|
Hello Tim,
Thanks for reviewing draft-ietf-tictoc-ptp-enterprise-profile-24, and pointing out what is still unclear as well as making other suggestions. I have created a new draft, but submissions are currently closed. I will post the new version when they open. In
the meantime here is the new draft in text and pdf formats, in case you are bored. I would love to here if things seem clearer now.
Regards,
Doug
From: Tim Chown via Datatracker <noreply@xxxxxxxx>
Sent: Thursday, March 7, 2024 9:33 AM To: ops-dir@xxxxxxxx <ops-dir@xxxxxxxx> Cc: draft-ietf-tictoc-ptp-enterprise-profile.all@xxxxxxxx <draft-ietf-tictoc-ptp-enterprise-profile.all@xxxxxxxx>; last-call@xxxxxxxx <last-call@xxxxxxxx>; tictoc@xxxxxxxx <tictoc@xxxxxxxx> Subject: Opsdir last call review of draft-ietf-tictoc-ptp-enterprise-profile-24 Reviewer: Tim Chown
Review result: Has Nits Hi, I have reviewed this document as part of the Operational directorate's ongoing effort to review all IETF documents being processed by the IESG. These comments were written with the intent of improving the operational aspects of the IETF drafts. Comments that are not addressed in last call may be included in AD reviews during the IESG review. Document editors and WG chairs should treat these comments just like any other last call comments. The document describes a PTP Profile for use in enterprise networks, be they IPv4 or IPv6. Overall, the document is well written. I would currently say it is Ready with Nits. General comments I’m not familiar enough with PTP to know what a Profile is, or looks like. Section 5 begins with “This PTP Profile SHALL operate only in…” but it’s not obvious to me what part(s) of the document constitute the Profile, and in the extensive glossary of technical terms, ‘Profile’ is not included. Perhaps this could be clearer. The document includes several negative comments about multicast, without citing any RFCs or other references as to why multicast is problematic. This would be helpful. I am familiar for example with RFC 9119 on multicast in wireless networks, and am a co-author of RFC 8115 on deprecation of inter-domain ASM, but the issues hinted at here don’t fall under either of those documents. The third paragraph seems to suggest PTP nodes “throw away 99% of multicast”, but usually one would assume multicast is used because the information sent is of interest to multiple nodes concurrently. The document uses SHALL quite extensively rather than MUST. This is unusual, but in line with RFC 2119. I suspect readers will be more used to seeing MUST. Other comments: Technical terms The section doesn’t clearly differentiate e2e delay measurement mechanism and p2p delay measurement - I assume the timeTransmitter and timeReceiver may not be directly connected, and relay via a Boundary clock? If so, is the Boundary clock not a transmitter and receiver also, or at least the definition implies that? Problem statement I believe you can use hardware timestamping for general NTP, and we are doing so in our own network with a notable improvement in stability. So perhaps here be clearer about why hardware timestamping with PTP is advantageous. Section 5 The text appears a little inconsistent over IPv4 and IPv6 use. It says if both are present, they MUST be treated as separate paths (implying duplication over a path between dual-stack devices), but then a PTP domain MUST use IPv4 or IPv6 but not both. Perhaps be clearer, and also mention how the IP version is selected when communicating devices are dual-stack. It’s also not clear to me why the source address changes at a Transparent clock. I’m sure there’s a good reason, given in another RFC, but it would be useful to have a pointer to that reason included here. Does the address also need to have at least the scope of the e2e communication (more relevant for IPv6)? Section 6 Maybe cite https://www.iana.org/assignments/ipv6-multicast-addresses/ipv6-multicast-addresses.xhtml for the multicast reserved address, and likewise IPv4. I note 182-184 are reserved also for PTP alternates. Section 11 What’s a ‘servo loop’? Best wishes, Tim |
TICTOC Working Group D.A. Arnold
Internet-Draft Meinberg-USA
Intended status: Standards Track H.G. Gerstung
Expires: 12 September 2024 Meinberg
11 March 2024
