With an IBM-compatible personal computer (PC) and BARR/RJE, you can access large host computers or mainframes with powerful computer languages, large databases, and increased computational capacities from your office, classroom, lab, or field station. This chapter briefly discusses Remote Job Entry (RJE) concepts to help you understand BARR/RJE’s role in PC-to-mainframe communication.
Mainframe computers support remote workstations that send files to and receive reports from the mainframe RJE system. RJE is the term used to describe this process of sending files and printing reports at high speeds. An RJE workstation operator has complete console control of the job flow between the workstation and mainframe.
The RJE workstation is called a remote because it usually is located some distance from the host computer. The workstation connects to the host through a modem or local area network (LAN). When you send jobs from the remote workstation to the host computer, the process is called remote job entry.
BARR/RJE is compatible with these mainframe RJE systems:
MVS/JES2
MVS/JES3
VSE/POWER
VM/RSCS
VS1/RES
A PC equipped with software and either a Barr synchronous communications adapter or an IBM Token Ring adapter replaces expensive RJE workstations such as IBM 3777, System/36, or AS/400. In fact, the PC’s higher throughput and easy-to-master user interface uniformly out perform the older technology.
The Barr software and hardware allow the PC to emulate an RJE workstation or 3270 terminal. (The 3270 emulation requires Barr RJE+3270 software.)
An RJE workstation consists of a PC, a communications adapter, and software. You can also attach peripheral devices such as a modem and printers. If the PC is on a LAN, you can access LAN directories and devices.
For more information about modems, see section 2.3. For more information about RJE workstations and 3270 terminals, see Chapter 3.
RJE devices are the paths, or streams, over which you exchange data between the host computer and PC workstation. The RJE workstation uses RJE devices for the following applications:
Sending programs and data files to the mainframe computer for processing
Sending commands to the mainframe to control output flow and inquire about the status of other RJE devices
Receiving job output from the mainframe to the PC
Receiving job setup messages from the host
The host programmer enters parameters at the host to allow the host computer and the PC workstation to communicate and to set up the RJE devices over which data, messages, and commands flow (see Figure 2-1).
Figure 2-1. RJE devices allow the PC workstation and the host computer to exchange data and messages.
The requirements at your site determine which RJE devices to use. Review the available devices below and then discuss your RJE needs with your host communications consultant.
Command – The command device sends commands from the remote workstation to the host computer. You can use commands to request the following:
Information about files waiting in print or punch queues
That print or punch files be sent to the remote workstation
RJE device status
Reader – You can send data and job files from the remote workstation to the host computer on the reader device. The reader is an input device that accepts files. Historically, a card reader read 80-column punched cards for input to the host. Now you can transfer data files on the reader to the host or send them with job files to be processed by the host. Job files contain job control language (JCL) instructions that tell the host how to process the job.
Console – The console device receives messages from the host computer and displays them at the remote workstation. These messages tell you the status of jobs and RJE devices such as printers and punches. The console is especially important for displaying messages when you print special forms such as invoices and checks.
Printer – BARR/RJE sends print output produced by host programs to the remote workstation on the RJE printer. BARR/RJE formats each page of this output with carriage control characters. You can send output files directly from the mainframe print stream to PC printers or save files to disk at the remote workstation for later printing.
Punch – The mainframe transfers data files on the punch to the PC workstation. These files do not include carriage control characters and usually are not printed. Instead, these files can be processed by programs on the PC. (Historically you received data to a card punch that recorded data on 80-column punched cards.)
The PC workstation running BARR/RJE is compatible with dot matrix, nonimpact, laser, and line (band) printers. You can choose the type of printer according to your printing needs. You can attach up to seven parallel interface and serial interface printers to the PC through the parallel or serial ports. Barr Systems also offers special support for printers that use the Dataproducts Interface (requires BARR/DPI) and the IBM S/370 channel interface (requires PRINT370).
You can request information about configuring peripheral devices to work with BARR/RJE from Barr Systems. The configuration information includes switch settings and control data for various printers, plotters, and modems.
The rest of this section discusses the parallel and serial interfaces and how they work with BARR/RJE.
Parallel Ports – The PC parallel port transfers all eight bits of a data byte simultaneously. By sending each data bit across one of eight wires, each data bit travels side by side with the other bits. This simultaneous data transmission is faster than the serial port transmission rate. The parallel adapter interface standard, also known as the Centronics Printer Interface, is the preferable way to connect high-speed printers to the PC. The printer must be within 20 feet of the PC. DOS names for parallel ports are LPT1, LPT2, and LPT3.
Serial Ports – The serial port transfers all eight bits of a byte sequentially. A single wire sends the data from the PC to the printer one bit at a time. Another wire sends responses from the printer to the PC. Printers with a serial interface use the RS232 standard. This asynchronous serial convention supports longer cable distances, usually up to 50 feet, which allows you to place the printer farther away from the PC. The serial port supports the XON/XOFF and DTR (Data Terminal Ready) flow control mechanisms. Appendix C describes the serial port interface. DOS names for serial ports are COM1, COM2, COM3, and COM4.
The communication link is the type of physical connection between the remote workstation and host computer.
You can communicate with the host these ways:
Through a modem for the SDLC, X.25, or gateway ADLC communication links
Through a direct connection to a communications controller with a synchronous modem eliminator (SME) for SDLC
Through the LAN for the 802.2 or gateway LAN communication links
Through a direct connection to a communications controller with the Coax communication link
BARR/RJE works equally well when you connect to the host through a dial-up line, dedicated line, or LAN.
Dial-Up Line – With a dial-up (switched) line, you connect through modems by dialing the mainframe’s telephone number. Ask your host communications consultant which modem types the mainframe supports and the telephone number to use with your modem. The Barr adapters used with modems support speeds up to 384,000 bits per second (bps). The actual speed achieved on your communication line depends on the speed supported by your data communication equipment.
Dedicated Line – With a dedicated line (non-switched, leased), the host computer and remote workstation connect directly. No dial-up procedure is required. The communication lines can be privately owned or furnished by a telephone company. You can achieve faster communication speeds on a dedicated line than on a dial-up line. The actual speed achieved on your communication line depends on the speed supported by your data communication equipment. BARR/RJE supports dedicated-line speeds up to T1 (1,536,000 bps) and E1 (2,048,000 bps).
802.2 Network – The mainframe connects to the 802.2 network to communicate with IBM 3174, 3725, and 3745 communications controllers. The PC workstation uses a token ring or Ethernet adapter to connect to the network.
LAN Gateway – RJE workstations can connect to the host computer through the BARR GATEWAY, which maintains the physical connection to the host. You can connect to the gateway through a LAN or a dial-up connection with an asynchronous modem. BARR/RJE supports these LAN protocols: Novell IPX, NetBIOS, 802.2 LLC (token ring), and TCP/IP.
You can transmit data between the PC and host computer through telephone lines. The word modem is derived from the terms modulate and demodulate. When the PC workstation sends data, the modem converts (modulates) digital signals to the analog signals the telephone system uses. When the PC receives data, the modem restores (demodulates) the signal to digital form. See your Barr modem hardware manual for more information about synchronous and asynchronous communication, modem standards, and external and internal modems.