Lancom Systems 821 - Manual (Page 9)

LANCOM 821 ADSL/ISDN – LANCOM 1621 ADSL/ISDN – LANCOM 1711 VPN
̈ Chapter 1: Introduction
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1 Introduction
The models LANCOM 821 ADSL/ISDN, LANCOM 1621 ADSL/ISDN and
LANCOM 1711 VPN 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 VPN option, which is either integrated already or can be activated subs-
quently, enables the LANCOM 1621 ADSL/ISDN and LANCOM 1711 VPN to
act as powerful Dynamic VPN gateways for external offices or mobile users.
The LANCOM models offer each a DSL or ADSL connector and also an ISDN
connector. The ISDN line can be used as back-up for the DSL connection, for
remote management of the router, as basis for the office communication via
LANCAPI or for establishing VPN connections to remote sites with dynamic IP
addresses.
1.1 How does ADSL work?
For LANCOM 821
ADSL/ISDN and
LANCOM 1621
ADSL/ISDN only Since the late 1980s, scientists have been working on the idea of using con-
ventional telephone lines for video and multimedia applications.
High speed via standard telephone lines
Their approach was based on the use of telephone lines only for the distance
between the subscriber and the next local exchange. From the switching
center, the data is then transferred via high-speed connections to the desired
destination or target network (i.e. the Internet). This minimization of the tel-
ephone line distance used permits considerably higher transfer rates than
would be possible when relying solely on the telephone network.
All DSL technologies, of which ADSL is the most common, are based on this
concept. Thanks to their high transfer speeds, DSL connections are well-suited
for Internet access.
ADSL connection via
telephone line
Internet
Local exchange (central office)
LANCOM
LAN