Internet DRAFT - draft-bernardos-raw-multidomain
draft-bernardos-raw-multidomain
RAW WG CJ. Bernardos
Internet-Draft UC3M
Intended status: Standards Track A. Mourad
Expires: 14 September 2023 InterDigital
13 March 2023
RAW multidomain extensions
draft-bernardos-raw-multidomain-02
Abstract
This document describes the multi-domain RAW problem and explores and
proposes some extensions to enable RAW multi-domain operation.
Status of This Memo
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Table of Contents
1. Introduction and Problem Statement . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. RAW multi-domain extensions . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
7. Informative References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction and Problem Statement
Wireless operates on a shared medium, and transmissions cannot be
fully deterministic due to uncontrolled interferences, including
self-induced multipath fading. RAW (Reliable and Available Wireless)
is an effort to provide Deterministic Networking on across a path
that include a wireless interface. RAW provides for high reliability
and availability for IP connectivity over a wireless medium. The
wireless medium presents significant challenges to achieve
deterministic properties such as low packet error rate, bounded
consecutive losses, and bounded latency. RAW extends the DetNet
Working Group concepts to provide for high reliability and
availability for an IP network utilizing scheduled wireless segments
and other media, e.g., frequency/time-sharing physical media
resources with stochastic traffic: IEEE Std. 802.15.4 timeslotted
channel hopping (TSCH), 3GPP 5G ultra-reliable low latency
communications (URLLC), IEEE 802.11ax/be, and L-band Digital
Aeronautical Communications System (LDACS), etc. Similar to DetNet,
RAW technologies aim at staying abstract to the radio layers
underneath, addressing the Layer 3 aspects in support of applications
requiring high reliability and availability.
As introduced in [I-D.ietf-raw-architecture], RAW separates the path
computation time scale at which a complex path is recomputed from the
path selection time scale at which the forwarding decision is taken
for one or a few packets. RAW operates at the path selection time
scale. The RAW problem is to decide, amongst the redundant solutions
that are proposed by the Patch Computation Element (PCE), which one
will be used for each packet to provide a Reliable and Available
service while minimizing the waste of constrained resources. To that
effect, RAW defines the Path Selection Engine (PSE) that is the
counter-part of the PCE to perform rapid local adjustments of the
forwarding tables within the diversity that the PCE has selected for
the Track. The PSE enables to exploit the richer forwarding
capabilities with Packet (hybrid) ARQ, Replication, Elimination and
Ordering (PAREO), and scheduled transmissions at a faster time scale.
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There are several use cases [I-D.ietf-raw-use-cases] where
reliability and availability are key requirements for wireless
heterogeneous networks. A couple of relevant examples are (i) the
manufacturing sector, where a plethora of devices are interconnected
and generate data that need to be reliably delivered to the control
and monitoring agents; and (ii) the residential gaming, with eXtended
Reality (XR).
We can refer to domains managed by a single PCE, as “single-domain
RAW”, where nodes are typically run and managed by a single
administration entity. In this scenario, the PSE can make use of
“tracks” and paths involving only the nodes belonging to this RAW
domain.
There are scenarios where hosts are connected to different RAW
domains and they need to communicate to each other with certain
reliability and/or availability guarantees, for example in large
factories where networks might be organized in domains (per
production lines or building/sites), in residential environments
where there are different networks (e.g., one at home and one in the
garden), or even vehicular scenarios (e.g., hosts connected to
different vehicles).
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____________________________________________
| |
| ( ( o ) ) |
| * ^ |
| * / \ |
| * / \ |
| ** ------+-- |
| * | RAW |P| |
| ( ( o ) )* * |node |S| |
| ^ *( ( o ) ) | 1-1 |E| +------+
| / \ ^ * ------+-- | PCE1 |
| / \ / \ ** +------+
| +-----+ / \ *( ( o ) ) |
| |host1| ------+-- ^ |
| | | | RAW |P| / \ |
| | | |node |S| / \ |
| | o | | 1-2 |E| ------+-- |
| +-----+ ------+-- | RAW |P| |
| \ / |node |S| |
| RAW \ / | 1-3 |E| |
| domain 1 v ------+-- |
| ( ( o ) ) |
| **** |
|______________ *____**** ______________|
____________ *__________***** _____________
| * ** |
| * ****( ( o ) ) |
| * **** ^ |
| ( ( o ) )**** / \ |
| ^ * / \ |
| / \ * ------+-- |
| / \ * | RAW |P| |
| ------+-- * |node |S| |
| | RAW |P| * | 2-1 |E| +------+
| |node |S| * ------+-- | PCE2 |
| | 2-2 |E| * +------+
| ------+-- *( ( o ) ) |
| * ^ |
| ( ( o ) ) / \ |
| ^ / \ |
| / \ ------+-- |
| / \ | RAW |P| |
| +-----+ |node |S| |
| RAW |host2| | 2-3 |E| |
| domain 2 +-----+ ------+-- |
|___________________________________________|
Figure 1: Exemplary scenario showing multiple RAW domains
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Figure 1 shows an example of communication involving two RAW domains.
