Juniper JUNOSE 11.2, Configuration Manual

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Application
Some users need more bandwidth than a T1 or an E1 channel can provide, but cannot
afford the expense or do not need the bandwidth of T3 or E3. Equal-cost multipath
(ECMP) is one way to achieve the desired bandwidth. MLPPP is commonly used as an
alternative to ECMP to deliver
NxT1 service. NxT1 service provides bandwidth greater
than DS1 service without going up to the expense and infrastructure required for DS3
service. Cost-analysis of NxT1 versus DS3 service typically imposes a practical limit of
8xT1 service; that is, aggregation of no more than eight T1 or E1 connections into an MLPPP
bundle.
The NxT1 implementation of MLPPP logically aggregates up to eight T1 or E1 connections
into a single virtual connection, or bundle, to a given customer site, as shown in Figure
35 on page 300.
Figure 35: MLPPP Aggregation of T1 Lines into a Single Bundle
Because MLPPP aggregates multiple link-layer channels onto a single network-layer IP
interface, protocol layering within the router is different than for non-multilink PPP.
Figure 36 on page 300 illustrates interface stacking with MLPPP.
Figure 36: Structure of MLPPP
MLPPP LCP Extensions
Multilink PPP adds the following LCP negotiation options:
•
Multilink maximum received reconstructed unit (MRRU) option—The MRRU option
has two functions. First, it informs the other end of the link the maximum size of the
PPP packet payload that the router can receive. Second, it informs the other end that
the router supports MLPPP. When you enable multilink on your router, the router
includes the MRRU option in LCP negotiation with the value set to the maximum
received unit (MRU) value for PPP. If the remote system rejects this option, the local
Copyright © 2010, Juniper Networks, Inc. 300
JunosE 11.2.x Link Layer Configuration Guide