Network Load in the SAP Server Network 

The data traffic between the SAP servers is not as easy to describe as the traffic between SAP frontends, since it depends more heavily on the application. The following sections describe several basic "rules of thumb" for the different types of data traffic. These rules can help when you make an initial estimate of the required bandwidth in the server network.

To obtain more accurate data, you must make measurements from a real system. For a useful measurement, you must have realistic data in the system and all data flows must be considered.

Interactive Users

In the three-tiered architecture of the SAP Systems, data is mainly processed on the application servers and the database. The thin frontend only receives the data sent over the network that you want to display. The amount of data between the SAP application servers and the database is at least one order of magnitude greater than between the application server and the frontend. This is because the system must transmit not only the data that is displayed but also data that is not displayed.

The average data transmitted in different, typical applications (standard SAP benchmarks) between the application server and database is approximately 20-40 KB in each dialog step. This amount can vary greatly depending on which transaction is executed and how much data is in the system.

In addition to the required network bandwidth, the runtime of packets in the network is also very important for system performance since a lot of queries and responses are sent back and forth ("round trips") when the database is accessed. Therefore, choose a network technology with the shortest delay time, for example, layer 2 switches. "Slow" network components such as routers usually should not be placed within the server network.

The data traffic between the application servers of an SAP System is much lower than between the application servers and the database. However, short network runtimes are also important for this type of data traffic.

Background Jobs

In addition to the load generated by interactive applications, you must also consider batch jobs. They generate a similar load for each processing step as the interactive applications. The difference is that there is no delay between the processing steps as with interactive users. This is why the network load of a background job is much higher than the load an interactive user generates.

External Communication

External programs that use CPI-C or RFC to communicate with the SAP System also generate network load. It is difficult to make a general statement about network load. If the external program executes a similar action to an interactive SAP transaction, the data traffic between the application server and the database is generally comparable to this transaction since the data must be updated in the same way. Therefore, the network traffic between the application server and the database is also one order of magnitude greater for external programs than for data traffic between external programs and the application server.

Database Backup

Along with the SAP System data traffic, there are other applications necessary for operating the SAP System that generate load in the server network, for example, management functions and file access. The most important of these functions is backing up the database. The data traffic generated by this action has the same order of magnitude as accessing the database. In large installations, you may have to back up the database using a separate network adapter and a special backup network (for example, a Storage Area Network).

Other Applications

If other applications are running on the same network or even on the same servers, you must consider this when you determine the network bandwidth. In a large SAP System, we recommend that for each system you set up a separate network that is solely reserved for the data traffic between the application server and the database.