Oracle shared server default connection

Question

We are currently trying to use shared server on an Oracle 11.1.0.7 standard edition database.
We don't have any problem regarding parameters or performance yet. We can connect either with dedicated or shared connection.
Our problem or issue is with tnsnames.ora.
trdb =
(DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = X.X.X.X)(PORT = 1521))
(CONNECT_DATA =
(SID = orcl)
We do not specify if this connection is shared neither dedicated. Connection defaults to dedicated and we would like to force that users connect to a shared server connection.
It would be really usefull to avoid having to go client by client on remote sites. We do no have any centralized management tool to change the file (not on remote sites).
We could, of course make the application to distribute a new file, but since every client is unique, it could be risky.

Answer 1

Try to use SERVICE_NAME instead of SID in tnsnames.ora and make sure this service is mapped to a dispatcher in database init. file.
Example with 11.2.0.1:
1. DISPATCHERS parameter
SQL> show parameter dispatchers
NAME                                 TYPE        VALUE
dispatchers                          string      (PROTOCOL=TCP) (SERVICE=DB112XDB)
max_dispatchers                      integer2. TNSNAMES.ORA:
$cat tnsnames.ora
DB112 =
(DESCRIPTION =
   (ADDRESS_LIST =
     (ADDRESS = (PROTOCOL = TCP)(HOST = lx01.localdomain)(PORT = 1521))
(CONNECT_DATA =
   (SERVICE_NAME = DB112XDB)
)3. Test with SQL*Plus:
sqlplus  system/xxx@DB112 @tss
SQL*Plus: Release 11.2.0.1.0 Production on Mon Feb 15 21:37:35 2010
Copyright (c) 1982, 2009, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> select username, program, server, service_name
  2  from v$session
  3  where server<> 'DEDICATED';
USERNAME                       PROGRAM
SERVER    SERVICE_NAME
SYSTEM                         [email protected] (TNS V1-V3)
SHARED    DB112XDB