DetNet B. Varga, Ed.
Internet-Draft J. Farkas
Intended status: Informational Ericsson
Expires: November 6, 2019 L. Berger
D. Fedyk
LabN Consulting, L.L.C.
A. Malis
S. Bryant
Huawei Technologies
J. Korhonen
May 5, 2019
DetNet Data Plane Framework
draft-ietf-detnet-data-plane-framework-00
Abstract
This document provides an overall framework for the Deterministic
Networking data plane. It covers concepts and considerations that
are generally common to any Deterministic Networking data plane
specification.
Status of This Memo
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This Internet-Draft will expire on November 6, 2019.
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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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Terms Used in This Document . . . . . . . . . . . . . . . 4
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
3. DetNet Data Plane Overview . . . . . . . . . . . . . . . . . 5
3.1. Data Plane Characteristics . . . . . . . . . . . . . . . 6
3.2. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 7
3.4. DetNet IP Data Plane . . . . . . . . . . . . . . . . . . 8
3.5. DetNet MPLS Data Plane . . . . . . . . . . . . . . . . . 8
3.6. Further DetNet Data Plane Considerations . . . . . . . . 9
3.6.1. Service Protection . . . . . . . . . . . . . . . . . 11
3.6.2. Aggregation Considerations . . . . . . . . . . . . . 13
3.6.3. End-System Specific Considerations . . . . . . . . . 14
3.6.4. Sub-Network Considerations . . . . . . . . . . . . . 14
4. Controller Plane (Management and Control)
Considerations . . . . . . . . . . . . . . . . . . . . . . . 15
4.1. DetNet Controller Plane Requirements . . . . . . . . . . 15
4.2. Generic Controller Plane Considerations . . . . . . . . . 16
4.2.1. Flow Aggregation Control . . . . . . . . . . . . . . 17
4.2.2. Explicit Routes . . . . . . . . . . . . . . . . . . . 18
4.2.3. Contention Loss and Jitter Reduction . . . . . . . . 19
4.2.4. Bidirectional Traffic . . . . . . . . . . . . . . . . 19
4.3. IP-Specific Controller Plane Considerations . . . . . . . 20
4.3.1. Flow Identification and Aggregation . . . . . . . . . 20
4.4. MPLS-Specific Controller Plane Considerations . . . . . . 20
4.4.1. S-Label and F-Label Assignment and Distribution . . . 20
4.5. Packet Replication, Elimination, and Ordering (PREOF) . . 22
4.6. Contention Loss and Jitter Reduction . . . . . . . . . . 22
5. Security Considerations . . . . . . . . . . . . . . . . . . . 22
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 23
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.1. Normative References . . . . . . . . . . . . . . . . . . 25
9.2. Informative References . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction
Deterministic Networking (DetNet) provides a capability to carry
specified unicast or multicast data flows for real-time applications
with extremely low packet loss rates and assured maximum end-to-end
delivery latency. A description of the general background and
concepts of DetNet can be found in [I-D.ietf-detnet-architecture].
This document describes the concepts needed by any DetNet data plane
specification and provides considerations for any corresponding
implementation. It covers the building blocks that provide the
DetNet service, the forwarding sub-layer functions, and the flow
identification as described in the DetNet Architecture.
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
is used to provide congestion protection (low loss, assured latency,
and limited reordering) and leverages Traffic Engineering mechanisms.
As part of the service sub-layer functions, this document describes
typical DetNet node data plane operation. It describes the function
and operation of the Packet Replication (PRF) Packet Elimination
(PEF) and the Packet Ordering (POF) functions within the service sub-
layer. It also describes the forwarding sub-layer that is used to
eliminate (or reduce) contention loss and provide bounded latency for
DetNet flows.
DetNet flows may be carried over network technologies that can
provide the DetNet required level of service. 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.
Different traffic types, or application flows, can be mapped on top
of DetNet. DetNet can optionally reuse header information provided
by, or shared with, applications. An example of shared header fields
can be found in [I-D.ietf-detnet-ip].
This document also covers concepts related to the controller plane
and Operations, Administration, and Maintenance (OAM) functions.
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2. Terminology
2.1. Terms Used in This Document
This document uses the terminology established in the DetNet
architecture [I-D.ietf-detnet-architecture], and the reader is
assumed to be familiar with that document and its terminology.
2.2. Abbreviations
The following abbreviations are used in this document:
CW Control Word.
DetNet Deterministic Networking.
L2 Layer 2.
L2VPN Layer 2 Virtual Private Network.
LSR Label Switching Router.
MPLS Multiprotocol Label Switching.
MPLS-TE Multiprotocol Label Switching - Traffic Engineering.
OAM Operations, Administration, and Maintenance.
PEF Packet Elimination Function.
PRF Packet Replication Function.
PREOF Packet Replication, Elimination and Ordering Functions.
POF Packet Ordering Function.
PSN Packet Switched Network.
PW PseudoWire.
QoS Quality of Service.
TSN Time-Sensitive Network.
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3. DetNet Data Plane Overview
This document describes how application flows, or app-flows, are
carried over DetNet networks. The DetNet Architecture,
[I-D.ietf-detnet-architecture], models the DetNet related data plane
functions decomposed into two sub-layers: a service sub-layer and a
forwarding sub-layer.
