MPLS Working Group
Internet Engineering Task Force (IETF) T. Saad
Internet-Draft
Request for Comments: 9791 Cisco Systems, Inc.
Intended status:
Category: Informational K. Makhijani
Expires: 27 March 2025
ISSN: 2070-1721 Independent
H. Song
Futurewei Technologies
G. Mirsky
Ericsson
23 September 2024
May 2025
Use Cases for MPLS Network Action Indicators and MPLS Ancillary Data
draft-ietf-mpls-mna-usecases-15
Abstract
This document presents use cases that have a common feature that may
be addressed by encoding network action indicators and associated
ancillary data within MPLS packets. There is community interest in
extending the MPLS data plane to carry such indicators and ancillary
data to address the these use cases that are described in this document. cases.
The use cases described in this document are not an exhaustive set, set
but rather the ones that are have been actively discussed by members of
the IETF MPLS, PALS, and DetNet working groups Working Groups from the beginning of
work on the MPLS Network Action (MNA) until the publication of this
document.
Status of This Memo
This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents valid
approved by the IESG are candidates for a maximum any level of Internet
Standard; see Section 2 of six months RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 27 March 2025.
https://www.rfc-editor.org/info/rfc9791.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Conventions used in this document . . . . . . . . . . . . 3
1.2.1. Acronyms and Abbreviations . . . . . . . . . . . . . 3
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. No Further Fast Reroute . . . . . . . . . . . . . . . . . 4
2.2. Applicability of Hybrid Measurement Methods . . . . . . . 4
2.2.1. In-situ In Situ OAM . . . . . . . . . . . . . . . . . . . . . 5
2.2.2. Alternate Marking Method . . . . . . . . . . . . . . 5
2.3. Network Slicing . . . . . . . . . . . . . . . . . . . . . 6
2.4. NSH-based NSH-Based Service Function Chaining . . . . . . . . . . . 6
2.5. Network Programming . . . . . . . . . . . . . . . . . . . 7
3. Co-existence Coexistence with the Existing MPLS Services Using Post-Stack
Headers . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Co-existence Coexistence of the MNA Use Cases . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1.
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2.
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Use Cases for Continued Discussion . . . . . . . . . 13
A.1. Generic Delivery Functions . . . . . . . . . . . . . . . 13
A.2. Delay Budgets for Time-Bound Applications . . . . . . . . 13
A.3. Stack-Based Methods for Latency Control . . . . . . . . . 14
Contributors' Addresses . . . . . . . . . . . . . . . . . . . . . 14
Acknowledgements
Contributors
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
This document describes use cases that introduce functions that
require special processing by forwarding hardware. The current state
of the art requires allocating a new special-purpose label Special-Purpose Label (SPL)
[RFC3032] or extended special-purpose label Extended Special-Purpose Label (eSPL). SPLs are a very
limited resource, while eSPL requires an extra Label Stack Entry label stack entry per
Network Action,
network action, which is expensive. Therefore, an MPLS Network
Action (MNA) [RFC9613] approach was proposed to extend the MPLS
architecture. MNA is expected to enable functions that may require
carrying additional ancillary data within the MPLS packets, as well
as a means to indicate that the ancillary data is present and a
specific action needs to be performed on the packet.
This document lists various use cases that could benefit extensively
from the MNA framework [I-D.ietf-mpls-mna-fwk]. [RFC9789]. Supporting a solution of the
general MNA framework provides a common foundation for future network
actions that can be exercised in the MPLS data plane.
1.1. Terminology
The following terminology is used in the document:
RFC 9543 Network Slice
is interpreted Slice:
Interpreted as defined in [RFC9543]. Furthermore, this This document uses "network
slice" interchangeably as a shorter version of the RFC term "RFC 9543
Network Slice term.
The Slice".
MPLS Ancillary Data:
Data is that can be classified as:
* residing within the MPLS label stack and referred (referred to as In-
Stack Data, "in-stack
data"), and
* residing after the Bottom of Stack (BoS) and referred (referred to as
Post-Stack Data. "post-
stack data").
