
Dial Services Overview
1-13
Figure 1-7 shows how secondary lines support a primary line.
Figure 1-7. Bandwidth-on-Demand
Bandwidth-on-Demand Lines and Pools
To provide one or more secondary lines to aid a primary line, you establish a
bandwidth-on-demand pool. A bandwidth-on-demand pool is a collection of
secondary lines that the primary line can use. A bandwidth-on-demand pool with
more than one secondary line increases the availability of lines for a congested
primary line.
You can connect the secondary lines to a modem or directly to an ISDN network
(using a router with integrated ISDN capability). Each bandwidth-on-demand
pool is identified by a bandwidth-on-demand pool ID.
Lines in a bandwidth pool can reside across three slots and these lines may
operate at different speeds. PPP multilink, the protocol the router uses for
bandwidth-on-demand circuits, can manage lines of varying speed, distribute
traffic across lines, and monitor traffic.
When the primary line becomes congested, the router searches its associated
bandwidth-on-demand pool for an available secondary line. You designate each
slot as either preferred, reserved, or local. This designation determines the order
of slots that the router searches for available lines; the preferred slot is first. If no
available lines are found, the reserved slot is next, and finally, the local slot is last.
The local slot is the slot containing the first leased line that came up. Once the
router finds a line, it dials the destination using a phone number from the user-
specified outgoing phone list.
Remote Site BCentral Site A
Primary line running PPP Multilink-64 Kb/s
Secondary lines-ISDN B Channels
Router
Router
ISDN
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