neither client nor server be I

[beachdog]

I have a C# web services application that has to act as both a client
and a server. I send a request (HTTP/SOAP), and receive a response
from a server (which I will write), which basically is just
acknowledging the request and starting to work on it. Then the server
will send me notifications as the work item is processed.

I am guessing this is not an uncommon pattern, so I want to fall into
whatever implementation pattern is deemed appropriate for this. In
particular, I want to know if it is common for the request initiator
to establish a keepalive TCP socket over which all of these messages
are sent? Or, alternatively, would it be more common that the initial
request and response is sent over one TCP/HTTP connection, and then a
separate connection is initiated back from the handler of the initial
request to send each follow-up notification back to the requestor?