Enterprise Profile for the Precision Time Protocol With Mixed Multicast
and Unicast messages
draft-ietf-tictoc-ptp-enterprise-profile-25
Abstract
This document describes a PTP Profile for the use of the Precision
Time Protocol in an IPv4 or IPv6 Enterprise information system
environment. The PTP Profile uses the End-to-End delay measurement
mechanism, allows both multicast and unicast Delay Request and Delay
Response messages.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 12 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Technical Terms . . . . . . . . . . . . . . . . . . . . . . . 4
4. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 6
5. Network Technology . . . . . . . . . . . . . . . . . . . . . 7
6. Time Transfer and Delay Measurement . . . . . . . . . . . . . 8
7. Default Message Rates . . . . . . . . . . . . . . . . . . . . 9
8. Requirements for TimeTransmitter Clocks . . . . . . . . . . . 9
9. Requirements for TimeReceiver Clocks . . . . . . . . . . . . 10
10. Requirements for Transparent Clocks . . . . . . . . . . . . . 10
11. Requirements for Boundary Clocks . . . . . . . . . . . . . . 10
12. Management and Signaling Messages . . . . . . . . . . . . . . 11
13. Forbidden PTP Options . . . . . . . . . . . . . . . . . . . . 11
14. Interoperation with IEEE 1588 Default Profile . . . . . . . . 11
15. Profile Identification . . . . . . . . . . . . . . . . . . . 11
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
18. Security Considerations . . . . . . . . . . . . . . . . . . . 12
19. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
19.1. Normative References . . . . . . . . . . . . . . . . . . 12
19.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
The Precision Time Protocol ("PTP"), standardized in IEEE 1588, has
been designed in its first version (IEEE 1588-2002) with the goal to
minimize configuration on the participating nodes. Network
communication was based solely on multicast messages, which unlike
NTP did not require that a receiving node in IEEE 1588-2019
[IEEE1588] need to know the identity of the time sources in the
network. This document describes clock roles and PTP Port states
using the optional alternative terms timeTransmitter, in stead of
master, and timeReceiver, in stead of slave, as defined in the IEEE
1588g [IEEE1588g] amendment to IEEE 1588-2019 [IEEE1588] .
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The "Best TimeTransmitter Clock Algorithm" (IEEE 1588-2019 [IEEE1588]
Subclause 9.3), a mechanism that all participating PTP nodes MUST
follow, set up strict rules for all members of a PTP domain to
determine which node MUST be the active reference time source
(Grandmaster). Although the multicast communication model has
advantages in smaller networks, it complicated the application of PTP
in larger networks, for example in environments like IP based
telecommunication networks or financial data centers. It is
considered inefficient that, even if the content of a message applies
only to one receiver, it is forwarded by the underlying network (IP)
to all nodes, requiring them to spend network bandwidth and other
resources, such as CPU cycles, to drop the message.
The third edition of the standard (IEEE 1588-2019) defines PTPv2.1
and includes the possibility to use unicast communication between the
PTP nodes in order to overcome the limitation of using multicast
messages for the bi-directional information exchange between PTP
nodes. The unicast approach avoided that. In PTP domains with a lot
of nodes, devices had to throw away more than 99% of the received
multicast messages because they carried information for some other
node.
PTPv2.1 also includes PTP Profiles (IEEE 1588-2019 [IEEE1588]
subclause 20.3). This construct allows organizations to specify
selections of attribute values and optional features, simplifying the
configuration of PTP nodes for a specific application. Instead of
having to go through all possible parameters and configuration
options and individually set them up, selecting a PTP Profile on a
PTP node will set all the parameters that are specified in the PTP
Profile to a defined value. If a PTP Profile definition allows
multiple values for a parameter, selection of the PTP Profile will
set the profile-specific default value for this parameter.
