Re: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05

["Prof. Diego Dujovne" <[e-mail]>]

+1

El mié., 18 de jul. de 2018 19:53, Black, David <[e-mail]>
escribió:

> +1, Thanks, --David
>
>
>
> *From:* Lou Berger [mailto:[e-mail]]
> *Sent:* Wednesday, July 18, 2018 6:52 PM
> *To:* Norman Finn; Janos Farkas; Black, David
> *Cc:* DetNet WG
> *Subject:* Re: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05
>
>
>
> This sounds sensible to me...
>
> Lou
> ------------------------------
>
> On July 18, 2018 6:47:01 PM Norman Finn <[e-mail]>
> wrote:
>
> "Congestion loss protection" is better than "congestion protection".
> That's good.
>
>
>
> It's a big change, and makes the document unnecessarily wordy.  That's bad.
>
>
>
> I would use "congestion protection" but explain somewhere that we are not
> talking about source throttling.
>
>
>
> And if adding that explanation is difficult or controversial, I would
> stick with "congestion protection".
>
>
>
> -- Norm
>
>
> ------------------------------
>
> *From:* detnet [[e-mail]] on behalf of Janos Farkas [
> [e-mail]]
> *Sent:* Wednesday, July 18, 2018 2:26 PM
> *To:* Black, David
> *Cc:* DetNet WG
> *Subject:* Re: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05
>
> Both “congestion protection” and “congestion loss protection” work for me.
>
>
>
> Note that the architecture document is quite populated with the term
> “congestion protection”. I do not know the other documents by heart.
>
>
>
> So it would be a bit of a change..
>
>
>
> I’d like to have the group’s opinion before making such a change, e.g.,
> any objections?
>
>
>
> Thanks,
>
> Janos
>
>
>
>
>
> *From:* Black, David <[e-mail]>
> *Sent:* Wednesday, July 18, 2018 8:19 PM
> *To:* Janos Farkas <[e-mail]>
> *Cc:* DetNet WG <[e-mail]>
> *Subject:* RE: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05
>
>
>
> Hi Janos,
>
>
>
> That text works nicely.  In briefly talking to Lou, a related suggestion
> surfaced: “congestion protection” -> “congestion loss protection” where
> possible (may need to be abbreviated in the Figure) .
>
>
>
> This change would make it clearer that the primary focus is protection
> from losses caused by congestion as opposed to protection from all
> congestion.  DetNet should be able to tolerate some modest congestion
> (e.g., in nodes that don’t have reserved DetNet resources) as long as
> delivery is reliable and timely.
>
>
>
> Thanks, --David
>
>
>
> *From:* Janos Farkas [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* Wednesday, July 18, 2018 11:45 AM
> *To:* Black, David
> *Cc:* DetNet WG
> *Subject:* RE: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05
>
>
>
> Hi David,
>
>
>
> This implies updating the definition of the DetNet service layer, e.g., to:
>
> DetNet service layer
>
> The layer at which A DetNet Service, e.g., service protection is provided.
>
>
>
> The definition of the DetNet transport layer remains the same:
>
> DetNet transport layer
>
> The layer that optionally provides congestion protection for
>
> DetNet flows over paths provided by the underlying network.
>
>
>
> Regards,
>
> Janos
>
>
>
>
>
> *From:* Black, David <[e-mail]>
> *Sent:* Monday, July 16, 2018 3:21 PM
> *To:* Janos Farkas <[e-mail]>
> *Cc:* DetNet WG <[e-mail]>
> *Subject:* RE: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05
>
>
>
> Don’t use “congestion protection” in the definitions for both levels.
>
>
>
> Thanks, --David
>
>
>
> *From:* János Farkas [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* Sunday, July 15, 2018 10:43 PM
> *To:* Black, David
> *Cc:* DetNet WG
> *Subject:* Re: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05
>
>
>
> Thank you David!
>
> I think we are set. :-)
>
> You got a point, we should update
> "DetNet service layer is the layer at which A DetNet Service, such as
> congestion or service protection is provided."
> to
> "DetNet service layer is the layer at which A DetNet Service, such as
> congestion protection and/or service protection is provided."
