TreeDN- Tree-based CDNs for Live Streaming to Mass Audiences
draft-ietf-mops-treedn-07

MOPS                                                         L. Giuliano
Internet-Draft                                          Juniper Networks
Intended status: Informational                                 C. Lenart
Expires: 22 February 2025                                        Verizon
                                                                 R. Adam
                                                                   GEANT
                                                          21 August 2024

      TreeDN- Tree-based CDNs for Live Streaming to Mass Audiences
                       draft-ietf-mops-treedn-07

Abstract

   As Internet audience sizes for high-interest live events reach
   unprecedented levels and bitrates climb to support 4K/8K/Augmented
   Reality (AR), live streaming can place a unique type of stress upon
   network resources.  TreeDN is a tree-based CDN architecture designed
   to address the distinctive scaling challenges of live streaming to
   mass audiences.  TreeDN enables operators to offer Replication-as-
   a-Service (RaaS) at a fraction the cost of traditional, unicast-based
   CDNs- in some cases, at no additional cost to the infrastructure.  In
   addition to efficiently utilizing network resources to deliver
   existing multi-destination traffic, this architecture also enables
   new types of content and use cases that previously were not possible
   or economically viable using traditional CDN approaches.  Finally,
   TreeDN is a decentralized architecture and a democratizing technology
   in the way that it makes content distribution more accessible to more
   people by dramatically reducing the costs of replication.

Status of This Memo

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   This Internet-Draft will expire on 22 February 2025.

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Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Multicast Challenges in the Past  . . . . . . . . . . . . . .   4
   4.  TreeDN Architecture . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  TreeDN Overlays . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  TreeDN Native On-Net  . . . . . . . . . . . . . . . . . .   6
   5.  Replication-as-a-Service (RaaS) . . . . . . . . . . . . . . .   7
   6.  Decentralization/Democratization of Content Sourcing  . . . .   8
   7.  Transport Layer-Related Differences between TreeDN and
           Traditional CDNs  . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Integration with Unicast  . . . . . . . . . . . . . . . .   9
     7.2.  Reliability, Adaptive Bitrate and Congestion Control  . .   9
     7.3.  Authorization and Encryption  . . . . . . . . . . . . . .  10
   8.  TreeDN Deployments  . . . . . . . . . . . . . . . . . . . . .  10
   9.  Operational Considerations  . . . . . . . . . . . . . . . . .  11
   10. Security Consideration  . . . . . . . . . . . . . . . . . . .  11
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     13.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Appendix A.  Netverses  . . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Problem Statement

   Live streaming to mass audiences can impose unique demands on network
   resources.  For example, live sporting events broadcast over the
   Internet to end users has much lower tolerance for long playout
   buffers than typical on-demand video streaming.  Viewers of live
   sporting events have long been conditioned by broadcast television to
   expect to see the content in real time, with only very short buffers

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   for broadcast delays to prevent profanity and other objectionable
   content from making on the air (the "seven-second delay"
   [BROADCAST-DELAY]).  With micro-betting, even this 5-10 second delay
   can be too long.  By comparison, when watching on-demand movies, an
   extra one- or two-minute playout buffer tends to be perfectly
   acceptable for viewers.  If playout buffers for live sports are that
   long, viewers run the risk of being alerted to the game winning score
   from text messages from friends or cheers from the bar across the
   street, minutes before they view it themselves.

   Another unique characteristic of live streaming is join rate.  While
   on-demand video streaming can consume massive amounts of network
   resources, the viewing rates tend to be smooth and predictable.
   Service Providers observe gradual levels of traffic increases over
   the evening hours corresponding to prime-time viewing habits.  By
   comparison, viewing rates of live video streams can more closely
   resemble a step function with much less predictability as mass
   audiences of viewers tune in to watch the game at the same time.

   Previous efforts at more efficient network replication of multi-
   destination traffic have experienced mixed success in terms of
   adoption.  IP multicast is widely deployed on financial networks,
   video distribution networks, L3VPN networks and certain enterprises.
   But most of these deployments are restricted to "walled-garden"
   networks.  Multicast over the global Internet has failed to gain
   traction, as only a very small portion of the Internet is multicast-
   enabled at this time.

