DetNet Data Plane solution
draft-dt-detnet-dp-sol-00
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| Authors | Jouni Korhonen , Loa Andersson , Yuanlong Jiang , Balazs Varga , János Farkas , Carlos J. Bernardos , Tal Mizrahi | ||
| Last updated | 2017-03-13 | ||
| Replaced by | draft-ietf-detnet-dp-sol | ||
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draft-dt-detnet-dp-sol-00
DetNet J. Korhonen, Ed.
Internet-Draft Broadcom
Intended status: Informational L. Andersson
Expires: September 14, 2017 Y. Jiang
Huawei
B. Varga
J. Farkas
Ericsson
CJ. Bernardos
UC3M
T. Mizrahi
Marvell
March 13, 2017
DetNet Data Plane solution
draft-dt-detnet-dp-sol-00
Abstract
This document specifies a PseudoWire-based Deterministic Networking
data plane solution. The data plane solution can be applied over
either IP or MPLS Packet Switched Networks.
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
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This Internet-Draft will expire on September 14, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements language . . . . . . . . . . . . . . . . . . . . 4
4. DetNet data plane Overview . . . . . . . . . . . . . . . . . 4
4.1. DetNet data plane solution requirements . . . . . . . . . 6
5. DetNet data plane solution . . . . . . . . . . . . . . . . . 6
5.1. DetNet Control Word . . . . . . . . . . . . . . . . . . . 7
5.2. DetNet flow identity word . . . . . . . . . . . . . . . . 7
5.3. DetNet encapsulation . . . . . . . . . . . . . . . . . . 8
6. PE reference model considerations . . . . . . . . . . . . . . 11
6.1. Forwarded clarifications . . . . . . . . . . . . . . . . 11
6.2. DA-T-PE processing clarifications . . . . . . . . . . . . 12
6.3. DA-S-PE processing clarifications . . . . . . . . . . . . 14
7. Other DetNet considerations . . . . . . . . . . . . . . . . . 15
7.1. Class of Service . . . . . . . . . . . . . . . . . . . . 15
7.2. Quality of Service . . . . . . . . . . . . . . . . . . . 15
7.3. Time synchronization . . . . . . . . . . . . . . . . . . 15
7.4. Bidirectional traffic . . . . . . . . . . . . . . . . . . 16
8. Control plane considerations . . . . . . . . . . . . . . . . 17
8.1. PW Label assignment and distribution . . . . . . . . . . 17
9. Security considerations . . . . . . . . . . . . . . . . . . . 17
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
12.1. Normative References . . . . . . . . . . . . . . . . . . 18
12.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Example of DetNet data plane operation . . . . . . . 19
Appendix B. Example of pinned paths using IP PSN . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
This document specifies a Deterministic Networking (DetNet) data
plane solution. The solution is based on PseudoWires (PW) [RFC3985]
and makes use of the multi-segment (MS-PW) [RFC6073] to map DetNet
Relay and Edge Nodes
[I-D.ietf-detnet-architecture][I-D.ietf-detnet-dp-alt] to PW
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architecture. The PW-based data plane can be run over either an IP
or MPLS [RFC4448][RFC6658] Packet Switched Network (PSN).
For the purpose of DetNet data plane, this document specifically
specifies the PW encapsulation for DetNet flows, a DetNet Control
Word (CW), a DetNet label, how MS-PW derived DetNet Relay and Edge
nodes work, and as a specific new PW feature how the Packet
Replication and Elimination function (PREF) is implemented using PWs.
This document does not define the associated control plane functions,
or operations and management (OAM).
2. Terminology
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:
DA-T-PE A DetNet aware PseudoWire Terminating Provider Edge
(T-PE).
DA-S-PE A DetNet aware PseudoWire Switching Provider Edge
(S-PE).
T-Label A hop-by-hop tunnel label layer between label switching
routers (LSR).
