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44 lines
1.8 KiB
Plaintext
44 lines
1.8 KiB
Plaintext
=== PTP transparent clock (E2E)
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ifdef::topdoc[:imagesdir: {topdoc}../../test/case/ptp/transparent_clock]
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==== Description
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Verify that an E2E or P2P Transparent Clock (TC) passes timing transparently
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through a hardware switch without adding a boundary-clock hop, and that the
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downstream time receiver converges to the grandmaster's time.
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Three nodes are connected in a chain: a grandmaster Ordinary Clock
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(`priority1=1`), a Transparent Clock, and a time-receiver Ordinary Clock
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(`priority1=128`).
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The TC updates the correction field in each Sync and Delay_Req message to
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account for its own residence time. Because a TC is transparent, the time
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receiver's `steps-removed` counter must equal 1 — unlike a Boundary Clock,
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which would give 2. A TC passes ANNOUNCE messages unchanged (`stepsRemoved=0`
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from the GM), and the time receiver adds 1 when it stores the value in
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`currentDS`, giving a total of 1. A BC increments `stepsRemoved` to 1 before
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forwarding, and the receiver adds 1 more, giving 2. The time receiver's offset must converge within the configured threshold
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(default is tighter when the topology provides hardware timestamping links).
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The delay mechanism (E2E or P2P) is controlled by the test suite for
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IEEE 1588 runs. When the profile is IEEE 802.1AS the delay mechanism is
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always P2P (mandated by the standard) and Layer 2 transport is used.
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==== Topology
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image::topology.svg[PTP transparent clock (E2E) topology, align=center, scaledwidth=75%]
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==== Sequence
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. Set up topology and attach to DUTs
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. Configure grandmaster (OC, priority1=1, {dm})
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. Configure transparent clock ({dm}-tc, {profile})
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. Configure time receiver (OC, priority1=128, client-only)
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. Wait for grandmaster port to become time-transmitter
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. Wait for time receiver to reach time-receiver state
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. Verify time receiver steps-removed equals 1
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. Wait for time receiver offset to converge
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