Telnet Server exhausts private storage and takes an abend878

Technote (troubleshooting)


Scenario 1 -
Same domain application sending HOTIO. As the Telnet server attempts to send the data to the client, the TCP/IP window is exceeded and the connection is Write Blocked. At the same time the application continues to send more data to the Telnet Server which queues the data. This sequence repeats itself until the Telnet Server exhausts its private storage.

Scenario 2 -
Telnet client at MSG10 sends in a PA2. The MSG10 screen is refreshed. Client is broke and continuously sends in PA2s. The TCP/IP send window will go Write Blocked. The PA2s continue to arrive and the subsequent MSG10s are queued. Eventually, the Telnet Server will exhaust its private storage.


Abend878 and the Telnet Server terminates


Broken application or client

Diagnosing the problem

Review dump contents with IBM Support

Resolving the problem

APAR PM73261 introduces MAXTCPSENDQ, a new parameter in the Telnet profile, to prevent large amounts of storage from being held for data that is destined for an unresponsive Telnet client.

To enable the TN3270 client-bound data queueing limit, you need to specify the MAXTCPSENDQ parameter in the Telnet profile.

One thing to consider when you select a value for MAXTCPSENDQ is what type of sessions the client is used for (e.g., a printer client might be expected to have more data destined for it at any one point in time than a client that is used for interactive sessions.).

The following SRLs are changed:


For details about the changes, see this URL:

Document information

More support for:

z/OS Communications Server

Software version:

1.13, 2.1

Operating system(s):


Software edition:

All Editions

Reference #:


Modified date:


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