> in the definitions as well to make it clear.
>
> Thanks,
> Janos
>
> On 7/16/2018 3:03 AM, Black, David wrote:
>
> Moving the only two open items to the top …
>
>
>
> -- Section 4
>
>
>
> > We could add some introductory text to 4.1 or 4.1.1, for instance:
> > The functionality needed for DetNet (Section 3) are implemented in the
> DetNet layer which comprises the DetNet service layer and the DetNet
> transport layer.
>
> > The DetNet service layer functions rely on flow identification and
> sequencing. The DetNet transport layer function may rely on flow
> identification.
> >
> > What do you think?
>
>
>
> I prefer functional (what it does) characterization to mechanistic (how it
> works) characterization in an overview, e.g., excerpting from what I
> originally wrote:
>
> ·         The DetNet Service layer provides timely reliable in-order
> DetNet flow delivery to applications that use DetNet.
>
> ·         The DetNet Transport layer insulates DetNet flows from
> interference by network mechanisms, primarily queuing and routing
>
> I understand the principle.
>
> What about just copying the two definitions here:
> DetNet service layer is the layer at which A DetNet Service, such as
> congestion or service protection is provided.
> DetNet transport layer optionally provides congestion protection for
> DetNet flows over paths provided by the underlying network.
>
>
>
> David> Yes, that works, although I don’t think “congestion” was meant to
> be included in the first definition …
>
>
>
>    Many real-time networks rely on physical rings or chains of two-port
>
>    devices, with a relatively simple ring control protocol.
>
>
>
> How does a “ring control protocol” control “chains”?  Suggest: “ring
> control protocol” -> “control protocol”
>
> Also, are paired chains between common endpoints intended, or a more
> general notion of chains?
>
> This text refers to typical factory deployment, which is chain or ring..
> It seems better to keep “ring control protocol” because they are often
> very different from generic control protocols applicable to mesh networks.
>
> Would flipping chain and ring resolve your concern?
>
>    Many real-time networks rely on physical chains or rings of two-port
>
>    devices, with a relatively simple ring control protocol.
>
>
>
> *[David>] *It feels like “ring control protocol” is an important phrase
> to retain.   In the original text, would it be reasonable to add “(applies
> to both rings and chains)” to the end of the sentence?
>
> Well, I guess the point is that there are many specific ring protocols,
> but we are looking for a generic solution.
> What about deleting "chains" from the sentence?
>
>
>
> David> Yes, if the sentence is all about rings, it’s clear.
>
>
>
> Thanks, --David
>
>
>
> *From:* János Farkas [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* Sunday, July 15, 2018 7:25 PM
> *To:* Black, David
> *Cc:* DetNet WG
> *Subject:* Re: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05
>
>
>
> Hi David,
>
> Please see in-line.
>
> Thank you!
> Janos
>
> On 7/6/2018 11:50 PM, Black, David wrote:
>
> -- Bridged path definition
>
>
>
> >  Or should we do something else?
>
> > There is only one occurrence of "bridged path" in the text in brackets.
>
> That sounds like a better suggestion – change that occurrence and remove
> the definition of “bridged path” from the draft.  That occurrence is in
> Section 4.1.1:
>
>
>
>    Congestion protection
>
>            The DetNet transport layer provides congestion protection.
>
>            See Section 4.5.  The actual queuing and shaping mechanisms
>
>            are typically provided by underlying subnet layers, these can
>
>            be closely associated with the means of providing paths for
>
>           DetNet flows (e.g., MPLS LSPs or bridged paths), the path and
>
>            the congestion protection are conflated in this figure.
>
>
>
> Perhaps: (e.g., MPLS LSPs or bridged paths) -> (MPLS LSPs or other network
> paths)
>
> or just delete the entire parenthetical example.
>
> OK. Let's just delete the entire parenthetical example.
>
>
>
> -- Section 4
>
>
>
> > We could add some introductory text to 4.1 or 4.1.1, for instance:
> > The functionality needed for DetNet (Section 3) are implemented in the
> DetNet layer which comprises the DetNet service layer and the DetNet
> transport layer.
