This clause defines network services needed for the operation of UAFX and their remote management (see 7.2). Network services defined in this document's release include topology discovery (see 7.3) and time synchronization (see 7.4).
This subclause defines remote management for UAFX Stations for networking features, including those defined in Clause 6, as well as the services and capabilities defined in Clause 7. For interoperable remote management, UAFX uses the Network Configuration Protocol (NETCONF) as a remote management protocol (see 7.2.2).
Figure 12 shows an example network consisting of two UAFX Stations and one IA-station. The Network Provisioning Entity uses NETCONF as the common remote management protocol for network configuration during commissioning (see OPC 10000-80, Figure 6) as required for the site. This configuration may contain, amongst others, VLAN configuration, IP subnet configuration, time synchronization configuration, and QoS configuration. In addition, remote management enables network monitoring and communication fault diagnostics.
NOTE 1 This specification does not make use of SSH as a secure transport for NETCONF.
NOTE 2 A future release of this specification will define NETCONF capabilities (for both client and server) and YANG modules to be supported by a UAFX Station.
A single management entity controls all components of a UAFX Station. Figure 13 shows a UAFX Station comprised of two End Station Components and one Bridge Component, all controlled by a single management entity.
NETCONF messages are recommended to be transmitted using priority information defined for Remote Management in Table 1.
UAFX defines the use of LLDP for the discovery of IA-stations, their external ports, and their external connectivity (see 7.3.2). A Topology Discovery Entity (TDE) queries this information by remote management to derive the physical network topology and provide it to a System Engineer (see Figure 14).
NOTEA Topology Discovery Entity (TDE) can be run from anywhere in the network with reachability to the to-be-discovered devices.
UAFX defines the use of the LLDP protocol for IA-stations to announce themselves to their peers for device and topology discovery. By default, announcements from a UAFX Station contain, among others, the management address(es) and system capabilities (see 184.108.40.206.4).
For adaptability of the operational behaviour and the announced information of LLDP, all UAFX Stations support the LLDP local system YANG (see 220.127.116.11.5). UAFX Stations that include a Bridge Component also receive and store LLDP announcement information received from their peers in the LLDP remote systems YANG.
A remote management protocol (see 7.2) is used between the TDE and IA-stations to query the local system YANG and remote systems YANG. The management address information in the retrieved remote systems YANG allows the TDE to discover and query new IA-stations. The correlation of an IA-station’s local system data with a neighbouring IA-station’s remote systems data enables the TDE to discover the physical network topology.
Figure 15 illustrates an example network showing the LLDP agents and their management in a UAFX Station consisting of a single End Station Component, an IA-station, and a UAFX Station with an End Station Component and a Bridge Component.
NOTEAccording to IEEE Std 802.1AB2016, 9.1.1 c), changes to the local system that impact information exchanged via LLDP immediately trigger the transmission of an LLDPDU to communicate the local changes as quickly as possible to any neighbouring systems.
A UAFX Station shall support LLDP transmit mode (adminStatus enabledTxOnly) on an external End Station Component port and may support transmit and receive mode (adminStatus enabledRxTx) on that port (see IEEE Std 802.1AB-2016, 10.5.1).
The destination address shall be the nearest bridge group MAC address, i.e. 01-80-C2-00-00-0E, to limit the scope of LLDPDU propagation to a single physical link (see IEEE Std 802.1AB2016, 7.1 item a).
NOTE IEEE 802.1AB-2016 defines LLDPDUs to be transmitted untagged, i.e., frames do not carry priority information for traffic class selection. At the same time, IEEE 802.1AB-2016 neither specifies a well-defined device-internal priority nor management capabilities for the configuration of the traffic class to be used for the transmission of LLDPDUs.
A UAFX Station transmitting LLDPDUs shall include the LLDP TLVs selected in this sub-clause. A UAFX Station receiving LLDPDUs shall process LLDPDUs and include the information in the LLDP Remote System’s YANG.
Each transmitted LLDPDU shall contain the following LLDP TLVs defined in IEEE 802.1AB-2016, 8.5:
- exactly one Chassis ID TLV, as defined in 18.104.22.168.4.2,
- exactly one Port ID TLV, as defined in 22.214.171.124.4.3,
- exactly one Time To Live TLV,
- exactly one System Capabilities TLV, as defined in chapter 126.96.36.199.4.4,
- one or more Management Address TLVs, as defined in 188.8.131.52.4.5, and
- zero or more additional TLVs not listed in this requirement.
