SDISC Assembler Call - NetEx

Design Efficiency and FlexibilityThe NETEX design enables many applications on the same processor to share the use of the network facility.Programs calling NETEX can be written without regard to the other programs calling NETEX or other drivers.Once NETEX accepts data from the caller, it assumes responsibility for the delivery of the data to its destination.The NETEX subsystem on each host handles flow control, error recovery, and any other special considerationssuch as satellite links.NETEX is designed to optimize data transfer throughput using a high degree of “parallelism”. That is, undernormal circumstances, adapter I/O, NETEX buffer management, and user file I/O will all be taking place concurrently.This means that the effective data transfer rate will be as fast as possible (in the multi-megabitrange).Block SegmentingThe NETEX products provide block segmenting at the transport layer. NETEX will partition data into segmentsof a specified size for transmission across the network, and will reassemble the segments on the remotehost before delivering the data to the Session-layer calling program on the remote NETEX. This segmentingis transparent to the session user, but provides control of the transmitted block segment size (especially usefulfor satellite communication).Alternate Path RetryAlternate path retry provides the capability for connections to be automatically rerouted on different networkpaths when a failure on a path is detected. This rerouting takes place with no loss of data.User ExitsNETEX provides user exits at well-defined points within the NETEX subsystem for security and accountingpurposes. These exits are essentially “do-nothing” routines that may be replaced by user modules at installationtime. User exits exist before each request starts processing and after processing is complete. It should benoted that, because of the wide variety of user needs, NETEX does not create generalized security and accountinginformation, but allows user exits to provide for these needs.Remote Operator InterfaceNETEX provides a remote operator interface that allows users to issue NETEX operator commands to otherdefined NETEX hosts on the network. Other users may also be the remote operator for this NETEX. See“REMOTE Command” for more information. Security features are provided.Basic I/O FlowThe figure shows the basic I/O flow between two programs using host based NETEX. The calling programcommunicates with NETEX through the NETEX user interface. NETEX then uses the appropriate networkhardware to communicate with the calling program on the other processor.Page 2 Introduction MAN-REF-H307IP-04