Oracle Net also has the capability to send and receive data requests in an
asynchronous manner; this allows it to support the shared server architecture.
Connect Descriptors
The server and instance portions of an object??™s global object name in Oracle Net are identified
by means of a connect descriptor. A connect descriptor specifies the communications protocol,
the server name, and the instance??™s service name to use when performing the query. Because
of the protocol-independence of Oracle Net, the descriptor also includes hardware connectivity
information. The generic format for an Oracle Net connect descriptor is shown in the following
516 Oracle Database 11g DBA Handbook
example, which uses the TCP/IP protocol and specifies a connection to an instance named LOC
on a server named HQ (note that the keywords are protocol specific):
(DESCRIPTION=
(ADDRESS=
(PROTOCOL=TCP)
(HOST=HQ)
(PORT=1521))
(CONNECT DATA=
(SERVICE_NAME=LOC)))
In this connect descriptor, the protocol is set to TCP/IP, the server (HOST) is set to HQ, and
the port on that host that should be used for the connection is port 1521 (which is the Oracle
registered port assignment for Oracle Net). The instance name is specified in a separate part of
the descriptor as the SID assignment. The instance name or SID can be specified, but neither is
required when the service name is specified. When a service name is specified, an instance name
is only needed if you want to connect to a specific instance in a RAC database.
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