How to configure Connection String for Oracle Database Extended Agent

There are three kinds of connection string for agent configuration.

1) easy connect path as "//<host>:<port>/<service>", for example:
//tivp56.cn.ibm.com:1521/oradb
Note: this requires the easy connection mode(ezconnect) is enabled in the listener configure file sqlnet.ora.
NAMES.DIRECTORY_PATH=(ezconnect, tnsnames)

2) full description path as "(DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=<servicename>))(ADDRESS=(PROTOCOL=TCP)(HOST=<hostname or ip>)(PORT=1521)))"
for example:
(DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=oradb))(ADDRESS=(PROTOCOL=TCP)(HOST=9.123.98.85)(PORT=1521)))

3) TNS service name like ORCL.
The service name entry should be defined in the file tnsnames.ora and user need to set environment variable TNS_ADMIN to specify the path of tnsnames.ora before starting agent.

User can also verify if the connection string is valid by Oracle utility $ORACLE_HOME/bin/tnsping.

Command: tnsping <connection string>
for example:
#su - oracle
[oracle@tivpc027 ~]$ tnsping "//tivpc027:1521/oradb"
TNS Ping Utility for Linux: Version 11.2.0.1.0 - Production on 19-SEP-2012 22:43:08
Copyright (c) 1997, 2009, Oracle. All rights reserved.

Used parameter files:
Used HOSTNAME adapter to resolve the alias
Attempting to contact (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=oradb))(ADDRESS=(PROTOCOL=TCP)(HOST=9.123.98.85)(PORT=1521)))
OK (10 msec)
[oracle@tivpc027 ~]$ tnsping "(DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=oradb))(ADDRESS=(PROTOCOL=TCP)(HOST=9.123.98.85)(PORT=1521)))"

TNS Ping Utility for Linux: Version 11.2.0.1.0 - Production on 19-SEP-2012 22:44:37

Copyright (c) 1997, 2009, Oracle. All rights reserved.

Attempting to contact (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=oradb))(ADDRESS=(PROTOCOL=TCP)(HOST=9.123.98.85)(PORT=1521)))
OK (0 msec)
[oracle@tivpc027 ~]$ tnsping ORADB

TNS Ping Utility for Linux: Version 11.2.0.1.0 - Production on 19-SEP-2012 22:44:41
Copyright (c) 1997, 2009, Oracle. All rights reserved.
Used parameter files:

Used TNSNAMES adapter to resolve the alias Attempting to contact
(DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = tivpc027.cn.ibm.com)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = oradb)))
OK (0 msec)