Parameters not allowing multiple values are set to the value defined
in the PTP Profile. Many PTP features and functions are optional,
and a PTP Profile should also define which optional features of PTP
are required, permitted, and prohibited. It is possible to extend
the PTP standard with a PTP Profile by using the TLV mechanism of PTP
(see IEEE 1588-2019 [IEEE1588] subclause 13.4), defining an optional
Best TimeTransmitter Clock Algorithm and a few other ways. PTP has
its own management protocol (defined in IEEE 1588-2019 [IEEE1588]
subclause 15.2) but allows a PTP Profile to specify an alternative
management mechanism, for example NETCONF.
In this document the term PTP Port refers to a logical access point
of a PTP instantiation for PTP communincation in a network.
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2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
appear in all capitals, as shown here.
3. Technical Terms
* Acceptable TimeTransmitter Table: A PTP timeReceiver Clock may
maintain a list of timeTransmitters which it is willing to
synchronize to.
* Alternate timeTransmitter: A PTP timeTransmitter Clock, which is
not the Best timeTransmitter, may act as a timeTransmitter with
the Alternate timeTransmitter flag set on the messages it sends.
* Announce message: Contains the timeTransmitter Clock properties of
a timeTransmitter Clock. Used to determine the Best
TimeTransmitter.
* Best timeTransmitter: A clock with a PTP Port in the
timeTransmitter state, operating consistently with the Best
TimeTransmitter Clock Algorithm.
* Best TimeTransmitter Clock Algorithm: A method for determining
which state a PTP Port of a PTP clock should be in. The algorithm
works by identifying which of several PTP timeTransmitter capable
Clocks is the best timeTransmitter. Clocks have priority to
become the acting Grandmaster, based on the properties each
timeTransmitter Clock sends in its Announce message.
* Boundary Clock: A device with more than one PTP Port. Generally
Boundary Clocks will have one PTP Port in timeReceiver state to
receive timing and other PTP Ports in timeTransmitter state to re-
distribute the timing.
* Clock Identity: In IEEE 1588-2019 this is a 64-bit number assigned
to each PTP clock which MUST be globally unique. Often it is
derived from the Ethernet MAC address.
* Domain: Every PTP message contains a domain number. Domains are
treated as separate PTP systems in the network. Clocks, however,
can combine the timing information derived from multiple domains.
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* End-to-End delay measurement mechanism: A network delay
measurement mechanism in PTP facilitated by an exchange of
messages between a timeTransmitter Clock and a timeReceiver Clock.
These messages might traverse Transparent Clocks and PTP unaware
switches. This mechanism might not work properly if the Sync and
Delay Request messages traverse different network paths.
* Grandmaster: the primary timeTransmitter Clock within a domain of
a PTP system
* IEEE 1588: The timing and synchronization standard which defines
PTP, and describes the node, system, and communication properties
necessary to support PTP.
* TimeTransmitter Clock: a clock with at least one PTP Port in the
timeTransmitter state.
* NTP: Network Time Protocol, defined by RFC 5905, see RFC 5905
[RFC5905]
* Ordinary Clock: A clock that has a single Precision Time Protocol
PTP Port in a domain and maintains the timescale used in the
domain. It may serve as a timeTransmitter Clock, or be a
timeReceiver Clock.
* Peer-to-Peer delay measurement mechanism: A network delay
measurement mechanism in PTP facilitated by an exchange of
messages over the link between adjacent devices in a network.
This mechanism might not work properly unless all devices in the
network support PTP and the Peer-to-peer measurement mechanism.
* Preferred timeTransmitter: A device intended to act primarily as
the Grandmaster of a PTP system, or as a back up to a Grandmaster.
* PTP: The Precision Time Protocol: The timing and synchronization
protocol defined by IEEE 1588.
* PTP Port: An interface of a PTP clock with the network. Note that
there may be multiple PTP Ports running on one physical interface,
for example, mulitple unicast timeReceivers which talk to several
Grandmaster Clocks in different PTP Domains.
* PTP Profile: A set of constraints on the options and features of
PTP, designed to optimize PTP for a specific use case or industry.
The profile specifies what is required, allowed and forbidden
among options and attribute values of PTP.
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* PTPv2.1: Refers specifically to the version of PTP defined by IEEE
1588-2019.