NOTE The concatenation of the Chassis ID and Port ID fields enables the recipient of an LLDPDU to identify the sending LLDP agent/port.
The Chassis ID subtype field should contain subtype 4, indicating that the Chassis ID field contains a MAC address to achieve the Chassis ID's desired deployment-wide uniqueness. For UAFX Stations with multiple unique MAC addresses, any one of the UAFX Station’s MAC addresses may be used and shall be the same for all external ports of that UAFX Station.
The Port ID field shall contain the same value for all transmitted LLDPDUs for a given external port, i.e., be a non-volatile, UAFX Station-unique identifier of the LLDPDU-transmitting port.
The Port ID subtype field should contain subtype 5, indicating that the Port ID field contains the interface name (name) according to IETF RFC 8343.
A UAFX Station with at least one End Station Component and at least one Bridge Component shall set the system and enabled capabilities fields to Station Only (i.e., bit 8 set to “1”) and C-VLAN component (i.e., bit 9 set to “1”) for all transmitted LLDPDUs.
NOTEThe combination of the Station Only and C-VLAN component flags is used as a marker indicating to the TDE that the internal structure of the UAFX Station consists of multiple components. This is a deliberate deviation from a footnote in IEEE Std 802.1AB2016, Table 8-4.
A UAFX Station supporting the remote systems YANG shall be able to store information from at least one neighbour per external port. Receiving LLDPDUs from more neighbours than supported on a given port shall result in the last one received being saved to the remote systems YANG as described in IEEE Std 802.1AB2016, 184.108.40.206.5.
UAFX defines the use of a time synchronization protocol to ensure a common sense of time among participating IA-stations.
UAFX defines the use of gPTP as defined in IEEE Std 802.1AS2020 for time synchronization of UAFX Stations. Figure 16 illustrates an exemplary time-synchronized network with two gPTP domains (see 220.127.116.11.1). The usage of an application clock as ClockSource or ClockTarget depends on the IEEE Std 802.1AS defined role for synchronization. Each instance of ClockSource or ClockTarget is bound to one PTP Instance. The number and type of PTP Instances residing on a UAFX Station depend on the gPTP domains it participates in and its composition, e.g., the presence of a Bridge Component. A UAFX Station can host more than one PTP Instance, e.g., UAFX Stations 1 and 2. A Grandmaster PTP Instance can reside on any grandmaster-capable UAFX Station, e.g., UAFX Station 3. UAFX Station 2 and IA-station support the forwarding of corrected time information in both gPTP domains via PTP Relay Instances (see 18.104.22.168.2).
The gPTP generates a tree-structure clock relationship between PTP Instances in the network. The clocks in all PTP Instances within a gPTP domain derive their time from a clock known as the Grandmaster Clock.
The following subclauses provide further informative descriptions of IEEE Std 802.1AS2020 terminology and how it applies to UAFX.
IEEE Std 802.1AS2020 defines a gPTP domain in which system timing is consistent. A gPTP domain defines the scope of gPTP message communication, state, operations, parameters, and timescale. The Grandmaster PTP Instance is the root of a gPTP domain.
UAFX supports the following two types of gPTP domains:
A PTP Instance operates in a single Bridge Component or End Station Component within exactly one gPTP domain. A UAFX Station can contain more than one PTP Instance in the same gPTP domain (see 22.214.171.124.4).
A UAFX Station can support one or more gPTP domains. Each gPTP domain is represented by a PTP Instance which can have an associated ClockSource or ClockTarget. A PTP Instance with an associated ClockSource is a Grandmaster PTP Instance. A ClockSource and ClockTarget can serve as a provider of time for a UAFX Application (e.g., sequence of events).
Figure 17 and Figure 18 show examples of a UAFX Station consisting of a single End Station Component supporting one or two gPTP domains. Each gPTP domain has an associated PTP End Instance, which connects via a PTP Port to an Ethernet port.
Figure 19 shows an example of a UAFX Station consisting of a single End Station Component and Bridge Component, each supporting two gPTP domains. This example includes Bridge Component ClockTargets and End Station Component PTP End Instances and ClockTargets for both domains. ClockTargets and PTP End Instances may be omitted in an implementation depending on the expected usage of time.
