

============================ TAO Time Service==============================

This is a complete implementation of the CORBA time service spec. The
service offers a globally synchronized time to a requesting
client. The Time Service interface has been implemented as two servants:
the clerk and the server. Clients who wish to use the service talk to
clerks and the clerks in turn keep their time synchronized
globally. The clerks do this by talking to the servers running on
different machines.

There needs to be at least one time server running in the network. The Clerks
update their time periodically from the servers. The servers and clerks
export their IORs through the
  * Naming Service.
  * Files
The Servers can also be activated on demand by the Clerks if they have been
registered with an Implementation Repository.

If Naming Service is being used the clerks and servers are registered in
different Naming Contexts as :

For the clerks : ClerkContext->Clerk:<local_host_name>
For the server : ServerContext->Server:<local_host_name>

The machine name is included to make the object name unique and distinguish
between the various servers and clerks.

A sample run of the TimeService can be done as follows :

* Using the Naming Service :

1. Run TAO/orbsvcs/Time_Service/server on different machines.
2. Run TAO/orbsvcs/Time_Service/clerk -t 5 on some machines.
3. Run the TAO/orbsvcs/tests/Time/client on one of the machines where a clerk
   is running.

* Using Files :

1. Run TAO/orbsvcs/Time_Service/server -o server_ior on different machines.
2. Run TAO/orbsvcs/Time_Service/clerk -t 5 -f server_ior -o clerk_ior on some
   machines.
3. Run the TAO/orbsvcs/tests/Time/client -f clerk_ior on one of the machines
   where a clerk is running.

* Using the Implementation Repository :

1. Run the Implementation Repository service as :

   TAO/orbsvcs/Time_Service> ../ImplRepo_Service/ImplRepo_Service -ORBsvcconf
                             implrepo.conf -ORBobjrefstyle url -d 1

2. Run the Server as

   TAO/orbsvcs/Time_Service> server -o server_ior -r -i

3. Run the Clerk as

   TAO/orbsvcs/Time_Service> clerk -f server_ior -t 5 -o clerk_ior

4. Run the client as

   TAO/orbsvcs/tests/Time/client -f clerk_ior

Algorithms
----------

Currently, updating the system time involves taking the average of all
the times received from the servers. This can be extended by using a
more elaborate distributed time synchronization algorithm.

Version Updates : (10th March, 1999)
-----------------

The TAO Time Service has been updated to include the timezone information
in the Universal Time Object. This object now also has an inaccuracy estimate
in it. The inaccuracy is a measure of the skew in the synchronization of
the clerks time. It is the difference between the highest and the lowest times
from the servers that the clerk synchronizes its time with. The high-inaccuracy
and the low-inaccuracy fields are also being calculated from the inaccuracy as
follows :

		Inaccuracy 64-bits
	|------------------------------------|
	|         | inacchi |   inacclo      |
	|------------------------------------|
	  16-bits   16-bits     32-bits

Thanks to Brian Dance <Brian_Dance@UECCS.co.uk> for reporting this.

Future Versions of the service could include other measures of inaccuracy too,
say the one based on precision in the time reported by servers. In this case
the servers will have to supply an estimate of inaccuracy in their times.