* Rogue timeTransmitter: A clock with a PTP Port in the
timeTransmitter state, even though it should not be in the
timeTransmitter state according to the Best TimeTransmitter Clock
Algorithm, and does not set the Alternate timeTransmitter flag.
* TimeReceiver Clock: a clock with at least one PTP Port in the
timeReceiver state, and no PTP Ports in the timeTransmitter state.
* TimeReceiver Only clock: An Ordinary Clock which cannot become a
timeTransmitter Clock.
* TLV: Type Length Value, a mechanism for extending messages in
networked communications.
* Transparent Clock. A device that measures the time taken for a
PTP event message to transit the device and then updates the
message with a correction for this transit time.
* Unicast Discovery: A mechanism for PTP timeReceivers to establish
a unicast communication with PTP timeTransmitters using a
configured table of timeTransmitter IP addresses and Unicast
Message Negotiation.
* Unicast Negotiation: A mechanism in PTP for timeReceiver Clocks to
negotiate unicast Sync, Announce and Delay Request message
transmission rates from timeTransmitters.
4. Problem Statement
This document describes a version of PTP intended to work in large
enterprise networks. Such networks are deployed, for example, in
financial corporations. It is becoming increasingly common in such
networks to perform distributed time tagged measurements, such as
one-way packet latencies and cumulative delays on software systems
spread across multiple computers. Furthermore, there is often a
desire to check the age of information time tagged by a different
machine. To perform these measurements, it is necessary to deliver a
common precise time to multiple devices on a network. Accuracy
currently required in the Financial Industry range from 100
microseconds to 1 nanoseconds to the Grandmaster. This PTP Profile
does not specify timing performance requirements, but such
requirements explain why the needs cannot always be met by NTP, as
commonly implemented. Such accuracy cannot usually be achieved with
a traditional time transfer such as NTP, without adding non-standard
customizations such as on-path support, similar to what is done in
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PTP with Transparent Clocks and Boundary Clocks. Such PTP support is
commonly available in switches and routers, and many such devices
have already been deployed in networks. Because PTP has a complex
range of features and options it is necessary to create a PTP Profile
for enterprise networks to achieve interoperability between equipment
manufactured by different vendors.
Although enterprise networks can be large, it is becoming
increasingly common to deploy multicast protocols, even across
multiple subnets. For this reason, it is desired to make use of
multicast whenever the information going to many destinations is the
same. It is also advantageous to send information which is only
relevant to one device as a unicast message. The latter can be
essential as the number of PTP timeReceivers becomes hundreds or
thousands.
PTP devices operating in these networks need to be robust. This
includes the ability to ignore PTP messages which can be identified
as improper, and to have redundant sources of time.
Interoperability among independent implementations of this PTP
Profile has been demonstrated at the ISPCS Plugfest ISPCS [ISPCS].
5. Network Technology
This PTP Profile MUST operate only in networks characterized by UDP
RFC 768 [RFC0768] over either IPv4 RFC 791 [RFC0791] or IPv6 RFC 8200
[RFC8200], as described by Annexes C and D in IEEE 1588 [IEEE1588]
respectively. Clocks which communicate using IPv4 can interact with
clocks using IPv6 if, and only if, there is an intermediary device
which simultaneously communicates with both IP versions. A Boundary
Clock might perform this function, for example. The PTP system MAY
include switches and routers. These devices MAY be Transparent
Clocks, Boundary Clocks, or neither, in any combination. PTP Clocks
MAY be Preferred timeTransmitters, Ordinary Clocks, or Boundary
Clocks. The Ordinary Clocks may be TimeReceiver Only Clocks, or be
timeTransmitter capable.
Note that clocks SHOULD always be identified by their Clock ID and
not the IP or Layer 2 address. This is important since Transparent
Clocks will treat PTP messages that are altered at the PTP
application layer as new IP packets and new Layer 2 frames when the
PTP messages are retranmitted. In IPv4 networks some clocks might be
hidden behind a NAT, which hides their IP addresses from the rest of
the network. Note also that the use of NATs may place limitations on
the topology of PTP networks, depending on the port forwarding scheme
employed. Details of implementing PTP with NATs are out of scope of
this document.