   TreeDN is a tree-based CDN architecture that is the result of the
   evolution of network-based replication mechanisms based on lessons
   learned from what has and has not worked well in the past.  TreeDN
   addresses the fundamental issues of what has hindered multicast from
   adoption on the global Internet and enables service providers the
   opportunity to deliver new Replication-as-a-Service (RaaS) offerings
   to content providers, while more efficiently utilizing network
   resources by eliminating duplicated traffic, and thus, improving the
   experience of end users.  TreeDN accomplishes this with the
   combination of a simplified model of native multicast along with
   network overlays to reach receivers on unicast-only parts of the
   Internet.

   By more efficiently supporting multi-destination traffic, TreeDN is
   an architecture that can enable new types of content, such as
   Augmented Reality (AR) live streaming to mass audiences, that
   previously weren't possible or economically viable on the Internet
   due to the inefficiencies of unicast.

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2.  Applicability

   While the primary use case mentioned throughout this document is live
   streaming of multimedia content (audio, video, AR, real-time
   telemetry data), the TreeDN architecture can provide efficient
   delivery for any content that needs to be replicated and delivered to
   multiple destinations.  For example, large software file updates (eg,
   OS upgrades) that need to be delivered to many end users in a very
   short window of time can cause significant strain on network
   resources.  Using TreeDN, this use case can be handled much more
   efficiently by the network.

3.  Multicast Challenges in the Past

   The following issues have been the some of the primary challenges for
   deployment of IP multicast over the global Internet.  This is not
   intended to be an exhaustive list, but to rather to provide context
   to the solution and how it addresses these primary challenges.

   *  The "All or Nothing" Problem: IP multicast requires every layer-3
      hop between source and receivers to be multicast-enabled.  To
      achieve ubiquitous availability on the global Internet, this
      essentially means nearly every interface on every router and
      firewall between all end hosts must support a multicast routing
      protocol like Protocol Independent Multicast - Sparse Mode (PIM-
      SM) [RFC7761] or Multipoint Label Distribution Protocol (mLDP)
      [RFC6388].  This requirement creates a bar to deployment that is
      practically impossible to overcome.

   *  The "It's Too Complex" Problem: operators have long complained
      that multicast routing protocols like PIM-SM are simply too
      complex, making it costly to design, configure, manage and
      troubleshoot IP multicast in the network.

   *  The "Chicken and Egg" Problem: there's not much multicast content
      because there's not much of a multicast-enabled audience, but
      there's not much of a multicast-enabled audience because there's
      not much multicast content.

   TreeDN is the evolution of network-based replication based on lessons
   learned over decades and is designed to address the problems listed
   above.

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4.  TreeDN Architecture

   TreeDN leverages a simplified model for multicast deployment combined
   with network overlays to deliver traffic to receiving hosts on
   unicast-only networks.  With network overlays, a service can be
   achieved and delivered to end users while recognizing and tolerating
   the practical realities of what is possible over a network as diverse
   as the global Internet.  That is, the replication service is
   available to users and applications across the global Internet
   regardless of what protocols may exist in the underlying networks
   that constitute the underlay.

                           TreeDN Provider
                   +-------------------------------+
                   |                               |
                   |   Native Multicast On-Net     |
   +----------+    |         (PIM-SSM)             |
   | Content/ |----+                               |
   | Mcast    |    |                               |
   | Source   |    |                   +-----------+
   +----------+    +---|-------|-------| AMT Relay |  +--------------+
                       |       |       +----|------+  | Unicast-Only |
                      +-+     +-+           .         |    Network   |
                      +-+     +-+           ..........|........      |
                    Native Content        AMT Tunnel  +-------.------+
                       Receivers                              .
                                                     AMT     +-+
                                                     Gateway +-+
                                                              |
                                                          Content
                                                          Receiver

                     Figure 1: TreeDN Provider Example

4.1.  TreeDN Overlays

   One overlay technology that TreeDN leverages is Automatic Multicast
   Tunneling (AMT) [RFC7450].  With AMT, end hosts on unicast-only
   networks (AMT Gateways) can dynamically build tunnels to routers on
   the multicast-enabled part of the network (AMT Relays) and receive
   multicast streams.  The AMT Gateway is a thin software client which
   typically sits on the receiving end host and initiates the tunnel at
   an AMT Relay, which is a tunnel server that typically sits at the
   border of the multicast network.  AMT allows any end host on the
   Internet to receive multicast content regardless of whether their
   local provider supports multicast (aka, "off-net receivers"), which
   addresses the "All or Nothing" Problem.  Links and devices that do
   not support multicast are simply tunneled over- they no longer

