4.1 Understanding Oracle Net Stack Communication for Client/Server Applications
A database server is the Oracle software managing a database, and a client is an application that requests information from the server. The way the client and server communicate is known as the client/server stack.
Information passed from a client application sent by the client communication stack across a network protocol is received by a similar communication stack on the database server side. The process flow on the database server side is the reverse of the process flow on the client side, with information ascending through the communication layers.
The following diagram illustrates the various layers on the client and on the database server after a connection has been established.
Figure 4-1 Layers Used in a Client/Server Application Connection
Description of "Figure 4-1 Layers Used in a Client/Server Application Connection"
This communication architecture is based on the Open Systems Interconnection (OSI) model. In the OSI model, communication between separate computers occurs in a stack-like fashion with information passing from one node to the other through several layers of code, including:
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Physical layer
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Data link layer
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Network layer
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Transport layer
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Session layer
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Presentation layer
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Application layer
The following diagram shows how Oracle Net software consisting of the Oracle Net foundation layer and Oracle Protocol Support fits into the session layer of the OSI model.
This section contains the following topics:
Parent topic: Understanding the Communication Layers
4.1.1 About the Client Communication Stack
The client communication stack includes the following:
4.1.1.1 Client Application Layer
During a session with the database, the client uses Oracle Call Interface (OCI) to interact with the database server. OCI is a software component that provides an interface between the application and SQL.
See Also:
Parent topic: About the Client Communication Stack
4.1.1.2 Presentation Layer
Character set differences can occur if the client and database server run on different operating systems. The presentation layer resolves any differences. It is optimized for each connection to perform conversion when required.
The presentation layer used by client/server applications is Two-Task Common (TTC). TTC provides character set and data type conversion between different character sets or formats on the client and database server. At the time of initial connection, TTC is responsible for evaluating differences in internal data and character set representations and determining whether conversions are required for the two computers to communicate.
Parent topic: About the Client Communication Stack
4.1.1.3 Oracle Net Foundation Layer
The Oracle Net foundation layer is responsible for establishing and maintaining the connection between the client application and database server, as well as exchanging messages between them. The Oracle Net foundation layer can perform these tasks because of Transparent Network Substrate (TNS) technology. TNS provides a single, common interface for all industry-standard OSI transport and network layer protocols. TNS enables peer-to-peer application connectivity, where two or more computers can communicate with each other directly, without the need for any intermediary devices.
On the client side, the Oracle Net foundation layer receives client application requests and resolves all generic computer-level connectivity issues, such as:
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The location of the database server or destination
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How many protocols are involved in the connection
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How to handle interrupts between client and database server based on the capabilities of each
On the server side, the Oracle Net foundation layer performs the same tasks as it does on the client side. It also works with the listener to receive incoming connection requests.
In addition to establishing and maintaining connections, the Oracle Net foundation layer communicates with naming methods to resolve names and uses security services to ensure secure connections.
Parent topic: About the Client Communication Stack
4.1.1.4 Oracle Protocol Support Layer
Oracle protocol support layer is positioned at the lowest layer of the Oracle Net foundation layer. It is responsible for mapping TNS functionality to industry-standard protocols used in the client/server connection. This layer supports the following network protocols:
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TCP/IP with Transport Layer Security (TLS)
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Named Pipes
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Sockets Direct Protocol (SDP)
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Exadirect
All Oracle software in the client/server connection process requires an existing network protocol stack to establish the computer-level connection between the two computers for the transport layer. The network protocol is responsible for transporting data from the client computer to the database server computer, at which point the data is passed to the server-side Oracle protocol support layer.
Related Topics
Parent topic: About the Client Communication Stack
4.1.2 About the Server Communication Stack
The server communication stack uses the same layers as the client stack with the exception that the database uses Oracle Program Interface (OPI). For each statement sent from OCI, OPI provides a response. For example, an OCI request to fetch 25 rows would elicit an OPI response to return the 25 rows after they have been fetched.