Brochure/Catalogue

CSMA/CD
An access procedure where several network stations have
access to the transmission medium. In the CSMA-system the
transmitting station listens to the channel (carrier sensing)
before it transmits. A station can then only transmit if the
transmission medium has not yet been occupied by another
station. If the transmission medium is occupied, the station
waits till it is free and can transmit. Because of the signalling
times it is still possible for two devices to transmit at the
same time. To avoid data loss in this type of collision, both
transmitters have to detect the collision (collision detect) and
after a randomly-selected waiting time send each of their
data packets again. CSMA/CD is a widespread standard
process in 10-MBit-networks with hubs.
In Industrial Ethernet networks the CSMA/CD system is only
used rarely nowadays, because of high demands on network
performance.
DCE
(Data Communication Equipment)
Any facility that can relay data between data terminal
equipment. DCEs are part of the infrastructure and not
terminal equipment.
DHCP
DHCP (Dynamic Host Conguration Protocol) enables a
specially congured server to allocate dynamic IP addresses
and other network parameters to the computers in a
network.
DNS-Server
On the Internet, computers are addressed using their
numeric IP address (e.g., 211.163.5.38). The DNS server
maintains the structure of the domain name system (DNS).
It administers and updates the logical names which are
associated with the IP addresses. The name server converts
less-accessible dotted-decimal-notation numbers into
domain addresses. It then makes this information available
to DNS clients on request. A network may include an
unlimited number of name servers. Since DNS servers must
have built-in redundancy, a server implementation consists
of two servers: the primary (PNS) and secondary (SNS) name
server. If the primary name server is down, the secondary
name server, running in parallel, takes over.
DTE
(Data Terminal Equipment) data terminal unit: Every device
in the network where a communications route starts or
nishes. A station (computer or host) in the network that
can transmit or receive data.
DynDNS
DynDNS stands for dynamic domain name system. DNS
is responsible for resolving host names to IP addresses.
Services such as DynDNS were developed for users using
a DSL connection with dynamic IP addresses. DynDNS
enables the registration of a dynamic (changeable) IP
address to a host name. For this to work, a DSL router must
support it or a DynDNS client must be installed on a PC.
Error Detection
The error detection code is a detection code (CRC or
checksum) used where errors are identied but not
corrected as in ECC.
Ethernet
Ethernet is computer networking technology for local
networks (LANs). It refers to cable types and signalling for
the bit transfer layer (physical layer), packet formats and
protocols for checking media access (media access control,
MAC) / link layer of the OSI model. Ethernet is standardised
to a large extent in the IEEE norm 802.3.
Fast-Ethernet
Nowadays a very widespread version of Ethernet with
100Mbps over a twisted pair cable according to category 5
or higher. The maximum range is 100 m.
Fibre-optic cables
A type of cable with bre-optics or plastic core that transmits
digital signals in the form of light pulses. (Wave lengths
850 nm in 10BaseFL and 100BaseSX or 1300 nm in
100BaseFX).
Flow Control
This is a function to modify transmission to the capacity of
the receiver. Flow control regulates transmission between
the transmitter and receiver by causing the transmitter
only to send as much data as the receiver can deal with.
The different types of Ethernet have different ow control
systems. In credit systems (FO cable) the receiver relays
to the transmitter the number of data packets that can be
transmitted without conrmation. Duplex connections use
the PAUSE signal for ow control and back pressure is used
in semi-duplex systems to control the data rate.
Glossary
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Technical appendix
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