IBM Nways 2216, Руководство по обслуживанию и ремонту

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magnetization, and zeros are represented by the
absence of change. Only the one signals are explicitly
recorded. (Previously called
non-return-to-zero
inverted, NRZI, recording.)
NRZ-1. Non-return-to-zero change-on-ones recording.
NSAP. Network service address point.
NSC. Network Support Center.
NVDM. NetView Distribution Manager/6000.
O
OC. Optical carrier.
OSI. Open systems interconnection.
P
packet loss ratio. The probability that a packet will
not reach its destination or not reach it within a
specified time.
packet mode operation. Synonym for packet
switching.
packet switching. (1) The process of routing and
transferring data by means of addressed packets so
that a channel is occupied only during transmission of a
packet. On completion of the transmission, the channel
is made available for transfer of other packets. (I)
(2) Synonymous with
packet mode operation. See also
circuit switching.
PBX. Private branch exchange.
PCM. Pulse code modulation.
PDH. Plesiochronous digital hierarchy.
permanent virtual circuit (PVC). In X.25 and frame
relay communications, a virtual circuit that has a logical
channel permanently assigned to it at each data
terminal equipment (DTE).
physical circuit. A circuit established without
multiplexing. See also
data circuit. Contrast with virtual
circuit.
PM. Presentation Manager.
PMF. Parameter Management Frame.
PNP. Private numbering plan.
Point-to-Point Protocol (PPP). A protocol that
provides a method for encapsulating and transmitting
packets over serial point-to-point links.
port. (1) An access point for data entry or exit. (2) A
connector on a device to which cables for other devices
such as display stations and printers are attached.
Synonymous with
socket. (3) The representation of a
physical connection to the link hardware. A port is
sometimes referred to as an adapter; however, there
can be more than one port on an adapter. There may
be one or more ports controlled by a single DLC
process. (4) In the Internet suite of protocols, a 16-bit
number used to communicate between TCP or the User
Datagram Protocol (UDP) and a higher-level protocol or
application. Some protocols, such as File Transfer
Protocol (FTP) and Simple Mail Transfer Protocol
(SMTP), use the same well-known port number in all
TCP/IP implementations. (5) An abstraction used by
transport protocols to distinguish among multiple
destinations within a host machine.
PPP. Point-to-Point Protocol.
PR/SM. Processor Resource/Systems Manager.
private branch exchange (PBX). A private telephone
exchange for transmission of calls to and from the
public telephone network.
problem determination. The process of determining
the source of a problem; for example, a program
component, machine failure, telecommunication
facilities, user or contractor-installed programs or
equipment, environmental failure such as a power loss,
or user error.
Processor Resource/Systems Manager (PR/SM).
The feature on a 3090 Processor Complex that offers
flexible partitioning of a 3090 processing system into a
number of logical partitions. Each partition within a
PR/SM environment supports its own MVS or VSE
image and VTAM, resulting in a multi-MVS or VSE
environment.
PRS. Primary reference source.
PSN. Public switched network.
PSTN. Public switched telephone network.
PTM. Packet transfer mode.
PVC. Permanent virtual circuit.
Q
QoS. Quality of service.
Glossary
X-7