5.2 About the Listener and Connection Requests

Each listener is configured with one or more protocol addresses that specify its listening endpoints. The protocol address defines the protocol the listener listens on and any other protocol-specific information. For example, the listener could be configured to listen at the following protocol address:

(DESCRIPTION=
   (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=1521)))

The preceding example shows a TCP/IP address that specifies the host of the listener (sales-server) and a port number (1521).

Clients configured with a protocol address can send connection requests to the listener. When a client request reaches the listener, it selects an appropriate service handler to service the request and forwards the request to the handler. A service handler is a dispatcher or a dedicated server process that acts as a connection point to a database.

The following figure illustrates the role of the listener during the establishment of a connection. The figure shows a browser making an HTTP connection and a client making a database connection.

1. The browser or client send a connection request to the listener.

2. The listener parses the request and forwards it to the service handler for the database service requested.

3. The browser or client connect to the database.

Figure 5-3 Listener Architecture

Description of "Figure 5-3 Listener Architecture"