Hi Angus,

Thank you for the quick response.

On 9/8/2013 6:36 PM, Angus Robertson - Magenta Systems Ltd wrote:

To an extent, this depends on how many clients are connected, since servers
have limits.

If low, you can keep TCP/IP connections open and just design your own protocol
to send packets of data back and forward between client and server.  I designed
a simple ASCII protocol with 50 different messages.

For one of the projects, we are looking at it only being around 10 - 15 clients, so your first suggestion probably works well there. We just want the client to know that the processing is completed so that it can download the results and present it to the user. We are currently using email as the way to achieve this, but there's no client software right now, so this is an upgrade.

For thousands of clients, you may be better have the clients regularly polling
every few minutes, or send a UDP message to ask the client to poll, or a mix of
the two.  This is what I used for a large client application.

This is interesting for another project that we want to do. We expect that there may be a few thousand connected clients - so, this is very similar to the mobile phone push scenario. We want to alert the connected system that there is a message pending for the user... in that sense, it is very similar to email but we want to keep the latency low on the client side. So, something like the specification of IMAP-IDLE sounds quite good but I'm admittedly a bit lost on where to start.

Would "keep TCP/IP connections open" be the same as persistent connections?

Best Regards,

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