Android Question HttpJob PostString timeout

during a post operation, sometimes I get the following error

java.net.SocketTimeoutException: timeout

I'm trying to pinpoint the possible cause: can a very lenghty post data cause a timeout exception, or it can be caused only by a connection error or by the server not responding at all?
The timeout is already 30 seconds, and the message is logged exactly after 30 second from the post call