Figure 1 reproduced from the [I-D.ietf-detnet-architecture],shows a
logical DetNet service with the two sub-layers.
| packets going | ^ packets coming ^
v down the stack v | up the stack |
+-----------------------+ +-----------------------+
| Source | | Destination |
+-----------------------+ +-----------------------+
| Service sub-layer: | | Service sub-layer: |
| Packet sequencing | | Duplicate elimination |
| Flow replication | | Flow merging |
| Packet encoding | | Packet decoding |
+-----------------------+ +-----------------------+
| Forwarding sub-layer: | | Forwarding sub-layer: |
| Resource allocation | | Resource allocation |
| Explicit routes | | Explicit routes |
+-----------------------+ +-----------------------+
| Lower layers | | Lower layers |
+-----------------------+ +-----------------------+
v ^
\_________________________/
Figure 1: DetNet data plane protocol stack
The DetNet forwarding sub-layer may be directly provided by the
DetNet service sub-layer, for example by IP or MPLS. Alternatively
an overlay approach may be used in which the packet is natively
carried between key nodes within the DetNet network (say between
PREOF nodes) and a sub-layer is used to provide the information
needed to reach the next hop in the overlay.
This forwarding sub-layer provides the quality underpin needed by the
DetNet Service sub-layer. 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 service sub-layer provides additional support beyond the
connectivity function of the forwarding sub-layer. An example of
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this is Packet Replication, Elimination, and Ordering (PREOF)
function see Section 4.5.
The method of instantiating each of the layers is specific to the
particular DetNet data plane method. There may be more than approach
that is applicable to a given bearer network type.
3.1. Data Plane Characteristics
There are two major characteristics to the data plane:
1. How the data plane is constructed: The DetNet service sub-layer
provides its functions for the DetNet application flows by using
or applying existing standardized headers and/or encapsulations.
The Detnet forwarding sub-layer may provide capabilities
leveraging that same header or encapsulation technology e.g.
Figure 2 or it may be achieved by other standardized technologies
e.g. Figure 3.
2. Extensibility of that Data Plane: Whether or not the DetNet data
plane includes the facility to carry additional information
(metadata) that can be used to provide an enhanced service to the
DetNet packet.
DetNet +-------+ +---------+
Services | DN IP | | DN MPLS |
+-------+ +---------+
Figure 2: DetNet Services
+-----+
| TSN |
+-------+ +-+-----+-+
DetNet | DN IP | | DN MPLS |
Service +--+--+----+----+ +-+---+-----+-+
Examples | TSN | DN MPLS | | TSN | DN IP |
+-----+---------+ +-----+-------+
Figure 3: DetNet Service Encapsulations
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3.2. Encapsulation
The encapsulation of the DetNet flows allows them to be sent over a
data plane of a type other than their native type. Encapsulation is
essential if, for example, it is required to send Ethernet TSN stream
as a DetNet Application over a data plane such as MPLS. Figure 3
illustrates some encapsulation combinations.
The use of encapsulation is also required if additional information
(meta-data) is needed by the DetNet data plane and their is either no
ability to include it in the client data packet, or the specification
of the client data plane does not permit the modification of the
packet to include additional data. An example of such meta-data is
the inclusion of a sequence number required by the PREOF function.
Encapsulation is also needed if the DetNet flow or aggregate flow is
not easily recognised from its encapsulation.
3.3. Metadata
Metadata can be a useful way of identifying packets that need to be
treated as a flow or flow aggregate. It is also useful as a way of
including a sequence number the packet for use by the PREOF function
or as a place to carry OAM indications or OAM information to
instrument DetNet data plane operation.
Explicit inclusion of metadata is possible through the use of IP
options or IP extension headers. New IP options are almost
impossible to get standardized or to deploy in an operational network
and will not be discussed further in this text. IPv6 extensions
headers are finding popularity in current IPv6 development work,
particularly in connection with Segment Routing of IPv6 (SRv6) and IP
OAM. The design of a new IPv6 extension header or the modification
of an existing one is a technique available in the tool box of the
DetNet IP data plane designer.
Explicit inclusion of metadata in an IP packet is also possible
through the inclusion of an MPLS label stack and the MPLS DetNet
Control Word using one of the methods for carrying MPLS over IP
[I-D.mpls-over-udp-ip]. This is described in more detail in
Section 3.6.4.
Implicit metadata can be included through the use of the network
programming paradigm [I-D.spring-srv6-network-programming] in which
the suffix of an IPv6 address is used to encode additional
information for use by the network of the receiving host. Examples
of such information include the sequence number for use by the PREOF
function, or even all the essential information being included into
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the DetNet over MPLS label stack (the DetNet Control Word and the
DetNet Service label).
3.4. DetNet IP Data Plane
An IP data plane may operate natively or through the use of an
encapsulation. There are many IP encapsulations that may be
interposed between the DetNet data plane IP header and the DetNet
payload, and it is anticipated that more than one encapsulation may
be deployed.
One method of operating an IP DetNet data plane without encapsulation
is to use "6-tuple" based flow identification, where "6-tuple" refers
to information carried in IP and higher layer protocol headers.
