P2MP MPLS-TP Framework: A Framework for Point-to-Multipoint MPLS in Transport Networks
How MPLS Transport Profile sends data from one source to multiple destinations.
Frost, D., Bryant, S., Bocci, M., and L. Berger, "A Framework for Point-to-Multipoint MPLS in Transport Networks", RFC 7167, DOI 10.17487/RFC7167, April 2014, <https://www.rfc-editor.org/info/rfc7167>.
@misc{rfc7167,
series = {Request for Comments},
number = 7167,
howpublished = {RFC 7167},
publisher = {RFC Editor},
doi = {10.17487/RFC7167},
url = {https://www.rfc-editor.org/info/rfc7167},
author = {D. Frost and S. Bryant and M. Bocci and L. Berger},
title = {{A Framework for Point-to-Multipoint MPLS in Transport Networks}},
pagetotal = 12,
year = 2014,
month = apr,
} RFC text
Contents
Internet Engineering Task Force (IETF) D. Frost
Request for Comments: 7167 Blue Sun
Category: Informational S. Bryant
ISSN: 2070-1721 Cisco Systems
M. Bocci
Alcatel-Lucent
L. Berger
LabN Consulting
April 2014
A Framework for Point-to-Multipoint MPLS in Transport Networks
Abstract
The Multiprotocol Label Switching Transport Profile (MPLS-TP) is the
common set of MPLS protocol functions defined to enable the
construction and operation of packet transport networks. The MPLS-TP
supports both point-to-point and point-to-multipoint transport paths.
This document defines the elements and functions of the MPLS-TP
architecture that are applicable specifically to supporting point-to-
multipoint transport paths.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7167.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 4
3. MPLS-TP P2MP Requirements . . . . . . . . . . . . . . . . . . 4
4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. MPLS-TP Encapsulation and Forwarding . . . . . . . . . . 6
5. Operations, Administration, and Maintenance . . . . . . . . . 6
6. Control Plane . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. P2MP LSP Control Plane . . . . . . . . . . . . . . . . . 8
6.2. P2MP PW Control Plane . . . . . . . . . . . . . . . . . . 8
7. Survivability . . . . . . . . . . . . . . . . . . . . . . . . 8
8. Network Management . . . . . . . . . . . . . . . . . . . . . 9
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
1. Introduction
The Multiprotocol Label Switching Transport Profile (MPLS-TP) is the
common set of MPLS protocol functions defined to meet the
requirements specified in [RFC5654]. The MPLS-TP Framework [RFC5921]
provides an overall introduction to the MPLS-TP and defines the
general architecture of the Transport Profile, as well as the aspects
specific to point-to-point transport paths. The purpose of this
document is to define the elements and functions of the MPLS-TP
architecture applicable specifically to supporting point-to-
multipoint transport paths.
1.1. Scope
This document defines the elements and functions of the MPLS-TP
architecture related to supporting point-to-multipoint transport
paths. The reader is referred to [RFC5921] for the aspects of the
MPLS-TP architecture that are generic or are concerned specifically
with point-to-point transport paths.
1.2. Terminology
Term Definition
------- ---------------------------------------------------
CE Customer Edge
LSP Label Switched Path
LSR Label Switching Router
MEG Maintenance Entity Group
MEP Maintenance Entity Group End Point
MIP Maintenance Entity Group Intermediate Point
MPLS-TE MPLS Traffic Engineering
MPLS-TP MPLS Transport Profile
OAM Operations, Administration, and Maintenance
OTN Optical Transport Network
P2MP Point-to-multipoint
PW Pseudowire
RSVP-TE Resource Reservation Protocol - Traffic Engineering
SDH Synchronous Digital Hierarchy
tLDP Targeted LDP
Detailed definitions and additional terminology may be found in
[RFC5921] and [RFC5654].
2. Applicability
The point-to-multipoint connectivity provided by an MPLS-TP network
is based on the point-to-multipoint connectivity provided by MPLS
networks. Traffic Engineered P2MP LSP support is discussed in
[RFC4875] and [RFC5332], and P2MP PW support is being developed based
on [P2MP-PW-REQS] and [VPMS-FRMWK-REQS]. MPLS-TP point-to-multipoint
connectivity is analogous to that provided by traditional transport
technologies such as Optical Transport Network point-to-multipoint
[G.798] and drop-and-continue [G.780], and thus supports the same
class of traditional applications, e.g., video distribution.
