Glossary - 28
FORE Systems ES-2810 Ethernet Switch User's Manual
Glossary
Protocol Control Information - the information exchanged between corresponding entities
using a lower layer connection to coordinate their joint operation.
Protocol Data Unit (PDU) - a unit of data specified in a layer protocol and consisting of protocol
control information and layer user data.
Proxy - the process in which one system acts for another system to answer protocol requests.
Proxy Agent - an agent that queries on behalf of the manager, used to monitor objects that are
not directly manageable.
Public Data Network (PDN) - a network designed primarily for data transmission and intended
for sharing by many users from many organizations.
Pulse Code Modulation (PCM) - a modulation scheme that samples the information signals and
transmits a series of coded pulses to represent the data.
Q.2931 - Derived from Q.93B, the narrowband ISDN signalling protocol, an ITU standard
describing the signalling protocol to be used by switched virtual circuits on ATM LANs.
Quality of Service (QoS) - Quality of Service is defined on an end-to-end basis in terms of the
following attributes of the end-to-end ATM connection:
Cell Loss Ratio
Cell Transfer Delay
Cell Delay Variation
Queuing Delay (QD) - refers to the delay imposed on a cell by its having to be buffered because
of unavailability of resources to pass the cell onto the next network function or element. This
buffering could be a result of oversubscription of a physical link, or due to a connection of
higher priority or tighter service constraints getting the resource of the physical link.
Radio Frequency Interference (RFI) - the unintentional transmission of radio signals. Computer
equipment and wiring can both generate and receive RFI.
Real-Time Clock - a clock that maintains the time of day, in contrast to a clock that is used to
time the electrical pulses on a circuit.
Red Alarm - In T1, a red alarm is generated for a locally detected failure such as when a condi-
tion like OOF exists for 2.5 seconds, causing a CGA, (Carrier Group Alarm).
Reduced Instruction Set Computer (RISC) - a generic name for CPUs that use a simpler instruc-
tion set than more traditional designs.
Redundancy - In a data transmission, the fragments of characters and bits that can be elimi-
nated with no loss of information.
Registration - The address registration function is the mechanism by which Clients provide
address information to the LAN Emulation Server.
Relaying - a function of a layer by means of which a layer entity receives data from a corre-
sponding entity and transmits it to another corresponding entity.
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