As opposed to a single-domain scenario, where a single PCE may
compute all possible “tracks” at longer time scale, and the PSE
functionality may perform “subtrack” selection and optimization at a
shorter time scale using all information available at the domain,
multidomain scenarios pose additional burdens that are not solved
yet.
Each RAW domain operates independently of the other domains. While
there exist inter-PCE solutions today, allowing one domain’s PCE to
learn some inter-domain paths, this would not be sufficient, as the
PSE of one domain would not have full visibility nor capability to
act on the other domains (e.g., there are no multi-domain OAM
solutions in place yet), limiting its capability to guarantee any
given SLA. Therefore, there is a need to define inter-PSE
coordination mechanisms across domains.
There exist today standardized solutions, such as the ones in the
context of Path Computation Element (PCE), enabling computing multi-
/inter-domain paths. As an example, the Hierarchical PCE (G-PCE) was
defined in RFC 6805 [RFC6805] and is described hereafter. A parent
PCE maintains a domain topology map that contains the child domains
(seen as vertices in the topology) and their interconnections (links
in the topology). The parent PCE has no information about the
content of the child domains; that is, the parent PCE does not know
about the resource availability within the child domains, nor does it
know about the availability of connectivity across each domain
because such knowledge would violate the confidentiality requirement
and either would require flooding of full information to the parent
(scaling issue) or would necessitate some form of aggregation. The
parent PCE is used to compute a multi-domain path based on the domain
connectivity information. A child PCE may be responsible for single
or multiple domains and is used to compute the intra-domain path
based on its own domain topology information.
Solutions like the above are not sufficient alone to solve the multi-
domain RAW problem, as the PSEs need to have some additional
information from the other involved domains to be sensitive/reactive
to transient changes, in order to ensure a certain level of
reliability and availability in a multi-domain wireless heterogeneous
mesh network.
Within a single domain, the RAW framework architecture works, by
having the PCE in charge of computing the paths (tracks) and the
PSE(s) taking the short time decisions of which sub-tracks to use.
Note that the PSE is assumed to be either a distributed functionality
(performed by every RAW router of the path, which takes forwarding
decisions based on the local and OAM information that they have), or
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a centralized functionality played by the entry (ingress) router in
the domain (note that if there are multiple ingress nodes, then there
might be multiple PSEs), which then performs source routing.
In scenarios with multiple connected RAW domains, running
uncoordinated RAW solutions in each domain is not sufficient. PSEs
would need to have global end-to-end information as well as be
capable of running OAM mechanisms [I-D.ietf-raw-oam-support] to
monitor the quality of the selected paths.
2. Terminology
The following terms used in this document are defined by the IETF:
PAREO. Packet (hybrid) ARQ, Replication, Elimination and
Ordering. PAREO is a superset Of DetNet's PREOF that includes
radio-specific techniques such as short range broadcast, MUMIMO,
constructive interference and overhearing, which can be leveraged
separately or combined to increase the reliability.
PSE. The Path Selection Engine (PSE) is the counter-part of the
PCE to perform rapid local adjustments of the forwarding tables
within the diversity that the PCE has selected for the Track. The
PSE enables to exploit the richer forwarding capabilities with
PAREO and scheduled transmissions at a faster time scale over the
smaller domain that is the Track, in either a loose or a strict
fashion.
3. RAW multi-domain extensions
Here we specify the new mechanisms and signaling extensions to enable
inter-domain RAW connectivity.
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+-----+-+ +----+ +----+ +-----+-+ +-----+-+
| RAW |P| | | | | | RAW |P| | RAW |P|
|node |S| |PCE1| |PCE2| |node |S| |node |S|
| 1-2 |E| | | | | | 2-1 |E| | 2-2 |E|
+-----+-+ +----+ +----+ +-----+-+ +-----+-+
| | | | |
1.Path compute req| | | |
(src=node1-2, | | | |
dst=node2-3, SLA)| | | |
|··········>| | | |
| |2.Path compute req | |
| |(src={node2-1,node2-2}, | |
| | dst=node2-3) | |
| |···········>| | |
| |3.Path compute resp | |
| |({tracks2},{links_quality})| |
| |<···········| | |
4.Path compute resp | | |
({{tracks1},{tracks2}}, | | |
PSE={node2-1,node2-2}, | | |
{SLA1,SLA2}) | | | |
|<··········| | | |
|5.RAW inter-domain path | | |
|({{tracks1,tracks2}},{SLA1,SLA2}) | |
|······································>| |
|····················································>|
| | 6.RAW inter-domain path ACK |
|<······································| |
|<····················································|
| | | | |
|7.RAW OAM(flow/track,SLA1) | |
<···>|<···> | | 7.RAW OAM(flow/track,SLA1)|
| | | <··>|<··> <··>|<··>
| 8.RAW OAM (flow/track, metrics) |
|<·····································>| |
|<···················································>|
| | | | |
Figure 2: Multi-domain RAW signaling
Figure 2 shows a signaling flow diagram, taking as baseline scenario
the one shown in Figure 1, where host1 (connected to node1-2) wants
to communicate with host2 (connected to node2-3). An ingress RAW
node (node1-2) gets a request for connectivity, with a given
destination RAW node (node2-3) and the desired SLA in terms of
reliability and availability. The source and/or destination RAW
nodes might be hostss. We next explain each of the steps illustrated
in the figure:
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1. The ingress node plays the role of PSE (also referred to as
PSE@domain1) and requests the computation of the tracks towards
the destination node2-3 with the intended SLA to the PCE of the
domain (PCE1).