The scope of this document is limited to point-to-multipoint
functions and it does not discuss multipoint-to-multipoint support.
3. MPLS-TP P2MP Requirements
The requirements for MPLS-TP are specified in [RFC5654], [RFC5860],
and [RFC5951]. This section provides a brief summary of point-to-
multipoint transport requirements as set out in those documents; the
reader is referred to the documents themselves for the definitive and
complete list of requirements. This summary does not include the RFC
2119 [BCP14] conformance language used in the original documents as
this document is not authoritative.
From [RFC5654]:
o MPLS-TP must support traffic-engineered point-to-multipoint
transport paths.
o MPLS-TP must support unidirectional point-to-multipoint transport
paths.
o MPLS-TP must be capable of using P2MP server (sub)layer
capabilities as well as P2P server (sub)layer capabilities when
supporting P2MP MPLS-TP transport paths.
o The MPLS-TP control plane must support establishing all the
connectivity patterns defined for the MPLS-TP data plane (i.e.,
unidirectional P2P, associated bidirectional P2P, co-routed
bidirectional P2P, unidirectional P2MP) including configuration of
protection functions and any associated maintenance functions.
o Recovery techniques used for P2P and P2MP should be identical to
simplify implementation and operation.
o Unidirectional 1+1 and 1:n protection for P2MP connectivity must
be supported.
o MPLS-TP recovery in a ring must protect unidirectional P2MP
transport paths.
From [RFC5860]:
o The protocol solution(s) developed to perform the following OAM
functions must also apply to point-to-point associated
bidirectional LSPs, point-to-point unidirectional LSPs, and point-
to-multipoint LSPs:
* Continuity Check
* Connectivity Verification, proactive
* Lock Instruct
* Lock Reporting
* Alarm Reporting
* Client Failure Indication
* Packet Loss Measurement
* Packet Delay Measurement
o The protocol solution(s) developed to perform the following OAM
functions may also apply to point-to-point associated
bidirectional LSPs, point-to-point unidirectional LSPs, and point-
to-multipoint LSPs:
* Connectivity Verification, on-demand
* Route Tracing
* Diagnostic Tests
* Remote Defect Indication
From [RFC5951]:
o For unidirectional (P2P and point-to-multipoint (P2MP))
connection, proactive measurement of packet loss and loss ratio is
required.
o For a unidirectional (P2P and P2MP) connection, on-demand
measurement of delay measurement is required.
4. Architecture
The overall architecture of the MPLS-TP is defined in [RFC5921]. The
architecture for point-to-multipoint MPLS-TP comprises the following
additional elements and functions:
o Unidirectional point-to-multipoint LSPs
o Unidirectional point-to-multipoint PWs
o Optional point-to-multipoint LSP and PW control planes
o Survivability, network management, and Operations, Administration,
and Maintenance functions for point-to-multipoint PWs and LSPs.
The following subsection summarises the encapsulation and forwarding
of point-to-multipoint traffic within an MPLS-TP network, and the
encapsulation options for delivery of traffic to and from MPLS-TP CE
devices when the network is providing a packet transport service.
4.1. MPLS-TP Encapsulation and Forwarding
Packet encapsulation and forwarding for MPLS-TP point-to-multipoint
LSPs is identical to that for MPLS-TE point-to-multipoint LSPs.
MPLS-TE point-to-multipoint LSPs were introduced in [RFC4875] and the
related data-plane behaviour was further clarified in [RFC5332].
MPLS-TP allows for both upstream-assigned and downstream-assigned
labels for use with point-to-multipoint LSPs.
Packet encapsulation and forwarding for point-to-multipoint PWs has
been discussed within the PWE3 Working Group [P2MP-PW-ENCAPS], but
such definition is for further study.
