Network to Serial » VScom Serial Device Servers

ID #1053

The NetCom Server do not "timeout" a TCP session and therefore forbid another client to connect.

This behaviour works as designed. In TCP there is no definition of a timeout. When no data is transmitted, neither data nor control information is sent over network. So there is no chance of implementing a timeout based function. Any possible timeout is implemented in a higher layer of communication.
This is especially true in the TCP RAW communication modes on NetCom.

To help network connections to stay enabled, TCP provides a so-called "Keep-Alive" option. This will send periodic TCP packages with no user data. On NetCom you can use a side effect. When the packages are no longer acknowledged the NetCom will detect this. And as a result it will discard the now dead connection.

This Keep-Alive option is available in the Server Parameters of the NetCom. By default it is configured as Off to minimize network traffic. Define a period for checks, not less than two minutes. This option supervises all established TCP connections with the NetCom.

In TCP RAW Server mode you can also raise the number of allowed clients. This way a new client may connect before NetCom finally detects the previous connection is dead. This previous connection is discarded later, while the new client already communicates.


In Driver mode only one client is allowed. However for each serial port there is a Keep-Alive option implemented in the Driver Mode protocol. The default configuration will detect a previous dead connection when a new client attempts to control the serial port. This attempt will fail, but causes the NetCom to check the previous connection. If it is dead it is discarded, so the next attempt to connect will succeed.

Change the configuration for Polling Mode, with a period not less than two minutes. The NetCom will soon detect a failed connection, discard it, and accept new clients.


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Last update: 2009-11-13 17:05
Author: Support
Revision: 1.0

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