Transferring 4MB file via Community Server can cause client disconnection

Technote (troubleshooting)


Problem

When a file larger than 4 MB is sent via the server the client gets disconnected.

Cause

As a defensive measure against a client attack, STMux counts consecutive
incoming messages sent from a client. If the count passes the predefined
threshold, the Mux will disconnect the client. By default the threshold
is 2000 messages. When a file is sent via the server (not
client-to-client), it is split by the client into chunks, where each
chunk is sent as a client message. Thus for files larger than 4 MB, more
then 2000 messages are sent, and the client gets disconnected.


Resolving the problem

For example, to allow 10 MB file transfer set the following flags in sametime.ini under [config] :


VPMX_THRESHOLD_MSG_COUNT=7200
VPMX_THRESHOLD_SEND_MSG_COUNT=5200

These flags change the threshold values. VPMX_THRESHOLD_SEND_MSG_COUNT
defines the threshold for messages of the type used (among other things)
when sending a file. While VPMX_THRESHOLD_MSG_COUNT defines the
threshold for all messages (both of the type mentioned and other of
types, such as channel creation and destruction messages).

The values mentioned here are derived as follows:
The client sends 2000-Byte-sized chunks. The default file size limit for transfer is 10,000 KB.
So the maximum possible amount of received messages during a file transfer would be
10,000 KB / 2000 B = 5120, and 5200 is chosen to slightly pad that value.
Also, The default threshold for messages of the other type (channel creation and
destruction) is 2000. So The threshold for all messages should be 5200 + 2000 = 7200.


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Document information


More support for:

IBM Sametime
Community Server

Software version:

8.5.2, 8.5.2.1

Operating system(s):

AIX, Linux, Solaris, Windows

Reference #:

1621182

Modified date:

2013-01-03

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