| DetNet | J. Korhonen, Ed. |
| Internet-Draft | |
| Intended status: Standards Track | L. Andersson |
| Expires: January 1, 2018 | Y. Jiang |
| N. Finn | |
| Huawei | |
| B. Varga | |
| J. Farkas | |
| Ericsson | |
| CJ. Bernardos | |
| UC3M | |
| T. Mizrahi | |
| Marvell | |
| L. Berger | |
| LabN | |
| June 30, 2017 |
DetNet Data Plane Encapsulation
draft-dt-detnet-dp-sol-01
This document specifies Deterministic Networking data plane encapsulation solutions. The described data plane solutions can be applied over either IP or MPLS Packet Switched Networks.
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 http://datatracker.ietf.org/drafts/current/.
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This Internet-Draft will expire on January 1, 2018.
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Deterministic Networking (DetNet) is a service that can be offered by a network to DetNet flows. DetNet provides these flows extremely low packet loss rates and assured maximum end-to-end delivery latency. General background and concepts of DetNet can be found in [I-D.ietf-detnet-architecture].
This document specifies the DetNet data plane. It defines how DetNet traffic is encapsulated at the network layer, and how DetNet-aware nodes can identity DetNet flows. Two data plane definitions are given.
It is worth noting that while PWs are designed to work over IP PSNs this document describes a native-IP solution that operates without PWs. The primary reason for this is the benefit gained by enabling the use of a normal application stack, where transport protocols such as TCP or UDP are directly encapsulated in IP.
This document specifies the encapsulation for DetNet flows, including a DetNet Control Word (CW). Furthermore, it describes how DetNet flows are identified, how DetNet Relay and Edge nodes work, and how the Packet Replication and Elimination function (PREF) is implemented with these two data plane solutions. This document does not define the associated control plane functions, or Operations, Administration, and Maintenance (OAM). It also does not specify traffic handling capabilities required to deliver congestion protection and latency control to DetNet flows as this is defined to be provided by the underlying MPLS or IP network.
This document uses the terminology established in the DetNet architecture [I-D.ietf-detnet-architecture] and the DetNet Data Plane Solution Alternatives [I-D.ietf-detnet-dp-alt].
The following terms are also used in this document:
The following abbreviations used in this document:
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL" "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
This document describes how to use IP and/or MPLS to support a data plane method of flow identification and packet formwarding over layer-3. Two different cases are covered: (i) the inter-connect scenario, in which IEEE802.1 TSN is routed over a layer-3 network (i.e., to enlarge the layer-2 domain), and (ii) native connectivity between DetNet-aware end systems. Figure 1 illustrates an exemplary scenario.
TSN Edge Transit Relay DetNet
End System Node Node Node End System
+---------+ +.........+ +---------+
| Appl. |<---:Svc Proxy:-- End to End Service ---------->| Appl. |
+---------+ +---------+ +---------+ +---------+
| TSN | |TSN| |Svc|<-- DetNet flow ---: Service :-->| Service |
+---------+ +---+ +---+ +---------+ +---------+ +---------+
|Transport| |Trp| |Trp| |Transport| |Trp| |Trp| |Transport|
+-------.-+ +-.-+ +-.-+ +--.----.-+ +-.-+ +-.-+ +---.-----+
: Link : / ,-----. \ : Link : / ,-----. \
+........+ +-[ Sub ]-+ +........+ +-[ Sub ]-+
[Network] [Network]
`-----' `-----'
Figure 1: A simple DetNet enabled network architecture
Figure 2 illustrates how DetNet can provide services for IEEE 802.1TSN end systems over a DetNet enabled network. The edge nodes insert and remove required DetNet data plane encapsulation. The 'X' in the edge and relay nodes represents a potential DetNet flow packet replication and elimination point. This conceptually parallels L2VPN services, and could leverage existing related solutions as discussed below.
