Experimental Physics and
Industrial Control System

Matthias Clausen DESY -MKS-2/KRYK- <[email protected]> · Wed, 9 Apr 1997 16:10:14 +0200 (MET-DST)

At last also some comments from my side...

cdev , CORBA , CA

How do they fit together or could any replace the other?
The question is - as in many cases - what type of functionality do your need from your 
network layer and what are the performance requirements?

At first CORBA does not provide such a complex functionality like cdev but it come close 
to it. CORBA solves the problem of distributed object (or services) over a heterogenious 
environment of different operating systems. Where an object is not ment to be a (EPICS) 
channel but more likely an IOC could be an object providing a special service like 
'power_supply_controls'. In this case any CORBA client can talk to this server providing 
this service and talk to the channels which are available under this service. You could 
have another service i.e. 'vacuum' on the same (IOC) server which provides these channels. 
The way you exchange the data is up to you. You'll implement your data exchange routines 
i.e. get,set,get_name,get_history... Since you are using CORBA the problem of data 
conversion is handeled by the CORBA implementation for the specific platform. So client 
and server programs can be 'easily' written.
Norihiko Kamikubota from KEK was working on such an implementation here at DESY and 
fortunately he finished the work for exchanging data between different platforms for a set 
of routines which provide the services to exchange float,int,historical data, names, 
strings etc. . Currently this implementation lacks in functionality in one point that 
there's currnelty only one service on each server possible. Which is a problem of the 
current implementation but not of CORBA itself.

So CORBA helpd to solve the following problem:
Data exchange betreen different platforms (like RPC with XDR)
Resolving the location of services on the net (through the CORBA broker)
The latter is the reason why initial connections through CORBA take longer that normal IP 
connections. The throughput of CORBA connections though can - in special cases - be even 
better than IP RPC connections. -> refer to Nirihiko

Result:
Can CORBA replace CA - no way! because of the response time (even though the complex data 
types are still on the whish list!)
Can CORBA replace cdev - well in fact the cdev object definiton and the client-oriented 
API are much different from the CORBA client/server approach. A CORBA service under cdev 
would really make sense and it would be good if we could agree on the functions we will 
implement and support under the cdev/CERBA service. In such a case more common services 
could be implemented and - of course - shared.

For more informations about Nirihiko's work please have a look at:

http://herao1.desy.de/cc/www/help/help_corba.html

Please let me know if this page is locked for public.

Matthias

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System