L-Label A DetNet topology overlay label that is used between
DA-*-PE devices.
flow-ID A DetNet flow identity that uniquely identifies a
DetNet flow in a DetNet network. The flow-ID is part
of the PseudoWire Encapsulation header.
local-ID A DA-T-PE and DA-S-PE node internal construct that
uniquely identifies a DetNet flow. The local-ID can be
equal to flow-ID or be derived using other means, e.g.,
programming required label to local-ID mappings
directly into the label information base (LFIB).
PW Label A PseudoWire label that is used to identify DetNet flow
related PW Instances within a PE node.
PREF A Packet Replication and Elimination Function (PREF)
does the replication and elimination processig of
DetNet flow packets in DA-T-PE or DA-S-PE nodes. The
replication function is essentially the existing 1+1
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protection mechanism. The elimination function reuses
and extends the existing [RFC3985] PseudoWire
sequencing provided duplicate detection mechanism to
operate over multiple (separate) PseudoWires that are
sub-flows of a compound DetNet flow.
3. Requirements language
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].
4. DetNet data plane Overview
[Ed. to be written.. describe the scope here fot this document: this
document only addresses the inter-connect case i.e., 802.1 over
routed network (enlarge the layer-2 domain - EVPAN', and the native
DetNet case.]
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.
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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
+---+ | |DA-T-PE1|==========|DA-S-PE1|=======|DA-T-PE2| | +---+
| |--|----|._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 DetNet service can be provided.
In this case, the end systems are able to send and receive DetNet
flows. For example, put application data in PseudoWire (PW) and
encapsulated in IP. 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 replacing IP with MPLS or 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
+---+ | |DA-S-PE1|=======|DA-S-PE2|=======|DA-S-PE3| | +---+
| X...DFa...|._X_....|..DF1..|.__ ___.|..DF3..|...._X_.|.DFa..|.X |
|CE1|========| \ | | X | | / |======|CE2|
| | | | \_.|..DF2..|._/ \__.|..DF4..|._/ | | | |
+---+ | |=======| |=======| | +---+
^ +--------+ +--------+ +--------+ ^
| Relay Node Relay Node Relay Node |
| |
|<-- End to End Time Sensitive Networking (TSN) Service -->|
Figure 3: Native DetNet
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4.1. DetNet data plane solution requirements
Two major groups of scenarios can be distinguished which require flow
identification during transport:
1. DetNet function related scenarios:
* Congestion protection: usage of allocated resources (queuing,
policing, shaping).
* Explicit routes: select/apply the flow specific path.
* Service protection: recognize compound / member flows for
replication an elimination.
2. OAM function related scenarios:
* troubleshooting (e.g., identify misbehaving flows, etc.)
* recognize flow(s) for analytics (e.g, increase counters, etc.)
* correlate events with flows (e.g., volume above threshold,
etc.)
* etc.
Each node (DA-T-PE, DA-S-PE and P) use a local-ID of the DetNet-
(compound)-flow in order to accomplish its role during transport.
Recognizing the flow-ID is more relaxed for DA-T-PE and DA-S-PE
nodes, as they are fully aware of both the DetNet service and
transport layers. The DetNet role of intermediate "P" nodes is
limited to ensure congestion protection from the above listed DetNet
functions. However, P nodes can usually recognize only "T-label" and
cannot consider the whole label stack for flow recognition.
Therefore, identifying each individual DetNet flow on a P node may
not be achieved in some network scenarios.
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 DA-T-PE and DA-S-PE nodes. Local-ID
MUST be unambiguously bound to the Flow-ID encoded in the DetNet
packet.
5. DetNet data plane solution
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5.1. DetNet Control Word
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 4.
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 4: DetNet Control Word
[Editor's note: Shoudl we care about high speed links, here 16 bits
of sequence number wraps fast? For example, in a case of 100Gb/s
link, 16 bits of sequence number will wrap in ~6.6ms assuming 1250
octets of packets and ~3.3ms for 625 octets packets. Both numbers
mean quite long fiber distances, though.]