>
> > The DetNet service layer functions rely on flow identification and
> sequencing. The DetNet transport layer function may rely on flow
> identification.
> >
> > What do you think?
>
>
>
> I prefer functional (what it does) characterization to mechanistic (how it
> works) characterization in an overview, e.g., excerpting from what I
> originally wrote:
>
>    - The DetNet Service layer provides timely reliable in-order DetNet
>    flow delivery to applications that use DetNet.
>    - The DetNet Transport layer insulates DetNet flows from interference
>    by network mechanisms, primarily queuing and routing
>
> I understand the principle.
>
> What about just copying the two definitions here:
> DetNet service layer is the layer at which A DetNet Service, such as
> congestion or service protection is provided.
> DetNet transport layer optionally provides congestion protection for
> DetNet flows over paths provided by the underlying network.
>
>
> > Should we also rearrange, e.g., indent the text after Figure 2 such that
> > Packet sequencing, Duplicate elimination, Flow replication, Flow
> merging, Packet encoding, and Packet decoding get under Service layer
> > and
> > Congestion protection and Explicit routes get under Transport layer?
>
>
>
> No, I don’t think that’s necessary – Figure 2 provides sufficient
> structure.
>
> OK.
>
>
>
> Plus a few more minor comments inline …
>
>
>
> Thanks, --David
>
>
>
> *From:* János Farkas [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* Wednesday, July 4, 2018 2:15 PM
> *To:* Black, David
> *Cc:* DetNet WG
> *Subject:* Re: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05
>
>
>
> Hi David,
>
> Thank you very much for your review and comments!
>
> Please see in-line.
>
> On 6/29/2018 4:10 PM, Black, David wrote:
>
> The -06 version of this draft is much improved over the -05 version – lots
> of diligent work by the authors is evident and appreciated.
>
>
>
> I have two minor content concerns and some smaller editorial items.
>
>
>
> ** Content
>
>
>
> -- Section 2.2
>
>
>
> The definition of “bridged path” looks like a definition of “bridged
> forwarding” – the definition needs to encompass the notion of a path that
> involves more than one bridge.
>
>
>
>    bridged path
>
>            A VLAN bridge uses the VLAN ID and the destination MAC
>
>            address to select the outbound port hence the path for a
>
>            frame.
>
>
>
> You are right, it looks like the emphasis is on bridge forwarding rather
> than path.
> However, the superposition of the outbound ports provides a path, which
> was tried to be captured by "hence the path".
> The idea was to keep it simple not dive into the details, which are not
> necessary in this document.
>
> Would it be good to update to:
>
>    bridged path
>
>            A VLAN bridge uses the VLAN ID and the destination MAC
>
>            address to select the outbound port. The superposition
>
>            of the outbound ports is the path for a frame.
>
> ?
>
> Or should we do something else?
> There is only one occurrence of "bridged path" in the text in brackets.
>
> -- Section 4
>
>
>
> Figure 2 in Section 4.1.1 introduces the Detnet service and transport
> layers.   The associated text quickly dives into explaining the
> functionality in those layers, but it would be helpful to start with an
> initial high level description of each of those layers that helps motivate
> their separation.  It appears that:
>
> - The DetNet Service layer provides timely reliable in-order DetNet flow
> delivery to applications that use DetNet.   A DetNet flow at the top of the
> DetNet Service layer may or may not be a compound flow at the bottom of
> that layer.
>
> - The DetNet Transport layer insulates DetNet flows (at the bottom of the
> DetNet Service layer) from interference by network mechanisms, primarily
> queuing and routing, where congestion is an indication of queueing
> interference.  A DetNet flow at the top of the DetNet Transport layer may
> or may not be a member flow that is part of a compound flow, depending on
> what is done in the DetNet Service layer.
>
>
> You are right, section 4 jumps into the details without much of an
> introduction. I guess we had a kind of chicken and egg problem here. Figure
> 4 provides a higher level view than Figure 2. However, Figure 4 captures
> different aspects, dives into the details of data plane options. So, it
> seems better to keep the order.
