|
Glossary
G-41
Protocol
An ASCII text file found on Transmission Control Protocol/Internet
Protocol (TCP/IP) systems that lists the codes used in the Protocol field of
the IP
header. This field identifies the transport layer protocol that generated
the data
carried within the datagram, ensuring that the data reaches the appropriate
process on the receiving computer. The protocol numbers are registered by
the
Internet Assigned Numbers Authority (IANA) and are derived from the
“Assigned
Numbers” Request for Comments document.
protocol data unit (PDU) A generic term for the data constructions created
by the
protocols operating at the various layers of the Open Systems
Interconnection
(OSI) reference model. For example, the PDUs created by data-link layer
protocols are called frames, and network layer PDUs are called datagrams.
protocol driver The driver responsible for offering four or five basic
services to
other layers in the network, while “hiding” the details of how the services
are
implemented. Services performed include session management, datagram
service,
data segmentation and sequencing, acknowledgment, and possibly routing
across
a wide area network (WAN).
protocol stack The multilayered arrangement of communications protocols that
provides a data path ranging from the user application to the network
medium.
Although based on the Open Systems Interconnection (OSI) reference model,
not
every layer in the model is represented by a separate protocol. On a
computer
connected to a local area network (LAN), for example, the protocol stack
generally consists of protocols at the application, transport, network, and
data-link
layers, the last of which includes a physical layer specification.
proxy server An application layer firewall technique that enables
Transmission
Control Protocol/Internet Protocol (TCP/IP) client systems to access
Internet
resources without being susceptible to intrusion from outside the network. A
proxy server is an application that runs on a computer with a registered IP
address, whereas the clients use unregistered IP addresses, making them
invisible
from the Internet. Client applications are configured to send their Internet
service
requests to the proxy server instead of directly to the Internet, and, using
its own
registered address, the proxy server relays the requests to the appropriate
Internet
server. On receiving a response from the Internet server, the proxy server
relays it
back to the original client. Proxy servers are designed for specific
applications,
and the client must be configured with the address of the proxy server.
Adminis-
trators can also configure the proxy server to cache Internet information
for later
use and to restrict access to particular Internet sites. Compare with
network
address translation (NAT). See also firewall.
PSTN
See Public Switched Telephone Network (PSTN).
public key The nonsecret half of a cryptographic key pair that is used with
a public
key algorithm. Public keys are typically used when encrypting a session key,
|
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)