2. PCE1 knows that the destination is in another domain (domain2)
and that the PCE of the destination domain is PCE2. PCE1 also
knows the ingress nodes in domain2 that are connected to domain1.
How this is done is outside of the scope of this document. These
nodes (node2-1 and node2-2) play the role of PSEs@domain2. PCE1
requests to PCE2 to compute the available tracks from
PSEs@domain2 to the destination, and the characteristics of the
links (link_quality) forming these tracks. The detail and nature
of the information provided by PCE2 regarding the links might
vary depending on the deployment, and is meant to be used by PCE1
and the PSE@domain1 (node1-2) to compute how to distribute the
SLA among the domains.
3. PCE2 computes the tracks and responds to PCE1, including also the
characteristics of the links (link_quality). Examples of
potential information elements including in the link_quality are:
available bandwidth, observed reliability, delay, link
variability/mobility, etc.
4. PCE1 provides to the PSE@domain1 the tracks to reach the
destination, as well as the split of SLAs among domain1 and
domain2 (SLA1 and SLA2). An SLA, or a Quality of Service (QoS)
figure, may include aspects such as, among others: max. delay,
assured BW, max. Jitter, packet loss ratio, availability ratio,
etc. PCE1 also provides the PSEs@domain2.
5. The PSE@domain1 sends a message to each PSE@domain2, in order to
set-up a direct communication channel to provide OAM information
useful to the PSE@domain1 for computing the subtracks to use for
the traffic. This message includes the SLA that each domain has
to monitor and guarantee (SLA1 and SLA2).
6. Each of the PSEs@domain2 acknowledges the message. At this
point, the communication channel is established and the
PSE@domain1 can start taking decisions at a forwarding time scale
regarding which paths (subtracks) to use.
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7. All PSEs, at each domain, start performing OAM procedures
[I-D.ietf-raw-oam-support], which are key to observe if traffic
is meeting the desired SLAs (SLA1 and SLA2) and adapt the
subtracks and tracks if needed. OAM mechanisms can be applied
in-band (sharing the traffic's fate) or out-of band. Note that
this per-domain distributed OAM is critical to ensure that the
required SLAs (reliability and availability) are met by reacting
on a short time scale at each of the involved domains.
8. PSEs share aggregated and pre-processed information among them to
facilitate early detection of issues and computation of
subtracks. If a violation of an SLA is detected, the respective
PSE would notify the domain PCE and the other PSE, so a reaction
measure can be taken (e.g., selecting different subtracks, taking
different PAREO decisions, requesting the PCEs to recompute the
paths and/or adjust the split of the SLAs across the domains).
Note that this example covers the direction host1-to-host2. If there
is traffic in the opposite direction, the process has to be repeated
in the reverse direction, as paths might not be bidirectional.
4. IANA Considerations
TBD.
5. Security Considerations
TBD.
6. Acknowledgments
The work of Carlos J. Bernardos in this document has been partially
supported by the Horizon Europe PREDICT-6G (Grant 101095890) and
UNICO I+D 6G-DATADRIVEN-04 project.
7. Informative References
[I-D.ietf-raw-architecture]
Thubert, P., "Reliable and Available Wireless
Architecture", Work in Progress, Internet-Draft, draft-
ietf-raw-architecture-11, 7 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-raw-
architecture-11>.
[I-D.ietf-raw-oam-support]
Theoleyre, F., Papadopoulos, G. Z., Mirsky, G., and C. J.
Bernardos, "Operations, Administration and Maintenance
(OAM) features for RAW", Work in Progress, Internet-Draft,
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draft-ietf-raw-oam-support-06, 5 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-raw-oam-
support-06>.
[I-D.ietf-raw-use-cases]
Bernardos, C. J., Papadopoulos, G. Z., Thubert, P., and F.
Theoleyre, "RAW Use-Cases", Work in Progress, Internet-
Draft, draft-ietf-raw-use-cases-08, 22 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-raw-use-
cases-08>.
[RFC6805] King, D., Ed. and A. Farrel, Ed., "The Application of the
Path Computation Element Architecture to the Determination
of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
DOI 10.17487/RFC6805, November 2012,
<https://www.rfc-editor.org/info/rfc6805>.
Authors' Addresses
Carlos J. Bernardos
Universidad Carlos III de Madrid
Av. Universidad, 30
28911 Leganes, Madrid
Spain
Phone: +34 91624 6236
Email: cjbc@it.uc3m.es
URI: http://www.it.uc3m.es/cjbc/
Alain Mourad
InterDigital Europe
Email: Alain.Mourad@InterDigital.com
URI: http://www.InterDigital.com/
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