TSN |<---------- End to End DetNet Service ------>| TSN
Service | Transit Transit | Service
TSN (AC) | |<-Tunnel->| |<-Tnl->| | (AC) TSN
End | V V 1 V V 2 V V | End
System | +--------+ +--------+ +--------+ | System
+---+ | | E1 |==========| R1 |=======| E2 | | +---+
| |--|----|._X_....|..DetNet..|.._ _...|..DF3..|...._X_.|---|---| |
|CE1| | | \ | Flow 1 | X | | / | | |CE2|
| | | \_.|...DF2....|._/ \_..|..DF4..|._/ | | |
+---+ | |==========| |=======| | +---+
^ +--------+ +--------+ +--------+ ^
| Edge Node Relay Node Edge Node |
| |
|<----- Emulated Time Sensitive Networking (TSN) Service ---->|
Figure 2: IEEE 802.1TSN over DetNet
Figure 3 illustrates how end to end PW-based DetNet service can be provided. In this case, the end systems are able to send and receive DetNet flows. For example, an end system sends data encapsulated in PseudoWire (PW) and in MPLS. Like earlier the 'X' in the end systems, edge and relay nodes represents potential DetNet flow packet replication and elimination points. Here the relay nodes may change the underlying transport, for example tunneling IP over MPLS, or simply interconnect network segments.
DetNet DetNet
Service Transit Transit Service
DetNet | |<-Tnl->| |<-Tnl->| | DetNet
End | V 1 V V 2 V | End
System | +--------+ +--------+ +--------+ | System
+---+ | | R1 |=======| R2 |=======| R3 | | +---+
| X...DFa...|._X_....|..DF1..|.__ ___.|..DF3..|...._X_.|.DFa..|.X |
|CE1|========| \ | | X | | / |======|CE2|
| | | | \_.|..DF2..|._/ \__.|..DF4..|._/ | | | |
+---+ | |=======| |=======| | +---+
^ +--------+ +--------+ +--------+ ^
| Relay Node Relay Node Relay Node |
| |
|<--------------- End to End DetNet Service -------------->|
Figure 3: PW-Based Native DetNet
Figure 4 illustrates how end to end IP-based DetNet service can be provided. In this case, the end systems are able to send and receive DetNet flows. [Editor's note: TBD]
NOTE: This figures is TBD
DetNet DetNet
Service Transit Transit Service
DetNet | |<-Tnl->| |<-Tnl->| | DetNet
End | V 1 V V 2 V | End
System | +--------+ +--------+ +--------+ | System
+---+ | | R1 |=======| R2 |=======| R3 | | +---+
| X...DFa...| | | | | | .|.X |
| H1|========| | | | | |======| H2|
| | | | | | | | | | | |
+---+ | |=======| |=======| | +---+
^ +--------+ +--------+ +--------+ ^
| Relay Node Relay Node Relay Node |
| |
|<--------------- End to End DetNet Service -------------->|
Figure 4: IP-Based Native DetNet
Two major groups of scenarios can be distinguished which require flow identification during transport:
Each node (edge, relay and transit) use a local-ID of the DetNet-(compound)-flow in order to accomplish its role during transport. Recognizing the DetNet flow is more relaxed for edge and relay nodes, as they are fully aware of both the DetNet service and transport layers. The primary DetNet role of intermediate transport nodes is limited to ensuring congestion protection and latency control for the above listed DetNet functions.
The DetNet data plane allows for the aggregation of DetNet flows, e.g., via MPLS hierarchical LSPs, to improved scaling. When DetNet flows are aggregated, transit nodes may have limited ability to provide service on per-flow DetNet identifiers. Therefore, identifying each individual DetNet flow on a transit node may not be achieved in some network scenarios, but DetNet service can still be assured in these scenarios through resource allocation and control.
On each node dealing with DetNet flows, a local-ID is assumed to determine what local operation a packet goes through. Therefore, local-IDs MUST be unique on each edge and relay nodes. Local-ID MUST be unambiguously bound to the DetNet flow.
The DetNet data plane encapsulation should include two DetNet specific information element in each packet of a DetNet flow: (1) flow identification and (2) sequence number.
The DetNet data plane encapsulation may consists further elements used for overlay tunneling, to distinguish between DetNet member flows of the same DetNet compound flow or to support OAM functions.
This document specifies two encapsulations for the DetNet data plane: (1) PseudoWire (PW) for MPLS PSN and (2) native IPv6 based encapsulation for IP PSN.
