Draft: draft-ietf-detnet-data-plane-framework

Commentary: changes look good
Paragraph (version A):
The DetNet Architecture models the DetNet related data plane
functions decomposed into two sub-layers: a service sub-layer and a
forwarding sub-layer.  The service sub-layer is used to provide
DetNet service protection and reordering.  The forwarding sub-layer
leverages Traffic Engineering mechanisms and provides congestion
protection (low loss, assured latency, and limited out-of-order
delivery).
Paragraph (version B):
The DetNet Architecture models the DetNet related data plane
functions decomposed into two sub-layers: a service sub-layer and a
forwarding sub-layer.  The service sub-layer is used to provide
DetNet service protection and reordering.  The forwarding sub-layer
leverages Traffic Engineering mechanisms and provides congestion
protection (low loss, assured latency, and limited out-of-order
delivery).  A particular forwarding sub-layer may have capabilities
that are not available on other forwarding-sub layers.  DetNet makes
use of the existing forwarding sub-layers with their respective
capabilities and does not require 1:1 equivalence between different
forwarding sub-layer capabilities.
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DetNet flows may be carried over network technologies that can
provide the DetNet required service characteristics.  For example,
DetNet MPLS flows can be carried over IEEE 802.1 Time Sensitive
Network (TSN) IEEE802.1TSNTG sub-networks.  However, IEEE 802.1 TSN
support is not required and some of the DetNet benefits can be gained
by running over a data link layer that has not been specifically
enhanced to support TSN.
Paragraph (version B):
DetNet flows may be carried over network technologies that can
provide the DetNet required service characteristics.  For example,
DetNet MPLS flows can be carried over IEEE 802.1 Time Sensitive
Network (TSN) IEEE802.1TSNTG sub-networks.  However, IEEE 802.1 TSN
support is not required in DetNet.  TSN frame preemption is an
example of a forwarding layer capability that is typically not
replicated in other forwarding technologies.  Most of DetNet benefits
can be gained by running over a data link layer that has not been
specifically enhanced to support all TSN capabilities but for certain
networks and traffic mixes delay and jitter performance may vary due
to the forwarding sub-layer intrinsic properties.
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This document also covers basic concepts related to the controller
plane and Operations, Administration, and Maintenance (OAM).  Data
plane OAM specifics are out of scope for this docuement.
Paragraph (version B):
This document also covers basic concepts related to the controller
plane and Operations, Administration, and Maintenance (OAM).  Data
plane OAM specifics are out of scope for this document.
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Control Word.
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DetNet Control Word.
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Deterministic Networking.
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DetNet.
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Generic Routing Encapsulation.
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IP Security.
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Layer 2.
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Label Switching Router.
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Multiprotocol Label Switching.
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Multiprotocol Label Switching - Traffic Engineering.
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Operations, Administration, and Maintenance.
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Packet Elimination Function.
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Packet Replication Function.
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Packet Replication, Elimination and Ordering Functions.
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Packet Ordering Function.
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Packet Switched Network.
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PseudoWire.
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Quality of Service.
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DetNet "service" label.
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Time-Division Multiplexing.
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Time-Sensitive Network.
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Border Gateway Protocol.
Control Word.
DetNet Control Word.
Deterministic Networking.
DetNet.
Generalized Multiprotocol Label Switching.
Generic Routing Encapsulation.
IP Security.
Layer 2.
Label Switched Path.
Label Switching Router.
Multiprotocol Label Switching.
Multiprotocol Label Switching - Traffic Engineering.
Operations, Administration, and Maintenance.
Path Computation Element Communication Protocol.
Packet Elimination Function.
Packet Replication Function.
Packet Replication, Elimination and Ordering Functions.
Packet Ordering Function.
Packet Switched Network.
PseudoWire.
Quality of Service.
DetNet "service" label.
Time-Division Multiplexing.
Time-Sensitive Network.
Yet Another Next Generation.
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The forwarding sub-layer provides the QoS related functions needed by
the DetNet flow.  It may do this directly through the use of queuing
techniques and traffic engineering methods, or it may do this through
the assistance of its underlying connectivity.  For example it may
call upon Ethernet TSN capabilities defined in IEEE 802.1 TSN
IEEE802.1TSNTG.
Paragraph (version A):
The service sub-layer provides additional support beyond the
connectivity function of the forwarding sub-layer.  An example of
this is Packet Replication, Elimination, and Ordering functions see
PREOF.
