Chapter 9: Glossary
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Micro-filter
A filter designed to be connected between the ADSL line and every phone that is
connected to the line.
PPP
The protocol used to carry TCP/IP traffic to the ISP across modem and ISDN links.
PPP incorporates authentication (username/password checking). Because of its
historical use for modem and ISDN users, ISPs favour the use of PPP as an
encapsulating protocol for ADSL users.
PPP over ATM - RFC 2364
PPP over ATM (PPPoATM) is the most elegant and simple implementation that
provides PPP encapsulation over a routed ADSL connection. Microsoft provides a
PPP over ATM stack in Windows 98SE, Windows Me and Windows 2000 and this
provides an almost ideal implementation for ‘passive’ ADSL modems such as
internal cards and USB devices.
PPP over Ethernet
PPP over Ethernet (PPPoE) is used in some existing ADSL services. It is a less
than elegant solution since it requires a custom ‘driver’ in the user’s PC. This
driver works in a similar manner to Dial-Up Networking, but Microsoft have not
implemented it so 3rd-party software is required. So, even if you’re using an
intelligent (as opposed to ‘passive’) device, you’re dependent on the PPP over
Ethernet (PPPoE) client being available for your operating system platform.
RFC 1483
This RFC includes 4 options, only two of which are relevant to ADSL:
•
IP over LLC/SNAP is a routed connection method, sometimes referred to
as “RFC1483R”
•
Ethernet over LLC/SNAP is a bridged connection method, sometimes
referred to as “RFC1483B”
Note that ‘RFC 1483’ by itself doesn’t tell you what the protocol is - you need to
know if the connection is bridged or routed to know what ‘RFC 1483’ means.
RFC 2516
‘Informational’ RFC describing PPP over Ethernet.
Showtime
Jargon for the ADSL state (that may be signalled by a green ‘line’ LED being
permanently on rather than flashing) equivalent to the ‘CD’ LED or ‘CONNECT’
message from a modem.
May mean (if you’re unlucky and the line is bad) that you have a 32kbps
connection to the DSLAM in your local exchange, since this is normally the
‘minimum’ speed defined as ‘acceptable’. Note that this does not mean you can
get past the DSLAM and transmit any data; for a useful connection you need to
be using the correct ATM VPI/VCI and the correct encapsulation across the ADSL
link. Of course, this is not part of the ADSL specification.
Splitter
Filter with a low pass (telephone) socket and a high pass socket which is used to
connect to the ADSL modem. At the local exchange another splitter is connected
to the telephone network (low pass) and the DSLAM (high pass)