General background on the use of IP headers, and "5-tuples", to
identify flows and support Quality of Service (QoS) can be found in
[RFC3670]. [RFC7657] also provides useful background on the delivery
differentiated services (DiffServ) and "tuple" based flow
identification. DetNet flow aggregation may be enabled via the use
of wildcards, masks, prefixes and ranges. The operation of this
method is described in detail in [I-D.ietf-detnet-ip].
The DetNet forwarding plane may use explicit route capabilities and
traffic engineering capabilities to provide a forwarding sub-layer
that is responsible for providing resource allocation and explicit
routes. It is possible to include metadata in a native IP packet
explicitly, or implicitly.
3.5. DetNet MPLS Data Plane
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.
MPLS also provides the ability to identify a service instance that is
used to process the packet through the use of a label that maps the
packet to a service instance.
In cases where metadata is needed to process an MPLS encapsulated
packet at the service sub-layer, this has been been provided through
the use of a shim layer also called a control word (CW) [RFC4385].
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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3.6. Further DetNet Data Plane Considerations
This section needs further work.
This section provides informative considerations related to providing
DetNet service to flows which are identified based on their header
information. At a high level, the following are provided on a per
flow basis:
Reservation and Allocation of resources:
Reservation of resources can allocate resources to specific DetNet
flows. This can eliminate packet contention and loss for DetNet
traffic. This also can reduce jitter for the DetNet traffic.
DetNet flows are assumed to behave with respect to the reserved
traffic profile. If other traffic shares the link resources, the
use of (queuing, policing, shaping) policies can be used to ensure
that the allocation of resources reserved for DetNet is met.
Queuing and shaping of DetNet traffic could be required to ensure
that DetNet traffic does not exceed its reserved profile but this
would impact the DetNet service characteristics.
Explicit routes:
Use of a specific path for a flow. This allows control of the
network delay by steering the packet with the ability to influence
the physical path. Explicit routes complement reservation by
ensuring that a consistent path can be associated with its
resources for the duration of that path. Coupled with the traffic
mechanism, this limits misordering and bounds latency. Explicit
route computation can encompass a wide set of constraints and
optimize the path for a certain characteristic e.g. highest
bandwidth or lowest jitter. In these cases the "best" path for
any set of characteristics may not be a shortest path. The
selection of path can take into account multiple network metrics.
Some of these metrics are measured and distributed by the routing
system as traffic engineering metrics.
Service protection:
Use of multiple packet streams using multiple paths, for example
1+1 or 1:1 linear protection. For DetNet this primarily relates
to packet replication and elimination capabilities. Changing the
explicit path after a failure is detected to an already
established path in order to restore delivery of the required
DetNet service characteristics is another protection mechanism for
example MPLS hitless protection. Path changes, even in the case
of failure recovery, can lead to the out of order delivery of data
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requiring packet ordering functions either within the DetNet
service or at a high layer in the application traffic.
Establishment of new paths after a failure is out of scope for
DetNet services.
Network Coding:
Network Coding, not to be confused with network programming,
comprises several techniques where multiple data flows are
encoded. These resulting flows can then be sent on different
paths. The encoding operation can combine flows and error
recovery information. When the encoded flows are decoded and
recombined the original flows can be recovered. Note that Network
coding uses an alternative to packet by packet PREOF. Therefore,
for certain network topologies and traffic loads, Network Coding
can be used to improve a network's throughput, efficiency,
latency, and scalability, as well as resilience to partition,
attacks, and eavesdropping, as compared to traditional methods.
DetNet could utilized Network coding as an alternative to other
protection means. Network coding is often applied in wireless
networks and is being explored for other network types.
Load sharing:
Use of packet by packet distribution of the same DetNet flow over
multiple paths is not recommended except for the cases listed
above where PREOF is utilized to improve protection of traffic and
maintain order. Packet by packet load sharing, e.g., via ECMP or
UCMP, impacts ordering and possibly jitter.
Troubleshooting:
Since Detnet leverages many different forwarding sub-layers, those
technologies also support a number of tools to troubleshoot
connectivity for example, to support identification of misbehaving
flows. At the service layer again there are existing mechanisms
to troubleshoot or monitor flows. Many of these mechanisms exist
for IP and MPLS networks. A client of a DetNet service can
introduce any monitoring applications which can detect and monitor
delay and loss.
Recognize flow(s) for analytics:
To a large degree this follows the logic in the previous section.
Analytics can be inherited from the two sub-layers. At the DetNet
service edge packet and bit counters e.g. sent, received, dropped,
and out of sequence are maintained.
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Correlate events with flows:
The provider of a DetNet service may allow other capabilities to
monitor flows such as more detail loss statistics and time
stamping of events. The details of these capabilities are
currently out of scope for this document.
Several of these capabilities are expanded upon in more detail below.
3.6.1. Service Protection
Service protection allow DetNet services to increase reliability and
maintain a DetNet Service Assurance in the case of network congestion
or some failures. Detnet relies on the underlying technology
capabilities for various protection schemes. Protection schemes
enable partial or complete coverage of the network paths and active
protection with combinations of PRF, PRE, and POF.
3.6.1.1. Linear Service Protection
An example DetNet MPLS network fragment and packet flow is
illustrated in Figure 4.