>
> We could add some introductory text to 4.1 or 4.1.1, for instance:
> The functionality needed for DetNet (Section 3) are implemented in the
> DetNet layer which comprises the DetNet service layer and the DetNet
> transport layer. The DetNet service layer functions rely on flow
> identification and sequencing. The DetNet transport layer function may rely
> on flow identification.
>
> What do you think?
>
> Should we also rearrange, e.g., indent the text after Figure 2 such that
> Packet sequencing, Duplicate elimination, Flow replication, Flow merging,
> Packet encoding, and Packet decoding get under Service layer
> and
> Congestion protection and Explicit routes get under Transport layer?
>
>
>
> There’s a related paragraph of text between Figures 3 and 4 in Section
> 4.1.2, but it doesn’t provide useful intuition about which functionality
> belongs in which layer.
>
>
>
> ** Editorial
>
> -- Section 2.1
>
>
>
> “expected” seems off in the definition of reservation:
>
>
>
>    reservation
>
>            The set of resources allocated between a source and one or
>
>            more destinations through transit nodes and subnets
>
>            associated with a DetNet flow, to provide the expected DetNet
>
>            Service.
>
>
>
> Suggest either “to provide the provisioned DetNet Service to that flow”
>
> I like this one, will update to this one.
>
> or “to provide the specified DetNet Service to that flow.”
>
>
>
> -- Section 3.1
>
>
>
>    o  An upper bound on out-of-order packet delivery.  It is worth
>
>       noting that some DetNet applications are unable to tolerate any
>
>       out-of-order delivery.
>
>
>
> Is that a sequence bound or a time bound or both?   I suspect that a
> sequence bound (maximum degree of reordering in a flow, independent of flow
> rate) was intended.  An analogous clarification would be helpful in section
> 3.2.2.1 .
>
> It is intentionally kept high level in the architecture draft. Details are
> to be provided by the flow information model draft. Please see my previous
> mail:
> https://mailarchive.ietf.org/arch/msg/detnet/AWG2eemg_AWsvF2FwtREyd_xtC8.
>
> *[David>] *OK.
>
>
>
> -- Section 3.2.3
>
>
>
> I don’t understand “defined” in:
>
>
>
>    Even the use of
>
>    redundant paths through a network defined, e.g., by [RFC6372] do not
>
>    eliminate the chances of packet loss.
>
>
>
> Was “e.g., as defined by [RFC6372],” intended?
>
> Yes, this was the intention, will update to this one.
>
>    Many real-time networks rely on physical rings or chains of two-port
>
>    devices, with a relatively simple ring control protocol.
>
>
>
> How does a “ring control protocol” control “chains”?  Suggest: “ring
> control protocol” -> “control protocol”
>
> Also, are paired chains between common endpoints intended, or a more
> general notion of chains?
>
> This text refers to typical factory deployment, which is chain or ring.
> It seems better to keep “ring control protocol” because they are often
> very different from generic control protocols applicable to mesh networks.
>
> Would flipping chain and ring resolve your concern?
>
>    Many real-time networks rely on physical chains or rings of two-port
>
>    devices, with a relatively simple ring control protocol.
>
>
>
> *[David>] *It feels like “ring control protocol” is an important phrase
> to retain.   In the original text, would it be reasonable to add “(applies
> to both rings and chains)” to the end of the sentence?
>
> Well, I guess the point is that there are many specific ring protocols,
> but we are looking for a generic solution.
> What about deleting "chains" from the sentence?
>
>
>
>    Explicit routes can be established various ways,
>
>
>
> established various -> established in various
>
> OK.
>
>
>
>    This is
>
>    irrespective of the distribution method used, also applies to service
>
>    protection over explicit routes.
>
>
>
> used, also -> used, and also
>
> OK.
>
>
>
> -- Figure 5 (Section 4.1.3)
>
>
>
> The UNI acronym is introduced without expansion or definition – please
> correct that, e.g., by defining UNI in Section 2.1.
>
> DetNet-UNI is there among the definitions. It seems enough to me.
>
> *[David>] *That’s fine – I overlooked that definition, sorry.
>
>
>
> -- Figure 9 (Section 4.7.2)
>
>
>
> I think I understand what’s going on, but the use of “add/remove” in the
> figure should be explained in associated text.
