Axel AX4000 User's Manual Manuel d'utilisateur télécharger pdf (Page 95)

Appendix

AXEL Office Server 89

A.8 - KEEPALIVE FUNCTION

The keepalive is a mechanism that allows a TCP/IP device to regularly check its

TCP/IP connection status.

A.8.1 - Why a Keepalive Function is Needed?

A TCP/IP device is not able to detect in real time a network problem (remote

host down, cable problem, etc).

A network problem can only be detected when data is sent and the destination

host acknowledgement is not received. In this case, when the

acknowledgement is not received, the remote TCP/IP device is considered

'unreachable' and its associated resources are released. This release is

performed few minutes after the data was sent.

A.8.2 - Example of Potential Issue

Take for example an Office Server channel, set as a telnet server with the

DialOut/IP driver under Windows. The Windows host opens a connection to the

Office Server in order to associate a Windows COM port the Office Server.

In the event of a (network) problem Windows will react and the DialOut/IP

connection will be closed. But the disconnection request will not be received by

the Office Server (the TCP/IP link is broken). A 'Zombie' connection is now

associated with the Office Server channel. Even After the network problem has

been repaired, further Window’s connection requests will be refused by the

Office Server (the channel is still associated with the zombie connection).

Note: the Office Server channel will be released, either on Office Server reboot

or when data is sent to Windows (the network problem will be detected).

A.8.3 - Keepalive Mechanism

The principle of keepalive is the Office Server checks regularly the TCP/IP

connection status. These automatic checks are performed when the TPC/IP

connection is idle.

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Axel AX4000 User's Manual Manuel d'utilisateur Page 95