1 1.1 1.1 1.2.1 1.2.1 1.2.2
CE1----EN1--------R1-------R2-------R3--------EN2-----CE2
\ 1.2.1 / /
\1.2 /-----+ /
+------R4------------------------+
1.2.2
Figure 4: Example Packet Flow in DetNet protected Network
In Figure 4 the numbers are used to identify the instance of a
packet. Packet 1 is the original packet, and packets 1.1, and 1.2
are two first generation copies of packet 1. Packet 1.2.1 is a
second generation copy of packet 1.2 etc. Note that these numbers
never appear in the packet, and are not to be confused with sequence
numbers, labels or any other identifier that appears in the packet.
They simply indicate the generation number of the original packet so
that its passage through the network fragment can be identified to
the reader.
Customer Equipment CE1 sends a packet into the DetNet enabled
network. This is packet (1). Edge Node EN1 encapsulates the packet
as a DetNet Packet and sends it to Relay node R1 (packet 1.1). EN1
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makes a copy of the packet (1.2), encapsulates it and sends this copy
to Relay node R4.
Note that along the path from EN1 to R1 there may be zero or more
nodes which, for clarity, are not shown. The same is true for any
other path between two DetNet entities shown in Figure 4 .
Relay node R4 has been configured to send one copy of the packet to
Relay Node R2 (packet 1.2.1) and one copy to Edge Node EN2 (packet
1.2.2).
R2 receives packet copy 1.2.1 before packet copy 1.1 arrives, and,
having been configured to perform packet elimination on this DetNet
flow, forwards packet 1.2.1 to Relay Node R3. Packet copy 1.1 is of
no further use and so is discarded by R2.
Edge Node EN2 receives packet copy 1.2.2 from R4 before it receives
packet copy 1.2.1 from R2 via relay Node R3. EN2 therefore strips
any DetNet encapsulation from packet copy 1.2.2 and forwards the
packet to CE2. When EN2 receives the later packet copy 1.2.1 this is
discarded.
The above is of course illustrative of many network scenarios that
can be configured. Between a pair of relay nodes there may be one or
more transit nodes that simply forward the DetNet traffic, but these
are omitted for clarity.
This example also illustrates 1:1 protection scheme meaning there is
traffic and path for each segment of the end to end path. Local
DetNet relay nodes determine which packets are eliminated and which
packets are forwarded. A 1+1 scheme where only one path is used for
traffic at a time, could use the same topology. In this case there
is no PRF function and traffic is switched upon detection of failure.
An OAM scheme that monitors the paths detects the loss of path or
traffic is required to initiate the switch. A POF may still be used
in this case to prevent misordering of packets. In both cases the
protection paths are established and maintained for the duration of
the DetNet service.
3.6.1.2. Ring Service Protection
Ring protection may also be supported if the underlying technology
supports it. Many of the same concepts apply however Rings are
normally 1+1 protection for data efficiency reasons. [RFC8227] is an
example of MPLS-TP data plane that supports Ring protection.
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3.6.2. Aggregation Considerations
The DetNet data plane also allows for the aggregation of DetNet
flows, to improved scaling by reducing the state per hop. How this
is done is data plane or control plane dependent. When DetNet flows
are aggregated, transit nodes provide service to the aggregate and
not on a per-DetNet flow basis. When aggregating DetNet flows the
flows should be compatible i.e. the same or very similar QoS and CoS
characteristics. In this case, nodes performing aggregation will
ensure that per-flow service requirements are achieved.
If bandwidth reservations are used, the sum of the reservations
should be the sum of all the individual reservations, in other words,
the reservations should not create an over subscription of bandwidth
reservation. If maximum delay bounds are used the system should
ensure that the aggregate does not exceed the delay bounds of the
component flows.
DetNet encapsulation is a data plane mechanism that can be used to
aggregate traffic. Encapsulation can either be in the same service
type or in a different service type see Figure 3 for examples. When
an encapsulation is used the choice of reserving a maximum resource
level and then tracking the services in the aggregated service or
adjusting the aggregated resources as the services are added is
implementation and technology specific.
DetNet flows at edges must be able to handle rejection to an
aggregation group due to lack of resources as well as conditions
where general requirements are not satisfied.
3.6.2.1. IP Aggregation
IP aggregation has both data plane and controller plane aspects. For
the data plane flows may be aggregated for treatment based on shared
characteristics such as 5-tuple. Alternatively, an IP encapsulation
may be used to tunnel an aggregate number of DetNet Flows between
relay nodes.
3.6.2.2. MPLS Aggregation
MPLS aggregation similarly has data plane and controller plane
aspects. In the case of MPLS flows are often tunneled in a
forwarding sub-layer and reservation is associated with that MPLS
tunnel.
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3.6.3. End-System Specific Considerations
Data-flows requiring DetNet service are generated and terminated on
end-systems. Encapsulation depends on application and its
preferences. For example, a DetNet MPLS domain the DN functions use
the d-CWs, S-Labels and F-Labels to provide DetNet services.
However, an application may exchange further flow related parameters
(e.g., time-stamp), which are not provided by DN functions.
