What may be the reasons of connection timeout when consuming a Web service ?

Connection Timeouts (assuming a local network and several client machines) typically result from :

a) Some kind of firewall on the way that simply eats the packets without telling the sender things like "No Route to host"

b) Packet loss due to wrong network configuration or line overload.

c) Too many requests overloading the server.

d) A small number of simultaneously available threads / processes on the server which leads to all of them being taken.

    This happens especially with requests that take a long time to run and may combine with c)