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   present a barrier to the overall replication service for end users.
   Those networks that do deploy and support multicast, as well as the
   content providers that serve up multicast content, are able to enjoy
   the benefits of efficient replication and delivery.  Further, these
   benefits can serve as incentives for operators who do not yet support
   multicast to enable it on their networks, a key benefit of
   incremental deployment described in section 4.3 of [RFC9049].  Once
   the cost of carrying duplicated unicast tunnels is perceived by those
   operators to exceed the cost of deploying multicast, they are more
   likely to enable multicast on their networks.  In this way, TreeDN
   effectively supports incremental deployment in a way that was not
   previously possible with traditional (non-overlay) multicast
   networking.  Finally, AMT also addresses the "Chicken and Egg"
   Problem, as all end hosts on the global Internet that have access to
   an AMT Relay are capable of becoming audience members.

   To support receiving on both native and non-native networks,
   receiving hosts can first attempt to join the traffic natively and,
   if no multicast traffic is received, fallback to AMT.  This fallback
   mechanism can be handled by the application layer.

   In addition to AMT, other overlay technologies like Locator/ID
   Separation Protocol (LISP) [RFC9300] can be utilized to deliver
   content from multicast-enabled networks to end hosts that are
   separated by portions of the network (at the last/middle/first mile)
   that do not support multicast.

4.2.  TreeDN Native On-Net

   Networks that support multicast provide the native on-net component
   of TreeDN.  The primary requirement of the native on-net is to
   support Source-Specific Multicast (SSM) [RFC4607].  PIM-SSM, which is
   merely a subset of PIM-SM, is the multicast routing protocol
   typically used in SSM.  However, any multicast routing protocol
   capable of supporting SSM can be used as a TreeDN native on-net, such
   as mLDP, Global Table Multicast (GTM) [RFC7716] and BGP-based
   Multicast [I-D.ietf-bess-bgp-multicast], or even BGP-MVPN [RFC6513]
   for those operators who carry the global routing table in a VRF.
   Likewise, any data plane technology that supports SSM, including BIER
   [RFC8279] and SR-P2MP [I-D.ietf-spring-sr-replication-segment] can be
   used.

   The key benefit of SSM as the native on-net component of TreeDN is
   that it radically simplifies the control plane needed to support
   replication in the network.  This simplification comes by moving
   source discovery from the network layer to some sort of out-of-band
   mechanism, usually in the application layer.  In SSM, the receiver
   uses Internet Group Management Protocol, Version 3 (IGMPv3) [RFC3376]

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   for IPv4 or Multicast Listener Discovery Version 2 (MLDv2) [RFC3810]
   for IPv6 to specify both the source and group address of the
   multicast stream.  This allows the last hop router to immediately
   join the multicast stream along the shortest-path tree (SPT) without
   the need for shared trees.  This benefit addresses the "It's Too
   Complex" Problem.  By eliminating the need for network-based source
   discovery, most of the complexity of multicast is then eliminated,
   which reduces the cost of deploying and operating a multicast
   network.  Further rationale for this SSM-only approach can be found
   in Any-Source Multicast (ASM) Deprecation [RFC8815].

5.  Replication-as-a-Service (RaaS)

   Content providers have traditionally used CDNs to distribute content
   that needs to be delivered to large audiences, essentially
   outsourcing the task of replication to CDN providers.  Most CDNs
   utilize unicast delivery, as multicast is not an option due to its
   lack of general availability on the global Internet.  TreeDN is a CDN
   architecture that leverages tree-based replication to more
   efficiently utilize network resources to deliver simultaneous multi-
   destination traffic.  By leveraging overlay networking to address the
   "All or Nothing" and "Chicken and Egg" Problems and SSM to address
   the "It's Too Complex" Problem, TreeDN avoids the practical issues
   that previously prevented multicast from being a viable option for
   CDN providers.

   TreeDN has several advantages over traditional unicast-based CDN
   approaches.  First, the TreeDN functionality can be delivered
   entirely by the existing network infrastructure.  Specifically, for
   operators with routers that support AMT natively, multicast traffic
   can be delivered directly to end users without the need for
   specialized CDN devices, which typically are servers that need to be
   racked, powered, cooled and connected to ports on routers that could
   otherwise have been consumed by paying customers.  In this way, SPs
   can offer new RaaS functionality to content providers at potentially
   zero additional cost in new equipment.

