Sending notification of updates from server to client

Hi there,

I am teasing out an issue which I was hoping you guys could help me with. I have multiple smart clients and one server. Each client has a seperate table depending on where it is. There will be updates for these clients, but only rarely - perhaps even once a year.

I was coming up with all possible methods for getting notification of updates. The top 3 are....

1. The client contacts server at a specified interval to check for updates..
Possible problems with this approach: extra resources being used by client constantly checking for updates that may only require changing once a year!

2. Server contacts client to notify it of updates
Possible problems with this approach: server will have to keep an up to date list of every client location, port number etc and update its record every time a client makes contact because if the client cannot be found the server will be unable to send out updates.

3. Include a single boolean field in every async response from the server after a successful upload etc. that states whether or not the client needs to contact the server for an update..

Is there a fourth option, or have I covered all my options here?

Cheers!