>
> What about updating the sentence above Figure 9 to:
> A packet with corresponding Flow-IDs is illustrated in Figure 9, which
> also indicates where Flow-ID can be added or removed.
>
> *[David>] *Sure, with one minor edit: “where Flow-ID” -> “where each
> Flow-ID”
>
> OK.
>
>
>
> Thanks, --David
>
>
> Thank you!
> Janos
>
>
>
> *From:* detnet [mailto:[e-mail] <[e-mail]>] *On
> Behalf Of *János Farkas
> *Sent:* Thursday, June 28, 2018 9:09 PM
> *To:* Lou Berger; Stewart Bryant; [e-mail] >> DetNet WG
> *Subject:* Re: [Detnet] WG Last Call: draft-ietf-detnet-architecture-05
>
>
>
> Dear all,
>
> Off-line discussions among Lou, Stewart, and authors followed the
> discussions to properly address the WGLC comments, including the detailed
> comments.
>
> A new revision of the draft has been uploaded:
> draft-ietf-detnet-architecture-06.
>
> In addition to the changes already described in this thread, the following
> bigger changes have been made to the draft:
>
>
> *Section 2.1 Terms used in this document*
>
> Some definitions refined as suggested by the detailed comments
>
> New definitions have been added:
>
>    "allocation
>            Resources are dedicated to support a DetNet flow.  Depending
>            on an implementation, the resource may be reused by non-
>            DetNet flows when it is not used by the DetNet flow.
>
>
>    PEF     A Packet Elimination Function (PEF) eliminates duplicate
>            copies of packets to prevent excess packets flooding the
>            network or duplicate packets being sent out of the DetNet
>            domain.  PEF can be implemented by an edge node, a relay
>            node, or an end system.
>
>   PRF     A Packet Replication Function (PRF) replicates DetNet flow
>            packets and forwards them to one or more next hops in the
>            DetNet domain.  The number of packet copies sent to each next
>            hop is a DetNet flow specific parameter at the node doing the
>            replication.  PRF can be implemented by an edge node, a relay
>            node, or an end system.
>
>    PREOF   Collective name for Packet Replication, Elimination, and
>            Ordering Functions.
>
>    POF     A Packet Ordering Function (POF) re-orders packets within a
>            DetNet flow that are received out of order.  This function
>            can be implemented by an edge node, a relay node, or an end
>            system.
>
>   DetNet service proxy
>            Maps between App-flows and DetNet flows.
>
>    bridged path
>            A VLAN bridge uses the VLAN ID and the destination MAC
>            address to select the outbound port hence the path for a
>            frame."
>
>
> *Section 3.1 Primary goals defining the DetNet QoS*
>
> A new QoS aspect has been added:
>    "o  An upper bound on out-of-order packet delivery.  It is worth
>       noting that some DetNet applications are unable to tolerate any
>       out-of-order delivery."
>
>
> The 3rd paragraph on loss on page 8 after the bullet list has been
> extended to:
>    "After congestion, the most important contributions to packet loss are
>    typically from random media errors and equipment failures.  Service
>    protection is the name for the mechanisms used by DetNet to address
>    these losses.  The mechanisms employed are constrained by the
>    requirement to meet the users' latency requirements.  Packet
>    replication and elimination (Section 3.2.2) and packet encoding
>    (Section 3.2.2.3) are described in this document to provide service
>    protection; others may be found.  For instance, packet encoding can
>    be used to provide service protection against random media errors,
>    packet replication and elimination can be used to provide service
>    protection against equipment failures.  This mechanism distributes
>    the contents of DetNet flows over multiple paths in time and/or
>    space, so that the loss of some of the paths does need not cause the
>    loss of any packets."
>
>
> *3.2.2.  Service Protection*
>
> Service protection is used as a more generic term. Introductory text added:
>    "Service protection aims to mitigate or eliminate packet loss due to
>    equipment failures, random media and/or memory faults.  These types
>    of packet loss can be greatly reduced by spreading the data over
>    multiple disjoint forwarding paths.  Various service protection
>    methods are described in [RFC6372], e.g., 1+1 linear protection.