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   Additionally, TreeDN is an open architecture that leverages mature,
   IETF-specified and widely implemented network protocols.  TreeDN also
   requires far less coordination between the content provider and the
   CDN operator.  That is, there are no storage requirements for the
   data, nor group-key management issues since a TreeDN provider merely
   forwards packets.  A TreeDN provider simply needs to have enough
   accounting data (eg, traffic data, number of AMT tunnels, etc) to
   properly bill customers for the service.  By contrast, traditional
   unicast-based CDNs often incorporate proprietary, non-interoperable
   technologies and require significant coordination between the content
   provider and the CDN to handle such things as file storage, data
   protection and key-management.

   TreeDN introduces a deployment model that requires new considerations
   for transport layer mechanisms that are frequently relied upon by
   traditional unicast-based CDNs.  A discussion on these considerations
   and differences can be found in section 7.

6.  Decentralization/Democratization of Content Sourcing

   TreeDN is an inherently decentralized architecture.  This reduces the
   cost for content sourcing, as any host connected to a multicast-
   enabled network, or on a source-capable overlay, can send out a
   single data stream that can be reached by an arbitrarily large
   audience.  By effectively reducing to zero the marginal cost of
   reaching each additional audience member, from the perspective of the
   source, TreeDN democratizes content sourcing on the Internet.

7.  Transport Layer-Related Differences between TreeDN and Traditional
    CDNs

   The focus of this document is on the network layer components that
   comprise the TreeDN architecture.  This section introduces some of
   the key transport layer-related differences between TreeDN and
   traditional unicast-based CDNs that should be taken into
   consideration when deploying TreeDN-based services.  In many cases,
   these issues are more related to TCP-UDP differences than unicast-
   multicast differences, thus UDP-based solutions can be leveraged to
   address most gaps.  The aim of this section is to point to some of
   the existing work to address these gaps, as well as suggest further
   work that could be undertaken within the IETF.  Further details of
   these transport layer mechanisms are beyond the scope of this
   document.

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7.1.  Integration with Unicast

   Since SSM inherently implies unidirectional traffic flows from one to
   many, mechanisms that rely on bidirectional communication between
   receivers and the content provider, such as bespoke advertising,
   telemetry data from receivers detailing end user experience,
   distribution of decryption keys, switching to higher/lower bandwidth
   streams, etc, are not well suited to SSM delivery.  As such, separate
   unicast streams between receivers and content providers may be used
   for this type of "out-of-band" functions while SSM is used to deliver
   the actual content of interest.  These "out-of-band" unicast streams
   SHOULD use the same congestion control and authentication mechanisms
   that are used today for mass audience unicast delivery.  Generally
   speaking, this hybrid unicast-multicast approach is best handled by
   the application layer and further detail is beyond the scope of this
   document.

7.2.  Reliability, Adaptive Bitrate and Congestion Control

   Traditional unicast-based CDNs frequently rely on HTTPS over TCP
   transport and are thus able to leverage the granularity of TCP-based
   mechanisms for reliability, congestion control and adaptive bitrate
   streaming.  But this granularity comes at a cost of sending a
   separate datastream to each viewer.  Multicast transmissions usually
   employ UDP, which inherently lacks many of the aforementioned
   benefits of TCP, but can scale much better for mass audiences of
   simultaneous viewers.  Forward Error Correction (FEC) is a mechanism
   that has demonstrated full recovery for up to 5% packet loss and
   interruptions up to 400ms for multicast datastreams in
   [EUMETSAT-TERRESTRIAL].  NACK-Oriented Reliable Multicast (NORM)
   [RFC5740] leverages FEC-based repair and other Reliable Multicast
   Transport building blocks to provide end-to-end reliable transport
   over multicast networks.

   QUIC [RFC9000] is another popular transport used by traditional
   unicast-based CDNs.  While QUIC does use UDP, it does not currently
   support multicast.  Multicast extensions to QUIC have been proposed
   in [I-D.jholland-quic-multicast].

   Section 4.1 of [RFC8085] describes how a sender can distribute data
   across multiple multicast source-group channels so that each receiver
   can join the most appropriate channels for its own reception rate
   capability, thus providing adaptive bitrate capabilities for
   multicast streams.  DVB MABR [DVB-MABR] and MAUD [MAUD] extensively
   describe an architecture that enables reliability and dynamic bitrate
   adaptation.