Figure 5 illustrates a DetNet PW encapsulation over an MPLS PSN. The PW-based encapsulation of the DetNet flows fits perfectly for the Layer-2 interconnect deployment cases (see Figure 2). Furthermore, end to end DetNet service i.e., native DetNet deployment (see Figure 3) is also possible if DetNet-aware end systems are capable of initiating and termination MPLS encapsulated PWs. It is also possible use the same encapsulation format with a Packet PW over MPLS [RFC6658]. Transport of IP encapsulated DetNet flows, see Section 5.2.2, over DetNet PWs is also possible. Interworking between PW- and IPv6-based encapsulations is discussed further in Section 7.6.
The PW-based DetNet data plane encapsulation consists of:
RFC3985 Encapsulation DetNet PW Encapsulation
+---------------------+
| Payload | +---------------------------------+
/=====================\ | |
H Payload Convergence H--. | DetNet Flow |
H---------------------H | | Payload Packet |
H Timing H +-\ | |
H---------------------H | \ /=================================\
H Sequencing H--' \-->H DetNet Control Word H
\=====================/ \=================================/
| PW Demultiplexer |--------->| PW Label |
+---------------------+ +---------------------------------+
| PSN Convergence | .--->| Optional MPLS S-Label |
+---------------------+ | +---------------------------------+
| PSN |-----+--->| MPLS T-Label(s) |
+---------------------+ +---------------------------------+
| Data-Link |
+---------------------+
| Physical |
+---------------------+
Figure 5: Encapsulation of a DetNet flow in a PW with MPLS(-TP) PSN
The DetNet control word (d-CW) is identical to the control word defined for Ethernet over MPLS networks in [RFC4448]. The DetNet control word is illustrated in Figure 6.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0| reserved - set to 0 | 16 bit Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: DetNet Control Word
Figure 7 illustrates a DetNet native IPv6 encapsulation. The native IPv6 encapsulation is meant for end to end Detnet service use cases, where the end stations are DetNet-aware (see Figure 4). Technically it is possible to use the IPv6 encapsulation to tunnel any traffic over a DetNet enabled network, which would make native IPv6 encapsulation also a valid data plane choice for an interconnect use case (see Figure 2).
The native IPv6-based DetNet data plane encapsulation consists of:
A DetNet-aware end station (a host) or an intermediate node initiating an IPv6 packet is responsible for setting the Flow Label, adding the required DetNet Destination Option, and possibly adding a routing header such as the segment routing option (for pre-defined paths [I-D.ietf-6man-segment-routing-header]). The payload of the native IPv6 encapsulation is any payload protocol that can be identified using the Next Header field either in the IPv6 packet header or in the last IPv6 extension header.
A DetNet-aware end station (a host) or an intermediate node receiving an IPv6 packet destined to it and containing a DetNet Destination Option does the appropriate processing of the packet. This may involve packet duplication and elimination (PREF processing), terminating a tunnel or delivering the packet to the upper layers/Applications.
+---------------------------------+
| |
| DetNet Flow |
| Payload |
| |
/---------------------------------\
H DetNet Control Word DstOpt Hdr H
\---------------------------------/
| IPv6 header |
| (with set Flow label) |
+---------------------------------+
Figure 7: Encapsulation of a native IPv6 DetNet flow
A DetNet flow must carry sequencing information for packet replication and elimination function (PREF) purposes. This document specifies a new IPv6 Destination Option: the DetNet Destination Option for that purpose. The format of the option is illustrated in Figure 8.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD1 | 4 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 16 bit Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: DetNet Destination Option
The Option Type for the DetNet Destination Option is set to TBD1. [To be removed from the final version of the document: The Option Type MUST have the two most significant bits set to 10b]
Duplicate elimination depends on flow identification. Mapping between packet fields and Local-ID may impact the implementation of duplicate elimination.
RFC3985 Section 5.2.1. describes PW sequencing provides a duplicate detection service among other things. This specification clarifies this definition as follows:
From the label stack processing point of view receiving the same label from multiple sources is analogous to Fast Reroute backup tunnel behavior [RFC4090]. The PW Label for a DetNet flow can be different on each PW segment.