5. Operations, Administration, and Maintenance
The requirements for MPLS-TP OAM are specified in [RFC5860]. The
overall OAM architecture for MPLS-TP is defined in [RFC6371], and
P2MP OAM design considerations are described in Section 3.7 of that
RFC.
All the traffic sent over a P2MP transport path, including OAM
packets generated by a MEP, is sent (multicast) from the root towards
all the leaves, and thus may be processed by all the MIPs and MEPs
associated with a P2MP MEG. If an OAM packet is to be processed by
only a specific leaf, it requires information to indicate to all
other leaves that the packet must be discarded. To address a packet
to an intermediate node in the tree, Time-to-Live-based addressing is
used to set the radius and additional information in the OAM payload
is used to identify the specific destination. It is worth noting
that a MIP and MEP may be instantiated on a single node when it is
both a branch and leaf node.
P2MP paths are unidirectional; therefore, any return path to an
originating MEP for on-demand transactions will be out of band. Out-
of-band return paths are discussed in Section 3.8 of [RFC5921].
A more detailed discussion of P2MP OAM considerations can be found in
[MPLS-TP-P2MP-OAM].
6. Control Plane
The framework for the MPLS-TP control plane is provided in [RFC6373].
This document reviews MPLS-TP control-plane requirements as well as
provides details on how the MPLS-TP control plane satisfies these
requirements. Most of the requirements identified in [RFC6373] apply
equally to P2P and P2MP transport paths. The key P2MP-specific
control-plane requirements are:
o requirement 6 (P2MP transport paths),
o requirement 34 (use P2P sub-layers),
o requirement 49 (common recovery solutions for P2P and P2MP),
o requirement 59 (1+1 protection),
o requirement 62 (1:n protection), and
o requirement 65 (1:n shared mesh recovery).
[RFC6373] defines the control-plane approach used to support MPLS-TP
transport paths. It identifies GMPLS as the control plane for MPLS-
TP LSPs and tLDP as the control plane for PWs. MPLS-TP allows that
either, or both, LSPs and PWs to be provisioned statically or via a
control plane. Quoting from [RFC6373]:
The PW and LSP control planes, collectively, must satisfy the
MPLS-TP control-plane requirements. As with P2P services, when
P2MP client services are provided directly via LSPs, all
requirements must be satisfied by the LSP control plane. When
client services are provided via PWs, the PW and LSP control
planes can operate in combination, and some functions may be
satisfied via the PW control plane while others are provided to
PWs by the LSP control plane. This is particularly noteworthy for
P2MP recovery.
6.1. P2MP LSP Control Plane
The MPLS-TP control plane for P2MP LSPs uses GMPLS and is based on
RSVP-TE for P2MP LSPs as defined in [RFC4875]. A detailed listing of
how GMPLS satisfies MPLS-TP control-plane requirements is provided in
[RFC6373].
[RFC6373] notes that recovery techniques for traffic engineered P2MP
LSPs are not formally defined, and that such a definition is needed.
A formal definition will be based on existing RFCs and may not
require any new protocol mechanisms but, nonetheless, should be
documented. GMPLS recovery is defined in [RFC4872] and [RFC4873].
Protection of P2MP LSPs is also discussed in [RFC6372] Section 4.7.3.
6.2. P2MP PW Control Plane
The MPLS-TP control plane for P2MP PWs should be based on the LDP
control protocol used for point-to-point PWs [RFC4447], with updates
as required for P2MP applications. A detailed specification of the
control plane for P2MP PWs is for further study.
7. Survivability
The overall survivability architecture for MPLS-TP is defined in
[RFC6372], and Section 4.7.3 of that RFC in particular describes the
application of linear protection to unidirectional P2MP entities
using 1+1 and 1:1 protection architecture. For 1+1, the approach is
for the root of the P2MP tree to bridge the user traffic to both the
working and protection entities. Each sink/leaf MPLS-TP node selects
the traffic from one entity according to some predetermined criteria.
For 1:1, the source/root MPLS-TP node needs to identify the existence
of a fault condition impacting delivery to any of the leaves. Fault
notification happens from the node identifying the fault to the root
node via an out-of-band path. The root then selects the protection
transport path for traffic transfer. More sophisticated
survivability approaches such as partial tree protection and 1:n
protection are for further study.
