Mlppp Link Selection - Juniper JUNOSE SOFTWARE 11.0.X - LINK LAYER CONFIGURATION GUIDE 4-1-2010 Configuration Manual

NOTE: The router does not bring up a link if the MRU value received from a peer
device differs from the MRRU value received from the peer.

MLPPP Link Selection

By default, E Series routers use a round-robin algorithm to select the link on which
to transmit data on an MLPPP interface. The round-robin link selection method
applies to both best-effort packets, such as data, and non-best-effort (high-priority)
packets, such as voice and video. Best-effort packets are encapsulated with an MLPPP
header that contains a sequence number, whereas non-best-effort packets are
encapsulated with a PPP header that does not contain a sequence number.
The member links in an MLPPP bundle can experience different queuing delays due
to the volume of traffic transmitted on the MLPPP interface. These delays can cause
packets to arrive out of order at the remote router. The effect of such delays differs
for best-effort packets and non-best effort packets, as follows:
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 system determines that the remote system
does not support multilink PPP and it terminates the link without negotiation.
Short sequence number (SSN) header format option (not currently
supported) The SSN option indicates that the transmitting router wants to use
a short sequence number (12 bits) in the MLPPP header rather than a long
sequence number (24 bits). The router currently supports only long sequence
numbers.
Endpoint discriminator option The endpoint discriminator option identifies the
router transmitting the packet. If the receiving router determines that packets
on another link have the same endpoint discriminator option, this link must be
joined to that bundle. If the receiving router determines that no packets on other
links have the same option, the receiving router must create a new bundle from
this link.
The endpoint discriminator is generated internally; you cannot configure it. The
endpoint discriminator option is the same for all links on one end of the bundle;
at the other end, all links also share a common endpoint discriminator. The two
endpoint discriminators are different if the MLPPP bundle is set up between two
E Series routers.
For best-effort packets that arrive out of order from the E Series router, the
remote router can use the sequence number to reorder and forward the packets
in the correct order, regardless of the order in which the packets were received.
For non-best-effort packets that arrive out of order from the E Series router, the
lack of a sequence number prevents the remote router from being able to
determine the correct order in which to forward the packets. This can cause
problems with applications that require high-priority voice and video traffic
transmitted on MLPPP interfaces to be received in the same order transmitted
by the peer applications.
Chapter 8: Configuring Multilink PPP
Overview
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