Original text:
4.9. <del> [JiK] Should be documented somewhere else.. possible in it own document.  Time sync not part of the data plane.  [JiK] 802.1AS over routers?  Who is doing that.  In 802.1 is doing ".1AS over time aware systems?"  Provide a reference.  [JiK] Check TICTOC, [Editor's NOTE: delete this section (scope time synchronization solution outside data plane).] SB> This section should point the reader to RFC8169 (residence time in MPLS n/w.  We need to consider if we need to introduce the same concept in IP. Agree.  For IP we could reference to PTPv2 or v3 over UDP/IP, since it measures residence time among other things. [Editor's note: describe a bit of issues and deployment considerations related to time-synchronization within DetNet.  Refer to DT discussion and the slides that summarize different approaches and rough synchronization performance numbers.  Finally, scope time- synchronization solution outside data plane.] When DetNet is used, there is an underlying assumption that the applicaton(s) require clock synchronization such as the Precision Time Protocol (PTP) IEEE1588.  The relay nodes may or may not utilize clock synchronization in order to provide zero congestion loss and controlled latency delivery.  In either case, there are a few possible approaches of how synchronization protocol packets are forwarded and handled by the network: PTP packets can be sent either as DetNet flows or as high-priority best effort packets.  Using DetNet for PTP packets requires careful consideration to prevent unwanted interactions between clock-synchronized network nodes and the packets that synchronize the clocks. PTP packets are sent as a normal DetNet flow through network nodes that are not time-synchronized: in this approach PTP traffic is forwarded as a DetNet flow, and as such it is forwarded in a way that allows a low delay variation.  However, since intermediate nodes do not take part in the synchronization protocol, this approach provides a relatively low degree of accuracy. PTP with on-path support: in this approach PTP packets are sent as ordinary or as DetNet flows, and intermediate nodes take part in the protocol as Transparent Clocks or Boundary Clocks IEEE1588. The on-path PTP support by intermediate nodes provides a higher degree of accuracy than the previous approach.  The actual accuracy depends on whether all intermediate nodes are PTP- capable, or only a subset of them. Time-as-a-service: in this approach accurate time is provided as- a-service to the DetNet source and destination, as well as the intermediate nodes.  Since traffic between the source and destination is sent over a provider network, if the provider supports time-as-a-service, then accurate time can be provided to both the source and the destination of DetNet traffic.  This approach can potentially provide the highest degree of accuracy. It is expected that the latter approach will be the most common one, as it provides the highest degree of accuracy, and creates a layer separation between the DetNet data and the synchronization service. It should be noted that in all four approaches it is not recommended to use replication and elimination for synchronization packets; the replication/elimination approach may in some cases reduce the synchronization accuracy, since the observed path delay will be bivalent. SB> I am not sure why we sould not use PREP.  We should explain to the reader. Agree that a this can be opened a bit more in detail.  The issue is explained briefly in the last sentence but it could be more clear. </del>  5.

Reviewer comments:
Aligned the Time Synchronization text with the MPLS equivalent text. Added an informative ref to RFC8169 Deleted ref to IEEE1588 as not needed Slightly reduced the width of Fig 3 by deleting one column of spaces and "-" in the middle to stop the compile warning.

Revised text:
4.9.  <ins> Editor's Note: A detailed discussion of time synchronization is outside the scope of this document, and the production of a specialist text discussing this topic is encouraged.  This section will be updated if such a documents is available before publication of this text. Time synchronization is important both from the perspective of operating the DetNet network itself and from the perspective of transferring time across the network between client applications. Some clients may be able to use the DetNet as their provider of time and frequency, others may require the DetNet to transfer time between a client clock source and a client clock user. The reader's attention is drawn to RFC8169 which describes a method of recording the packet queuing time in an MPLS LSR on a packet by per packet basis and forwarding this information to the egress edge system.  This allows compensation for any variable packet queuing delay to be applied at the packet receiver.  Whether a similar mechanism needs to be defined for IP is for further study.  Such a mechanism may have wider application than basic time transfer in a DetNet. A more detailed discussion of time synchronization is outside the scope of this document. </ins> 5.