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Glossary
N (Continued)
NTP
O
OFDM
OID
OPSEC
OS
OSI
OSI Layer 2
OSI Layer 3
226
Network Time Protocol, an Internet standard protocol (built on top of
TCP/IP) that assures accurate synchronization to the millisecond of
computer clock times in a network of computers. Based on UTC, NTP
synchronizes client workstation clocks to the U.S. Naval Observatory
Master Clocks in Washington, DC and Colorado Springs CO. Running
as a continuous background client program on a computer, NTP sends
periodic time requests to servers, obtaining server time stamps and
using them to adjust the client's clock. (RFC1305)
Orthogonal frequency division multiplexing, a method of digital
modulation in which a signal is split into several narrowband
channels at different frequencies. OFDM is similar to conventional
frequency division multiplexing (FDM). The difference lies in the way
in which the signals are modulated and demodulated. Priority is given
to minimizing the interference, or crosstalk, among the channels and
symbols comprising the data stream. Less importance is placed on
perfecting individual channels.
OFDM is used in European digital audio broadcast services. It is also
used in wireless local area networks.
Object Identifier.
OPSEC (Open Platform for Security) is a security alliance program
created by Check Point to enable an open industry-wide framework
for interoperability of security products and applications. Products
carrying the "Secured by Check Point" seal have been tested to
guarantee integration and interoperability.
Operating system.
Open System Interconnection. An ISO standard for worldwide
communications that defines a networking framework for
implementing protocols in seven layers. Control is passed from one
layer to the next, starting at the application layer in one station, down
through the presentation, session, transport, network, data link layer
to the physical layer at the bottom, over the channel to the next station
and back up the hierarchy.
At the Data Link layer (OSI Layer 2), data packets are encoded and
decoded into bits. The data link layer has two sublayers:
> The Logical Link Control (LLC) layer controls frame
synchronization, flow control and error checking
> The Media Access Control (MAC) layer controls how a computer on
the network gains access to the data and permission to transmit it.
The Network layer (OSI Layer 3) provides switching and routing
technologies, creating logical paths, known as virtual circuits, for
transmitting data from node to node. Routing and forwarding are
functions of this layer, as well as addressing, internetworking, error
handling, congestion control and packet sequencing.
Summit WM20 User Guide, Software Release 4.2
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