As a general rule, DetNet domains are capable of forwarding any
DetNet flows and the DetNet domain does not mandate the end-system or
edge system encapsulation format. Unless there is a proxy of some
form present, end-systems peer with similar end-systems using the
same application encapsulation format. For example, as shown in
Figure 5, IP applications peer with IP applications and Ethernet
L2VPN applications peer with Ethernet L2VPN applications.
+-----+
| X | +-----+
+-----+ | X |
| Eth | ________ +-----+
+-----+ _____ / \ | Eth |
\ / \__/ \___ +-----+
\ / \ /
0======== tunnel-1 ========0_
| \
\ |
0========= tunnel-2 =========0
/ \ __/ \
+-----+ \__ DetNet MPLS domain / \
| X | \ __ / +-----+
+-----+ \_______/ \_____/ | X |
| IP | +-----+
+-----+ | IP |
+-----+
Figure 5: End-Systems and The DetNet MPLS Domain
3.6.4. Sub-Network Considerations
Any of the DetNet service types may be transported by another DetNet
service. MPLS nodes may interconnected by different sub-network
technologies, which may include point-to-point links. Each of these
sub-network technologies need to provide appropriate service to
DetNet flows. In some cases, e.g., on dedicated point-to-point links
or TDM technologies, all that is required is for a DetNet node to
appropriately queue its output traffic. In other cases, DetNet nodes
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will need to map DetNet flows to the flow semantics (i.e.,
identifiers) and mechanisms used by an underlying sub-network
technology. Figure 6 shows several examples of header formats that
can be used to carry DetNet MPLS flows over different sub-network
technologies. L2 represent a generic layer-2 encapsulation that
might be used on a point-to-point link. TSN represents the
encapsulation used on an IEEE 802.1 TSN network, as described in
[I-D.mpls-over-tsn]. UDP/IP represents the encapsulation used on a
DetNet IP PSN, as described in [I-D.mpls-over-udp-ip].
+------+ +------+ +------+
App-Flow | X | | X | | X |
+-----+======+--+======+--+======+-----+
DetNet-MPLS | d-CW | | d-CW | | d-CW |
+------+ +------+ +------+
|Labels| |Labels| |Labels|
+-----+======+--+======+--+======+-----+
Sub-Network | L2 | | TSN | | UDP |
+------+ +------+ +------+
| IP |
+------+
| L2 |
+------+
Figure 6: Example DetNet MPLS Sub-Network Formats
4. Controller Plane (Management and Control) Considerations
4.1. DetNet Controller Plane Requirements
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 [I-D.ietf-detnet-architecture] and data plane
as defined herein.
The primary requirements of the DetNet controller plane are that it
must be able to:
o Instantiate DetNet flows in a DetNet domain (which may include
some or all of explicit path determination, link bandwidth
reservations, restricting flows to IEEE 802.1 TSN links, node
buffer and other resource reservations, specification of required
queuing disciplines along the path, ability to manage
bidirectional flows, etc.) as needed for a flow.
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o In the case of MPLS Manage DetNet S-Label and F-Label allocation
and distribution, where the DetNet MPLS encapsulation is in use
see Section 4.4.
o The ability to support DetNet flow aggregation.
o Advertise static and dynamic node and link resources such as
capabilities and adjacencies to other network nodes (for dynamic
signaling approaches) or to network controllers (for centralized
approaches).
o Scale to handle the number of DetNet flows expected in a domain
(which may require per-flow signaling or provisioning).
o Provision flow identification information at each of the nodes
along the path. Flow identification may differ depending on the
location in the network and the DetNet functionality (e.g. transit
node vs. relay node).
These requirements, as stated earlier, could be satisfied using
distributed control protocol signaling (such as RSVP-TE), centralized
network management provisioning mechanisms (such as BGP, PCEP, YANG
[I-D.ietf-detnet-flow-information-model], etc.) or hybrid
combinations of the two, and could also make use of MPLS-based
segment routing.
In the abstract, the results of either distributed signaling or
centralized provisioning are equivalent from a DetNet data plane
perspective - flows are instantiated, explicit routes are determined,
resources are reserved, and packets are forwarded through the domain
using the DetNet data plane.
However, from a practical and implementation standpoint, they are not
equivalent at all. Some approaches are more scalable than others in
terms of signaling load on the network. Some can take advantage of
global tracking of resources in the DetNet domain for better overall
network resource optimization. Some are more resilient than others
if link, node, or management equipment failures occur. While a
detailed analysis of the control plane alternatives is out of the
scope of this document, the requirements from this document can be
used as the basis of a later analysis of the alternatives.
4.2. Generic Controller Plane Considerations
This section covers control plane considerations that are independent
of the data plane technology used for DetNet service delivery.
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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, and the DetNet architecture
[I-D.ietf-detnet-architecture] refers to these collectively as the
'Controller Plane'. This document therefore does not distinguish
between information provided by distributed control plane protocols,
e.g., RSVP-TE [RFC3209] and [RFC3473], or by centralized network
management mechanisms, e.g., RestConf [RFC8040], YANG [RFC7950], and
the Path Computation Element Communication Protocol (PCEP)
[I-D.ietf-pce-pcep-extension-for-pce-controller] or any combination
thereof. Specific considerations and requirements for the DetNet
Controller Plane are discussed in Section 4.1.
