Glossary
Glossary-9
P
P-NNI
Private Network-to-Node
Interface. The interface between
two ATM switches or between
an ATM switch and an entire
switching system in a private
network. A Public NNI refers to
the interface between an ATM
switch in a public network and a
switch in either a private or a
public network.
Packet-Switching
A communication technology
that is appropriate for variable
bit rate services such as data and
full-motion video. It is used by
ATM in combination with
circuit-switching.
PCI
Peripheral Component
Interconnect. A local bus
technology that allows SCSI host
adapters, video cards, and other
peripherals to send data directly
to and receive data directly from
the computer ’s CPU. PCI is a
much faster bus than ISA or
EISA.
PCR
Peak Cell Rate. A type of ATM
traffic flow. The maximum rate
at which cells can be
transmitted, defined by the
minimum possible space
between two cells.
PDU
Protocol Data Unit. A generic
term for the format used to send
information in a
communications protocol,
typically a packet with its
headers and trailers. Typically,
the PDU is passed back and
forth between the protocol
layers, by the layers themselves.
Physical-Layer (PHY)
Short for Physical Layer. The
layer below the ATM layer in the
Protocol Reference Model that
passes data from the media to
the ATM layer and vice-versa.
Also refers to OSI Layer 1.
PMD
Physical (layer) Media
Dependent. Refers to the part of
the NIC’s design that has to
interface with (and is therefore
dependent on) the chosen
transmission medium (MMF,
UTP, and so forth)
Protocol
Rules for communicating,
particularly for the formatting
and transmission of data.
PTI
Payload Type Identifier. A 3-bit
descriptor found in ATM cell
headers, indicating what type of
payload the cell contains.
Payload types include user and
management cells.
PVC
Permanent Virtual Connection/
Circuit. A logical (rather than
physical) connection between
endpoints established by an
administrator which stays intact