Engineered time-synchronization spanning tree (sync tree) for a given gPTP domain refers to the usage of external port configuration instead of BMCA to construct a desired sync tree with the Grandmaster PTP Instance as the root (see IEEE Std 802.1AS2020, 10.3.1).
One of the advantages of engineered sync trees is to enable a planned, deterministic, and stable configuration of the IEEE Std 802.1AS2020 sync tree for a given gPTP domain, e.g., prevent sync tree changes in case of UAFX Station addition or removal from the network. Working Clock is a use case of the engineered sync tree.
An external sync tree management entity should use the remote management interface described in clause 126.96.36.199.4 to set up an engineered sync tree.
- The externalPortConfigurationEnabled parameter is set to TRUE;
- The ptpPortEnabled parameter is set to TRUE.
For validation that the computed sync tree configuration can be applied to all PTP Ports intended to participate in the given gPTP domain, the management entity configuring the sync tree will, for example, verifies that these ports are up, IEEE Std 802.1AS2020capable, and satisfy topology constraints by checking the following parameters:
- The status of oper-status parameter is up (see IETF RFC 8343) for all participating Ethernet links;
- The status of isMeasuringDelay (see IEEE Std 802.1AS2020, 14.16.4) parameter is TRUE;
- The status of asCapable (see IEEE Std 802.1AS2020, 14.8.7) is TRUE;
- The status of asCapableAcrossDomains (see IEEE Std 802.1AS2020, 14.16.5);
- The status of gmCapable (see IEEE Std 802.1AS2020, 14.2.7) is TRUE, only applicable to the Grandmaster PTP Instance;
- Verify that the number of PTP Relay Instances (hops) between the Grandmaster PTP Instance and any given PTP End Instance is within the limit prescribed by an external sync tree management entity;
- Verify per PTP link that the value of meanLinkDelay (see IEEE Std 802.1AS2020, 14.16.6) is less than or equal to meanLinkDelayThresh (see IEEE Std 802.1AS2020, 14.16.7 and IEEE Std 802.1AS2020 Table 11-1) value to detect, e.g., an anomaly in propagation delay;
NOTEEven if neighbouring PTP Instances do report asCapable, it can be that the link between asCapable neighbouring PTP Instances is not asCapable due to, for example, the wrong setting of meanLinkDelayThresh value. The meanLinkDelayThresh value reflects the estimated propagation delay of the installed link.
The sync tree must have the following properties to ensure consistent protocol behaviour and time synchronization:
- The desiredState of all PTP Ports of the Grandmaster PTP Instance is set to MasterPort;
- The desiredState of exactly one PTP Port of all the other PTP Instances is set to SlavePort;
- The desiredState of remaining PTP Ports that are part of sync tree in non-Grandmaster PTP Relay Instances is set to MasterPort.
- The desiredState of all other PTP Ports is set to PassivePort.
After synthesis, the configuration of the gPTP domain and its engineered sync tree may then be applied and validated, for example:
NOTEClocks are currently not modelled in OPC UA, and it is a vendor decision to select a gPTP domain for use at the application layer if multiple gPTP domains are supported. Clock representation in OPC UA needs to be added in a future release for UAFX.
A UAFX Station supporting gPTP time synchronization shall support at least two gPTP domains in a Bridge Component for Working Clock and Global Time and at least one gPTP domain in an End Station Component for Working Clock or Global Time.
The gPTP message priority is defined in IEEE Std 802.1AS2020, 8.4.4.
NOTE IEEE Std 802.1AS2020 defines gPTP messages to be transmitted untagged, i.e., frames do not carry priority information for traffic class selection. At the same time, IEEE Std 802.1AS2020 neither specifies a well-defined device-internal priority nor management capabilities for the configuration of the traffic class to be used for the transmission of gPTP messages.
IETF RFC 8343 – A YANG Data Model for Interface Management, March 2018
IEEE Std 802.1AS-2011 – IEEE Standard for Local and Metropolitan Area Networks – Timing and Synchronization for Time-Sensitive Applications in Bridged Local Area Networks
IEEE Draft Std P802.1ASdn – Draft Standard for Local and Metropolitan Area Networks: Timing and Synchronization for Time-Sensitive Applications – Amendment: YANG Data Model