
Configuring Dial Services
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When a leased line or bundle becomes congested, the router searches for an
available dial-up line from its associated bandwidth-on-demand pool. Lines in a
bandwidth-on-demand pool can reside on any slot, but each secondary circuit can
use only three slots.
To determine the order in which the router searches the slots, you designate each
slot as preferred or reserved. The router uses the preferred slot first. If there are no
available lines, the router uses the reserved slot. If there are still no available lines,
the router automatically uses the local slot, which is the slot containing the first
leased line that was activated. Once the router finds a line, it dials the destination
using a phone number from the user-configured outgoing phone list.
How Lines, Pools, and Circuits Work Together
You assign a pool ID for each leased circuit or demand circuit. If the line or
bundle becomes congested, the router activates a dial-up line from the pool. The
dial-up circuit that runs over this line inherits the configuration and protocol
characteristics of the leased circuit.
You can assign the same bandwidth pool ID to more than one circuit. If you want
a pool of dial-up lines dedicated to a specific bandwidth circuit, assign the pool
exclusively to that circuit. Remember to first configure a leased or demand
connection before configuring bandwidth-on-demand service.
Activating Dial-up Lines to Relieve Congestion
If one dial-up line from the bandwidth pool does not relieve the congestion, the
router adds up to 29 lines until the congestion is relieved. The router activates
additional lines only for a congested line, not for a failed line.
PPP multilink detects a state of congestion based on byte counts and the
user-defined monitor parameters. (Byte counts are measured prior to data
compression.) The monitor parameters let you define congestion thresholds for
the leased or demand circuit. If data traffic exceeds a threshold, the router tries to
activate a dial-up line. At this point, if you configure BAP, it manages the addition
and removal of lines from the multilink bundle, based on the monitor parameters.
For more details about BAP, refer to Chapter 7.
Once the volume of traffic on the congested line falls below the congestion
threshold, the router again uses only the leased line, demand line, or bundle. Refer
to Chapter 11 for details about the monitor parameters.
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