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131
Glossary
DHCP
Dynamic Host Configuration Protocol
DHCP handles the automatic assignment of
IP addresses
to network components. It was
developed because in large networks – especially the
Internet
– the defining of IP
addresses is very complex as participants frequently move, drop out or new ones join.
A DHCP Server automatically assigns the connected network components (DHCP
Cli-
ents
)
Dynamic IP addresses
from a defined
IP pool range
thus saving a great deal of con-
figuration work. In addition, the address blocks can be used more effectively: since not
all participants are on the network at the same time, the same IP address can be
assigned to different network components in succession as and when required.
The Gigaset SE551 WLAN dsl/cable includes a DHCP server and uses it to assign auto-
matic IP addresses to PCs in the local network. You can specify that the IP addresses for
certain PCs are never changed.
DHCP Server
See
DHCP
DMZ
Demilitarised Zone
DMZ describes a part of a network that is outside the
Firewall
. A DMZ is set up, as it
were, between a network you want to protect (e.g. a
LAN
) and an insecure network
(e.g. the
Internet
). A DMZ is useful if you want to offer
Server
services on the Internet
which for security reasons are not to be run from behind the firewall or if Internet appli-
cations do not work properly behind a firewall. A DMZ permits unrestricted access from
the Internet to only one or a few network components, while the other network com-
ponents remain secure behind the firewall.
DNS
Domain Name System
DNS permits the assignment of IP addresses to computers or
Domain names
that are
easier to remember. A DNS server must administer this information for each
LAN
with
an
Internet
connection. As soon as a page on the Internet is called up, the browser
obtains the corresponding IP address from the DNS Server so that it can establish the
connection.
On the Internet the assignment of domain names to IP addresses follows a hierarchical
system. A local PC only knows the address of the local Name Server. This in turn knows
all the addresses of the PCs in the local network and the superordinated Name Servers,
which again know addresses and the next superordinated Name Servers.
DNS server
See
DNS
Domain name
The Domain name is the reference to one or more Web servers on the
Internet
.
The Domain name is mapped via the
DNS
service to the corresponding
IP address
.
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132
Glossary
DoS attack
Denial of Service
A DoS attack is a particular form of hacker attack directed at computers and networks
with a connection to the
Internet
. The aim is not so much to steal data but to paralyse
the computer or network so severely that the network resources are no longer available.
A typical hacker attack involves making a remote computer announce that it is acting for
the paralysed computer, for example, and receive the data meant for you.
DSL
Digital Subscriber Line
DSL is a data transmission technique in which a connection to the
Internet
can be run
at 1.5
Mbps
over normal telephone lines. A DSL connection is provided by an
Internet
Provider
. It requires a DSL modem.
Dynamic IP address
A dynamic
IP address
is assigned to a network component automatically by the
DHCP
.
This means that the IP address of a network component can change with every login or
at certain intervals.
See also
Static IP address
DynDNS
Dynamic DNS
The assignment of
Domain names
and
IP addresses
is handled by the Domain Name
Service (
DNS
). For
Dynamic IP addresses
this service is now enhanced with so-called
Dynamic DNS (DynDNS). It enables the use of a network component with a dynamic
IP address as a
Server
on the Internet. DynDNS ensures that a service can always be
addressed on the
Internet
under the same Domain name regardless of the current
IP address.
Encryption
Encryption protects confidential information against unauthorised access. With an
encryption system, data packets can be sent securely over a network. The Gigaset SE551
WLAN dsl/cable offers
WEP
encryption and
WPA
for secure data transmission over wire-
less networks.
Ethernet
Ethernet is a network technology for local networks (
LANs
) defined by the
IEEE
as stand-
ard IEEE 802.3. Ethernet uses a base band cable with a transmission rate of 10 or 100
Mbps
.
Exposed Host
Exposed Host refers to a PC outside the firewall.
See also
DMZ
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133
Glossary
Firewall
Firewalls are used by network operators as protection against unauthorised external
access. This involves a whole bundle of hardware and software actions and technologies
that monitor and control the data flow between the private network to be protected and
an unprotected network such as the
Internet
.
See also
NAT
Flat rate
Flat rate is a particular billing system for
Internet
connections The
Internet Provider
charges a monthly fee regardless of the duration and number of logins.
Full duplex
Data transmission mode in which data can be sent and received at the same time.
See also
Half duplex
Gateway
A gateway is a device for connecting networks with completely different architectures
(addressing, protocols, application interfaces etc.). Although it is not totally correct, the
term is also used as a synonym for
Router
.