5.2. DetNet flow identity word
The DetNet flow identity word (flow-ID) identifies a DetNet flow
uniquely within a DetNet network. The flow-ID is also associated
with the sequence number carried in the DetNet control word and used
also for PREF purposes.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved |D| 24 bit flow identity |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: DetNet flow identity word
The management and assignment of the flow-IDs is outside of this
specification. It is assumed that each DA-T-PE node have either a
preconfigured flow-ID number space or some dynamic control plane
protocol is able to coordinate the allocation of the flow-IDs across
the DA-T-PE nodes, or a central entity, e.g., a Software Defined
Networking controller.
The D bit defines the direction of the flow. The value 0 means
'east' and the value 1 means 'west'. The D bit can be used in ring
topologies to allow DetNet flows with the same flow-ID cross with or
without PREF processing taking place. Whether a DA-*-PE checks for
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the D bit is based on a local policy setting. The support for D bit
is optional. If a DA-*-PE does not support the D bit it MUST be
treated as 0.
The reserved field in the flow-ID MUST be set to zero and ignored
when received.
[Editor's note: we need some configuration knob defined for this
feature.]
5.3. DetNet encapsulation
The DetNet data plane follows PW encapsulation. This document
specifies a single encapsulation that can be used over both MPLS and
IP packet switched Networks (PSN). The DetNet data plane
encapsulation consists of a
o DetNet control word (d-CW): contains sequencing information for
packet replication and duplicate elimination purposes. There is a
separate sequence number space per each DetNet label.
o DetNet flow-ID (f-ID): uniquely identifies a DetNet flow within a
DetNet network. Multiple DetNet PWs with different PW labels may
have the same f-ID, which then implies the PWs are actually
subflows of one compound flow.
o PseudoWire Label (PW Label;): a standard PW label that identifies
a PW Instance within a (DA-)T-PE or (DA-)S-PE device.
o DetNet topology overlay label (L-label): an optional label used
between (DA-)T-PE or (DA-)S-PE nodes. The main use of L-labels is
to tunnel PWs through a PE node and therefore effectively making a
PE node to behave like a P node.
In a case of MPLS-based PSN, the tunnel labels between LSRs are
referred as T-labels.
The DetNet CW and the Detnet flow-ID together constitute the DetNet
PseudoWire encapsulation header.
[Editor's note: The current design has the DetNet flow-ID as part
of the every DetNet flow packet. The flow-ID identifies the flow
uniquely within the DetNet network and together with the sequence
number information from the DetNet control word is used for PREF
purposes. The flow-ID makes is easy for the DA-*-PE node to
associate different PWs into one compound flow and perform the
elimination of duplicate packets. The flow-ID would point at the
node internal construct that holds the received packet history for
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each DetNet flow of interest. However, it could also be possible
to associate multiple PWs into one DetNet flow just using the
control plane provided information. In this case different PWs
(using any PW label) would be mapped internally within a node to a
local-ID (or similar construct), which again points at the
internal per DetNet flow received packets history construct. The
explicit in-band flow-ID is easy from the processing and control
plane point of view. The local-ID approach does not need the in-
band information (thus has less overhead) but requires more from
the control plane and the mapping information has to be stored
into the LFIB. Current design decision is the in-band flow-ID but
may be changed to local-ID if there is a strong reason to do the
change.]
Figure 6 illustrates a DetNet PseudoWire encapsulation using an MPLS
PSN. Similarly, Figure 7 illustrates the DetNet PseudoWire
encapsulation when IP PSN is used. The encapsulation is uniform
above the PSN.
Depending on the network topology the "overlay label" (L-label) may
be part of the label stack. The L-label tunnels guarantee PW labels
remain unchanged between DA-*-PE nodes. Furthermore, L-labels
tunnels allow selectively exposing the PW label to DA-*-PE nodes,
which means some overlay topologies may just pass through specific
DA-S-PEs without any DetNet specific processing.