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PTP, similar to NTP, assumes that the one-way network delay for Sync
messages and Delay Response messages are the same. When this is not
true it can cause errors in the transfer of time from the
timeTransmitter to the timeReceiver. It is up to the system
integrator to design the network so that such effects do not prevent
the PTP system from meeting the timing requirements. The details of
network asymmetry are outside the scope of this document. See for
example, ITU-T G.8271 [G8271].
6. Time Transfer and Delay Measurement
TimeTransmitter Clocks, Transparent Clocks and Boundary Clocks MAY be
either one-step clocks or two-step clocks. TimeReceiver Clocks MUST
support both behaviors. The End-to-End Delay measurement method MUST
be used.
Note that, in IP networks, Sync messages and Delay Request messages
exchanged between a timeTransmitter and timeReceiver do not
necessarily traverse the same physical path. Thus, wherever
possible, the network SHOULD be engineered so that the forward and
reverse routes traverse the same physical path. Traffic engineering
techniques for path consistency are out of scope of this document.
Sync messages MUST be sent as PTP event multicast messages (UDP port
319) to the PTP primary IP address. Two step clocks MUST send
Follow-up messages as PTP general multicast messages (UDP port 320).
Announce messages MUST be sent as multicast messages (UDP port 320)
to the PTP primary address. The PTP primary IP address is
224.0.1.129 for IPv4 and FF0X:0:0:0:0:0:0:181 for IPv6, where X can
be a value between 0x0 and 0xF, see IEEE 1588 [IEEE1588] Annex D,
Section D.3. These addresses are aloted by IANA, see the Ipv6
Multicast Address Space Registry [IPv6Registry]
Delay Request messages MAY be sent as either multicast or unicast PTP
event messages. TimeTransmitter Clocks MUST respond to multicast
Delay Request messages with multicast Delay Response PTP general
messages. TimeTransmitter Clocks MUST respond to unicast Delay
Request PTP event messages with unicast Delay Response PTP general
messages. This allows for the use of Ordinary Clocks which do not
support the Enterprise Profile, if they are timeReceiver Only Clocks.
Clocks SHOULD include support for multiple domains. The purpose is
to support multiple simultaneous timeTransmitters for redundancy.
Leaf devices (non-forwarding devices) can use timing information from
multiple timeTransmitters by combining information from multiple
instantiations of a PTP stack, each operating in a different PTP
Domain. Redundant sources of timing can be ensembled, and/or
compared to check for faulty timeTransmitter Clocks. The use of
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multiple simultaneous timeTransmitters will help mitigate faulty
timeTransmitters reporting as healthy, network delay asymmetry, and
security problems. Security problems include on-path attacks such as
delay attacks, packet interception / manipulation attacks. Assuming
the path to each timeTransmitter is different, failures malicious or
otherwise would have to happen at more than one path simultaneously.
Whenever feasible, the underlying network transport technology SHOULD
be configured so that timing messages in different domains traverse
different network paths.
7. Default Message Rates
The Sync, Announce, and Delay Request default message rates MUST each
be once per second. The Sync and Delay Request message rates MAY be
set to other values, but not less than once every 128 seconds, and
not more than 128 messages per second. The Announce message rate
MUST NOT be changed from the default value. The Announce Receipt
Timeout Interval MUST be three Announce Intervals for Preferred
TimeTransmitters, and four Announce Intervals for all other
timeTransmitters.
The logMessageInterval carried in the unicast Delay Response message
MAY be set to correspond to the timeTransmitter ports preferred
message period, rather than 7F, which indicates message periods are
to be negotiated. Note that negotiated message periods are not
allowed, see forbidden PTP options (Section 13).