Global IP address
See
Public IP address
Half duplex
Operating mode for data transfer. Only one party can receive or send data at a time.
See also
Full duplex
HTTP Proxy
An HTTP proxy is a
Server
that network components use for their
Internet
traffic. All
requests are sent via the proxy.
Hub
A Hub connects several network components in a star-topology network by sending all
the data it receives from one network component to all the other network components.
See also:
Switch
,
Bridge
,
Router
,
Gateway
IEEE
Institute of Electrical and Electronic Engineers
The IEEE is an international body for defining network standards, especially for stand-
ardising
LAN
technologies, transmission protocols and speeds, and wiring.
IEEE 802.11
IEEE
802.11 is a standard for wireless LANs operating in the 2.4 GHz band. In so-called
Infrastructure mode
, terminals can be connected to a base station (
Access Point
) or they
can connect with each other spontaneously (
Ad-hoc mode
).
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134
Glossary
IGMP
Internet Group Management Protocol
IGMP is an Internet
Protocol
that enables an Internet computer to inform neighbouring
routers that it is a member of a multicast group. With multicasting, a computer can send
content on the Internet to several other computers that have registered an interest in
the first computer's content. Multicasting can, for example, be used for multimedia pro-
grams for media streaming to recipients that have set up multicast group membership.
Infrastructure mode
Infrastructure mode is a way of operating wireless local networks (
WLANs
) in which an
Access Point
handles the data traffic. Network components cannot establish a direct
connection with each other as is the case in
Ad-hoc mode
.
Internet
The Internet is a wide-area network (
WAN
) linking several million users around the
world. A number of
Protocols
have been created for exchanging data, and these are
known collectively as
TCP/IP
. All participants on the Internet are identifiable by an
IP
address
. Servers are addressed by a
Domain names
(e.g. gigaset.com). Domain names
are assigned to IP addresses by the Domain Name Service (
DNS
).
Among the most important Internet services are:
u
electronic mail (email)
u
the World Wide Web (WWW)
u
file transfer (FTP)
u
discussion forums (Usenet / Newsgroups)
Internet Provider
An Internet Service Provider offers access to the
Internet
for a fee.
Internet telephony
Voice transmission via the
Internet
(Voice over
IP
).
IP
Internet Protocol
The IP
Protocol
is one of the
TCP/IP
protocols. It is responsible for addressing parties in a
network using
IP addresses
, and routes data from the sender to the recipient. It decides
the paths along which the data packets travel from the sender to the recipient in a com-
plex network (routing).
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135
Glossary
IP address
The IP address is the unique network-wide address of a network component in a net-
work based on the
TCP/IP
protocol (e.g. in a local network (
LAN
) or on the
Internet
). The
IP address has four parts (decimal numbers) separated by full stops (e.g. 192.168.1.1).
The IP address comprises the network number and the computer number. Depending
on the
Subnet mask
one, two or three parts form the network number, the remainder
forms the computer number. You can find out the IP address of your PC using the
ipconfig
command.
IP addresses can be assigned manually (see
Static IP address
) or automatically
(see
Dynamic IP address
).
On the Internet
Domain names
are normally used instead of the IP addresses.
DNS
is
used to assign domain names to IP addresses.
The Gigaset SE551 WLAN dsl/cable has a
Private IP address
and a
Public IP address
.
IP pool range
The Gigaset SE551 WLAN dsl/cable's IP address pool defines a range of
IP addresses
that
the router's
DHCP Server
can use to assign
Dynamic IP addresses
.
ISP
(Internet Service Provider)
Internet Provider
LAN
Local network
A local network links network components so that they can exchange data and share
resources. The physical range is restricted to a particular area (a site). As a rule the users
and operators are identical. A local network can be connected to other local networks
or to a wide-area network (
WAN
) such as the
Internet
.
With the Gigaset SE551 WLAN dsl/cable you can set up a wired local
Ethernet
network
and a wireless
IEEE 802.11g
standard network (
WLAN
).
Lease time
The lease time defines the period of time for which the PCs keep the
Dynamic IP address
assigned to them by the
DHCP
server without changing them.
Local IP address
See
Private IP address
MAC address
Media Access Control
The MAC address is used for the globally unique identification of a
Network adapters
. It
comprises six parts (hexadecimal numbers), e.g. 00-90-96-34-00-1A. The MAC address
is assigned by the network adapter manufacturer and cannot be changed.

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