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RFC3985 Encapsulation DetNet PW Encapsulation
+---------------------------------+
+---------------------+ | |
| Payload | | DetNet Flow |
/=====================\ | Payload Packet |
H Payload Convergence H--. | |
H---------------------H | /=================================\
H Timing H +-\ H DetNet Flow ID H
H---------------------H | \--->H---------------------------------H
H Sequencing H--' H DetNet Control Word H
\=====================/ \=================================/
| PW Demultiplexer |--------->| PW Label |
+---------------------+ +---------------------------------+
| PSN Convergence | .--->| Optional Topology overlay Label |
+---------------------+ | +---------------------------------+
| PSN |-----+--->| MPLS T-Label(s) |
+---------------------+ +---------------------------------+
| Data-Link |
+---------------------+
| Physical |
+---------------------+
Figure 6: Encapsulation of a DetNet flow in a PW with MPLS(-TP) PSN
When IP PSN is used, the label stack it transports is only inspected
when the IP packet destination address equals to the IP address of a
DA-*-PE or a P node. Essentially there are one more IP tunnels
between a number of DA-*-PE and/or P nodes. The LFIB and the
forwarding information base (FIB) combination determines whether a PW
gets terminated at the node or forwarded to another node within a new
IP tunnel.
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RRC3985 Encapsulation DetNet PW Encapsulation
+---------------------------------+
+---------------------+ | |
| Payload | | DetNet Flow |
/=====================\ | Payload Packet |
H Payload Convergence H--. | |
H---------------------H | /=================================\
H Timing H +-\ H DetNet Flow ID H
H---------------------H | \--->H---------------------------------H
H Sequencing H--' H DetNet Control Word H
\=====================/ \=================================/
| PW Demultiplexer |--------->| PW Label |
+---------------------+ +---------------------------------+
| PSN Convergence | .--->| Optional Topology overlay Label |
+---------------------+ | +---------------------------------+
| PSN |-----+ | Optional UDP Header |
+---------------------+ | +---------------------------------+
| Data-Link | `--->| IPv4 or IPv6 header |
+---------------------+ +---------------------------------+
| Physical |
+---------------------+
Figure 7: Encapsulation of a DetNet flow in a PW with IP PSN
6. PE reference model considerations
6.1. Forwarded clarifications
[Editor's note: The Detnet-aware "extended forwarder" does the heavy
lifting on maintaining the sequence numbers associated with the
DetNet labels. Extended forwarder is also responsible for packet
replication and duplicate elimination. See the excerpt from RFC3985
Section 4.2.1. about forwarder's functions. We extend that to PREF:
Some applications have to forward payload elements selectively
from one or more ACs to one or more PWs. In such cases, there
will also be a need to perform the inverse function on PWE3-PDUs
received by a PE from the PSN. This is the function of the
forwarder.
]
The DetNet specific new functionality in a DA-*-PE PW processing is
the packet replication and duplication elimination function (PREF).
This functional is a part of the "extended" forwarder. The PREF
processing is triggered by the LFIB actions i.e., not all PWs receive
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DetNet specific processing. Basically the LFIB has to be extended
with a "PREF enabled" boolean configuration switch that is associated
with the normal label actions (e.g., 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
packet (i.e., 1:M replication). The replicated packets MUST share
the same DetNet PW control word sequence number and flow identity
word flow-id.
The complex part of the DetNet PREF processing is tracking the
history of received packets for multiple PWs. These PWs do not have
the same PW label value while they still share the same PW sequence
number counter and the history information. That is where the DetNet
encapsulation header flow-ID plays an important role and binds the
control word sequence number to the flow specific shared counter and
history information within the PREF function.
The DetNet flow word contains a D flag bit (see Section 5.2), which
makes the DA-*-PE node aware of the direction the flow-ID arrived
from. If the node, based on the local policy, checks for the D bit
setting that effectively means the sequence number history has to
contain also the D bit information.
[Editor's note: draw here an example of LFIB with the elimination
action.]