The DetNet flow identification is based on the IPv6 Flow Label and the source address combination. The two fields uniquelly identify the end to end native IPv6 encapsulated DetNet flow. Obviously, the identification fails if any intermediate node modifies either the source address or the Flow Label.
This section applies equally to DetNet flows transported via IPv6 and MPLS. While flow identification and some header related processing will differ between the two, the considerations covered in this section are common to both.
The DetNet specific new functionality in an edge or relay node processing is the packet replication and duplication elimination function (PREF). This function is a part of the DetNet-aware "extended" forwarder. The PREF processing is triggered by the received packet of a DetNet flow. Basically the forwarding entry has to be extended with a "PREF enabled" boolean configuration switch that is associated with the normal forwarding actions (e.g., in case of MPLS a swap, push, pop, ..). The output of the PREF elimination function is always a single packet. The output of the PREF replication function is always one or more packets (i.e., 1:M replication). The replicated packets MUST share the same DetNet control word sequence number.
The complex part of the DetNet PREF processing is tracking the history of received packets for multiple DetNet member flows. These ingress DetNet member flows (to a node) MUST have the same local-ID if they belong to the same DetNet-(compound)-flow and share the same sequence number counter and the history information.
The edge and relay node internal procedures of the PREF are implementation specific. The order of a packet elimination or replication is out of scope in this specification. However, care should be taken that the replication function does not actually loopback packets as "replicas". Looped back packets include artificial delay when the node that originally initiated the packet receives it again. Also, looped back packets may make the network condition to look healthier than it actually is (in some cases link failures are not reflected properly because looped back packets make the situation appear better than it actually is).
The DetNet data plane solution overloads the edge node with DetNet Edge Node functions. Edge nodes are also aware of DetNet flows and may need to operate upon those. Figure 9 illustrates the overall edge device functions. The figure shows both physical attachment circuit (AC) (e.g., Ethernet [RFC4448]) connecting to the edge node, and a packet service connecting to the edge node via an embedded router function (similarly as described e.g., in [RFC6658]). Whether traffic flow from a client AC and PSN tunnel receives DetNet specific treatment is up to a local configuration and policy.
+---------------------------------------+
| DetNet Edge Device |
+---------------------------------------+ Egress/
| | Forwarder | | Ingress
| | | Single | member Inst.
Client PSN | "Packet o <-X-----> o Service o<---------->
tunnels | NSP" | | Repl. | Instance |
<---------->o | | Elim. +-------------+ Duplicate
| | : | | Egress
| | . | Single | member Inst.
| | +-> o Service o<---------->
| | | | Instance |
+-------------+ | +-------------+ Egress/
| | | | | Ingress
Client AC | NSP | Repl. | | Single | member Inst.
<---------->o o <-----X-> o Service o<---------->
| | Elim. | Instance |
+-------------+ +-------------+ Egress/
| | | | Ingress
Client AC | NSP | | Single | member Inst.
<---------->o o <-------> o Service o<---------->
| | | Instance |
+---------------------------------------+
Figure 9: DetNet Edge Node processing
An edge node participates to the packet replication and duplication elimination. Required processing is done within an extended forwarder function. In the case the native service processing (NSP) is IEEE 802.1CB [IEEE8021CB] capable, the packet replication and duplicate elimination MAY entirely be done in the NSP and bypassing the DetNet flow encapsulation and logic entirely, and thus is able to operate over unmodified implementation and deployment. The NSP approach works only between edge nodes and cannot make use of relay nodes (see Section 6.1.3).
The DetNet-aware extended forwarder selects the egress DetNet member flow based on the DetNet forwarding rules. In both "normal AC" and "Packet AC" cases there may be no DetNet encapsulation header available yet as it is the case with relay nodes (see Section 6.1.3). It is the responsibility of the extended forwarder within the edge node to push the DetNet specific encapsulation (if not already present) to the packet before forwarding it to the appropriate egress DetNet member flow instance(s). The extended forwarder MAY copy the sequencing information from the native DetNet packet into the DetNet sequence number field and vice versa. If there is no existing sequencing information available in the native packet or the forwarder chose not to copy it from the native packet, then the extended forwarder MUST maintain a sequence number counter for each DetNet flow (indexed by the DetNet flow identification).