1.2. Conventions used in this document
1.2.1. Acronyms and Abbreviations
MNA: MPLS Network Action
DEX: Direct Export
I2E: Ingress to Edge
HbH: Hop by Hop
PW: Pseudowire
BoS: Bottom of Stack
ToS: Top of Stack
NSH: Network Service Header
FRR: Fast Reroute
IOAM: In-situ In situ Operations, Administration, and Maintenance
G-ACh: Generic Associated Channel
LSP: Label Switched Path
LSR: Label Switch Switching Router
NRP: Network Resource Partition
SPL: Special Purpose Special-Purpose Label
eSPL: extended Special Purpose Special-Purpose Label
AMM: Alternative Marking Method
2. Use Cases
2.1. No Further Fast Reroute
MPLS Fast Reroute [RFC4090], [RFC5286], [RFC7490], and
[I-D.ietf-rtgwg-segment-routing-ti-lfa] [RFC4090] [RFC5286] [RFC7490] [SR-TI-LFA] is a
useful and widely deployed tool for minimizing packet loss in the
case of a link or node failure.
Several cases exist where, once a Fast Reroute (FRR) has taken place
in an MPLS network and a packet is rerouted away from the failure, a
second FRR impacts the same packet on another node and may result in
traffic disruption.
In such a case, the packet impacted by multiple FRR events may
continue to loop between the label switch routers Label Switching Routers (LSRs) that
activated FRR until the packet's TTL expires. That can lead to link
congestion and further packet loss. To avoid that situation, packets
that FRR has redirected will be marked using MNA to preclude further
FRR processing.
2.2. Applicability of Hybrid Measurement Methods
MNA can be used to carry information essential for collecting
operational information and measuring various performance metrics
that reflect the experience of the packet marked by MNA. Optionally,
the operational state and telemetry information collected on the LSR
may be transported using MNA techniques.
2.2.1. In-situ In Situ OAM
In-situ
In situ Operations, Administration, and Maintenance (IOAM), defined
in [RFC9197] and [RFC9326], might be used to collect operational and
telemetry information while a packet traverses a particular path in a
network domain.
IOAM can run in two modes: Ingress to Edge (I2E) and Hop by Hop
(HbH). In I2E mode, only the encapsulating and decapsulating nodes
will process IOAM data fields. In HbH mode, the encapsulating and
decapsulating nodes and intermediate IOAM-capable nodes process IOAM
data fields. The IOAM data fields, defined in [RFC9197], can be used
to derive the operational state of the network experienced by the
packet with the IOAM Header that traversed the path through the IOAM
domain.
Several IOAM Option-Types have been defined:
* Pre-allocated Trace
* Incremental Trace
* Edge-to-Edge
* Proof-of-Transit
* Direct Export (DEX)
With all IOAM Option-Types except for the Direct Export (DEX), the
collected information is transported in the trigger IOAM packet. In
the IOAM DEX Option Option-Type [RFC9326], the operational state and
telemetry information are collected according to a specified profile
and exported in a manner and format defined by a local policy. In
IOAM DEX, the user data packet is only used to trigger the IOAM data
to be directly exported or locally aggregated without being carried
in the IOAM trigger packets.
2.2.2. Alternate Marking Method
The Alternate Marking Method (AMM), defined in [RFC9341] and
[RFC9342])
[RFC9342]), is an example of a hybrid performance measurement method
([RFC7799])
[RFC7799] that can be used in the MPLS network to measure packet loss
and packet delay performance metrics. [RFC8957] defined defines the
Synonymous Flow Label framework to realize AMM in the MPLS network.
The MNA is an alternative mechanism that can be used to support AMM
in the MPLS network.
2.3. Network Slicing
An RFC 9543 Network Slice service ([RFC9543]) Service [RFC9543] provides connectivity
coupled with network resource commitments and is expressed in terms
of one or more connectivity constructs. Section 5 of
[I-D.ietf-teas-ns-ip-mpls] [NS-IP-MPLS]
defines a Network Resource Partition (NRP) Policy as a policy
construct that enables the instantiation of mechanisms to support one
or more network slice services. The packets associated with an NRP
may carry a marking in their network
layer network-layer header to identify this
association, which is referred to as an NRP Selector. The NRP
Selector maps a packet to the associated network resources and
provides the corresponding forwarding treatment onto the packet.