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   TreeDN deployments MUST follow the congestion control guidelines
   described in Section 4.1.4.2 of [RFC7450].  Multicast applications
   being distributed over TreeDN deployments SHOULD implement congestion
   control for its data transmission as described in Section 4.1 in
   [RFC8085].  The AMT gateway SHOULD use the topologically closest AMT
   relay.  Section 3.1 of [RFC8777] describes a set of procedures for
   optimal relay selection.

7.3.  Authorization and Encryption

   A multicast sender typically has little to no control or visibility
   about which end hosts may receive the datastream.  Encryption can be
   used to ensure that only authorized receivers are able to access
   meaningful data.  That is, even if unauthorized end hosts (eg, non-
   paying) receive the datastream, without decryption keys, the data is
   useless.  [I-D.ietf-ipsecme-g-ikev2] describes an extension to IKEv2
   for the purpose of group key management.  DVB MABR [DVB-MABR] and
   MAUD [MAUD] extensively describe an architecture that includes
   encryption of multicast streams.

8.  TreeDN Deployments

   EUMETCast Terrestrial is a service from EUMETSAT that delivers
   meteorological satellite data to end users for purposes such as
   operational monitoring of climate and detection of global climate
   changes.  EUMETCast Terrestrial connects to the GEANT network, which
   provides TreeDN services to deliver this real-time data natively to
   end users on multicast-enabled networks as well as to end users on
   unicast-only networks via a global deployment of AMT relays.  Details
   of the EUMETCast Terrestrial service over the GEANT TreeDN network
   are described in [EUMETCast-TERRESTRIAL-over-AMT].  Additional
   details on how this deployment uses encryption, authorization,
   reliability and unicast feedback channels for end-to-end file
   delivery monitoring can be found in [EUMETSAT-TERRESTRIAL].

   The Multicast Menu is a web-based portal that lists and can launch
   active multicast streams that are available on a global TreeDN
   network of various research and educations networks.  Details of the
   this TreeDN network, as well as the Multicast Menu, are described in
   [Multicast-Menu].

   The RARE network is a global testbed interconnecting several national
   research and education networks (NRENs) via routers running BIER.
   AMT relays are deployed to deliver multicast traffic from sources on
   the RARE network to receivers on unicast-only networks across the
   Internet.  Details of the RARE network are described in
   [BIER-AMT-Deployment].

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9.  Operational Considerations

   TreeDN is essentially the synthesis of SSM plus overlay networking
   technologies like AMT.  As such, any existing tools to manage,
   operate and troubleshoot a PIM-SSM domain and AMT deployment can be
   used to manage a TreeDN deployment.  Protocol error handling for PIM-
   SSM can be found in [RFC4607] and in section 4.8 of [RFC7761] and for
   AMT in [RFC7450].

   One potential operational benefit of a multicast-based approach like
   TreeDN over traditional, unicast-based CDNs is the visibility that
   multicast state provides in the routing infrastructure.  That is,
   multicast routers maintain a forwarding cache of multicast flows that
   usually includes the source address, group address, incoming/outgoing
   interfaces and forwarding rate.  Generally speaking, such flow state
   information is not typically available in core networks for unicast,
   so additional tools outside the routing infrastructure are usually
   required for monitoring CDN performance and troubleshooting issues
   like packet loss location.  Of course, this benefit comes at a cost
   of additional state being maintained in the routers for multicast.

   Additionally, since multicast leverages reverse-path forwarding
   (RPF), the source of the content can potentially have a greater
   influence over the path taken through the network from source to
   native receivers/AMT relays.  That is, the BGP peer advertising the
   reachability of the source's subnet can do so in ways that can prefer
   a particular path through the network for multicast distribution that
   are not as easy to accomplish with traditional, destination-based
   unicast routing.

10.  Security Consideration

   Since TreeDN is essentially the synthesis of SSM plus overlay
   networking technologies like AMT, the TreeDN architecture introduces
   no new security threats that are not already documented in SSM and
   the overlay technologies that comprise it.  In particular, Section 6
   of [RFC7450] candidly notes that AMT, like UDP, IGMP and MLD,
   provides no mechanisms for ensuring message delivery or integrity,
   nor does it provide confidentiality, since sources/groups joined
   through IGMP/MLD could be associated with the particular content
   being requested.

   [RFC4609] and [RFC8815] describes the additional security benefits of
   using SSM instead of ASM.

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11.  IANA Considerations

   This document has no IANA actions.

