gtps3m0bSystem Performance and Measurement Reference

TPF Message Processing

A typical TPF system consists of a central system and the local domain network controlled by the central system. The TPF system may participate with a cross-domain network through SDLC cross-domain links if the central system has the Advanced Communication Facility (ACF). This section does not intend to describe the aspects of networks. Those details are found in TPF Concepts and Structures. The discussion here focuses on the major flow in the central system and the message paths in the network.

The bulk of the load presented to the TPF system comes from conversational messages that originate at resources of the network (terminals, network addressable units, and others). These messages, normally transmitted at 2400 BPS or higher speeds, are known as high-speed messages. Teletype or low-speed messages are also counted and equated to multiple high-speed messages to obtain an average or weighted message rate for the total system. All the report statistics calculated on a per-message basis use this weighted message rate as a divisor.

Message Processing

A TPF message enters the processing cycle from a network resource over a communication line after the terminal interchange is polled. If an NCP is involved, the messages or path information units are queued in the NCP and sent to the CPU on a read operation from the CPU. After the input message is assembled, the message is placed on the input list to await processing by the application programs. The CPU loop scans the various lists looking for work. Top priority is given to messages in process waiting on the cross list. With the cross list empty, the system will normally pick up existing work from the ready list. When the ready list is empty, the system will normally pick up a new message from the input list, assign an entry control block (ECB), that will be associated with the message throughout the processing cycle, and branch to start processing by application programs. When all other lists are empty, the system will pick up the deferred list. These programs will edit the message, retrieve data records from file, log data to tape, obtain additional storage when required from the pools, and release blocks. These are tasks required to develop an output message in response to the input message from the agent. When file or tape operations occur, the application program normally relinquishes control so that I/O operations can be overlapped with CPU processing.

Processing will continue on this message when the I/O operations are complete, the message (ECB) appears on the top of the ready list, and the control program selects the top item and continues processing. When processing is complete, the output message is placed on a queue for the desired network resource. At the same time, the ECB assigned to the message is returned to the system. The message is sent to the network resource when it assumes first position in the queue, and the network resource is available to receive the message.

TPF Communications Networks

Consider a network configuration of a TPF system with ACF support. The network is identified as local-domain and cross-domain networks. Because major network control characteristics of the central TPF system can be observed from the network resource addressing scheme, some aspects of the addressing schemes are described as follows:

It must be reiterated that the objective of the message routing facility is to provide for the transfer of data from an origin point to a destination point in the system network domain.

A TPF system with ACF permits the message routing facility to use cross-domain SDLC links between two CPUs.