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ADSL 2/2+ Annex A
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ITU-T Standard G.992.1 that defines how ADSL works over plain
old telephone service (POTS) lines.
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ADSL 2/2+ Annex B
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ITU-T Standard G.992.1 that defines how ADSL works over Integrated
Services Digital Network (ISDN) lines.
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bandwidth on demand
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ISDN cost-control feature defining the bandwidth threshold that
must be reached on all links before a Services Router initiates
additional ISDN data connections to provide more bandwidth.
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Basic Rate Interface (BRI)
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ISDN interface intended for home and small enterprise applications.
BRI consists of two 64-Kbps B-channels and one 16-Kbps D-channel.
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callback
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Alternative feature to dial-in that enables a J-series Services Router to
call back the caller from the remote end of a backup ISDN connection.
Instead of accepting a call from the remote end of the connection,
the router rejects the call, waits a configured period of time, and
calls a number configured on the router's dialer interface. See also dial-in.
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caller ID
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Telephone number of the caller on the remote end of a backup
ISDN connection, used to dial in and also to identify the caller.
Multiple caller IDs can be configured on an ISDN dialer interface.
During dial-in, the router matches the incoming call's caller ID against
the caller IDs configured on its dialer interfaces. Each dialer interface
accepts calls from only callers whose caller IDs are configured on
it.
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channel service unit (CSU)
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Unit that connects a digital telephone line to a multiplexer
or other signal service.
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data service unit (DSU)
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Unit that connects a data terminal equipment (DTE) device—in
this case, a Services Router—to a digital telephone line.
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data terminal equipment–to–data communication
equipment (DTE–DCE) interface
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Interface that a Services Router (the DTE) uses to exchange
information with a serial device such as a modem (the DCE).
A DTE cable uses a male 9-pin or 25-pin connector, and a DCE
cable uses a female 9-pin or 25-pin connector.
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demand circuit
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Interface configured for dial-on-demand routing backup. In OSPF,
the demand circuit reduces the amount of OSPF traffic by removing
all OSPF protocols when the routing domain is in a steady state.
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dial backup
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Feature that reestablishes network connectivity through one
or more backup ISDN dialer interfaces after a primary interface fails.
When the primary interface is reestablished, the ISDN interface is
disconnected.
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dial-in
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Feature that enables J-series Services Routers to receive calls
from the remote end of a backup ISDN connection. The remote end of
the ISDN call might be a service provider, a corporate central location,
or a customer premises equipment (CPE) branch office. All incoming
calls can be verified against caller IDs configured on the router's
dialer interface. See also callback.
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dialer filter
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Stateless firewall filter that enables dial-on-demand routing
backup when applied to a physical ISDN interface and its dialer interface
configured as a passive static route. The passive static route has
a lower priority than dynamic routes. If all dynamic routes to an
address are lost from the routing table and the router receives a
packet for that address, the dialer interface initiates an ISDN backup
connection and sends the packet over it. See also dial-on-demand
routing backup; floating static route.
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dial-on-demand-routing (DDR) backup
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Feature that provides a J-series Services Router with full-time
connectivity across an ISDN line. When routes on a primary serial
T1, E1, T3, E3, Fast Ethernet, or PPPoE interface are lost, an ISDN
dialer interface establishes a backup connection. To save connection
time costs, the Services Router drops the ISDN connection after a configured
period of inactivity. Services Router with ISDN interfaces support two
types of dial-on-demand routing backup: on-demand routing with a dialer
filter and dialer watch. See also dialer filter; dialer
watch.
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dialer watch
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Dial-on-demand routing (DDR) backup feature that provides reliable
connectivity without relying on a dialer filter to activate the ISDN
interface. The ISDN dialer interface monitors the existence of each
route on a watch list. If all routes on the watch list are lost from
the routing table, dialer watch initiates the ISDN interface for failover
connectivity. See also dial-on-demand routing backup.
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“dying gasp” notification
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Ability of a Services Router with a digital subscriber line
(DSL) connection that has lost power to send a message informing the
attached DSL access multiplexer (DSLAM) that it is about to go offline.
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floating static route
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Route with an administrative distance greater than the administrative
distance of the dynamically learned versions of the same route. The
static route is used only when the dynamic routes are no longer available.
When a floating static route is configured on an interface with a
dialer filter, the interface can be used for backup.
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ISDN S/T interface
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Interface between an ISDN network and a network termination
device consisting of two twisted pairs, one each for transmitting
and receiving. The S/T interface usually resides in the customer premises
and operates at 192 Kbps, of which ISDN traffic accounts for
144 Kbps.
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ISDN U interface
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Single twisted–pair interface line connecting the customer
premises unit in an ISDN network to the central office. A U interface
runs at 144 Kbps (128 Kbps for two B channels and 16 Kbps
for the D channel).
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plain old telephone service (POTS)
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Standard telephone service that allows limited speed and bandwidth
of 52 Kbps, which is also know as public switched telephone network
(PSTN).
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Primary Rate Interface (PRI)
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ISDN service intended for higher-bandwidth applications than
ISDN BRI. ISDN PRI consists of a single D-channel for control and
signaling, plus a number of 64-Kbps B-channels—either 23 B-channels
on a T1 line or 30 B-channels on an E1 line—to carry network
traffic.
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