8. Requirements for TimeTransmitter Clocks
TimeTransmitter Clocks MUST obey the standard Best TimeTransmitter
Clock Algorithm from IEEE 1588 [IEEE1588]. PTP systems using this
PTP Profile MAY support multiple simultaneous Grandmasters if each
active Grandmaster is operating in a different PTP domain.
A PTP Port of a clock MUST NOT be in the timeTransmitter state unless
the clock has a current value for the number of UTC leap seconds.
If a unicast negotiation signaling message is received it MUST be
ignored.
In PTP Networks that contain Transparent Clocks, timeTransmitters
might receive Delay Request messages that no longer contains the IP
Addresses of the timeReceivers. This is becuase Transparent Clocks
might replace the IP address of Delay Requests with their own IP
address after updating the Correction Fields. For this deployment
scenario timeTransmitters will need to have configured tables of
timeReceivers' IP addresses and associated Clock Identities in order
to send Delay Responses to the correct PTP Nodes.
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9. Requirements for TimeReceiver Clocks
TimeReceiver Clocks MUST be able to operate properly in a network
which contains multiple timeTransmitters in multiple domains.
TimeReceivers SHOULD make use of information from all the
timeTransmitters in their clock control subsystems. TimeReceiver
Clocks MUST be able to operate properly in the presence of a rogue
timeTransmitter. TimeReceivers SHOULD NOT Synchronize to a
timeTransmitter which is not the Best TimeTransmitter in its domain.
TimeReceivers will continue to recognize a Best TimeTransmitter for
the duration of the Announce Time Out Interval. TimeReceivers MAY
use an Acceptable TimeTransmitter Table. If a timeTransmitter is not
an Acceptable timeTransmitter, then the timeReceiver MUST NOT
synchronize to it. Note that IEEE 1588-2019 requires timeReceiver
Clocks to support both two-step or one-step timeTransmitter Clocks.
See IEEE 1588 [IEEE1588], subClause 11.2.
Since Announce messages are sent as multicast messages timeReceivers
can obtain the IP addresses of a timeTransmitter from the Announce
messages. Note that the IP source addresses of Sync and Follow-up
messages might have been replaced by the source addresses of a
Transparent Clock, so, timeReceivers MUST send Delay Request messages
to the IP address in the Announce message. Sync and Follow-up
messages can be correlated with the Announce message using the Clock
ID, which is never altered by Transparent Clocks in this PTP Profile.
10. Requirements for Transparent Clocks
Transparent Clocks MUST NOT change the transmission mode of an
Enterprise Profile PTP message. For example, a Transparent Clock
MUST NOT change a unicast message to a multicast message.
Transparent Clocks SHOULD support multiple domains. Transparent
Clocks which syntonize to the timeTransmitter Clock will need to
maintain separate clock rate offsets for each of the supported
domains.
11. Requirements for Boundary Clocks
Boundary Clocks SHOULD support multiple simultaneous PTP domains.
This will require them to maintain separate clocks for each of the
domains supported, at least in software. Boundary Clocks MUST NOT
combine timing information from different domains.
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12. Management and Signaling Messages
PTP Management messages MAY be used. Management messages intended
for a specific clock, i.e. the IEEE 1588 [IEEE1588] defined attribute
targetPortIdentity.clockIdentity is not set to All 1s, MUST be sent
as a unicast message. Similarly, if any signaling messages are used
they MUST also be sent as unicast messages whenever the message is
intended for a specific PTP Node.
13. Forbidden PTP Options
Clocks operating in the Enterprise Profile MUST NOT use Peer-to-Peer
timing for delay measurement. Grandmaster Clusters are NOT ALLOWED.
The Alternate TimeTransmitter option is also NOT ALLOWED. Clocks
operating in the Enterprise Profile MUST NOT use Alternate
Timescales. Unicast discovery and unicast negotiation MUST NOT be
used. Clocks operating in the Enterprise Profile MUST NOT use any
optional feature that requires Announce messages to be altered by
Transparent Clocks, as this would require the Transparent Clock to
change the source address and prevent the timeReceiver nodes from
discovering the protocol address of the timeTransmitter.