>    This section describes the functional details of an additional method
>    in Section 3.2.2.2, which can be implemented as described in
>    Section 3.2.2.3 or as specified in [I-D.ietf-detnet-dp-sol-mpls] in
>    order to provide 1+n hitless protection.  The appropriate service
>    protection mechanism depends on the scenario and the requirements."
>
>
> New sub-section added:
>
> "3.2.2.1.  In-Order Delivery
>
>    Out-of-order packet delivery can be a side effect of service
>    protection.  Packets delivered out-of-order impact the amount of
>    buffering needed at the destination to properly process the received
>    data.  Such packets also influence the jitter of a flow.  The DetNet
>    service includes maximum allowed misordering as a constraint.  Zero
>    misordering would be a valid service constraint to reflect that the
>    end system(s) of the flow cannot tolerate any out-of-order delivery.
>    Service protection may provide a mechanism to support in-order
>    delivery."
>
>
> *3.2.2.2. Packet Replication and Elimination*
>
> New bullet added as the last one:
>    "o  The Packet Ordering Function (POF) uses the sequencing information
>       to re-order a DetNet flow's packets that are received out of
>       order."
>
> New sentence added after the bullet list:
> "The order in which a node applies the PEF and the PRF to a DetNet
> flow is implementation specific."
>
> 2nd paragraph after the bullet list has been updated to:
> "Some service protection mechanisms rely on switching from one flow to
>    another when a failure of a flow is detected.  Contrarily, packet
>    replication and elimination combines the DetNet member flows sent
>    along multiple different paths, and performs a packet-by-packet
>    selection of which to discard, e.g., based on sequencing information."
>
>
> *3.2.3.  Explicit routes*
>
> Out-of-order aspect added to the first paragraph, which is about
> distributed routing:
> "Furthermore, out-of-order
> packet delivery can be a side effect of route changes."
>
> New sentence added to the 3rd paragraph:
> "Explicit routes can be established various
> ways, e.g., with RSVP-TE [RFC3209], with Segment Routing (SR)
> [I-D.ietf-spring-segment-routing], via a Software Defined Networking
> approach [RFC7426], with IS-IS [RFC7813], etc."
>
> New paragraph added:
>    "Out-of-order packet delivery can be a side effect of distributing a
>    single flow over multiple paths especially when there is a change
>    from one path to another when combining the flow.  This is
>    irrespective of the distribution method used, also applies to service
>    protection over explicit routes.  As described in Section 3.2.2.1,
>    out-of-order packets influence the jitter of a flow and impact the
>    amount of buffering needed to process the data; therefore, DetNet
>    service includes maximum allowed misordering as a constraint.  The
>    use of explicit routes helps to provide in-order delivery because
>    there is no immediate route change with the network topology, but the
>    changes are plannable as they are between the different explicit
>    routes."
>
>
> * 4.1.1. Representative Protocol Stack Model*
>
> "Explicit routes" have been added to Figure 2 with the corresponding
> explanation:
>  "Explicit routes
>            The DetNet transport layer provides mechanisms to ensure that
>            fixed paths are provided for DetNet flows.  These explicit
>            paths avoid the impact of network convergence."
>
>
> Section 4.11 Connected islands vs. networks of v05 has been deleted
> because it was just a leftover from early drafts on what DetNet WG should
> do; which are covered by the charter anyways.
>
>
> References have been cleaned up and brought up-to-date.
>
>
> Refinements have been implemented in the draft according to Lou's detailed
> comments. They are not listed here because they are minor changes.
>
>
> Best regards,
> Janos
>
> On 6/12/2018 2:48 PM, Lou Berger wrote:
>
>
> Balázs,
>
> Thanks for the response -- please see below.
>
> ----------
> On June 12, 2018 4:07:35 AM Balázs Varga A <[e-mail]>
> <[e-mail]> wrote:
>
> Hi Lou, Thanks for the comments. See reactions inline. Document update in
> progress. Cheers Bala'zs
>
> -----Original Message-----
> From: detnet <[e-mail]> <[e-mail]> On
> Behalf Of Lou Berger
> Sent: 2018. június 1. 22:42
> To: DetNet WG <[e-mail]> <[e-mail]>;
> [e-mail]
> Subject: [Detnet] Promised comments on draft-ietf-detnet-architecture
>
> Hi,
>
>      I have a number of high level comments on the document that I'd like
> to  raise below.  I also have a number of more editorial/specific comments
> that  I'd like to review directly with the authors and then have them
> report back  on changes -- if any turn out to be more substantive
> discussions from the  author's perspective, I'll raise these on the list
> separately.
