
Configuring Dial Services
7-2 114062 Rev. B
PPP Multilink
Multilink is a feature of PPP that you can enable for individual PPP links. Site
Manager automatically configures PPP multilink when you configure circuits for
bandwidth-on-demand service.
Links are logical communication channels between two routers. A typical link
includes two ISDN B channels, one dial-up modem connection, and a leased 64
Kb/s line. Multilink enables you to
• Group lines of different speeds
• Distribute traffic more evenly among the lines
• Maintain packet sequence
• Monitor traffic volume (for bandwidth-on-demand service)
These features are particularly beneficial for bandwidth-on-demand
configurations, where the router activates additional dial-up lines to relieve
congestion over a single leased line, a leased multilink bundle, or a demand line.
Multilink lets you combine a set of lines between two routers into a single bundle,
which can consist of up to 30 links of different speeds. The actual number of links
in the bundle depends on the hardware platform, total bundle speed, the speed of
each link in the bundle, and the type of traffic.
Each bundle belongs to a separate circuit. Multilink distributes traffic over each
logical line in a bundle in an amount proportional to the bandwidth of the link.
The router sending the data divides the outbound traffic among all the lines in the
bundle. Once data reaches the destination router, multilink reassembles and
resequences packets arriving on different lines.
Figure
7-1 shows how multilink and bandwidth-on-demand work together. In this
figure, one router is the congestion monitor. This router monitors traffic volume
over the bandwidth circuit. If the monitor router detects congestion, it activates an
additional line, in this case, an ISDN B channel. If the volume of traffic is still
heavy, the monitor router adds more channels until congestion is relieved.
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