4.2.1. Flow Aggregation Control
Flow aggregation includes aggregation accomplished through the use of
hierarchical LSPs in MPLS and tunnels, in the case of IP, MPLS and
TSN, both of which aggregate multiple DetNet flows into a single new
DetNet flow. It can also be grouping of IP flows that share 5-tuple
of 6-tuple attributes or flow identifiers at the DetNet sub-layer.
Control of aggregation involves a set of procedures not necessarily
in a strict order:
o Traffic engineering resource collection and distribution:
Available resources are tracked through control plane or
management plane databases and distributed amongst controllers
or nodes that can manage resources.
o Path computation and resource allocation:
When DetNet services are provisioned or requested one or more
paths meeting the requirements are selected and the resources
verified and recorded.
o Resource assignment and data plane co-ordination:
The assignment of resources along the path depends on the
technology and it includes assignment of specific links and
coordination of the queuing and other traffic management
capabilities.
o Assigned Resource recording and updating:
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Depending on the specific technology the assigned resources are
updated and distributed in the databases preventing over
subscription.
4.2.2. Explicit Routes
Explicit routes are used to ensure that packets are routed through
the resources that have been reserved for them, and hence provide the
DetNet application with the required service. A requirement for the
DetNet Controller Plane will be the ability to assign a particular
identified DetNet IP flow to a path through the DetNet domain that
has been assigned the required nodal resources. This provides the
appropriate traffic treatment for the flow and also includes
particular links as a part of the path that are able to support the
DetNet flow. For example, by using IEEE 802.1 TSN links (as
discussed in [I-D.mpls-over-tsn] ) DetNet parameters can be
maintained. Further considerations and requirements for the DetNet
Controller Plane are discussed in Section 4.1.
Whether configuring, calculating and instantiating these routes is a
single-stage or multi-stage process, or in a centralized or
distributed manner, is out of scope of this document.
There are several of approaches that could be used to provide
explicit routes and resource allocation in the DetNet forwarding sub-
layer. For example:
o The path could be explicitly set up by a controller which
calculates the path and explicitly configures each node along that
path with the appropriate forwarding and resource allocation
information.
o The path could use a distributed control plane such as RSVP
[RFC2205] or RSVP-TE [RFC3473] extended to support DetNet IP
flows.
o The path could be implemented using IPv6-based segment routing
when extended to support resource allocation.
See Section 4.1 for further discussion of these alternatives. In
addition, [RFC2386] contains useful background information on QoS-
based routing, and [RFC5575] discusses a specific mechanism used by
BGP for traffic flow specification and policy-based routing.
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4.2.3. Contention Loss and Jitter Reduction
As discussed in Section 1, 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 Section 4.1
for further discussion of these requirements.
4.2.4. Bidirectional Traffic
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.
While the DetNet IP data plane must support bidirectional DetNet
flows, there are no special bidirectional features with respect to
the data plane other than the need for the two directions of a co-
routed bidirectional flow to take the same path. That is to say that
bidirectional DetNet flows are solely represented at the management
and control plane levels, without specific support or knowledge
within the DetNet data plane. Fate sharing and associated or co-
routed bidirectional flows, can be managed at the control level.
DetNet's use of PREOF may increase the complexity of using co-routing
bidirectional flows, since if PREOF is used, then the replication
points in one direction would have to match the elimination points in
the other direction, and vice versa, and the optimal points for these
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functions in one direction may not match the optimal points in the
other subsequent to the network and traffic constraints.
Control and management mechanisms need to support bidirectional
flows, but the specification of such mechanisms are out of scope of
this document. An example control plane solution for MPLS can be
found in . Related control plan mechanisms have been defined in
[RFC3473] , [RFC6387] and [RFC7551].
This is further discussed in Section 4.1.
4.3. IP-Specific Controller Plane Considerations
This section covers IP data plane specific control plane
considerations.
4.3.1. Flow Identification and Aggregation
Section 3 discussed the use of the IP "6-tuple" for flow
identification, and goes on to discuss how identified flows use
specific QoS mechanisms for flow-specific traffic treatment,
including path control and resource allocation. [I-D.ietf-detnet-ip]
contains detailed DetNet IP flow identification procedures. Flow
identification will play an important role for the DetNet controller
plane.
Section 3.6.2 and Section 3.6.2.1 discuss the use of flow aggregation
in DetNet. Flow aggregation can be accomplished using any of the
6-tuple fields defined in [I-D.ietf-detnet-ip] , using a DSCP
identified traffic class or other field. It will be the
responsibility of the DetNet controller plane to be able to properly
provision the use of these aggregation mechanisms. These
requirements are included in Section 4.1.
4.4. MPLS-Specific Controller Plane Considerations
This section covers MPLS data plane specific control plane
considerations. This section needs generalizing.
4.4.1. S-Label and F-Label Assignment and Distribution
[Editor's note - we may need additional text on resource allocation
in this section.]
DetNet S-Labels [I-D.ietf-detnet-mpls] for their definition) are
similar to other MPLS service labels that denote the contents of the
MPLS packet payload such as a layer 2 pseudowire, an IP packet that
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is routed in a VPN context with a private address, or an Ethernet
virtual private network (EVPN) service.
