With an IBM-compatible computer 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 topic briefly discusses 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 files from the mainframe RJE system. RJE is the term used to describe this process of sending files and printing files at high speeds. An RJE workstation operator has complete console control of the job flow between the workstation and mainframe. BARR/RJE is compatible with the MVS/JES2 mainframe system.
The RJE workstation is called a remote because it is typically located some distance from the host computer. The workstation connects to the host through a modem Short for modulator/demodulator. A communications device that enables a computer to transmit information over a standard telephone line. or LAN Acronym for Local Area Network. A group of computers and other devices dispersed over a relatively limited area and connected by a communications link that enables any device to interact with any other on the network. When you send jobs from the remote workstation to the host computer, the process is called remote job entry.
Users need two types of communications service.
Remote job entry for submitting jobs and RJE printers to print jobs
3270 interactive terminals to communicate with mainframe applications and 3270 printers
Workstations communicate with mainframe application software to perform tasks. For example, the BARR/RJE workstation communicates with the RJE system for remote printing.
RJE is comprised of two parts: workstations and the mainframe system.
Workstations – RJE workstations print files at remote sites, send large files directly into the JES Acronym for Job Entry Subsystems of the IBM MVS operating system. These subsystems are used for entering jobs into the MVS operating system and dispensing the output from the jobs., and control the status of mainframe jobs. An RJE workstation might be an IBM 3777-3, AS/400 running RJE emulation, or a computer running BARR/RJE. The BARR/RJE software emulates an IBM 3777-3 remote workstation.
Mainframe System – A mainframe RJE system manages job input and file output for remote sites. BARR/RJE is compatible with host computers that support the SNA Multiple Session RJE communications protocol A set of rules or standards designed to enable computers to connect with one another and to exchange information with as little error as possible. as the MVS/JES2 IBM system does. The RJE system communicates with VTAM, the universal SNA control program.
A remote workstation, sometimes called an RJE workstation, is a collection of input and output devices, such as a keyboard, a monitor, and printers. RJE devices are the paths, or streams, over which you exchange data between the host computer and computer workstation. The RJE workstation uses RJE devices for the following applications:
Sending programs and data files to the mainframe 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 computer
Receiving job setup messages from the host
The host programmer enters parameters at the host to allow the host computer and the computer workstation to communicate, and to set up the RJE devices over which data, messages, and commands flow, as shown in the following graphic.
RJE devices allow the computer workstation and
the host computer to exchange data and messages.
The requirements at your site determine which RJE devices to use. Review the following available devices, and then discuss your RJE needs with your host communications consultant.
There are four types of devices a remote workstation might have.
RJE Console – With the RJE Console, you can send commands to, and receive messages from, the host computer.
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 include JCL Acronym for Job Control Language. A command language used in IBM OS/360 mainframe systems. instructions that tell the host how to process the job.
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. All files are sent to the spool, then directed to various destinations.
Punch – The mainframe transfers data files on the punch to the computer workstation. These files do not include carriage control characters and usually are not printed. Instead, these files can be processed by programs on the computer. (Historically you received data to a card punch that recorded data on 80-column punched cards.)
SNA is the all-encompassing framework for communicating in the IBM mainframe environment. SNA is an evolving communications architecture that constantly adapts to the changing needs of business, research, and government. This topic describes the SNA network from the user’s viewpoint.
As shown in the following graphic, the SNA communications network connects user workstations in the network with mainframe applications.
IBM mainframes communicate through SNA networks.
IBM’s SNA architecture includes the VTAM and NCP Acronym for Network Control Protocol. The protocol responsible for negotiating network-layer details related to the transmission of TCP/IP packets over dial-up telephone connections. software components.
VTAM – VTAM is the most important product in the SNA environment and is common to all SNA host systems. VTAM is an operating system program that resides on the mainframe. It controls communication between the mainframe application software and remote workstations.
