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LANCOM 1722 VoIP – LANCOM 1724 VoIP
Chapter 1: Introduction
1 Introduction
LANCOM 1722 VoIP are fully-featured routers that therefore also can be used
in combination with the integrated firewall for providing secure Internet
access to a complete local network (LAN).
The integrated VPN option enables the devices to act as powerful Dynamic
VPN gateways for external offices or mobile users.
The LANCOM Router models offer each a DSL or ADSL connector and also an
ISDN connectors. One ISDN line can be used as back-up for the DSL connec-
tion, for remote management of the router, as basis for the office communi-
cation via LANCAPI or for establishing VPN connections to remote sites with
dynamic IP addresses.
By using the Voice over IP function, these devices can transfer voice data over
broadband Internet connections and ISDN interfaces as well.
1.1
How does ADSL and ADSL 2+ work?
ADSL (Asymmetric Digital Subscriber Line) is currently the most common
broadband Internet connection technology. Standard and almost ubiquitous
telephone lines (analog or DSL) are the basis for DSL data transfer to the near-
est telephone exchange. From here, the data is passed directly on to the Inter-
net over high-speed connections.
The asymmetric ADSL version of DSL was designed for applications in which
the user receives high volumes of data but only transmits relatively small vol-
umes, e.g. for accessing the world wide web (www). With an ADSL connec-
tion, a user can download at up to 8 Mbps ("downstream") and upload at up
to 800 Kbps ("upstream"). These maximum rates can be reduced as required
by the ADSL provider.
To satisfy the strongly increasing demand for higher bandwidths, the stand-
ards ADSL 2 and ADSL 2+ provider higher data rates as a basis for applica-
tions such as video streaming or high-definition TV (HDTV) over the Internet.
Depending on the Internet provider, ADSL 2 devices support data rates of up
to 12 Mbps, and ADSL 2+ devices support up to 24 Mbps. Handshake rou-
tines during connection establishment ensure that the standards ADSL,
ADSL 2 and ADSL 2+ are intercompatible.
With ADSL, all traditional telephony applications (telephone, fax, answering
machine, PBX) can still be used without restrictions. So-called splitters make
this possible. Splitters are devices that separate the telephone line's "voice
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