S-Labels are expected to be allocated in the same manner as any other
service labels. S-Labels uniquely identify a particular DetNet flow,
and are local to the node on which the label is allocated. In the
DetNet service sub-layer the explicit route consists of the set of
Relay Nodes that the DetNet flow must traverse. They can be used to
identify the DetNet flow that a packet belongs to as it traverses a
particular node in a DetNet domain. Because labels are local to each
node rather than being a global identifier within a domain, they must
be advertised to their upstream DetNet service-aware peer nodes
(e.g., a DetNet MPLS End System or a DetNet Relay or Edge Node and
interpreted in the context of their received F-Label.
As discussed in Section 3, the forwarding sub-layer uses one or more
F-Labels to forward DetNet packets between DetNet service-aware nodes
along explicitly defined routes at the DetNet forwarding sub-layer,
which in the context of this document is MPLS. F-Labels can also
provide context for an S-Label. In the DetNet Forwarding (MPLS) sub-
layer the explicit route consists of the set of DetNet nodes which
are LSRs, links, and possibly link bundle members and queues that the
DetNet packets of a flow must traverse between nodes in the DetNet
service sub-layer (i.e. between a specific Edge Node and the next hop
Relay Node, between specific Relay Nodes, and between a specific
Relay node and the egress Edge Node. Resource allocation
corresponding to the set of Services supported over the forwarding
sub-layer, which may or may not include aggregation, is required at
this sub-layer. Explicit routes are used to ensure that packets are
routed through the resources that have been reserved for them, and
hence provide the DetNet application with the required service.
Multiple F-Labels may be pushed after an S-Label and there is no
requirement for all F-Labels to be controlled via the same controller
mechanisms. For example in EVPN, some labels are distributed using
BGP while others are distributed using LDP or RSVP.
Whether configuring, calculating and instantiating these routes is a
single-stage or multi-stage process, or in a centralized or
distributed manner, is out of scope of this document.
There are a number of approaches that could be used to provide
explicit routes and resource allocation in the MPLS forwarding sub-
layer:
o The path could be explicitly set up by a controller which
calculates the path and explicitly configures each node along that
path with the appropriate forwarding and resource allocation
information.
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o The path could be set up using RSVP-TE signaling.
o The path could be implemented using MPLS-based segment routing
when extended to support resource allocation.
Much like other MPLS labels, there are a number of alternatives
available for DetNet S-Label and F-Label advertisement to an upstream
peer node. These include distributed signaling protocols such as
RSVP-TE, centralized label distribution via a controller that manages
both the sender and the receiver using NETCONF/YANG, BGP, PCEP, etc.,
and hybrid combinations of the two. The details of the controller
plane solution required for the label distribution and the management
of the label number space are out of scope of this document, but as
mentioned above, there are particular DetNet considerations and
requirements that are discussed in Section 4.1.
4.5. Packet Replication, Elimination, and Ordering (PREOF)
The controller plane protocol solution required for managing the
PREOF processing is outside the scope of this document. That said,
it should be noted that the ability to determine, for a particular
flow, optimal packet replication and elimination points in the DetNet
domain requires explicit support. There are be capabilities that can
be used, or extended, for example GMPLS end-to-end recovery [RFC4872]
and GMPLS segment recovery [RFC4873].
4.6. Contention Loss and Jitter Reduction
As discussed in Section 1, this document does not specify the
mechanisms needed to eliminate contention 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
will be a necessary part of the DetNet controller plane. It will
also be necessary to be able to control the required queuing
mechanisms used to provide these functions along a flow's path
through the network. See Section 4.1 for further discussion of these
requirements.
5. 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.
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6. IANA Considerations
This document makes no IANA requests.
7. Contributors
RFC7322 limits the number of authors listed on the front page of a
draft to a maximum of 5, far fewer than the many individuals below
who made important contributions to this draft. The editor wishes to
thank and acknowledge each of the following authors for contributing
text to this draft. See also Section 8.
Loa Andersson
Huawei
Email: loa@pi.nu
Yuanlong Jiang
Huawei
Email: jiangyuanlong@huawei.com
Norman Finn
Huawei
3101 Rio Way
Spring Valley, CA 91977
USA
Email: norman.finn@mail01.huawei.com
Janos Farkas
Ericsson
Magyar Tudosok krt. 11.
Budapest 1117
Hungary
Email: janos.farkas@ericsson.com
Carlos J. Bernardos
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain
Email: cjbc@it.uc3m.es
Tal Mizrahi
Marvell
6 Hamada st.
Yokneam
Israel
Email: talmi@marvell.com
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Lou Berger
LabN Consulting, L.L.C.
Email: lberger@labn.net
Stewart Bryant
Huawei Technologies
Email: stewart.bryant@gmail.com
Mach Chen
Huawei Technologies
Email: mach.chen@huawei.com
Andrew G. Malis
Huawei Technologies
Email: agmalis@gmail.com
Don Fedyk
LabN Consulting, L.L.C.
Email: dfedyk@labn.net
8. 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
Andrew Malis
Carlos J. Bernardos
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The DetNet chairs serving during the DetNet Data Plane Solution
Design Team:
Lou Berger
Pat Thaler
9. References
9.1. Normative References
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC3473, January 2003,
<https://www.rfc-editor.org/info/rfc3473>.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
February 2006, <https://www.rfc-editor.org/info/rfc4385>.
