How a Network Connection is Made
This topic describes how the SAP spool system uses connection timeouts, read-write timeouts, and automatic retries to do the following:
● Terminate an attempt to establish communication with a host spooler or print manager when a network connection is not working
● Automatically try to establish a network connection after a connection or read/write failure
Connection Timeouts
The SAP spool system uses its own internal timeouts to determine how long to wait for a network connection to a remote output device. If the spool system has not been able to establish a network link within the time limit specified in the time-out, then it breaks off the attempt to set up the connection.
The network software in your host system also imposes a time-out on the connection to a remote printer. The length of the time-out varies with the host operating system and network software. However, the time-out is usually set to 60 seconds.
The spool system’s attempt to reach an output device is terminated by whichever time-out occurs first: the network software time-out or the spool system time-out.
The other partner in setting up a connection to a remote output device can be either of the following:
● The host system that is responsible for the target device
● The SAPSprint service that is responsible for the output device
An elapsed time-out can therefore mean that the network connection to the remote system is down or that the host system or SAPSprint service is not running.
Automatic Retry
If a time-out elapses, then the spool system retries the connection. By default, it repeats the connection attempt 3 times, with a two-minute pause between each attempt.
If the system is not able to establish a connection after retries, then all jobs that are waiting for the output device are placed in a special waiting status, Hold: Communication problem.
If the output device is local (attached to the host system on which the SAP spool work process is running or accessible from the host system by way of host remote printing facilities), then these mechanisms do not need to be used. Passing an output request to the local host spool system requires only the execution of a print command.
The spool system keeps retrying the network connection as long as there are jobs with the status Hold: Communication problem waiting for the output device.
Read and Write Timeouts
In addition to connection timeouts, the system uses read and write timeouts to prevent unrestricted waiting for read or writes to remote output devices. If a read or write time-out elapses, then the SAP System retries the operation. The number of retries and pause between retries is determined by the same system profile parameters used for the connection time-out.
The system profile parameter defines write and read timeouts for all output devices; however, you can also define device-specific values.
Wide-Area Network (WAN) Connections
If you are using a wide-area network connection to an SAP transfer process, then timeouts can pose special problems. If data transmission across the WAN link is too slow, then the read-write time-out of the SAP spool system or of your host network software may be triggered while transmitting data across the connection. The minimum throughput for successful data transfer to an SAPSprint service is 1 kilobyte/minute.
Should this problem occur, a faster WAN link is the best solution to the problem. Should this not be possible, then one of the following measures should help:
● If the host spooler supports remote printers, then use the host’s remote printing facilities to access the printer. You will then no longer need the WAN link to the SAPSprint service. Data transmission may be more successful under the host’s remote printing facility than by way of SAPSprint.
For more information, see Defining Values for the Read and Write Process Timeouts.