The IETF has no experience with P2MP PW survivability as yet;
therefore, it is proposed that the P2MP PW survivability will
initially rely on the LSP survivability. Further work is needed on
this subject, particularly if a requirement emerges to provide
survivability for P2MP PWs in an MPLS-TP context.
8. Network Management
An overview of network management considerations for MPLS-TP can be
found in Section 3.14 of [RFC5921]. The provided description applies
equally to P2MP transport paths.
The network management architecture and requirements for MPLS-TP are
specified in [RFC5951]. They derive from the generic specifications
described in ITU-T G.7710/Y.1701 [G.7710] for transport technologies.
They also incorporate the OAM requirements for MPLS networks
[RFC4377] and MPLS-TP networks [RFC5860] and expand on those
requirements to cover the modifications necessary for fault,
configuration, performance, and security in a transport network.
[RFC5951] covers all MPLS-TP connection types, including P2MP.
[RFC6639] provides the MIB-based architecture for MPLS-TP. It
reviews the interrelationships between different MIB modules that are
not MPLS-TP specific and that can be leveraged for MPLS-TP network
management, and identifies areas where additional MIB modules are
required. While the document does not consider P2MP transport paths,
it does provide a foundation for an analysis of areas where MIB-
module modification and addition may be needed to fully support P2MP
transport paths. There has also been work in the MPLS working group
on a P2MP specific MIB, [MPLS-TE-P2MP-MIB].
9. Security Considerations
General security considerations for MPLS-TP are covered in [RFC5921].
Additional security considerations for P2MP LSPs are provided in
[RFC4875]. This document introduces no new security considerations
beyond those covered in those documents.
10. References
10.1. Normative References
[RFC4872] Lang, J., Rekhter, Y., and D. Papadimitriou, "RSVP-TE
Extensions in Support of End-to-End Generalized Multi-
Protocol Label Switching (GMPLS) Recovery", RFC 4872, May
2007.
[RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
"GMPLS Segment Recovery", RFC 4873, May 2007.
[RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
"Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
[RFC5332] Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS
Multicast Encapsulations", RFC 5332, August 2008.
[RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
and S. Ueno, "Requirements of an MPLS Transport Profile",
RFC 5654, September 2009.
[RFC5921] Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
Berger, "A Framework for MPLS in Transport Networks", RFC
5921, July 2010.
10.2. Informative References
[BCP14] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[G.7710] ITU-T, "Common equipment management function
requirements", ITU-T G.7710/Y.1701, July 2007.
[G.780] ITU-T, "Terms and definitions for synchronous digital
hierarchy (SDH) networks", ITU-T G.780/Y.1351, July 2010.
[G.798] ITU-T, "Characteristics of optical transport network
hierarchy equipment functional blocks", ITU-T G.798,
December 2012.
[MPLS-TE-P2MP-MIB]
Farrel, A., Yasukawa, S., and T. Nadeau, "Point-to-
Multipoint Multiprotocol Label Switching (MPLS) Traffic
Engineering (TE) Management Information Base (MIB)
module", Work in Progress, April 2009.
[MPLS-TP-P2MP-OAM]
Arai, K., Koike, Y., Hamano, T., and M. Namiki, "Framework
for Point-to-Multipoint MPLS-TP OAM", Work in Progress,
January 2014.
[P2MP-PW-ENCAPS]
Aggarwal, R. and F. Jounay, "Point-to-Multipoint Pseudo-
Wire Encapsulation", Work in Progress, March 2010.
[P2MP-PW-REQS]
Jounay, F., Kamite, Y., Heron, G., and M. Bocci,
"Requirements and Framework for Point-to-Multipoint
Pseudowires over MPLS PSNs", Work in Progress, February
2014.
[RFC4377] Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
Matsushima, "Operations and Management (OAM) Requirements
for Multi-Protocol Label Switched (MPLS) Networks", RFC
4377, February 2006.
[RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
Heron, "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC5860] Vigoureux, M., Ward, D., and M. Betts, "Requirements for
Operations, Administration, and Maintenance (OAM) in MPLS
Transport Networks", RFC 5860, May 2010.
