CCNA Cisco Certified Network Associate Study Guide - FTP Server

Glossary 697
Physical layer The lowest layer—Layer 1—in the OSI reference model, it
is responsible for converting data packets from the Data Link layer (Layer 2)
into electrical signals. Physical-layer protocols and standards define, for
example, the type of cable and connectors to be used, including their pin
assignments and the encoding scheme for signaling 0 and 1 values. See also:
Application layer, Data Link layer, Network layer, Presentation layer, Session
layer, and Transport layer.
ping packet Internet groper: A Unix-based Internet diagnostic tool, consisting
of a message sent to test the accessibility of a particular device on the
IP network. The acronym (from which the “full name” was formed) reflects
the underlying metaphor of submarine sonar. Just as the sonar operator
sends out a signal and waits to hear it echo (“ping”) back from a submerged
object, the network user can ping another node on the network and wait to
see if it responds.
pleisochronous Nearly synchronous, except that clocking comes from an
outside source instead of being embedded within the signal as in synchronous
transmissions.
PLP Packet Level Protocol: Occasionally called X.25 Level 3 or X.25 Protocol,
a Network-layer protocol that is part of the X.25 stack.
PNNI Private Network-Network Interface: An ATM Forum specification
for offering topology data used for the calculation of paths through the network,
among switches and groups of switches. It is based on well-known
link-state routing procedures and allows for automatic configuration in networks
whose addressing scheme is determined by the topology.
point-to-multipoint connection In ATM, a communication path going
only one way, connecting a single system at the starting point, called the
“root node,” to systems at multiple points of destination, called “leaves.”
See also: point-to-point connection.
point-to-point connection In ATM, a channel of communication that
can be directed either one way or two ways between two ATM end systems.
See also: point-to-multipoint connection.