Junos® OS Ethernet Interfaces Configuration ... - Juniper Networks

Junos ®
OS 12.3 Ethernet Interfaces Configuration Guide
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Documentation
Proactive Mode
246
measurements. The protocol data unit (PDU) used for a single-ended ETH-LM request
is referred to as a loss measurement message (LMM) and the PDU used for a single-ended
ETH-LM reply is referred to as a loss measurement reply (LMR).
•
Ethernet Frame Delay Measurements Overview on page 238
• Ethernet Frame Loss Measurement Overview on page 244
• Proactive Mode on page 246
• Configuring Routers to Support an ETH-DM Session on page 260.
• Junos® OS Ethernet Interfaces
In proactive mode, SLA measurements are triggered by an iterator application. An iterator
is designed to periodically transmit SLA measurement packets in form of
ITU-Y.1731-compliant frames for two-way delay measurement or loss measurement on
MX Series routers. This mode differs from on-demand SLA measurement, which is user
initiated. The iterator sends periodic delay or loss measurement request packets for each
of the connections registered to it. Iterators make sure that measurement cycles do not
occur at the same time for the same connection to avoid CPU overload. Junos OS supports
proactive mode for VPWS. For an iterator to form a remote adjacency and to become
functionally operational, the continuity check message (CCM) must be active between
the local and remote MEP configurations of the connectivity fault management (CFM).
Any change in the iterator adjacency parameters resets the existing iterator statistics
and restarts the iterator. Here, the term adjacency refers to a pairing of two endpoints
(either connected directly or virtually) with relevant information for mutual understanding,
which is used for subsequent processing. For example, the iterator adjacency refers to
the iterator association between the two endpoints of the MEPs.
For every DPC or MPC, only 30 iterator instances for a cycle time value of 10 milliseconds
(ms) are supported. In Junos OS, 255 iterator profile configurations and 2000 remote
MEP associations are supported.
Iterators with cycle time value less than 100 ms are supported only for infinite iterators,
whereas the iterators with cycle time value greater than 100 ms are supported for both
finite and infinite iterators. Infinite iterators are iterators that run infinitely until the iterator
is disabled or deactivated manually.
A VPWS service configured on a router is monitored for SLA measurements by registering
the connection (here, the connection is a pair of remote and local MEPs) on an iterator
and then initiating periodic SLA measurement frame transmission on those connections.
The end-to-end service is identified through a maintenance association end point (MEP)
configured at both ends.
For two-way delay measurement and loss measurement, an iterator sends a request
message for the connection in the list (if any) and then sends a request message for the
connection that was polled in the former iteration cycle. The back-to-back request
messages for the SLA measurement frames and their responses help in computing delay
variation and loss measurement.
Copyright © 2012, Juniper Networks, Inc.