[RFC5951] Lam, K., Mansfield, S., and E. Gray, "Network Management
Requirements for MPLS-based Transport Networks", RFC 5951,
September 2010.
[RFC6371] Busi, I. and D. Allan, "Operations, Administration, and
Maintenance Framework for MPLS-Based Transport Networks",
RFC 6371, September 2011.
[RFC6372] Sprecher, N. and A. Farrel, "MPLS Transport Profile (MPLS-
TP) Survivability Framework", RFC 6372, September 2011.
[RFC6373] Andersson, L., Berger, L., Fang, L., Bitar, N., and E.
Gray, "MPLS Transport Profile (MPLS-TP) Control Plane
Framework", RFC 6373, September 2011.
[RFC6639] King, D. and M. Venkatesan, "Multiprotocol Label Switching
Transport Profile (MPLS-TP) MIB-Based Management
Overview", RFC 6639, June 2012.
[VPMS-FRMWK-REQS]
Kamite, Y., Jounay, F., Niven-Jenkins, B., Brungard, D.,
and L. Jin, "Framework and Requirements for Virtual
Private Multicast Service (VPMS)", Work in Progress,
October 2012.
Authors' Addresses
Dan Frost
Blue Sun
EMail: frost@mm.st
Stewart Bryant
Cisco Systems
EMail: stbryant@cisco.com
Matthew Bocci
Alcatel-Lucent
Voyager Place, Shoppenhangers Road
Maidenhead, Berks SL6 2PJ
United Kingdom
EMail: matthew.bocci@alcatel-lucent.com
Lou Berger
LabN Consulting
Phone: +1-301-468-9228
EMail: lberger@labn.net
AI ELI5
On this page
§1Point-to-Multipoint in Transport Networks
Multiprotocol Label Switching Transport Profile (MPLS-TP) is a subset of MPLS designed specifically for carrier transport networks. It offers the operational rigor, fault detection, and management capabilities that service providers demand. MPLS-TP initially focused on point-to-point paths where one source connects to one destination. However, carriers need point-to-multipoint (P2MP) paths to deliver services like video distribution, IPTV, and IP multicast to many customers from a single source.
This document extends the MPLS-TP framework (defined in RFC 5921) to cover P2MP transport paths. Traditional transport technologies such as Optical Transport Network (OTN) have long supported P2MP through drop-and-continue mechanisms: a signal flows down a link, and intermediate nodes can extract and forward a copy to downstream branches. MPLS-TP P2MP operates on the same principle but at the packet/label level.
One sender (like a video studio) connects to one path down a tree-shaped network. At each branch point, a copy goes down each path. Every destination gets the same video.
§2What P2MP Must Support
The RFC summarizes requirements from RFC 5654, RFC 5860, and RFC 5951. MPLS-TP must support unidirectional P2MP transport paths: a single sender reaches multiple receivers, without a reverse path. P2MP paths must be traffic engineered, meaning the operator can specify the exact path the traffic takes, ensuring quality of service guarantees. The control plane must support establishing P2MP connectivity and configuring protection (recovery from failures).
Operations and maintenance (OAM) functions critical for transport networks must work with P2MP paths: continuity checks (is the path working?), connectivity verification (is traffic reaching all leaves?), packet loss measurement, packet delay measurement, and alarm reporting. Recovery must work: if a link fails, traffic should switch to a backup path with minimal disruption. Unidirectional 1+1 and 1:n protection must be supported, where backup paths carry redundant copies or stand ready to take over.
The operator picks the exact paths. All leaves must get the traffic. If a pipe breaks, automatic backup takes over. The network must monitor health and report problems.
§3MPLS-TP P2MP Architecture
The P2MP architecture comprises two main transport entity types:
P2MP Label Switched Paths (LSPs) are the primary mechanism. A Label Switched Path (LSP) is a path through MPLS routers (Label Switching Routers, or LSRs) where each hop forwards traffic based on a label (a short identifier) rather than a long IP address. A P2MP LSP has a root LSR (the sender) and one or more leaf LSRs (receivers). Each LSP is unidirectional: traffic flows from the root toward all leaves, but not back. The encapsulation and forwarding of P2MP LSPs is identical to MPLS Traffic Engineering (MPLS-TE) P2MP LSPs, defined in RFC 4875.
