What is PRESENTATION=RO in tnsnames.ora file

Check the entry in tnsnames.ora file:

      (SID = PLSExtProc)

In this article we will be discussing about the PRESENTATION clause in the entry.

Little history
The whole tnsnames.ora file is meant to be information for client softwares which will be connecting to the Oracle server (database).

The client must know where the database resides, which PROTOCOL to use for connection, unique identifier of the database etc.

But in this particular tnsnames.ora entry, Oracle uses this for connecting to external procedures. The examples of external procedures are the procedures written in C/C++/VB which are compiled as available as shared libraries (DLLs).

PRESENTATION in connect descriptor
There must be a presentation layer between client and server, if in case the charactersets of both are different. This layer ensures that information sent from within application layer of one system is readable by application layer of the other system.

The various presentation layer options available are
1. Two-Task Common (TTC)
2. JavaTTC
3. FTP
5. GIOP (for IIOP)
7. POP
8. IM APSSL (6, 7, and 8 are for email) etc
9. RO

TTC/Two-Task Common is Oracle's implementation of presentation layer. It provides characterset and datatype conversion between different charactersets or formats on the client and server. This layer is optimized on a per connection basis to perform conversion only when required.

Information obtained from: http://download-west.oracle.com/docs/cd/A87860_01/doc/network.817/a76933/architec.htm#1007271

This is a Java implementation of TTC for Oracle Net foundation layer capable of providing characterset and datatype conversion.

It is responsible for
  a. Negotiating protocol version and datatype
  b. Determining any conversions
  c. SQL statement execution

For external procedures the PRESENTATION layer value will be normally RO, meaning for "Remote Operation". By this parameter the application layer knows that a remote procedure call (RPC) has to be made.

The other layers will be discussed later.