HP ProCurve 7000dl Series Basic Management And Configuration Manual page 855

Presentation Layer 6 of the OSI model. This layer is responsible for the delivery and
Layer formatting of information to the Application Layer for further processing or
display. This layer deals with issues such as how strings are represented. It
also formats and encrypts data to be sent across a network, providing freedom
from compatibility problems. Layer 6 is sometimes called the syntax layer.
PRI Primary Rate Interface. A type of ISDN service offered by public carriers that
consists of one 64-Kbps D channel, and 23 64 Kbps B channels in North
America or 30 64 Kbps B channels in all other countries. The B channels carry
data, voice, or video traffic. The D channel is used to carry packet data and to
set up and maintain calls on the B channels.
Preshared Key A preshared key is an alphanumeric character string agreed upon by two
parties in advance. In IKE negotiations, peers can exchange a preshared key
that is between 8 and 255 characters in length to authenticate each other
before opening the IKE SA.
Protocol A set of standard rules required to send mutually-coherent information over
a communications channel. Each layer of the OSI model can include many
different protocols. For example, Data Link Layer protocols include (among
others) Ethernet, Frame Relay, PPP, and ATM, and these protocols dictate how
links between hosts on a network are initiated, maintained, and terminated.
Protocol Field See PFC.
Compression
PSTN Public Switched Telephone Network. The public network that provides
switched digital/analog voice and data services to customers.
PTT Public Telephone and Telegraph. State-owned and regulated companies, pri-
marily in Europe, that provide telecom services.
Public Carrier A generic term used to describe the public entity that provides telephone
services, as well as data communications services like DSL and ISDN. The
public carrier may be private or government-owned.
PVC Permanent Virtual Circuit. A logical connection between two nodes. A PVC is
a virtual circuit established for repeated use between the same data terminal
equipment (DTE). Like a dedicated physical connection, a PVC is an always-
open connection between two endpoints. However, the actual physical path
that frames take over the PVC may vary. PVCs are used in Frame Relay
networks, where each PVC is identified by a DLCI and in ATM networks, where
each PVC is identified by a VCI/VPI.
Appendix B: Glossary
B-41