6.2. DA-T-PE processing clarifications
The PW-based DetNet data plane solution overloads the T-PE with a
DetNet Edge Node function. Such T-PE is referred as DA-T-PE and
implies the T-PE is also aware of DetNet flows and may need to
operate upon those. Figure 8 illustrates the overall DA-T-PE device
functions. The figure shows both physical attachment circuit (AC)
(e.g., Ethernet [RFC4448]) connecting to the PE, and a packet service
connecting to the PE via an embedded label switching router (LSR)
function [RFC6658]. Whether traffic flow from from a client AC and
PSN LSP receives DetNet specific treatment is up to a local
configuration and policy. A DA-T-PE can also serve as a normal T-PE.
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+---------------------------------------+
| DA-T-PE Device |
+---------------------------------------+ Egress/
| | Forwarder | | Ingress
| LSR | | Single | PW Instance
Client PSN | ("Packet o <-X-----> o PW Instance o<---------->
LSPs | NSP") | | Repl. | |
<---------->o | | Elim. +-------------+ Duplicate
| | : | | Egress
| | . | Single | PW Instance
| | +-> o PW Instance o<---------->
| | | | |
+-------------+ | +-------------+ Egress/
| | | | | Ingress
Client AC | NSP | Repl. | | Single | PW Instance
<---------->o o <-----X-> o PW Instance o<---------->
| | Elim. | |
+-------------+ +-------------+ Egress/
| | | | Ingress
Client AC | NSP | | Single | PW Instance
<---------->o o <-------> o PW Instance o<---------->
| | | |
+---------------------------------------+
Figure 8: DetNet Edge Node as a DA-T-PE
A DA-T-PE 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 PW encapsulation and logic entirely, and thus is able to
operate over unmodified PW implementation and deployment. The NSP
approach works only between DA-T-PEs and cannot make use of DA-S-PEs
(see Section 6.3).
The DetNet-aware extended forwarder selects the egress segment PW
based on the rules described in [RFC4448] and [RFC6658]. In both
"normal AC" and "Packet AC" cases there is no DetNet encapsulation
header available yet as it is the case with DA-S-PEs (see
Section 6.3). It is the responsibility of the extended forwarder
within the DA-T-PE to push the DetNet encapsulation header (i.e., the
DetNet CW and the DetNet flow-ID) to the packet before forwarding it
to the appropriate egress PW instance(s). The extended forwarder MAY
copy the sequencing information from the native packet into the
DetNet CW and vice versa. If there is no existing sequencing
information available in the native packet or the forwarder chose not
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to copy it from the native packet, then the extended forwarder MUST
maintain a sequence number counter for each DetNet flow (indexed by
the flow-ID).
6.3. DA-S-PE processing clarifications
The PW-based DetNet data plane solution overloads a S-PE with a
DetNet Relay function. Such S-PE device is referred as DA-S-PE and
implies the S-PE is also aware of DetNet flows and may operate upon
those. Figure 9 illustrates the overall DA-S-PE device functions.
A DA-S-PE participates to the packet replication and duplication
elimination. This processing is done within an extended forwarder
function. Whether an ingress PW receives DetNet specific processing
depends on how the LFIB is programmed. For some PWs the DA-S-PE can
act as a normal S-PE and for some apply the DetNet specific
processing. It is also possible to treat the DA-S-PE as a P router
using the L-label tunnels. Again, this is entirely up to how the
LFIB has been programmed.
The DetNet-aware forwarder selects the egress segment PW based on the
PW label. The mapping of ingress PW label to egress PW label may be
statically or dynamically configured. Additionally the DetNet-aware
forwarder does duplicate frame elimination based on the DetNet flow-
ID and DetNet Control Word sequence number combination. The packet
replication is also done within the DetNet-aware forwarder. During
elimination and the replication process both DetNet CW sequence
number and DetNet flow-ID MUST be preserved and copied to the egress
PW.