A router that requires the forwarding of a packet that belongs to an
NRP may have to decide on the forwarding action to take based on
selected next-hop(s), next hop(s) and decide on the forwarding treatment (e.g.,
scheduling and drop policy) to enforce based on the associated per-hop per-
hop behavior.
In this case, routers that forward traffic over a physical link
shared by multiple NRPs need to identify the NRP to which the packet
belongs to enforce their respective forwarding actions and
treatments.
MNA technologies can signal actions for MPLS packets and carry data
essential for these actions. For example, MNA can carry the NRP
Selector [I-D.ietf-teas-ns-ip-mpls] [NS-IP-MPLS] in MPLS packets.
2.4. NSH-based NSH-Based Service Function Chaining
[RFC8595] describes how Service Function Chaining can be realized in
an MPLS network by emulating the Network Service Header (NSH)
[RFC8300] using only MPLS label stack elements.
The approach in [RFC8595] introduces some limitations limitations, which are
discussed in
[I-D.lm-mpls-sfc-path-verification]. [SFP-VERIF]. However, that the approach can benefit from the
MNA framework introduced with MNA in
[I-D.ietf-mpls-mna-fwk]. [RFC9789].
MNA can be used to extend NSH emulation using MPLS labels [RFC8595]
to support the functionality of NSH Context Headers, whether fixed or
variable-length.
variable length. For example, MNA could support Flow ID [RFC9263]
that may be used for load-balancing among Service Function Forwarders
and/or the Service Functions within the same Service Function Path.
2.5. Network Programming
In Segment Routing (SR), an ingress node steers a packet through an
ordered list of instructions called "segments". Each of these
instructions represents a function to be called at a specific
location in the network. A function is locally defined on the node
where it is executed and may range from simply moving forward in the
segment list to any complex user-defined behavior.
Network Programming combines SR functions to achieve a networking
objective beyond mere packet routing.
Encoding a pointer to a function and its arguments within an MPLS
packet transport header may be desirable. MNA can be used to encode
the FUNC::ARGs to support the functional equivalent of FUNC::ARG in
SRv6
Segment Routing over IPv6 as described in [RFC8986].
3. Co-existence Coexistence with the Existing MPLS Services Using Post-Stack Headers
Several services can be transported over MPLS networks today. These
include providing Layer-3 Layer 3 (L3) connectivity (e.g., for unicast and
multicast L3 services), services) and Layer-2 Layer 2 (L2) connectivity (e.g., for
unicast Pseudowires (PWs), PWs, multicast E-Tree, and broadcast E-LAN Ethernet LAN (E-LAN) L2
services). In those cases, the user service traffic is encapsulated
as the payload in MPLS packets.
For L2 service traffic, it is possible to use a Control Word (CW)
[RFC4385] and [RFC5085] immediately after the MPLS header to disambiguate
the type of MPLS payload, prevent possible packet misordering, and
allow for fragmentation. In this case, the first nibble of the data
that immediately follows after the MPLS BoS is set to 0b0000 to identify
the presence of the PW CW.
In addition to providing connectivity to user traffic, MPLS may also
transport OAM data (e.g., over MPLS Generic Associated Channels
(G-AChs) [RFC5586]). In this case, the first nibble of the data that
immediately follows after the MPLS BoS is set to 0b0001. It indicates the
presence of a control channel associated with a PW, LSP, or Section. section.
Bit Index Explicit Replication (BIER) [RFC8296] traffic can also be
encapsulated over MPLS. In this case, BIER has defined 0b0101 as the
value for the first nibble in of the data that immediately appears after follows the
bottom of the label stack for any BIER-encapsulated packet over MPLS.