12.  Acknowledgements

   Many thanks to those who have contributed to building and operating
   the first TreeDN network on the Internet, including Pete Morasca,
   William Zhang, Lauren Delwiche, Natalie Landsberg, Wayne Brassem,
   Jake Holland, Andrew Gallo, Casey Russell, Janus Varmarken, Csaba
   Mate, Frederic Loui, Max Franke, Todor Moskov, Erik Herz, Bradley
   Cao, Katie Merrill, Karel Hendrych, Haruna Oseni and Isabelle Xiong.
   The writing of this document to describe the TreeDN architecture was
   inspired by a conversation with Dino Farinacci and Mike McBride.
   Thanks also to Jeff Haas, Vinod Kumar, Ron Bonica, Jeffrey Zhang and
   Eric Vyncke for their thoughtful reviews and suggestions, Chris
   Lemmons for his detailed shepherd review and Stephen Farrell, Magnus
   Westerlund, Reese Enghardt, Jurgen Schonwalder, Carlos Pignataro,
   Erik Kline, Gunter Van de Velde, Warren Kumari and Zaheduzzaman
   Sarker for their last call reviews.

13.  References

13.1.  Normative References

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
              <https://www.rfc-editor.org/info/rfc3376>.

   [RFC3810]  Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
              Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
              DOI 10.17487/RFC3810, June 2004,
              <https://www.rfc-editor.org/info/rfc3810>.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
              <https://www.rfc-editor.org/info/rfc4607>.

   [RFC6388]  Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
              Thomas, "Label Distribution Protocol Extensions for Point-
              to-Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,
              <https://www.rfc-editor.org/info/rfc6388>.

   [RFC7450]  Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450,
              DOI 10.17487/RFC7450, February 2015,
              <https://www.rfc-editor.org/info/rfc7450>.

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   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/info/rfc7761>.

13.2.  Informative References

   [Algorhyme]
              "Algorhyme", Wikipedia , n.d.,
              <https://en.wikipedia.org/wiki/
              Radia_Perlman#Spanning_Tree_Protocol>.

   [BIER-AMT-Deployment]
              "BIER + AMT Deployment in GEANT/RARE Network", IETF112
              Proceedings , n.d.,
              <https://datatracker.ietf.org/meeting/112/materials/
              slides-112-mboned-bier-amt-depolyment-in-geantrare-
              network-00>.

   [BROADCAST-DELAY]
              "Broadcast Delay", Wikipedia , n.d.,
              <https://en.wikipedia.org/wiki/Broadcast_delay>.

   [DVB-MABR] "Adaptive media streaming over IP multicast", DVB Document
              A176 Rev.3 (Fourth edition) , n.d., <https://dvb.org/wp-
              content/uploads/2022/01/A176r3_Adaptive-Media-Streaming-
              over-IP-Multicast_Interim-Draft-TS-
              103-769-v121_March_2023.pdf>.

   [EUMETCast-TERRESTRIAL-over-AMT]
              "EUMETCast Terrestrial over AMT", IETF115 Proceedings ,
              n.d., <https://datatracker.ietf.org/meeting/115/materials/
              slides-115-mboned-eumetcast-over-amt>.

   [EUMETSAT-TERRESTRIAL]
              "EUMETSAT Terrestrial Service", IETF110 Proceedings ,
              n.d., <https://datatracker.ietf.org/meeting/110/materials/
              slides-110-mboned-eumetsat-multicast-over-the-mbone-00>.

   [I-D.ietf-bess-bgp-multicast]
              Zhang, Z. J., Giuliano, L., Patel, K., Wijnands, I.,
              Mishra, M. P., and A. Gulko, "BGP Based Multicast", Work
              in Progress, Internet-Draft, draft-ietf-bess-bgp-
              multicast-08, 3 June 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-bess-
              bgp-multicast-08>.

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   [I-D.ietf-ipsecme-g-ikev2]
              Smyslov, V. and B. Weis, "Group Key Management using
              IKEv2", Work in Progress, Internet-Draft, draft-ietf-
              ipsecme-g-ikev2-13, 21 August 2024,
              <https://datatracker.ietf.org/api/v1/doc/document/draft-
              ietf-ipsecme-g-ikev2/>.

   [I-D.ietf-spring-sr-replication-segment]
              Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
              J. Zhang, "SR Replication segment for Multi-point Service
              Delivery", Work in Progress, Internet-Draft, draft-ietf-
              spring-sr-replication-segment-19, 28 August 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
              sr-replication-segment-19>.

