Synthetic Loss Measurement (Eth-Sl) - Nokia 7302 Basics, Management And Oam Manual

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8.7 Synthetic Loss Measurement (ETH-SL)

This synthetic loss measurement approach is a single-ended feature that allows the
operator to run on-demand and proactive tests to determine "in", "out" loss and
"unacknowledged" packets. This approach can be used between peer MEPs in both
point to point and multipoint services. Only remote MEP peers within the association
and matching the unicast destination will respond to the SLM packet.
The specification uses various sequence numbers in order to determine in which
direction the loss occurred. ISAM has implemented the required counters to
determine loss in each direction. In order to properly use the information that is
gathered the following terms are defined;
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The per probe specific loss indicators are available when looking at the on-demand
test runs, or the individual probe information stored in the MIB.
The on-demand function can be executed from CLI or SNMP. The on demand tests
are meant to provide the carrier a means to perform on the spot testing. However,
this approach is not meant as a method for storing archived data for later processing.
The probe count for on demand SLM has a range of one to 1000 with configurable
probe spacing between one second and ten seconds. This means it is possible that
a single test run can be up to 1000 seconds in length. Although possible, it is more
likely the majority of on demand case will be run up to 100 probes or less at a one
second interval. A node may only initiate and maintain a single active on demand
SLM test at any given time. A maximum of one storage entry per remote MEP is
maintained in the results table. Subsequent runs to the same peer will overwrite the
results for that peer. This means when using on demand testing the test should be
run and the results checked prior to starting another test.
The ETH-SL packet format contains a test-id that will be internally generated and not
configurable. The test-id will be visible for the on demand test in the display
summary. It is possible a remote node processing the SLM frames will receive
overlapping test-ids as a result of multiple MEPs measuring loss between the same
remote MEP. For this reason, the uniqueness of the test is based on remote MEP-ID,
test-id and Source MAC of the packet. ETH-SL is applicable only to down MEPs and
as per the recommendation transparent to MIPs. There is no coordination between
various fault conditions that could impact loss measurement.
Issue: 10
Count — The number of probes that are sent when the last frame is not lost. When
the last frame(s) is/are lost, the count + unacknowledged equals the number of
probes sent.
Out-Loss (Far-end) — Packets lost on the way to the remote node, from test
initiator to test destination.
Unacknowledged — Number of packets at the end of the test that were not
responded to.
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