The network interface supports a platform independent interface to communicate between SAP systems. NI knows the following different operation modes:
The NI_RAW_IO mode is used to communicate between SAP applications without any further interpretation of the data blocks.
The NI_MSG_IO mode is the common used operation mode between SAP applications. The format is also called the SAP Protocol. A 4-byte header precedes each data block. These 4 bytes give the length of the data block (length without leading 4 bytes). This value is needed to recognize a complete data block, if underlying layers fragment it.
In addition this operation mode knows three special messages. They are recognized by a leading byte-string 'NI_PING\0', 'NI_PONG\0' or 'NI_RTERR\0'. The first two are used for keepalive tests, the third one for error messages (see NI Keepalive, NI Error Information and NI Control Messages).
Only the SAProuter uses the NI_ROUTE_IO mode. This mode is similar to the NI_MSG_IO mode, but keepalive messages are ignored. This is necessary for the keepalive test passing the SAProuter.