The DetNet data plane solution overloads a relay node with DetNet Relay node functions. Relay node is aware of DetNet flows and may operate upon those. Figure 10 illustrates the overall DetNet relay device functions.
A DetNet Relay node participates to the packet replication and duplication elimination. This processing is done within an extended forwarder function. Whether an ingress DetNet member flow receives DetNet specific processing depends on how the forwarding is programmed. For some DetNet member flows the relay node can act as a normal relay node and for some apply the DetNet specific processing (i.e., PREF). It is also possible to treat the relay node as a transit node, see Section 7.3. Again, this is entirely up to how the forwarding has been programmed.
The DetNet-aware forwarder selects the egress DetNet member flow segment based on the flow identification. The mapping of ingress DetNet member flow segment to egress DetNet member flow segment may be statically or dynamically configured. Additionally the DetNet-aware forwarder does duplicate frame elimination based on the flow identification and the sequence number combination. The packet replication is also done within the DetNet-aware forwarder. During elimination and the replication process the sequence number of the DetNet member flow MUST be preserved and copied to the egress DetNet member flow.
+---------------------------------------+
| DetNet Relay Device |
Ingress +---------------------------------------+
member | | Forwarder | | Egress
instance | Single | | Single | member Inst.
----------->o Service o --X-----> o Service o----------->
| Instance | | Elim. | Instance |
Ingress +-------------+ | +-------------+ Duplicate
member | | | | | Egress
instance | Single | | | Single | member Inst.
----------->o Service o --+ +-> o Service o----------->
| Instance | | | Instance |
Ingress +-------------+ | +-------------+
member | | | | | Egress
instance | Single | Repl. | | Single | member Inst.
----------->o Service o ------X-> o Service o----------->
| Instance | | Instance |
Ingress +-------------+ +-------------+
member | | | | Egress
instance | Single | | Single | member Inst.
----------->o Service o --------> o Service o----------->
| Instance | | Instance |
+---------------------------------------+
Figure 10: DetNet Relay Node processing
[Editor's note: this section is TBD.]
Class and quality of service, i.e., CoS and QoS, are terms that are often used interchangeably and confused. In the context of DetNet, CoS is used to refer to mechanisms that provide traffic forwarding treatment based on aggregate group basis and QoS is used to refer to mechanisms that provide traffic forwarding treatment based on a specific DetNet flow basis. Examples of existing network level CoS mechanisms include DiffServ which is enabled by IP header differentiated services code point (DSCP) field [RFC2474] and MPLS label traffic class field [RFC5462], and at Layer-2, by IEEE 802.1p priority code point (PCP).
CoS for DetNet flows carried in PWs and MPLS is provided using the existing MPLS Differentiated Services (DiffServ) architecture [RFC3270]. Both E-LSP and L-LSP MPLS DiffServ modes MAY be used to support DetNet flows. The Traffic Class field (formerly the EXP field) of an MPLS label follows the definition of [RFC5462] and [RFC3270]. The Uniform, Pipe, and Short Pipe DiffServ tunneling and TTL processing models are described in [RFC3270] and [RFC3443] and MAY be used for MPLS LSPs supporting DetNet flows. MPLS ECN MAY also be used as defined in ECN [RFC5129] and updated by [RFC5462].
CoS for DetNet flows carried in IPv6 is provided using the standard differentiated services code point (DSCP) field [RFC2474] and related mechanisms. The 2-bit explicit congestion notification (ECN) [RFC3168] field MAY also be used.
One additional consideration for DetNet nodes which support CoS services is that they MUST ensure that the CoS service classes do not impact the congestion protection and latency control mechanisms used to provide DetNet QoS. This requirement is similar to requirement for MPLS LSRs to that CoS LSPs do not impact the resources allocated to TE LSPs via [RFC3473].