14. Interoperation with IEEE 1588 Default Profile
Clocks operating in the Enterprise Profile will interoperate with
clocks operating in the Default Profile described in IEEE 1588
[IEEE1588] Annex I.3. This variant of the Default Profile uses the
End-to-End delay measurement mechanism. In addition, the Default
Profile would have to operate over IPv4 or IPv6 networks, and use
management messages in unicast when those messages are directed at a
specific clock. If either of these requirements are not met than
Enterprise Profile clocks will not interoperate with Annex I.3
Default Profile Clocks. The Enterprise Profile will not interoperate
with the Annex I.4 variant of the Default Profile which requires use
of the Peer-to-Peer delay measurement mechanism.
Enterprise Profile Clocks will interoperate with clocks operating in
other PTP Profiles if the clocks in the other PTP Profiles obey the
rules of the Enterprise Profile. These rules MUST NOT be changed to
achieve interoperability with other PTP Profiles.
15. Profile Identification
The IEEE 1588 standard requires that all PTP Profiles provide the
following identifying information.
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PTP Profile:
Enterprise Profile
Version: 1.0
Profile identifier: 00-00-5E-00-01-00
This PTP Profile was specified by the IETF
A copy may be obtained at
https://datatracker.ietf.org/wg/tictoc/documents
16. Acknowledgements
The authors would like to thank Richard Cochran, Kevin Gross, John
Fletcher, Laurent Montini and many other members of IETF for
reviewing and providing feedback on this draft.
This document was initially prepared using 2-Word-v2.0.template.dot
and has later been converted manually into xml format using an
xml2rfc template.
17. IANA Considerations
There are no IANA requirements in this specification.
18. Security Considerations
Protocols used to transfer time, such as PTP and NTP can be important
to security mechanisms which use time windows for keys and
authorization. Passing time through the networks poses a security
risk since time can potentially be manipulated. The use of multiple
simultaneous timeTransmitters, using multiple PTP domains can
mitigate problems from rogue timeTransmitters and on-path attacks.
Note that Transparent Clocks alter PTP content on-path, but in a
manner specified in IEEE 1588-2019 [IEEE1588] that helps with time
transfer accuracy. See sections 9 and 10. Additional security
mechanisms are outside the scope of this document.
PTP native management messages SHOULD NOT be used, due to the lack of
a security mechanism for this option. Secure management can be
obtained using standard management mechanisms which include security,
for example NETCONF NETCONF [RFC6241].
General security considerations of time protocols are discussed in
RFC 7384 [RFC7384].
19. References
19.1. Normative References
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[IEEE1588] Institute of Electrical and Electronics Engineers, "IEEE
std. 1588-2019, "IEEE Standard for a Precision Clock
Synchronization for Networked Measurement and Control
Systems."", November 2019, <https://www.ieee.org>.
[IEEE1588g]
Institute of Electrical and Electronics Engineers, "IEEE
std. 1588g-2022, "IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems Amendment 2: Master-Slave Optional
Alternative Terminology"", December 2022,
<https://www.ieee.org>.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 2119, DOI 10.17487/RFC2119,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
19.2. Informative References
[G8271] International Telecommunication Union, "ITU-T G.8271/
Y.1366, "Time and Phase Synchronization Aspects of Packet
Networks"", March 2020, <https://www.itu.int>.
[IPv6Registry]
Venaas, S., "IPv6 Multicast Address Space Registry",
February 2024, <https://iana.org/assignments/ipv6-
multicast-addresses/ipv6-multicast-addresses.xhtml>.
[ISPCS] Arnold, D., "Plugfest Report", October 2017,
<https://www.ispcs.org>.
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[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.
Authors' Addresses
Doug Arnold
Meinberg-USA
3 Concord Rd
Shrewsbury, Massachusetts 01545
United States of America
Email: doug.arnold@xxxxxxxxxxxxxxxx
Heiko Gerstung
Meinberg
Lange Wand 9
31812 Bad Pyrmont
Germany
Email: heiko.gerstung@xxxxxxxxxxx
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