PTP / ESMC / CFM / R-APS / 802.3ah OAM (P2)

Status: draft

Notes on PTP (IEEE 1588-2008), SyncE ESMC (ITU-T G.8264), Ethernet CFM / OAM (IEEE 802.1Q clause 21 = 802.1ag, ITU-T Y.1731) with the ERPS R-APS messages (ITU-T G.8032) and EFM OAM (IEEE 802.3 clause 57 = 802.3ah) (M7). The definitions live in crates/wpg-protocols/src/{ptp,esmc,cfm,efm_oam}.rs, the samples in templates/protocols/timing/ and templates/protocols/oam/.

Stacks and samples

ethernet2 / ptp_*                         # EtherType 0x88f7 (IEEE 1588 annex F)
ethernet2 / ipv4|ipv6 / udp / ptp_*       # UDP 319 (event messages), 320 (general messages)
ethernet2 / esmc                          # Slow Protocols 0x8809, subtype 0x0a
ethernet2 [/ dot1q] / cfm_*               # EtherType 0x8902, also behind 802.1Q / 802.1ad tags
ethernet2 / efm_oam_*                     # Slow Protocols 0x8809, subtype 0x03

The Slow Protocols EtherType 0x8809 is demultiplexed by its first octet, the subtype: 1 LACP, 2 Marker, 3 OAM, 0x0a ESMC (l2control::slow_protocols_peek; other subtypes decode as raw). Marker PDUs now decode as marker instead of lacp. UDP destination ports are not Auto: set 319 for Sync / Delay_Req / Pdelay_Req / Pdelay_Resp and 320 for the other messages.

Generic layer and dedicated messages

PTP, CFM and 802.3ah OAM follow the IS-IS pattern: one protocol per message (PTP), OpCode (CFM) or code (OAM), plus a generic layer (ptp, cfm, efm_oam: the common header and the rest as data octets). The parser decodes the generic layer first and re-decodes it as the dedicated one from message_type / opcode / code; values without a dedicated definition (CFM Linear APS, MCC, EXM / VSM, …) stay generic. When building, every dedicated protocol sets the EtherType / subtype by itself.

PTP

The 34-octet common header has major_sdo_id (transportSpecific), message_type, minor_version, version, message_length (Auto), domain_number, minor_sdo_id, flags (16 bits: two_step is bit 9, unicast bit 10, ptp_timescale bit 3, …), correction_field (signed, nanoseconds × 2^16), message_type_specific, the source port identity (clock_identity, port_number), sequence_id, control_field and log_message_interval (signed). The defaults of control_field and log_message_interval follow the message (0x7f where not applicable).

Every message ends with tlvs (16-bit type, 16-bit length of the value, Auto). They end at message_length, so the zero padding of a short Ethernet frame is not read as TLVs.

- protocol: ptp_signaling
  fields:
    flags: 0x0400 # unicast
    tlvs:
      - request_unicast_transmission: { message_type: announce, log_inter_message_period: 1, duration_field: 300 }
      - grant_unicast_transmission: { message_type: sync, log_inter_message_period: -4, duration_field: 300, renewal_invited: 1 }

ESMC

esmc is the OSSP header (subtype 0x0a, itu_oui 00-19-a7, itu_subtype 1), version (1), event_flag and the TLVs (8-bit type, 16-bit length including the 3-octet header, Auto): ql (ssm_code: prc, ssu_a, ssu_b, sec, dnu, and the option 2 codes) and extended_ql (enhanced_ssm_code, synce_clock_identity, flags (mixed EEC / eEEC, partial chain), cascaded_eeecs, cascaded_eecs). The padding after the TLVs decodes as one raw item.

CFM / Y.1731 / R-APS

The common header is md_level, version, opcode, the flags and first_tlv_offset; the flags are split per OpCode (CCM: rdi, period; LTM / LTR: use_fdb_only, fwd_yes, terminal_mep; AIS / LCK / CSF: period, CSF type; others: flags). first_tlv_offset is constant per OpCode (a warning when changed). The TLVs end with the End TLV (end, type 0); the Ethernet padding after it is padding, not more End TLVs (wpg-core Length::UntilTlv).

TLVs (8-bit type, 16-bit length of the value, Auto): end (0), sender_id (1: chassis_id_length Auto, chassis_id_subtype, chassis_id, management_address octets), port_status (2), data_tlv (3: value), interface_status (4), reply_ingress / reply_egress (5 / 6: action, MAC, port ID octets), ltm_egress_identifier (7), ltr_egress_identifier (8), organization_specific (31), test (32: pattern_type, test_pattern).

R-APS (cfm_raps, OpCode 40) defaults to version 1 (G.8032v2), first_tlv_offset 32 and R-APS(NR, RB). Send it to 01:19:a7:00:00:<ring ID>, usually on the R-APS VLAN at MEL 7.

802.3ah OAM

Every OAMPDU starts with subtype (3), flags (link fault, dying gasp, critical event, local / remote evaluating and stable; default 0x0050) and code.

Information / Event TLV lengths include the 2-octet header (Auto) and the list ends with end.

Not covered

• PTP: the authentication / security TLVs (IEEE 1588-2019 annex P), the data fields of the Management TLVs per management ID, PTP over other transports (annexes C, E-G except IPv6 / Ethernet), state machines and timestamping on transmit.
• CFM: the MAID / MEG ID is the 48 octets as sent (not split into name formats), the CRC-32 of the Test TLV is not computed; Linear APS, MCC, EXM / EXR and VSM / VSR have no dedicated definition (generic cfm).
• 802.3ah OAM: variable descriptors / containers are octets; the OAM discovery state machine.

Generated reference

Field reference of the protocols on this page (generated from the definitions):

lacp · marker · ptp · ptp_sync · ptp_delay_req · ptp_pdelay_req · ptp_pdelay_resp · ptp_follow_up · ptp_delay_resp · ptp_pdelay_resp_follow_up · ptp_announce · ptp_signaling · ptp_management · esmc · cfm · cfm_ccm · cfm_lbm · cfm_lbr · cfm_ltm · cfm_ltr · cfm_ais · cfm_lck · cfm_tst · cfm_raps · cfm_lmm · cfm_lmr · cfm_1dm · cfm_dmm · cfm_dmr · cfm_csf · cfm_slm · cfm_slr · cfm_1sl · efm_oam · efm_oam_information · efm_oam_event_notification · efm_oam_variable_request · efm_oam_variable_response · efm_oam_loopback_control · efm_oam_organization_specific · raw