Quality of Service (QoS) mechanisms for flow specific traffic treatment typically includes a guarantee/agreement for the service, and allocation of resources to support the service. Example QoS mechanisms include discrete resource allocation, admission control, flow identification and isolation, and sometimes path control, traffic protection, shaping, policing and remarking. Example protocols that support QoS control include Resource ReSerVation Protocol (RSVP) (RSVP) and RSVP-TE [RFC3209] and [RFC3473]. The existing MPLS mechanisms defined to support CoS [RFC3270] can also be used to reserve resources for specific traffic classes.
In addition to path pinning and packet replication and elimination, described in Section 5 above, DetNet provides zero congestion loss and bounded latency and jitter. As described in [I-D.ietf-detnet-architecture], there are different mechanisms that maybe used separately or in combination to deliver a zero congestion loss service. These mechanisms are provided by the either the MPLS or IP layers, and may be combined with the mechanisms defined by the underlying network layer such as 802.1TSN.
A baseline set of QoS capabilities for DetNet flows carried in PWs and MPLS can provided by MPLS with Traffic Engineering (MPLS-TE) [RFC3209] and [RFC3473]. TE LSPs can also support explicit routes (path pinning). Current service definitions for packet TE LSPs can be found in "Specification of the Controlled Load Quality of Service", [RFC2211], "Specification of Guaranteed Quality of Service", [RFC2212], and "Ethernet Traffic Parameters", [RFC6003]. Additional service definitions are expected in future documents to support the full range of DetNet services. In all cases, the existing label-based marking mechanisms defined for TE-LSPs and even E-LSPs are use to support the identification of flows requiring DetNet QoS.
QoS for DetNet flows carried in IPv6 MUST be provided locally by the DetNet-aware hosts and routers supporting DetNet flows. Such support will leverage the underlying network layer such as 802.1TSN. The traffic control mechanisms used to deliver QoS for IP encapsulated DetNet flows are expected to be defined in a future document. From an encapsulation perspective, and as defined in Section 5.2.2, the combination of the Flow Label together with the IP source address uniquely identifies a DetNet flow.
Packets that are marked with a DetNet Class of Service value, but that have not been the subject of a completed reservation, can disrupt the QoS offered to properly reserved DetNet flows by using resources allocated to the reserved flows. Therefore, the network nodes of a DetNet network SHOULD:
The ability to aggregate individual flows, and their associated resource control, into a larger aggregate is an important technique for improving scaling of control in the data, management and control planes. This document identifies the traffic identification related aspects of aggregation of DetNet flows. The resource control and management aspects of aggregation (including the queuing/shaping/policing implications) will be covered in other documents. The data plane implications of aggregation are independent for PW/MPLS and IP encapsulated DetNet flows.
DetNet flows transported via MPLS can leverage MPLS-TE's existing support for hierarchical LSPs (H-LSPs), see [RFC4206]. H-LSPs are typically used to aggregate control and resources, they may also be used to provide OAM or protection for the aggregated LSPs. Arbitrary levels of aggregation naturally falls out of the definition for hierarchy and the MPLS label stack [RFC3032]. DetNet nodes which support aggregation (LSP hierarchy) map one or more LSPs (labels) into and from an H-LSP. Both carried LSPs and H-LSPs may or may not use the TC field, i.e., L-LSPs or E-LSPs. Such nodes will need to ensure that traffic from aggregated LSPs are placed (shaped/policed/enqueued) onto the H-LSPs in a fashion that ensures the required DetNet service is preserved.
DetNet flows transported via IP have more limited aggregation options, due to the available traffic flow identification fields of the IP solution. One available approach is to manage the resources associated with a DSCP identified traffic class and to map (remark) individually controlled DetNet flows onto that traffic class. This approach also requires that nodes support aggregation ensure that traffic from aggregated LSPs are placed (shaped/policed/enqueued) in a fashion that ensures the required DetNet service is preserved.
In both the MPLS and IP cases, additional details of the traffic control capabilities needed at a DetNet-aware node may be covered in the new service descriptions mentioned above or in separate future documents. Management and control plane mechanisms will also need to ensure that the service required on the aggregate flow (H-LSP or DSCP) are provided, which may include the discarding or remarking mentioned in the previous sections.
