Lancom Systems 821 Introduction, How does ADSL work?, High speed via standard telephone lines

	LANCOM 821 ADSL/ISDN – LANCOM 1621 ADSL/ISDN – LANCOM 1711 VPN
	Chapter 1: Introduction
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	Since the late 1980s, scientists have been working on the idea of using con-
ADSL/ISDN and	ventional telephone lines for video and multimedia applications.
LANCOM 1621
ADSL/ISDN only	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.

EN

LAN

ADSL connection via

telephone line

Internet

LANCOM

Local exchange (central office)

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.

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