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Cisco 10000 Series Router Software Configuration Guide
OL-2226-23
Chapter 22 Configuring Multilink Point-to-Point Protocol Connections
MLPoE at PTA
ATM Overhead Accounting
Figure 22-6 shows that the outbound interface on the BRAS to the DSLAM is Ethernet. The
encapsulation from DSLAM to CPE can be ATM. The overhead must be accounted at the BRAS to avoid
the overrun at the subscriber line. The overhead is added by segmenting packets on the DSLAM. As a
result, ATM overhead must be accounted for, by applying the traffic shape. Per-MLPoE bundle shaping
with ATM overhead accounting is supported.
ATM overhead accounting for the MLPoE at PTA feature has the following restrictions:
• Overhead accounting is only supported on single-member MLPoE bundles.
• The line rate needs to be under-subscribed to prevent or reduce loss of traffic downstream.
• Overhead accounting is supported for bi-level service policies only.
• Overhead accounting support from Digital Subscriber Line Access Multiplexer (DSLAM) to CPE
in the downstream direction can be applied at both logical and class levels.
The MLPoE at PTA can be described in the following sections:
• Prerequisites of MLPoE at PTA, page 22-26
• Restrictions of MLPoE at PTA, page 22-26
• Memory and Performance Impact of MLPoE at PTA, page 22-27
• Configuration Examples of MLPoE at PTA, page 22-41
Prerequisites of MLPoE at PTA
The Cisco 10000 series router must be the PTA router.
Restrictions of MLPoE at PTA
In Cisco IOS Release 12.2(33)XNE, the MLPoE at PTA feature has the following restrictions:
• Interaction with L2TP is not supported.
• Only single-member MLP bundles are supported. The ppp multilink links maximum 1 command
must be configured to restrict the number of links that join the bundle.
• Maximum of 10240 single-member LFI bundles are supported
• No fragmentation of packets can be done in the downstream direction. The ppp multilink fragment
delay interval command does not affect MLPoE.
• High Availability (HA) is not supported.
• Only long-sequence numbers are supported for packets header format option.
• The outer-tag on the packet is a service-tag, or tag that identifies the DSLAM with the BRAS.
• The multilink interface CLI is not supported, because a MLPoE bundle is created dynamically. The
username and endpoint discriminator decide how a link joins a bundle.
• An MLPoE bundle must have a shaped PPPoE session configured.
• The number of bundles and links that MLPoE can use depend on single-member bundles and links
left unused by other MLP bundles, and vice versa. For example, if MLPoA is using 5000
single-member bundles with 5000 member-links, MLPoE can use up to only 5240 single-member
bundles with 5240 member-links, because the single-member bundle pool is exhausted. For