500pts: UDP/TCP to send a msg to users of a program?

Hi there,

I wonder if anyone can help, I have a program that is succesfully working, it is used by 100s of users. The program depends on webservices etc so from time to time i must take the program down.

I have no way of informing the users that the program is going offline so i was wondering if i could do this with udp or tcp. UDP i presume is a better choice..

Considering that the users probably don't have a FIXED ip.

Does anyone know of a sample where I could send a msg to 100's of users.

I presume i will have a small server program, and then i will build a small client into my program... this will receive a msg and then i will just used MEssageBox.Show to display it...

My confusion is.... which port do i use? and the server... does it need to send directly to IP (fixed) addresses.... I understand that with UDP i do not need to establish a connection so how would i send the info to the user then?

if there are 3 users for example that are in the same office connected by an adsl router then technically they would have the same IP address so how would this work?

I presume .net Vs2003 supports this?

Thanks in advance for any help

Who is Participating?
ozymandiasConnect With a Mentor Commented:
The polling may not be practical and multicasting is quite neat provided that it is supported.
Here is an example : http://www.codeproject.com/cs/internet/multicast.asp
So your server program is going to send a message to the client warning that the system is goind down for a while.
Your client application will have to listen on a port for a message sent to its Ip adress. It can be any port.
The other possibility would be to use multicast or broadcast.
Or you could just have the message client poll a message queue on the server, say, every 10 seconds and if it finds a message its displays it to the user.
That way you could just publish the shutdown warning on the message queue and within 20 seconds or so be pretty sure that every client has received it.
bromoseConnect With a Mentor Commented:
I have a multicasting solution that will work on a LAN, but getting multicasting working across the internet is a different story. How ever if you have Your users on a virtual LAN, and the routers will allow multicasting - it's an option. Let me know if you want the multicast-code. Otherwise I must concur with ozymandias on his comments on polling the server.

Best regards,
Kaj Bromose
ianinspainAuthor Commented:
thanks guys!

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