. If your XCOM parameter in general have not changed, you will want to turn on the XCOM trace facility on both the local and remote system. This will allow us to see, at the application level, how far the transfer went. Contact Support to report the problem. Have your traces, complete output of the job or xcom logs, and parameters available for review. 
   2. Have your Network Administrator issue some simple PING commands to test the network:

                  - ping  -a "ipaddress"  -- this will resolve, if possible, the Hostname of the IP address

                  - ping "ipaddress" -l "size"  -- this will allow you to test the size, in bytes, of the echo request packet from 32 to 65,527.

The latter PING command will help determine if there is a problem in which a small or large packet cannot be handled within the network. If that is the case, your Network Administrator should be able to trace the network to determine where the problem is. Sometimes it comes down to reviewing the MTU (maximum size of a single data unit ) size that was defined.