Communication Connections of the R/3 System 

The R/3 System supports the following communication connections:

You can also use these connections with SAProuter.

The following communication connections exist within an R/3 System:

Representation of External Communication Connections

The following graphic shows you all the different ways an R/3 System can communicate. The graphic includes TCP connections only. The R/3 System can consist of one or more different hosts. The communication connections within the R/3 System are described later.

The arrows show in which direction the TCP connections are set up.

The following describes these connections in detail.

Connection to Frontends

A dispatcher runs on each application server that can connect the SAPgui clients with dialog work processes, if needed. You can access this dispatcher under the TCP port sapdp<nr> , where <nr> is the instance number (00 to 99) of the application instance. The default value is sapdp00 and the corresponding TCP port number is 3200.

In each R/3 System there is one info service that can be used for the variable assignment of SAPgui frontends to an application server (dispatcher). This service is provided by the message server. You can use this info service to organize the frontends into groups (logon groups) and distribute them according to the load on the various application servers. The message server normally runs as part of the central instance of the R/3 System, and you can access it with the TCP port sapms<SID> . <SID> is the system ID of the R/3 System (for example, C11). You can choose different TCP port numbers for different R/3 Systems. They usually start at 3600 and increase by one each time.

Default values for instance number 00:

Dialog Service (dispatcher port): sapdp00 3200/TCP

Info Service (message server port) sapmsC11 3600/TCP

Connecting Printers

The R/3 System uses spool work processes to process print requests. There can be one or more spool work processes, which themselves can run on one or more application servers. The way in which the spool work processes print depends on your configuration. The system can print in one of the following ways:

Connections to External Partners or Other R/3 Systems

Each R/3 application server has an SAP gateway that it uses to communicate with other SAP Systems, or with other applications that use the SAP communication interfaces for CPI-C or RFC.

CPI-C (Common Programming Interface for Communications) is a standardized protocol for the simple transmission of data between two programs. CPI-C uses half duplex transmission. This means that only one party at a time can transmit data. The receiving party must keep receiving data until it is its turn to transmit.

RFC (Remote Function Call) is SAP's own communications interface. RFC communication always involves a caller (RFC client) and a receiver (RFC server). The RFC server provides one or more function modules that can be called. An RFC client can call one of these function modules, transmit data, and then read the results of the function module. Both the server and the client can be either external programs or the SAP System.

You can also use the gateway for communication between two applications within an SAP System. You can access the SAP Gateway on every application server under the TCP port sapgw<nr> , where <nr> is the instance number of the application instance.

Default values for instance number 00:

SAP Gateway port: sapgw00 3300/TCP

Connections with SAProuter

The SAProuter program helps you to set up and control remote connections easily. SAProuter functions as an intermediary between the source system and the target system. First, the source system sets up a TCP connection to SAProuter and tells it to which target system it wants to connect. SAProuter then sets up a connection to the target system. A SAProuter connection from a source system to a target system consists of multiple TCP connections.

If necessary, a connection can be made using multiple SAProuters in sequence. If this is the case, all SAP connections between the SAProuters are relayed through defined TCP ports between defined partners (SAProuters). This makes it much easier to implement mechanisms that protect access to the connections.

Separate organizational units that administrate their networks and security separately can also take advantage of double SAProuters. Each unit defines its own SAProuter as a communication port for all SAP communication that goes outside its limits. SAProuter then becomes an application level gateway that can run, for example, on a firewall host. You can use authorization tables to control who may set up a connection with whom.

Each organizational unit can allow or disallow connections as it wants.

When you start the program, you can determine under which port you want to access the SAProuter.

Default values: SAProuter port: sapdp99 3299/TCP

Internal Communications

The following section describes these connections in detail:

Connecting to the Database

The connection between the R/3 application servers and the database server is based on a Remote SQL database interface.

The TCP port you use depends on the individual database system:







MS SQL Server












Connecting to the Message Server

The various instances (application servers) use the message server to access central services, such as the enqueue or update services. The message server also receives regular information from all instances about current system load and the services that are on offer. This means that the message server can provide information on load balancing for different applications, such as the SAPgui or background applications.

When an R/3 application server is started it sets up a connection to the message server of the central system (more precisely, each dispatcher sets up connection to the message server port sapms<SID> ).

Connecting Application Servers

If application servers need to communicate with each other, a connection is set up between the SAP gateways of the application servers (port sapgw<nr> ). Once it is set up, this connection remains until the application server stops running.


Table of Communications Connections

R/3 Service

Default TCP service name

Default TCP port number

Possible range for TCP service name

Possible range for TCP port number




sapdp00 –

3200 –

Message server




Free choice

SAP Gateway



sapgw00 –

3300 –





Free choice




Free choice

Free choice

Test program




Free choice

Free choice

Oracle database




Informix database




MS SQL Server database




DB2 UDB for
AIX and NT database



Free choice

ADABAS database