Oracle Net Connectivity Overview
Oracle Net enables connections to various services, such as Oracle databases, non-Oracle databases, gateways, and external procedures.
Users initiate a connect request by passing a user name and password along with an identifier for the service to which they wish to connect. That identifier, called a connect identifier, identifies:
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The destination service
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The path, or network route, across the network to get to that service
A connect identifier is specified in several different ways. One of the most common ways is through use of a net service name, another name for the service, which maps to a connect descriptor. A connect descriptor contains destination service and network route information. The desired service is indicated by using its service name for Oracle9i or Oracle8i databases or its Oracle System Identifier (SID) for Oracle8 or Oracle7 databases. The network route provides, at a minimum, the location of the listener through use of a network address.
The following shows a net service name called sales mapped to a connect descriptor:
sales=
(DESCRIPTION=
(ADDRESS=(PROTOCOL=tcp)(HOST=sales-server1)(PORT=1521))
(CONNECT_DATA=(SERVICE_NAME=sales.us.example.com))
The listener, located on sales1-server, listens with the TCP/IP protocol on port 1521 for connection requests for a database service called sales.us.example.com.
The connect identifier and its connect descriptor is stored in at least one naming method. During a connection request, the client resolves the connect identifier (sales in the previous example) to a connect descriptor through a naming method. The client then contacts the listener specified in the connect descriptor.
The listener, through a protocol, accepts the client connection. It compares the client information with the information it has received from the database service through service registration, as well as information it has stored in its own configuration file, listener.ora. If the information matches, a connection is granted.
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