Bindings - which one?

[=?Utf-8?B?THVib21pcg==?=]

Hi,

We want to implement the folowing functionality:

1/ Client can send request to the server. Server will process request and
return required data. If the connection will be down data will be discarded.

2/ If there are changes on the server database, the server will notify all
clients, that there changes has been made.

The binding would be NetTcpBinding.

a)
It seems to me that I could use chanell request-reply for 1/ and calbacks
for 2/

b)
Is it possible to solve 1/ and 2/ simultannously by using a duplex channel
instead of
2 channels in a)?

Is there any better solution?

Thanks,
Lubomir