   [I-D.jholland-quic-multicast]
              Holland, J., Pardue, L., and M. Franke, "Multicast
              Extension for QUIC", Work in Progress, Internet-Draft,
              draft-jholland-quic-multicast-05, 7 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-jholland-
              quic-multicast-05>.

   [MAUD]     "Multicast-Assisted Unicast Delivery", IBC2023 Tech
              Papers , n.d., <https://www.ibc.org/technical-papers/
              ibc2023-tech-papers-multicast-assisted-unicast-
              delivery/10235.article>.

   [Multicast-Menu]
              "Offnet Sourcing with the Multicast Menu", IETF114
              Proceedings , n.d.,
              <https://datatracker.ietf.org/meeting/114/materials/
              slides-114-mboned-offnet-sourcing-with-the-multicast-menu-
              01>.

   [RFC4609]  Savola, P., Lehtonen, R., and D. Meyer, "Protocol
              Independent Multicast - Sparse Mode (PIM-SM) Multicast
              Routing Security Issues and Enhancements", RFC 4609,
              DOI 10.17487/RFC4609, October 2006,
              <https://www.rfc-editor.org/info/rfc4609>.

   [RFC5740]  Adamson, B., Bormann, C., Handley, M., and J. Macker,
              "NACK-Oriented Reliable Multicast (NORM) Transport
              Protocol", RFC 5740, DOI 10.17487/RFC5740, November 2009,
              <https://www.rfc-editor.org/info/rfc5740>.

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <https://www.rfc-editor.org/info/rfc6513>.

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   [RFC7716]  Zhang, J., Giuliano, L., Rosen, E., Ed., Subramanian, K.,
              and D. Pacella, "Global Table Multicast with BGP Multicast
              VPN (BGP-MVPN) Procedures", RFC 7716,
              DOI 10.17487/RFC7716, December 2015,
              <https://www.rfc-editor.org/info/rfc7716>.

   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
              March 2017, <https://www.rfc-editor.org/info/rfc8085>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [RFC8777]  Holland, J., "DNS Reverse IP Automatic Multicast Tunneling
              (AMT) Discovery", RFC 8777, DOI 10.17487/RFC8777, April
              2020, <https://www.rfc-editor.org/info/rfc8777>.

   [RFC8815]  Abrahamsson, M., Chown, T., Giuliano, L., and T. Eckert,
              "Deprecating Any-Source Multicast (ASM) for Interdomain
              Multicast", BCP 229, RFC 8815, DOI 10.17487/RFC8815,
              August 2020, <https://www.rfc-editor.org/info/rfc8815>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

   [RFC9049]  Dawkins, S., Ed., "Path Aware Networking: Obstacles to
              Deployment (A Bestiary of Roads Not Taken)", RFC 9049,
              DOI 10.17487/RFC9049, June 2021,
              <https://www.rfc-editor.org/info/rfc9049>.

   [RFC9300]  Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
              Cabellos, Ed., "The Locator/ID Separation Protocol
              (LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,
              <https://www.rfc-editor.org/info/rfc9300>.

   [Trees]    "Trees", Poetry Foundation , n.d.,
              <https://www.poetryfoundation.org/poetrymagazine/
              poems/12744/trees>.

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Appendix A.  Netverses

   With inspiration from (and apologies to) Radia Perlman [Algorhyme]
   and Joyce Kilmer [Trees], the following poem is not intended to
   provide any normative or informative technical value on TreeDN beyond
   (mild) amusement for the reader who made it this far in the document:

   I think that I shall never see
   A CDN more lovely than a tree.

   A tree whose crucial property
   Is efficient mass-audience delivery.

   Using SSM for simplified operation
   Of native branches that eliminate duplication.

   A tree extended by AMT,
   Enabling unicast-only receivers full delivery.

   A tree that scales to reach millions of places
   To viably support the highest of bitrate use cases.

   A CDN is built by folks like me,
   But only end users can generate enough demand to necessitate a tree.

Authors' Addresses

   Lenny Giuliano
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, VA 20171,
   United States of America
   Email: lenny@juniper.net

   Chris Lenart
   Verizon
   22001 Loudoun County Parkway
   Ashburn, VA 20147,
   United States of America
   Email: chris.lenart@verizon.com

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   Rich Adam
   GEANT
   City House
   126-130 Hills Road
   Cambridge
   CB2 1PQ
   United Kingdom
   Email: richard.adam@geant.org

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