Some DetNet applications generate bidirectional traffic. Using MPLS definitions [RFC5654] there are 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 transport path. This would be analogous of standard IP routing, or PWs running over two reciprocal unidirection LSPs. 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 allocations may differ in each direction. The concepts of associated bidirectional flows and co-routed bidirectional flows can be applied to DetNet flows as well whether IPv6 or MPLS is used.
While the IPv6 and MPLS data planes must support bidirectional DetNet flows, there are no special bidirectional features with respect to the data plane other than need for the two directions take the same paths. Fate sharing and associated vs co-routed bidirectional flows can be managed at the control level. Note, that there is no stated requirement for bidirectional DetNet flows to be supported using the same IPv6 Flow Labels or MPLS Labels in each direction. Control mechanisms will need to support such bidirectional flows for both IPv6 and MPLS, but such mechanisms are out of scope of this document. An example control plane solution for MPLS can be found in [RFC7551].
The Time-Sensitive Networking (TSN) Task Group of the IEEE 802.1 Working Group have defined (and are defining) a number of amendments to IEEE 802.1Q that provide zero congestion loss and bounded latency in bridged networks. IEEE 802.1CB defines packet replication and elimination functions that should prove both compatible with and useful to, DetNet networks.
As is the case for DetNet, a Layer 2 network node such as a bridge may need to identify the specific DetNet flow to which a packet belongs in order to provide the TSN/DetNet QoS for that packet. It also will likely need a CoS marking, such as the priority field of an IEEE Std 802.1Q VLAN tag, to give the packet proper service.
Although the flow identification methods described in IEEE 802.1CB are flexible, and in fact, include IP 5-tuple identification methods, the baseline TSN standards assume that every Ethernet frame belonging to a TSN stream (i.e. DetNet flow) carries a multicast destination MAC address that is unique to that flow within the bridged network over which it is carried. Furthermore, IEEE 802.1CB describes three methods by which a packet sequence number can be encoded in an Ethernet frame.
Ensuring that the proper Ethernet VLAN tag priority and destination MAC address are used on a DetNet/TSN packet may require further clarification of the customary L2/L3 transformations carried out by routers and edge label switches. Edge nodes may also have to move sequence number fields among Layer 2, PW, and IPv6 encapsulations.
[Editor's note: add considerations for interworking between PW-based and native IPv6-based DetNet encapsuations.]
[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:
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.
While management plane and control planes are traditionally considered separately, from the Data Plane perspective there is no practical difference based on the origin of flow provisioning information. This document therefore does not distinguish between information provided by a control plane protocol, e.g., RSVP-TE [RFC3209] and [RFC3473], or by a network management mechanisms, e.g., RestConf [RFC8040] and YANG [RFC7950].
[Editor's note: This section is a work in progress. discuss here what kind of enhancements are needed for DetNet and specifically for PREF and DetNet zero congest loss and latency control. Need to cover both traffic control (queuing) and connection control (control plane).]
The PW label distribution follows the same mechanisms specified for MS-PW [RFC6073]. The details of the control plane protocol solution required for the label distribution and the management of the label number space are out of scope of this document.
The IPv6 Flow Label distribution and the label number space are out of scope of this document. However, it should be noted that the combination of the IPv6 source address and the IPv6 Flow Label is assumed to be unique within the DetNet-enabled network. Therefore, as long as each node is able to assign unique Flow Labels for the source address(es) it is using the DetNet-enabled network wide flow identification uniqueness is guaranteed.
The control plane protocol solution required for managing the PREF processing is outside the scope of this document.
[TBD: based on MPLS TE and SR.]
[TBD]
[TBD]
The security considerations of DetNet in general are discussed in [I-D.ietf-detnet-architecture] and [I-D.sdt-detnet-security]. Other security considerations will be added in a future version of this draft.
TBD.
The author(s) ACK and NACK.
The following people were part of the DetNet Data Plane Solution Design Team:
The DetNet chairs serving during the DetNet Data Plane Solution Design Team:
[Editor's note: Add a simplified example of DetNet data plane and how labels etc work in the case of MPLS-based PSN and utilizing PREF. The figure is subject to change depending on the further DT decisions on the label handling..]
TBD.