For pseudowires, PWs, the Generic Associated Channel G-ACh [RFC7212] uses the first four bits of the PW
control word to provide the initial discrimination between data
packets and packets belonging to the associated channel, as described
in [RFC4385].
MPLS can be used as the data plane for DetNet Deterministic Networking
(DetNet) [RFC8655]. The DetNet sub-layers, forwarding, and service
are realized using the MPLS label stack, the DetNet Control Word control word
[RFC8964], and the DetNet Associated Channel Header [RFC9546].
MNA-based solutions for the use cases described in this document and
proposed in the future are expected to allow for coexistence and
backward compatibility with all existing MPLS services.
4. Co-existence Coexistence of the MNA Use Cases
Two or more of the discussed cases may co-exist coexist in the same packet.
That may require the presence of multiple ancillary data (whether In- in-
stack or Post-stack post-stack ancillary data) to be present in the same MPLS
packet.
For example, IOAM may provide essential functions along with network
slicing to help ensure that critical network slice SLOs Service Level
Objectives (SLOs) are being met by the network provider. In this
case, IOAM can collect key performance measurement parameters of a
network slice traffic flow as it traverses the transport network.
5. IANA Considerations
This document has no IANA actions.
6. Security Considerations
Section 7 of "MPLS Network Action (MNA) Framework",
[I-D.ietf-mpls-mna-fwk] the MNA framework [RFC9789] outlines security
considerations for non-
protocol specifying documents. documents that do not specify protocols. The
authors have verified that these considerations are fully applicable
to this document.
In-depth security analysis for each specific use case is beyond the
scope of this document and will be addressed in future solution
documents. It is strongly recommended that these solution documents
undergo review by a security expert review early in their development,
ideally during the Working Group Last Call phase.
8.
7. References
8.1.
7.1. Normative References
[I-D.ietf-mpls-mna-fwk]
[RFC9789] Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
Network Actions Action (MNA) Framework", Work in Progress,
Internet-Draft, draft-ietf-mpls-mna-fwk-10, 6 August 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-fwk-10>.
8.2. RFC 9789,
DOI 10.17487/RFC9789, May 2025,
<https://www.rfc-editor.org/info/rfc9789>.
7.2. Informative References
[I-D.zzhang-intarea-generic-delivery-functions]
[GDF] Zhang, Z. J., Z., Bonica, R., Kompella, K., and G. Mirsky,
"Generic Delivery Functions", Work in Progress, Internet-
Draft, draft-zzhang-intarea-generic-delivery-functions-03,
11 July 2022, <https://datatracker.ietf.org/doc/html/
draft-zzhang-intarea-generic-delivery-functions-03>.
[I-D.ietf-teas-ns-ip-mpls]
[NS-IP-MPLS]
Saad, T., Beeram, V. P., V., Dong, J., Wen, B., Ceccarelli,
D., Halpern, J. M., Peng, S., Chen, R., Liu, X.,
Contreras, L. M., Rokui, R., J., and L. Jalil, S. Peng,
"Realizing Network Slices in IP/MPLS Networks", Work in
Progress, Internet-Draft, draft-ietf-teas-ns-ip-mpls-04, 28 May
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
teas-ns-ip-mpls-04>. draft-ietf-teas-ns-ip-mpls-05, 2
March 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-teas-ns-ip-mpls-05>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
DOI 10.17487/RFC4090, May 2005,
<https://www.rfc-editor.org/info/rfc4090>.
[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>.
[RFC5085] Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual
Circuit Connectivity Verification (VCCV): A Control
Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085,
December 2007, <https://www.rfc-editor.org/info/rfc5085>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008,
<https://www.rfc-editor.org/info/rfc5286>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
[RFC7212] Frost, D., Bryant, S., and M. Bocci, "MPLS Generic
Associated Channel (G-ACh) Advertisement Protocol",
RFC 7212, DOI 10.17487/RFC7212, June 2014,
<https://www.rfc-editor.org/info/rfc7212>.
[RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
RFC 7490, DOI 10.17487/RFC7490, April 2015,
<https://www.rfc-editor.org/info/rfc7490>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/info/rfc7799>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
[RFC8595] Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
Forwarding Plane for Service Function Chaining", RFC 8595,
DOI 10.17487/RFC8595, June 2019,
<https://www.rfc-editor.org/info/rfc8595>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[RFC8957] Bryant, S., Chen, M., Swallow, G., Sivabalan, S., and G.
Mirsky, "Synonymous Flow Label Framework", RFC 8957,
DOI 10.17487/RFC8957, January 2021,
<https://www.rfc-editor.org/info/rfc8957>.
[RFC8964] Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
S., and J. Korhonen, "Deterministic Networking (DetNet)
Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
2021, <https://www.rfc-editor.org/info/rfc8964>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
Ed., "Data Fields for In Situ Operations, Administration,
and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
May 2022, <https://www.rfc-editor.org/info/rfc9197>.
[RFC9263] Wei, Y., Ed., Elzur, U., Majee, S., Pignataro, C., and D.
Eastlake 3rd, "Network Service Header (NSH) Metadata Type
2 Variable-Length Context Headers", RFC 9263,
DOI 10.17487/RFC9263, August 2022,
<https://www.rfc-editor.org/info/rfc9263>.
[RFC9326] Song, H., Gafni, B., Brockners, F., Bhandari, S., and T.
Mizrahi, "In Situ Operations, Administration, and
Maintenance (IOAM) Direct Exporting", RFC 9326,
DOI 10.17487/RFC9326, November 2022,
<https://www.rfc-editor.org/info/rfc9326>.
[RFC9341] Fioccola, G., Ed., Cociglio, M., Mirsky, G., Mizrahi, T.,
and T. Zhou, "Alternate-Marking Method", RFC 9341,
DOI 10.17487/RFC9341, December 2022,
<https://www.rfc-editor.org/info/rfc9341>.
[RFC9342] Fioccola, G., Ed., Cociglio, M., Sapio, A., Sisto, R., and
T. Zhou, "Clustered Alternate-Marking Method", RFC 9342,
DOI 10.17487/RFC9342, December 2022,
<https://www.rfc-editor.org/info/rfc9342>.
[RFC9543] Farrel, A., Ed., Drake, J., Ed., Rokui, R., Homma, S.,
Makhijani, K., Contreras, L., and J. Tantsura, "A
Framework for Network Slices in Networks Built from IETF
Technologies", RFC 9543, DOI 10.17487/RFC9543, March 2024,
<https://www.rfc-editor.org/info/rfc9543>.
[RFC9546] Mirsky, G., Chen, M., and B. Varga, "Operations,
Administration, and Maintenance (OAM) for Deterministic
Networking (DetNet) with the MPLS Data Plane", RFC 9546,
DOI 10.17487/RFC9546, February 2024,
<https://www.rfc-editor.org/info/rfc9546>.
[RFC9613] Bocci, M., Ed., Bryant, S., and J. Drake, "Requirements
for Solutions that Support MPLS Network Actions (MNAs)",
RFC 9613, DOI 10.17487/RFC9613, August 2024,
<https://www.rfc-editor.org/info/rfc9613>.
[I-D.lm-mpls-sfc-path-verification]
Liu, Y.
[SFP-VERIF]
Yao, L. and G. Mirsky, "MPLS-based Service Function
Path(SFP) Consistency Verification", Work in Progress,
June 2022, <https://datatracker.ietf.org/doc/html/draft-
lm-mpls-sfc-path-verification-03>.
[I-D.ietf-rtgwg-segment-routing-ti-lfa]
[SR-TI-LFA]
Bashandy, A., Litkowski, S., Filsfils, C., Francois, P.,
Decraene, B., and D. Voyer, "Topology Independent Fast
Reroute using Segment Routing", Work in Progress,
Internet-Draft, draft-ietf-rtgwg-segment-routing-ti-lfa-
17, 5 July 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-rtgwg-segment-routing-ti-lfa-17>.
[I-D.stein-srtsn]
21, 12 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-
segment-routing-ti-lfa-21>.
