Pilz PSSnet SHL 8T MRP User Manual
Page 337
Glossary
PSSnet SHL - Command Line Interface
Pilz GmbH & Co. KG, Felix-Wankel-Straße 2, 73760 Ostfildern, Germany
337
gateway recognizes the packet as
belonging to a computer within its
immediate neighborhood or domain.
That gateway then forwards the
packet directly to the computer
whose address is specified.
Because a message is divided into a
number of packets, each packet
can, if necessary, be sent by a
different route across the Internet.
Packets can arrive in a different
order than they were sent. The
Internet Protocol just delivers them.
It's up to another protocol, the
Transmission Control Protocol
(TCP) to put them back in the right
order. IP is a connectionless
protocol, which means that there is
no continuing connection between
the end points that are
communicating. Each packet that
travels through the Internet is
treated as an independent unit of
data without any relation to any
other unit of data. (The reason the
packets do get put in the right order
is because of TCP, the connection-
oriented protocol that keeps track of
the packet sequence in a message.)
In the Open Systems
Interconnection (OSI)
communication model, IP is in Layer
3, the Networking Layer. The most
widely used version of IP today is IP
version 4 (IPv4). However, IP
version 6 (IPv6) is also beginning to
be supported. IPv6 provides for
much longer addresses and
therefore for the possibility of many
more Internet users. IPv6 includes
the capabilities of IPv4 and any
server that can support IPv6 packets
can also support IPv4 packets.
J
Joint Test Action Group. An IEEE
group that specifies test framework
standards for electronic logic
components.
JTAG. See “Joint Test Action
Group” on page 337.
L
LAN. See “Local Area Network” on
page 338.
LDAP. See “Lightweight Directory
Access Protocol” on page 337.
Lightweight Directory Access
Protocol. A set of protocols for
accessing information directories.
LDAP is based on the standards
contained within the X.500 standard,
but is significantly simpler. Unlike
X.500, LDAP supports TCP/IP,
which is necessary for any type of
Internet access. Although not yet
widely implemented, LDAP should
eventually make it possible for
almost any application running on
virtually any computer platform to
obtain directory information, such as
e-mail addresses and public keys.
Because LDAP is an open protocol,
applications need not worry about
the type of server hosting the
directory.