Paragraph (version B):
The forwarding sub-layer provides the QoS related functions needed by
the DetNet flow.  It may do this directly through the use of queuing
techniques and traffic engineering methods, or it may do this through
the assistance of its underlying connectivity.  For example it may
call upon Ethernet TSN capabilities defined in IEEE 802.1 TSN
IEEE802.1TSNTG.  The forwarding sub-layer uses buffer resources for
packet queuing, as well as reservation and allocation of bandwidth
capacity resources.
Paragraph (version B):
The service sub-layer provides additional support beyond the
connectivity function of the forwarding sub-layer.  An example of
this is Packet Replication, Elimination, and Ordering functions see
PREOF.  The ordering (POF) uses sequence numbers added to packets
enabling a range of packet order protection from simple ordering and
dropping out-of-order packets to more complex reordering of a fixed
number of out-of-order, minimally delayed packets.  Reordering
requires buffer resources and has impact on the delay and jitter of
packets in the DetNet flow.
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DetNet encodes specific flow attributes (flow identity and sequence
number) in packets.  For example, in DetNet IP, zero encapsulation is
used and no sequence number is available, and in DetNet MPLS, DetNet
specific information may be added explicitly to the packets in the
format of S-label and d-CW.
Paragraph (version B):
DetNet encodes specific flow attributes (flow identity and sequence
number) in packets.  For example, in DetNet IP, zero encapsulation is
used and no sequence number is available, and in DetNet MPLS, DetNet
specific information may be added explicitly to the packets in the
format of S-label and d-CW I-D.ietf-detnet-mpls .
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MPLS provides the ability to forward traffic over implicit and
explicit paths to the point in the network where the next DetNet
service sub-layer action needs to take place.  It does this through
the use of a stack of one or more labels with various forwarding
semantics.
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MPLS provides a forwarding sub-layer for traffic over implicit and
explicit paths to the point in the network where the next DetNet
service sub-layer action needs to take place.  It does this through
the use of a stack of one or more labels with various forwarding
semantics.
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In cases where metadata is needed to process an MPLS encapsulated
packet at the service sub-layer, a shim layer called a control word
(CW) RFC4385 can be used.  Although such CWs are frequently 32 bits
long, there is no architectural constraint on its size of this
structure, only the requirement that it is fully understood by all
parties operating on it in the DetNet service sub-layer.  The
operation of this method is described in detail in I-D.ietf-detnet-
mpls.
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In cases where metadata is needed to process an MPLS encapsulated
packet at the service sub-layer, the d-CW I-D.ietf-detnet-mpls,
RFC4385,can be used.  Although such d-CWs are frequently 32 bits
long, there is no architectural constraint on its size of this
structure, only the requirement that it is fully understood by all
parties operating on it in the DetNet service sub-layer.  The
operation of this method is described in detail in I-D.ietf-detnet-
mpls.
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Reservation of resources can allocate resources to specific DetNet
flows.  This can eliminate packet contention and packet loss for
DetNet traffic.  This also can reduce jitter for DetNet traffic.
Resources allocated to a DetNet flow protect it from other traffic
flows.  On the other hand, DetNet flows are assumed to behave with
respect to the reserved traffic profile.  Misbehaving DetNet flows
must be detected and it have to be ensured that they do not
compromise QoS of other flows.  The use of (queuing, policing,
shaping) policies can be used to ensure that the allocation of
resources reserved for DetNet is met.
Paragraph (version B):
Reservation of resources can allocate resources to specific DetNet
flows.  This can eliminate packet contention and packet loss for
DetNet traffic.  This also can reduce jitter for DetNet traffic.
Resources allocated to a DetNet flow protect it from other traffic
flows.  On the other hand, DetNet flows are assumed to behave with
respect to the reserved traffic profile.  Misbehaving DetNet flows
must be able to be detected and ensure that they do not compromise
QoS of other flows.  Queuing, policing, and shaping policies can be
used to ensure that the allocation of resources reserved for DetNet
is met.