[SRTSN] Stein, Y. J., Y(J)., "Segment Routed Time Sensitive Networking",
Work in Progress, Internet-Draft, draft-stein-srtsn-01, 29
August 2021, <https://datatracker.ietf.org/doc/html/draft-
stein-srtsn-01>.
Appendix A. Use Cases for Continued Discussion
Several use cases for which MNA can provide a viable solution have
been discussed. The discussion of these aspirational cases is
ongoing at the time of publication of the document.
A.1. Generic Delivery Functions
The
Generic Delivery Functions (GDFs), defined in
[I-D.zzhang-intarea-generic-delivery-functions], [GDF], provide a new
mechanism to support functions analogous to those supported through
the IPv6 Extension Headers mechanism. For example, GDF can support
fragmentation/reassembly functionality in the MPLS network by using
the Generic Fragmentation Header. MNA can support GDF by placing a
GDF header in an MPLS packet within the Post-Stack Data post-stack data block
[I-D.ietf-mpls-mna-fwk].
[RFC9789]. Multiple GDF headers headers, organized as a list of headers, can
also be present in the same MPLS packet organized as a list of headers. packet.
A.2. Delay Budgets for Time-Bound Applications
The routers in a network can perform two distinct functions on
incoming packets, namely packets: forwarding (where the packet should be sent) and
scheduling (when the packet should be sent). IEEE-802.1 Time Time-
Sensitive Networking (TSN) and Deterministic Networking DetNet provide several mechanisms for
scheduling under the assumption that routers are time-synchronized.
The most effective mechanisms for delay minimization involve per-flow
resource allocation.
Segment Routing (SR) is a forwarding paradigm that allows encoding
forwarding instructions in the packet in a stack data structure
rather than being programmed into the routers. The SR instructions
are contained within a packet in the form of a First-in, First-out
stack First-In, First-Out
stack, dictating the forwarding decisions of successive routers.
Segment routing may be used to choose a path sufficiently short to be
capable of providing a bounded end-to-end latency but does not
influence the queueing of individual packets in each router along
that path.
When carried over the MPLS data plane, a solution is required to
enable the delivery of such packets that can be delivered to their final destination within
a given time budget. One approach to address this use case in SR-MPLS was SR
over MPLS (SR-MPLS) is described in [I-D.stein-srtsn]. [SRTSN].
A.3. Stack-Based Methods for Latency Control
One efficient data structure for inserting local deadlines into the
headers is a "stack", similar to that used in Segment Routing SR to carry forwarding
instructions. The number of deadline values in the stack equals the
number of routers the packet needs to traverse in the network, and
each deadline value corresponds to a specific router. The Top-of-Stack Top of
Stack (ToS) corresponds to the first router's deadline, while the
MPLS BoS refers to the last. All local deadlines in the stack are
later than or equal to the current time (upon which all routers
agree), and times closer to the ToS are always earlier than or equal
to times closer to the MPLS BoS.
The ingress router inserts the deadline stack into the packet
headers; no other router needs to know the time-bound flows'
requirements. requirements of the time-
bound flows. Hence, admitting a new flow only requires updating the
ingress router's information base.
MPLS LSRs that expose the ToS label can also inspect the associated
"deadline"
deadline carried in the packet (either in the MPLS stack as In-
Stack Data in-stack
data or after BoS as Post-Stack Data).
7. Acknowledgement post-stack data).
Acknowledgements
The authors gratefully acknowledge the input of the members of the
MPLS Open Design Team. Also, the authors sincerely thank Loa
Andersson, Xiao Min, Jie Dong, and Yaron Sheffer. Sheffer for their thoughtful
suggestions and help in improving the document.
Contributors' Addresses
Contributors
Loa Anderssen
Bronze Dragon Consulting
Email: loa@pi.nu
Authors' Addresses
Tarek Saad
Cisco Systems, Inc.
Email: tsaad.net@gmail.com
Kiran Makhijani
Independent
Email: kiran.ietf@gmail.com
Haoyu Song
Futurewei Technologies
Email: haoyu.song@futurewei.com
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com