Oracle supplies three key components that interact to locate services, establish connections, transport data, and handle exceptions. They are:

  • SQL*Net/Net8

  • Transparent Network Substrate (TNS)

  • Oracle Listener

While the interaction among these products does not generally require intervention beyond the initial installation, some customizations are often beneficial in an environment that is making heavy use of snapshots, symmetric replication, or other distributed functionality.

SQL*Net/Net8, TNS, and the OSI Reference Model

Both TNS and the Oracle protocol adapters may be described by the seven-layer Open Systems Interconnection (OSI) model, as seen in Table 2.1.

Table 2-1. TNS and Oracle Protocol Adapters in the OSI Model

Client-Side Stack


Server-Side Stack

Client application

7 (application)

Oracle server


6 (presentation)



5 (session)


Oracle protocol adapter

4 (transport)

Oracle protocol adapter


3 (network)


2 (data link)


1 (physical)


The OSI model uses the concept of a stack to describe the interaction of networked machines. Each layer of the stack communicates with its peer on a remote machine and with adjacent layers on the local machine, where data is passed down from the application through the various layers and finally passed to the remote machine at the physical layer.

There are different Oracle networking components associated with layers 4, 5, 6, and 7. The lower layers of the stack are related to routing and physical characteristics of the ...

Get Oracle Distributed Systems now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.