NCP – The mainframe connects to one or more IBM FEPs Acronym for Front-End Processor(s). (1) Generally, a computer or processing unit that produces and manipulates data before another processor receives it. (2) In communications, a computer that is located between communications lines and a main (host) computer and is used to relieve the host of housekeeping chores related to communications.. These communications processors manage communications links and connect to one or more remote terminals Terminals that are located at sites removed from the computer to which they are attached. Remote terminals rely on modems and telephone lines to communicate with the host computer. NCP resides in each processor and controls its operation.
The communication link is the type of physical connection between the remote workstation and host computer. The physical link between the computer workstation and the mainframe depends on which communication links your mainframe supports.
You can communicate with the mainframe using the following communication links.
Through a modem for SDLC Acronym for Synchronous Data Link Control. A low-level communications protocol for synchronous communications. (dial-up Of, pertaining to, or being a connection that uses the public switched telephone network rather than a dedicated circuit or some other type of private network. or dedicated line (1) A communications channel that permanently connects two or more locations. Dedicated lines are private or leased lines, rather than public ones. (2) A telephone line that is used for one purpose only, such as to receive or send faxes or to serve as a modem line. connections)
Through a direct connection to a communications controller A device used as an intermediary in transferring communications to and from the host computer to which it is connected. with a synchronous modem eliminator (SME) for SDLC
Through the LAN for the 802.2, HPR/IP, or gateway LAN communication links
Through a mainframe channel
Through an SNA gateway using LUA
BARR/RJE will also work when you connect to the host through a dial-up line, dedicated line, or LAN.
Dial-Up Line – With a dial-up (switched A standard dial-up telephone connection; the type of line established when a call is routed through a switching station.) 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 actual speed achieved on your communication line depends on the speed supported by your data communication equipment.
The IBM SNA world uses the synchronous Occurring at the same time. In computer transmissions,
a reference to activity governed by a clock or by synchronized timing.
modem standard, unlike the personal computer world, which uses an asynchronous Pertaining to, being, or characteristic of
something that is not dependent on timing. For example, asynchronous communications
can start and stop at any time instead of having to match the timing governed
by a clock.
standard.
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 A high-speed communications line that can handle digital communications and Internet access at the rate 1.544 MBps (megabytes per second). (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 computer workstation uses a token ring A LAN formed in a ring (closed loop) topology that uses token passing as a means of regulating traffic on the line. or Ethernet One of the LAN physical standards. It allows multiple stations to access the transmission medium. adapter to connect to the network.
HPR/IP Network – The mainframe connects to the IP network to communicate with IBM mainframe. The computer workstation uses an Ethernet One of the LAN physical standards. It allows multiple stations to access the transmission medium. adapter to connect to the network.
The following figure shows the communication components between the workstation and the mainframe using an SDLC connection.
SDLC communication components between
the mainframe and BARR/RJE workstation.
The following describes the communication process shown in the graphic.
An RJE JES2 or 3270 program communicates with VTAM
VTAM communicates with NCP
NCP communicates with a host modem
The host modem communicates with the telephone line
The telephone line communicates with a remote modem
The remote modem communicates with BARR/RJE
The SNA protocol, a layered communications protocol, connects both 3270 and SNA RJE to the host. The lowest SNA level is the SDLC. DLC Acronym for Data Link Control. An error-correction protocol in the SNA responsible for transmission of data between two nodes over a physical link. ensures that frames (blocks) of data are sent correctly through an error-recovery procedure. If SDLC receives a frame incorrectly, it requests for the frame to be re-sent. A frame-numbering scheme ensures that SDLC receives frames in order without missing or duplicate frames.
SNA defines the entities in the communications network. The main communications entity visible to the end user is the PU, which is subdivided into LUs. The PU corresponds to the physical connection to the host. LUs correspond to application sessions available through each PU connection.
The most common PUs are the IBM 3174 and 3274 control units and the RJE workstation. Each physical connection to the host must have a separate PU definition in VTAM.
Each LU is an independent entity within the parent PU. Separate LUs represent each of the 3270 sessions (terminals or printers) and RJE sessions (printers, punches, readers, console, and commands).
To distinguish the LUs in each PU, each LU has a unique number known as the LU’s local address (LOCADDR). Local addresses can range from 1 to 255. When data flows between an LU and the host, it includes the LU’s local address.