
PPP Concepts
114068 Rev. A 2-13
As Figure 2-4 shows, a bundle is a logical connection between two routers. Once
you have configured a circuit for multilink or bandwidth-on-demand operation, it
always uses PPP multilink encapsulation.
All lines in a circuit must negotiate and perform multilink. You cannot pair
non-multilink lines with multilink lines in a circuit. Multilink can resequence
packets sent over different lines of the link. Starting with Version 11.0, PPP
supports packet fragmentation and reassembly, as described in the section
“Using
Multilink Fragmentation” on page 2-14.
You can use the multilink feature over the following physical media:
• V.35
• MCT1/MCE1
• ISDN-B channel drivers
• Raise-DTR modems
• V.25bis modems
Compatibility with Previous Versions
A multiline circuit using PPP cannot communicate with a router running a
software version earlier than 9.0. Pre-9.0x versions use a multiline circuit with
LCP running on only one line. In this situation, you must use uniline PPP.
A multilink circuit can communicate only with a router running Version 10.0 or
later software (because earlier versions do not support the multilink feature).
Attempting to run multilink on a pre-10.0 version results in the multilink circuit
dropping back to multiline.
Configuring Multilink Operation
You configure a PPP multilink circuit by selecting the appropriate value in the
PPP Mode parameter for the intended circuit. This parameter controls whether the
local side of the bundle attempts to negotiate the multilink protocol, and whether
the local circuit operates as the congestion monitor for bandwidth-on-demand.
The congestion monitor locally monitors traffic congestion on the circuit. Only
one side of any connection should be the congestion monitor.
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