>
> ...
>
>
> - WRT Section 4.4.3, I think the inclusion of a distributed control plane
> in the "Network Plane" is inconsistent with other functional definitions
> and conflates where a function resides from the actual function and that
> whether control is implemented in a fully centralized, fully distributed or
> some hybrid form doesn't fundamentally change  the control function's role
> -- therefore I think the sections 4..4.2 and .3 should be revised
> accordingly
> [Balázs Varga A] Agree in principal. Let's discuss the details.
>
> Okay - I'll work with you off line and we can report back the
> results/proposed changes.
>
> - In several places it's not clear that DetNet service is always a L3
> service which is controlled using L3 identifiers, i.e., IP addresses --
> this is true even in the MPLS service case and the TSN over MPLS case. I
> think this is an important point to be clear on in the document.
> [Balázs Varga A] I am not sure. DetNet service is always provided over a
> L3 network (IP or MPLS), that is fine. However the service itself can be L2
> or L3. In case of TSN Ethernet frames are transported, so it is a L2
> service. In case of IP end systems IP packets are transported so it is a L3
> service.
>
>
> Humm - While I agree that DetNet is providing an (enhanced) L2VPN service,
> it is not itself providing control or service of L2 devices -- this is
> TSN's job.  The fact that DetNet is all about behavior of L3 nodes (i.e.,
> IP and PW/MPLS) and not L2 nodes (i.e., TSN bridges) is something the
> architecture should make unambiguous.
>
> Thanks,
> Lou
>
> Please let me know what you think.
>
> Cheers,
>
> Lou
>
>
> _______________________________________________
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> [e-mail]
> https://www.ietf.org/mailman/listinfo/detnet
> _______________________________________________
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> [e-mail]
> https://www.ietf.org/mailman/listinfo/detnet
>
>
>
>
>
> On 6/12/2018 6:27 PM, Stewart Bryant wrote:
>
> Dear Bala'zs
>
> Thank you your for your consideration of these points. I will just pick up
> a few that need some further thought:
>
>
>
>
>
>
>
>     DetNet transit node
>
>            A node operating at the DetNet transport layer, that utilizes
>
>            link layer and/or network layer switching across multiple
>
>            links and/or sub-networks to provide paths for DetNet service
>
>            layer functions.  Optionally provides congestion protection
>
>            over those paths.  An MPLS LSR is an example of a DetNet
>
>            transit node.
>
> SB> In that example it would have to be a DetNet enable/aware LSR. An
>
> SB> ordinary LSR would not know anything about DetNet.
>
>
>
> [Balázs Varga A] No, A DetNet aware LSR would be a relay node (S-PE).
>
>
> I think the confusion is what "DetNet Transport Layer" means. This
> technology touches on Transport Layer in  the L4 sense, and the
> Transport Network Layer as in the packet network that carries
> L3 packets.
>
> So I think that we need to clarify whether a DetNet transit node
> is an S-PE (i.e. a a transit node in the DetNet layer), or a P node
> (i.e. a transit node that is carrying DetNet packets but could be
> carrying any sort of MPLS packet)
>
> ============
>
>
>
>
>
>    These three techniques can be applied independently, giving eight
>
>    possible combinations, including none (no DetNet), although some
>
>    combinations are of wider utility than others.  This separation keeps
>
>    the protocol stack coherent and maximizes interoperability with
>
>    existing and developing standards in this (IETF) and other Standards
>
>    Development Organizations.  Some examples of typical expected
>
>    combinations:
>
>
>
>    o  Explicit routes plus service protection are exactly the techniques
>
>       employed by [HSR-PRP].  Explicit routes are achieved by limiting
>
>       the physical topology of the network, and the sequentialization,
>
>       replication, and duplicate elimination are facilitated by packet
>
>       tags added at the front or the end of Ethernet frames.
