Experimental Physics and
Industrial Control System

David A. Bryan <[email protected]> · Fri, 05 Sep 1997 12:53:40 EDT

	The nameserver is a completely stand alone server. The server itself
does not even speak CA. The client has an adaptor layer (which means almost
no changes to the internal workings of the client) that intercepts the 
search and connect request, sending the names (which it buffers) to the 
nameserver.  The nameserver replies with the information needed to claim
that channel (IP, port, CA_MINOR_VERSION etc...), and from there on, the 
client uses the existing CA code.  

> - how do you configure the nameserver?
>   - does it broadcast itself (at least once)
>   - is it based on static files?

	It does not broadcast itself. It is accessed via an environment 
variable. If the variable is not set, it falls through (see below..).
	
	It is designed to be populated with messages.  These messages are sent 
to it and contain the server name, port, etc. Duplication, dynamic add/delete
are supported -- if a server changes you just send the packet for that server
again. Right now, we send the information using a program that reads files the
IOC generates at boot time, and we populate it by running that program. You 
could run the program in an autoboot script, however...

> - ... and does a ca_search fall through to broadcast if the nameserver is not found?
> 

	Yes.  If the nameserver is down, has no information, the client will
fall through to the old search method.  The client also verifies that the IOC 
is up (although only once per IOC) before connecting (this was a non-issue 
when you got the information directly from the IOC) If the client doesn't 
specify an environment variable to locate the server it tries the default 
(defined at compile time) before giving up and using the old search.

	--David


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David A. Bryan - Computer Sciences Corporation 
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System