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+---------------------------------------+
| DA-S-PE Device |
+---------------------------------------+
Ingress | | Forwarder | | Egress
PW instance | Single | | Single | PW Instance
----------->o PW Instance o --X-----> o PW Instance o----------->
| | | Elim. | |
+-------------+ | +-------------+ Duplicate
Ingress | | | | | Egress
PW instance | Single | | | Single | PW Instance
----------->o PW Instance o --+ +-> o PW Instance o----------->
| | | | |
+-------------+ | +-------------+
Ingress | | | | | Egress
PW instance | Single | Repl. | | Single | PW Instance
----------->o PW Instance o ------X-> o PW Instance o----------->
| | | |
+-------------+ +-------------+
Ingress | | | | Egress
PW instance | Single | | Single | PW Instance
----------->o PW Instance o --------> o PW Instance o----------->
| | | |
+---------------------------------------+
Figure 9: DetNet Relay Node as a DA-S-PE
7. Other DetNet considerations
7.1. Class of Service
[Editor's note: Discuss the CoS.. and how that is archived when using
MPLS or IP PSN.]
7.2. Quality of Service
[Editor's note: Elaborate the QoS issues here..]
7.3. Time synchronization
[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 a clock
synchronization method is used, such as the Precision Time Protocol
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(PTP) [IEEE1588]. In this case, there are a few possible approaches
of how synchronization protocol packets are forwarded and handled by
the network:
o PTP packets are sent as a normal DetNet flow: 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.
o PTP with on-path support: in this approach PTP packets are sent 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.
o 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 three 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.
7.4. Bidirectional traffic
Some DetNet applications generate bidirectional traffic and may
require symmetric flows. There are already mechanisms that can be
used to create bidirectional tunnels at the transport network level,
such as MPLS-TP. The data plane solution SHOULD allow establishing
bidirectional symmetric flows. Control plane mechanisms would need
to also support this, though this is out of scope of this document.
[Summary of existing mechanisms to create bidirectional tunnels that
can be used.]
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8. Control plane considerations
[Editor's note: discuss here what kind of enhancements are needed for
DetNet and specifically for PREF.]
8.1. PW Label assignment and distribution
The PW label distribution follows the same mechanisms specified for
MS-PW [RFC6073].
9. Security considerations
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.
10. IANA Considerations
TBD.
11. Acknowledgements
The author(s) ACK and NACK.
The following people were part of the DetNet Data Plane Solution
Design Team:
Jouni Korhonen
Janos Farkas
Norman Finn
Balazs Varga
Loa Andersson
Tal Mizrahi
David Mozes
Yuanlong Jiang
Carlos J. Bernardos
The DetNet chairs serving during the DetNet Data Plane Solution
Design Team:
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Lou Berger
Pat Thaler
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
<http://www.rfc-editor.org/info/rfc3985>.
[RFC4448] Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, DOI 10.17487/RFC4448, April 2006,
<http://www.rfc-editor.org/info/rfc4448>.
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
Aissaoui, "Segmented Pseudowire", RFC 6073,
DOI 10.17487/RFC6073, January 2011,
<http://www.rfc-editor.org/info/rfc6073>.
[RFC6658] Bryant, S., Ed., Martini, L., Swallow, G., and A. Malis,
"Packet Pseudowire Encapsulation over an MPLS PSN",
RFC 6658, DOI 10.17487/RFC6658, July 2012,
<http://www.rfc-editor.org/info/rfc6658>.
12.2. Informative References
[I-D.ietf-detnet-architecture]
Finn, N. and P. Thubert, "Deterministic Networking
Architecture", draft-ietf-detnet-architecture-00 (work in
progress), September 2016.
[I-D.ietf-detnet-dp-alt]
Korhonen, J., Farkas, J., Mirsky, G., Thubert, P.,
Zhuangyan, Z., and L. Berger, "DetNet Data Plane Protocol
and Solution Alternatives", draft-ietf-detnet-dp-alt-00
(work in progress), October 2016.
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[I-D.sdt-detnet-security]
Mizrahi, T., Grossman, E., Hacker, A., Das, S.,
"Deterministic Networking (DetNet) Security
Considerations, draft-sdt-detnet-security, work in
progress", 2017.
[IEEE1588]
IEEE, "IEEE 1588 Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems Version 2", 2008.
[IEEE8021CB]
Finn, N., "Draft Standard for Local and metropolitan area
networks - Seamless Redundancy", IEEE P802.1CB
/D2.1 P802.1CB, December 2015,
<http://www.ieee802.org/1/files/private/cb-drafts/
d2/802-1CB-d2-1.pdf>.
