The SAP R/3 System has a three-tier client/server architecture. All data is stored in a database, and the data is processed in the application layer on the application servers. The SAPgui frontend (presentation layer) is the interface to the user. All three layers are connected to each other with networks. The following graphic depicts the client/server architecture of the R/3 System, and the communication requirements between the presentation and application layers and between the application and database layers:

Depending on your requirements, you can distribute the services to different hosts.

Smaller applications keep the database and the R/3 application on the same host. The large volume of data that passes between the R/3 application and the database (SAP server communication) is processed locally and not through a network.

The presentation layer is usually made up of PCs on which the SAPgui frontend is installed. The SAPgui is not a terminal emulation but an application program that displays R/3 application data graphically. This means that there are no great demands placed on the connection between the SAPgui frontend PCs and the R/3 application (access communication).

Higher processing demands on the R/3 application can be realized by additional application servers (application servers are hosts on which the R/3 application runs).

Very high demands are made on bandwidth and delay time between the application servers and the database server. You need to set up a suitable network connection to meet these demands.

You can speed up and secure data throughput to the database by placing the database on a separate host. The database server host then communicates only with the R/3 application servers. By isolating the database completely from the rest of the corporate network, you prevent unauthorized access to sensitive data and ensure high performance.

For data backup purposes you may need to connect the database server to a dedicated network (SAN = Storage Area Network).

Access communication covers all access to the R/3 System. This includes user access through the SAPgui, and also links to other R/3 Systems and external applications.

An access network is not a dedicated network segment, but includes all network segments through which the R/3 System is accessed.

• Block-oriented data traffic ® delay times in the network are relatively non-critical for the SAPgui
• Bandwidth must be determined separately for each location, depending on the number of users and their activities
• The availability of the network must also be specified according to the user group or location

Server communication covers all communication between the application servers and the database server, and is of great importance for the R/3 System. In each individual case you must decide whether you want to process the server communication through its own physical network (server network), or whether you want access and server communication to share a physical network. You must remember that any worsening in server communication also has a negative effect on the performance of the R/3 System.

A server network is the network connection between the servers (application servers and database servers) of an R/3 System.

• High throughput of data or high bandwidth
• Minimum delay time (round trip time)
• Includes the servers of the R/3 System only
• High availability
• No non-SAP data traffic (for example, data backup over the network)
• Direct server connection ® no expensive cabling
• Greatest possible security against unauthorized access to the database server if the server network is set up as a separate segment from the rest of the corporate network