>
>
>
> SB> ER can be done virtually as well as physically. RSVP is a type of
>
> SB> ER, as is Adj-SID based SR, and we can design other types.
>
>
>
> [Balázs Varga A] Agree, but these are examples. Statement is for HSR-PRP.
>
> So the question is whether we should expand the set of examples,
> particularly
> to more accessible ones.
>
> ============
>
>
>
>
>
>
>
>                     Packet replication and elimination
>
>
>
>                 > > > > > > > > > relay > > > > > > > >
>
>                > /------------+ R node E +------------\ >
>
>               > /                  v + ^               \ >
>
>       end    R +                   v | ^                + E end
>
>       system   +                   v | ^                +   system
>
>               > \                  v + ^               / >
>
>                > \------------+ R relay E +-----------/ >
>
>                 > > > > > > > > >  node > > > > > > > >
>
>
>
>                                  Figure 1
>
>
>
>    Packet replication and elimination does not react to and correct
>
>    failures; it is entirely passive.  Thus, intermittent failures,
>
>
>
> SB> I think it copes with intermittent failures OK.
>
>
>
> [Balázs Varga A] Yes, PRF and PEF can eliminate the effect of such
> failures. But text
>
> intends to say that it is passive. It is not reacting to such failures. No
> change in text.
>
>
>
>
> You say that PREF does not correct failures. I would contend that is
> exactly
> what it does. Sure it does not react but it does correct, and it does
> address intermittent failures.
>
>
>
> ===========
>
>
>
>    transported between the peer end systems.  Therefore, the following
>
>    possible types / formats of a DetNet flow are distinguished in this
>
>    document:
>
>
>
>    o  App-flow: native format of a DetNet flow.  It does not contain any
>
>       DetNet related attributes.
>
>
>
>    o  DetNet-t-flow: specific format of a DetNet flow.  Only requires
>
>       the congestion / latency features provided by the Detnet transport
>
>       layer.
>
>
>
>    o  DetNet-s-flow: specific format of a DetNet flow.  Only requires
>
>       the replication/elimination feature ensured by the DetNet service
>
>       layer.
>
>
>
>    o  DetNet-st-flow: specific format of a DetNet flow.  It requires
>
>       both DetNet service layer and DetNet transport layer functions
>
>       during forwarding.
>
> SB> I find the relisting of these types confusing. Wheren't they defined
>
> SB> in the section above?
>
>
>
> [Balázs Varga A] This is inline with the previous section " Grouping of
> end systems ".
>
> Surely if we have defined them we never need to do anything but name them
> in
> later sections. Redefinition is never a good idea because it often leads
> to
> conflicting definitions.
>
>
>
> ============
>
>
>
>
>
>
>
>    [HSR-PRP]  IEC, "High availability seamless redundancy (HSR) is a
>
>               further development of the PRP approach, although HSR
>
>               functions primarily as a protocol for creating media
>
>               redundancy while PRP, as described in the previous
>
>               section, creates network redundancy.  PRP and HSR are both
>
>               described in the IEC 62439 3 standard.",
>
>               <http://webstore.iec.ch/webstore/webstore.nsf/
>
>               artnum/046615!opendocument>.
>
>
>
> SB> Not available at the time of this review, but my recollection is
>
> SB> that this is not readily available without paying a large fee.
>
>
> If we decide that this is essential as a key reference, there needs to be
> some suitable text, as this will get raised a number of times between
> here an publication as first the directorates and then the ADs run
> into this.
>
>
>
> ===========
>
>
>
>
>
>
>
>    [ISA95]    ANSI/ISA, "Enterprise-Control System Integration Part 1:
>
>               Models and Terminology", 2000,
>
>               <https://www.isa.org/isa95/>.
>
>
>
> SB> Should that be 2000, or 2010.
>
> SB> Note that this seems to be a very expensive document to access.
>
>
>
> You did not comment on the correctness of the reference.
>
>
>
>
> Best Regards
>
> Stewart
>
>
>
>
>
>
>
>
>
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> https://www.ietf.org/mailman/listinfo/detnet
>
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> [e-mail]
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>