P2MP Pseudowires (PWs) are a second, emerging mechanism. Pseudowires emulate services (like Ethernet virtual circuits) over MPLS. P2MP PW specifications are still under development and marked for further study; the RFC notes that encapsulation and forwarding for P2MP PWs have not yet been formally defined.
MPLS-TP P2MP supports both upstream-assigned and downstream-assigned labels: labels chosen by the sending router or by each downstream router along the path.
A P2MP LSP is like a river that branches at each fork, sending water (traffic) down every branch. Each branch is labeled so routers know where to send packets. PWs are a newer way to do it, still being designed.
§4Operations, Maintenance, and Management
Operations and Maintenance (OAM) in P2MP paths presents unique challenges because all traffic—including OAM packets generated at the root—flows multicast toward all leaves. If an OAM packet must be processed by only one specific leaf, the sender must indicate this with a special tag. The RFC uses Time-to-Live (TTL)-based addressing to set the "radius" of an OAM packet (how many hops it travels), and additional payload information to identify the specific destination leaf.
P2MP paths are unidirectional, so any response to an OAM query must return via an out-of-band path (a separate channel, not part of the main P2MP path). This complicates fault detection: a leaf cannot directly report problems to the root; the network must use an alternate path.
Network management follows the framework in RFC 5951, which derives requirements from ITU-T standards for transport networks. P2MP paths require Management Information Base (MIB) modules for SNMP-based management. The RFC references ongoing work on P2MP-specific MIBs to manage configuration, performance, and faults.
Checking if a path works is tricky: a message sent to all leaves must say "only leaf #3 needs to answer." Replies come back a different way. Management tools must track and report on all those branches.
§5Control Plane and Recovery
The control plane is the mechanism for establishing and managing paths. For P2MP LSPs, MPLS-TP uses GMPLS (Generalized MPLS) and RSVP-TE (Resource Reservation Protocol with Traffic Engineering extensions). GMPLS is a generalization of MPLS that handles various types of data-plane devices; RFC 4875 defines RSVP-TE for P2MP LSPs. The control plane must communicate topology information, reserve bandwidth, signal which paths to use, and orchestrate recovery actions.
For P2MP Pseudowires, the control plane should use LDP (Label Distribution Protocol) with P2MP extensions. LDP is used for point-to-point PWs; extending it to P2MP is still under development and marked for further study.
Recovery and protection in P2MP is more complex than in point-to-point. 1+1 protection means the root sends traffic down both a working and a protection path; each leaf independently selects which copy to use. 1:n protection means multiple backup paths stand by; if the primary fails, traffic switches to a backup, and multiple failures can be protected. The RFC notes that recovery techniques for P2MP LSPs were not formally defined at the time and should be documented. More sophisticated approaches like partial tree protection and 1:n shared mesh recovery are identified as future work.
The control plane tells every router: "send this customer's video down this tree of pipes using label 1234." If a pipe breaks, a backup tree takes over. For very complex networks, fancier backup strategies are being designed.
§6Current Status and Future Work
RFC 7167 is a framework document that codifies the P2MP aspects of MPLS-TP. At the time of publication (April 2014), P2MP LSPs were well defined and could be deployed, building on prior work in MPLS Traffic Engineering. However, several areas were identified for further work: formal definition of recovery techniques for traffic-engineered P2MP LSPs, the complete control plane specification for P2MP pseudowires, encapsulation and forwarding definitions for P2MP PWs, and more sophisticated survivability approaches.
The RFC emphasizes that P2MP PWs are marked "for further study" because at that time, there was insufficient operational experience to define them fully. Over subsequent years, standards development continued on P2MP services, though P2MP PWs remain less widely deployed than P2MP LSPs.
P2MP LSPs (the main tree-path mechanism) were ready to use. P2MP PWs (simulating circuits) were still being designed. Later work has made them better, but trees are more common than circuit simulations.