Appendix A. Example of DetNet data plane operation
[Editor's note: 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..]
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T1 ->R1----->DA-S-PE1---->R2---->DA-S-PE2--->R3
L1 / L1 T2 L2 T3 \ L2
PW1 / PW1 L2 PW1 L2 \ PW1
#seq / #seq PW1 #seq PW1 \ #seq
FID1 / FID1 #seq FID1 #seq \ FID1
/ FID1 v
E1-->DA-T-PE1 DA-T-PE2-->E3
\ T5 T6 ^
T4 \ L2 L3 L4 L5 /
L2 \ PW1 PW2 PW1 PW2 /
PW1 \ #seq #seq #seq #seq /
#seq \ FID1 FID2 FID1 FID2 /
FID1 =>R4------------->DA-S-PE2--------------->R5
T11 / ^ \ L5
L3 / \ L9 \ PW2
PW2 / \ PW2 \ #seq
#seq / \ #seq \ FID2
FID2 / \ FID2 v
E2-->DA-T-PE3 R9<- T10 DA-T-PE4-->E4
\ T8 \ L9 T9 ^
T7 \ L6 L7 L7 \ PW2 L8 / L8
L6 \ PW2 PW2 PW2 \ #seq PW2 / PW2
PW2 \ #seq #seq #seq \FID2 #seq / #seq
#seq \ FID2 FID2 FID2 \ FID2 / FID2
FID2 ->R6---->DA-S-PE2---->R7---->DA-S-PE6---->R8
Figure 10: Replication and elimination example
[Editor's note: the LFIB Figure 11 content to be updated.]
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+========+================+=====================================+
| | | PREF | Forwarding Semantics |
| Device | In-Label |--------------|----------------------|
| | | flow-ID | D | Out-Label | Out-Link |
+========+================+==========+===+===========+==========+
| T-PE1 | N/A (from AC) | | | | |
| | | | | | |
+========+================+==========+===+===========+==========+
| T-PE2 | | | | | |
| | | | | | |
+========+================+==========+===+===========+==========+
| T-PE3 | N/A (from AC) | | | | |
| | | | | | |
+========+================+==========+===+===========+==========+
| T-PE4 | | | | | |
| | | | | | |
+========+================+==========+===+===========+==========+
| S-PE1 | | | | | |
+========+================+==========+===+===========+==========+
| S-PE2 | | | | | |
+========+================+==========+===+===========+==========+
| S-PE3 | | | | | |
+========+================+==========+===+===========+==========+
| S-PE4 | | | | | |
+========+================+==========+===+===========+==========+
| S-PE5 | | | | | |
+========+================+==========+===+===========+==========+
| S-PE6 | | | | | |
+========+================+==========+===+===========+==========+
| R1 | | N/A | | | |
+========+================+==========+===+===========+==========+
| R2 | | N/A | | | |
+========+================+==========+===+===========+==========+
Figure 11: LFIB contents
Appendix B. Example of pinned paths using IP PSN
Authors' Addresses
Jouni Korhonen (editor)
Broadcom
3151 Zanker Road
San Jose, CA 95134
USA
Email: jouni.nospam@gmail.com
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Loa Andersson
Huawei
Email: loa@pi.nu
Yuanlong Jiang
Huawei
Email: jiangyuanlong@huawei.com
Balazs Varga
Ericsson
Konyves Kalman krt. 11/B
Budapest 1097
Hungary
Email: balazs.a.varga@ericsson.com
Janos Farkas
Ericsson
Konyves Kalman krt. 11/B
Budapest 1097
Hungary
Email: janos.farkas@ericsson.com
Carlos J. Bernardos
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain
Phone: +34 91624 6236
Email: cjbc@it.uc3m.es
URI: http://www.it.uc3m.es/cjbc/
Tal Mizrahi
Marvell
6 Hamada st.
Yokneam
Israel
Email: talmi@marvell.com
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