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Network Coding, not to be confused with network programming,
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Network Coding, nwcrg not to be confused with network programming,
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In the preceding example, reordering of packets is dependent on the
number of out-of-order packets that can be buffered and the delay
difference of arriving packets.  DetNet uses configuration of the
number of maximum number out-of-order packets and the maximum delay
that out-of-order packets can be held before being delivered.  If the
differential delay between paths is large enough or the arrival rate
of packets large enough packets may be dropped instead of being
reordered.  Likewise elimination uses the sequence number to
eliminate duplicate packets and large differential delays combined
with high numbers of packets may exceed the ability of this
elimination function to eliminate all duplicate packets.  Path
selection for DetNet services needs to take these factors into
account.
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While the definition of controller plane for DetNet is out of the
scope of this document, there are particular considerations and
requirements for such that result from the unique characteristics of
the DetNet architecture RFC8655 and data plane as defined herein.
Paragraph (version B):
The Controller Plane corresponds to the aggregation of the Control
and Management Planes discussed in RFC7426 and RFC8655.  While more
details of any DetNet controller plane are out of the scope of this
document, there are particular considerations and requirements for
such that result from the unique characteristics of the DetNet
architecture RFC8655 and data plane as defined herein.
Paragraph (version A):
As discussed in sec_intro, this document does not specify the
mechanisms needed to eliminate packet contention, packet loss or
reduce jitter for DetNet flows at the DetNet forwarding sub-layer.
The ability to manage node and link resources to be able to provide
these functions is a necessary part of the DetNet controller plane.
It is also necessary to be able to control the required queuing
mechanisms used to provide these functions along a flow's path
through the network.  See I-D.ietf-detnet-ip and control-management-
requirements for further discussion of these requirements.
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DetNet applications typically generate bidirectional traffic.  IP and
MPLS typically treat each direction separately and do not force
interdependence of each direction.  MPLS has considered bidirectional
traffic requirements and the MPLS definitions from RFC5654 are useful
to illustrate terms such as associated bidirectional flows and co-
routed bidirectional flows.  MPLS defines a point-to-point associated
bidirectional LSP as consisting of two unidirectional point-to-point
LSPs, one from A to B and the other from B to A, which are regarded
as providing a single logical bidirectional forwarding path.  This is
analogous to standard IP routing.  MPLS defines a point-to-point co-
routed bidirectional LSP as an associated bidirectional LSP which
satisfies the additional constraint that its two unidirectional
component LSPs follow the same path (in terms of both nodes and
links) in both directions.  An important property of co-routed
bidirectional LSPs is that their unidirectional component LSPs share
fate.  In both types of bidirectional LSPs, resource reservations may
differ in each direction.  The concepts of associated bidirectional
flows and co-routed bidirectional flows can also be applied to DetNet
IP flows.
Paragraph (version B):
As discussed in sec_intro, this document does not specify the
mechanisms needed to eliminate packet contention, packet loss or
reduce jitter for DetNet flows at the DetNet forwarding sub-layer.
The ability to manage node and link resources to be able to provide
these functions is a necessary part of the DetNet controller plane.
It is also necessary to be able to control the required queuing
mechanisms used to provide these functions along a flow's path
through the network.  See I-D.ietf-detnet-ip and control-management-
requirements for further discussion of these requirements.  Some
forms of protection may minimize packet loss or change jitter
characteristics in the cases where packets are reordered when out-of-
order packets are received at the service sub-layer.
Paragraph (version B):
In many cases DetNet flows can be considered unidirectional and
independent.  However, there are cases where the DetNet service
requires bidirectional traffic from a DetNet application service
perspective.  IP and MPLS typically treat each direction separately
and do not force interdependence of each direction.  MPLS has
considered bidirectional traffic requirements and the MPLS
definitions from RFC5654 are useful to illustrate terms such as
associated bidirectional flows and co-routed bidirectional flows.
MPLS defines a point-to-point associated bidirectional LSP as
consisting of two unidirectional point-to-point LSPs, one from A to B
and the other from B to A, which are regarded as providing a single
logical bidirectional forwarding path.  This is analogous to standard
IP routing.  MPLS defines a point-to-point co-routed bidirectional
LSP as an associated bidirectional LSP which satisfies the additional
constraint that its two unidirectional component LSPs follow the same
path (in terms of both nodes and links) in both directions.  An
important property of co-routed bidirectional LSPs is that their
unidirectional component LSPs share fate.  In both types of
bidirectional LSPs, resource reservations may differ in each
direction.  The concepts of associated bidirectional flows and co-
routed bidirectional flows can also be applied to DetNet IP flows.
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This document makes no IANA requests.