IBM 990 manual Fiber

Draft Document for Review April 7, 2004 6:15 pm 6947glos.fm

local area network (LAN). A computer network located in a user’s premises within a limited geographic area.

Logical Channel Subsystem (LCSS). A defined subset of the CPC hardware (subchannels, channels, and I/O interfaces) that is used to support the operation of a Logical Channel Subsystem. The LCSS relieves the processor of direct I/O communication tasks, and performs path management functions. Uses a collection of subchannels (defined to the LCSS) to direct a channel to control the flow of information between its defined I/O devices and main storage.

logical control unit (LCU). A separately addressable control unit function within a physical control unit. Usually a physical control unit that supports several LCUs. For ESCON, the maximum number of LCUs that can be in a control unit (and addressed from the same ESCON fiber link) is 16; they are addressed from x’0’ to x’F’.

logical partition (LPAR). A set of functions that create a programming environment that is defined by the ESA/390 architecture. ESA/390 architecture uses this term when more than one LPAR is established on a processor. An LPAR is conceptually similar to a virtual machine environment, except that the LPAR is a function of the processor. Also, LPAR does not depend on an operating system to create the virtual machine environment.

logical switch number (LSN). A two-digit number used by the I/O Configuration Program (IOCP) to identify a specific ESCON Director.

logically partitioned (LPAR) mode. A central processor mode, available on the Configuration frame when using the PR/SM facility, that allows an operator to allocate processor hardware resources among logical partitions. Contrast with basic mode.

LPAR. See logical partition.

megabyte (MB). (1) For processor storage, real and virtual storage, and channel volume, 220 or 1 048 576 bytes. (2) For disk storage capacity and communications volumes, 1 000 000 bytes.

MT-RJ.An optical fibre cable duplex connector that terminates both jumper cable fibres into one housing and provides physical keying for attachment to an MT-RJ duplex receptacle. For technical details, see the NCITS - American National Standard for Information Technology - Fibre Channel Standards document FC-PI.

multi-mode optical fiber. A graded-index or step-index optical fiber that allows more than one bound mode to propagate. Contrast with single-mode optical fiber.

Multiple Image Facility (EMIF). In the ESA/390 architecture and z/Architecture, a function that allows LPARs to share a channel path by providing each LPAR with its own set of subchannels for accessing a common device.

National Committee for Information Technology Standards. NCITS develops national standards and its technical experts participate on behalf of the United States in the international standards activities of ISO/IEC JTC 1, information technology.

NCITS. See National Committee for Information Technology Standards.

ND. See node descriptor.

NED. See node-element descriptor.

node descriptor. In an ESCON and FICON environment, a node descriptor (ND) is a 32-byte field that describes a node, channel, ESCON Director port, FICON Director port or a control unit.

node-element descriptor. In an ESCON and FICON environment, a node-element descriptor (NED) is a

32-byte field that describes a node element, such as a DASD (Disk) device.

OEMI. See original equipment manufacturers information.

open system. A system whose characteristics comply with standards made available throughout the industry and that therefore can be connected to other systems complying with the same standards.

optical cable assembly. An optical cable that is connector-terminated. Generally, an optical cable that has been terminated by a manufacturer and is ready for installation. See also jumper cable and optical cable.

optical cable. A fiber, multiple fibers, or a fiber bundle in a structure built to meet optical, mechanical, and environmental specifications. See also jumper cable, optical cable assembly, and trunk cable.

optical fiber connector. A hardware component that transfers optical power between two optical fibers or bundles and is designed to be repeatedly connected and disconnected.

optical fiber. Any filament made of dialectic materials that guides light, regardless of its ability to send signals. See also fiber optics and optical waveguide.

optical waveguide. (1) A structure capable of guiding optical power. (2) In optical communications, generally a fiber designed to transmit optical signals. See optical

fiber.

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