Networking on z/OS
Previous topic | Next topic | Contents | Glossary | Contact z/OS | PDF


Hardware connectivity on the mainframe

Networking on z/OS

See the latest information on:

Network connections can be made in several different fashions. The mainframe originally relied upon the channel subsystem to offload I/O processing to channel programs. DASD is still accessed using ESCON channels, but for networking connectivity, OSA-Express cards offer better performance and availability.

The OSA-Express and OSA-Express2 cards provide redundancy capability, as well as throughput improvements when running in QDIO mode. QDIO mode allows direct access to central memory. QDIO mode can be emulated within a CPC by allowing memory to memory data transfer among LPARs running z/VM, Linux, or z/OS.

Connections for the mainframe

The design intention of the mainframe, and most of its evolution, is for the mainframe to be a highly available transaction processing server. Obviously, central processing capabilities are evolving to handle more and more transactions. However, in order to be an effective transaction processing server, there must be a proportional capability of moving data in and out of the central processor complex rapidly (CPC, the physical collection of hardware that consists of main storage, one or more central processors, timers, and channels). The result is that the I/O (input/output) options, capabilities and configuration choices of an IBM mainframe are varied, complex, and very performance oriented.

Mainframe computers are probably unique in that they require a Hardware Management Console, or HMC. The HMC is a separate interface to the central processor complex that is used for hardware configuration operations. It also provides an interface to the z/OS system console.

  • Channel subsystem (CSS)
    The heart of moving data into and out of a mainframe host is the channel subsystem, or CSS. The CSS is, from a central processor standpoint, independent of the processors of the mainframe host itself. This means that input/output (I/O) within a mainframe host can be done asynchronously.
  • The mainframe channel subsystem and network links
    A CHPID no longer directly corresponds to a hardware channel, and CHPID numbers may be arbitrarily assigned. A hardware channel is now identified by a physical channel identifier, or PCHID.
  • Hardware channels
    There are effectively three ways that network traffic can travel between an external network and a z/OS host: through a channel-command word channel, a coupling channel, or a QDIO channel.
  • HiperSockets
    Mainframe HiperSockets is a technology that provides high-speed TCP/IP connectivity within a central processor complex. It eliminates the need for any physical cabling or external networking connection between servers running in different LPARs.
  • The I/O cage
    The connections to the central processor complex are made in a physical area of the processor frame called an I/O cage. Within the cage, OSA cards and memory modules (and other devices) are physically attached to the central processor complex. Parallel, FICON and ESCON connections are all made within the cage as well, using an adapter card.
Parent topic: Introduction to networking on the mainframe

Go to the previous page   |   Go to the next page

Notices | Terms of use | Support | Contact z/OS



Copyright IBM Corporation 1990, 2010