9.2. Informative References
[I-D.ietf-detnet-architecture]
Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", draft-ietf-
detnet-architecture-12 (work in progress), March 2019.
[I-D.ietf-detnet-flow-information-model]
Farkas, J., Varga, B., Cummings, R., and Y. Jiang, "DetNet
Flow Information Model", draft-ietf-detnet-flow-
information-model-03 (work in progress), March 2019.
[I-D.ietf-detnet-ip]
Korhonen, J., Varga, B., "DetNet Data Plane: IP", 2019.
[I-D.ietf-detnet-mpls]
Korhonen, J., Varga, B., "DetNet Data Plane: MPLS", 2019.
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[I-D.ietf-pce-pcep-extension-for-pce-controller]
Zhao, Q., Li, Z., Negi, M., and C. Zhou, "PCEP Procedures
and Protocol Extensions for Using PCE as a Central
Controller (PCECC) of LSPs", draft-ietf-pce-pcep-
extension-for-pce-controller-01 (work in progress),
February 2019.
[I-D.mpls-over-tsn]
Korhonen, J., Varga, B., "DetNet Data Plane: MPLS over
IEEE 802.1 Time Sensitive Networking (TSN)", 2019.
[I-D.mpls-over-udp-ip]
Korhonen, J., Varga, B., "DetNet Data Plane: MPLS over
IP", 2019.
[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.
[I-D.spring-srv6-network-programming]
Filsfils, C., Camarillo, P., "SRv6 Network Programming,
draft-filsfils-spring-srv6-network-programming, work in
progress", 2019.
[IEEE802.1TSNTG]
IEEE Standards Association, "IEEE 802.1 Time-Sensitive
Networking Task Group", <http://www.ieee802.org/1/tsn>.
[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <https://www.rfc-editor.org/info/rfc2205>.
[RFC2386] Crawley, E., Nair, R., Rajagopalan, B., and H. Sandick, "A
Framework for QoS-based Routing in the Internet",
RFC 2386, DOI 10.17487/RFC2386, August 1998,
<https://www.rfc-editor.org/info/rfc2386>.
[RFC3670] Moore, B., Durham, D., Strassner, J., Westerinen, A., and
W. Weiss, "Information Model for Describing Network Device
QoS Datapath Mechanisms", RFC 3670, DOI 10.17487/RFC3670,
January 2004, <https://www.rfc-editor.org/info/rfc3670>.
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[RFC4872] Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
Ed., "RSVP-TE Extensions in Support of End-to-End
Generalized Multi-Protocol Label Switching (GMPLS)
Recovery", RFC 4872, DOI 10.17487/RFC4872, May 2007,
<https://www.rfc-editor.org/info/rfc4872>.
[RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
"GMPLS Segment Recovery", RFC 4873, DOI 10.17487/RFC4873,
May 2007, <https://www.rfc-editor.org/info/rfc4873>.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
and D. McPherson, "Dissemination of Flow Specification
Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
<https://www.rfc-editor.org/info/rfc5575>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
September 2009, <https://www.rfc-editor.org/info/rfc5654>.
[RFC6387] Takacs, A., Berger, L., Caviglia, D., Fedyk, D., and J.
Meuric, "GMPLS Asymmetric Bandwidth Bidirectional Label
Switched Paths (LSPs)", RFC 6387, DOI 10.17487/RFC6387,
September 2011, <https://www.rfc-editor.org/info/rfc6387>.
[RFC7551] Zhang, F., Ed., Jing, R., and R. Gandhi, Ed., "RSVP-TE
Extensions for Associated Bidirectional Label Switched
Paths (LSPs)", RFC 7551, DOI 10.17487/RFC7551, May 2015,
<https://www.rfc-editor.org/info/rfc7551>.
[RFC7657] Black, D., Ed. and P. Jones, "Differentiated Services
(Diffserv) and Real-Time Communication", RFC 7657,
DOI 10.17487/RFC7657, November 2015,
<https://www.rfc-editor.org/info/rfc7657>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8227] Cheng, W., Wang, L., Li, H., van Helvoort, H., and J.
Dong, "MPLS-TP Shared-Ring Protection (MSRP) Mechanism for
Ring Topology", RFC 8227, DOI 10.17487/RFC8227, August
2017, <https://www.rfc-editor.org/info/rfc8227>.
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Authors' Addresses
Balazs Varga (editor)
Ericsson
Magyar Tudosok krt. 11.
Budapest 1117
Hungary
Email: balazs.a.varga@ericsson.com
Janos Farkas
Ericsson
Magyar Tudosok krt. 11.
Budapest 1117
Hungary
Email: janos.farkas@ericsson.com
Lou Berger
LabN Consulting, L.L.C.
Email: lberger@labn.net
Don Fedyk
LabN Consulting, L.L.C.
Email: dfedyk@labn.net
Andrew G. Malis
Huawei Technologies
Email: agmalis@gmail.com
Stewart Bryant
Huawei Technologies
Email: stewart.bryant@gmail.com
Jouni Korhonen
Email: jouni.nospam@gmail.com
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