SSM

As Internet audience sizes for high-interest live events reach unprecedented levels and bitrates climb to support formats and applications such as 4K, 8K, and Augmented Reality (AR), live streaming can place a unique type of stress upon network resources. TreeDN is a tree-based Content Delivery Network (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 of 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 that makes content distribution more accessible to more people by dramatically reducing the costs of replication.

This document recommends deprecation of the use of Any-Source Multicast (ASM) for interdomain multicast. It recommends the use of Source-Specific Multicast (SSM) for interdomain multicast applications and recommends that hosts and routers in these deployments fully support SSM. The recommendations in this document do not preclude the continued use of ASM within a single organization or domain and are especially easy to adopt in existing deployments of intradomain ASM using PIM Sparse Mode (PIM-SM).

This document updates RFC 7450, "Automatic Multicast Tunneling" (or AMT), by modifying the relay discovery process. A new DNS resource record named AMTRELAY is defined for publishing AMT relays for source-specific multicast channels. The reverse IP DNS zone for a multicast sender's IP address is configured to use AMTRELAY resource records to advertise a set of AMT relays that can receive and forward multicast traffic from that sender over an AMT tunnel. Other extensions and clarifications to the relay discovery process are also defined.

During the transition to IPv6, there are scenarios where a backbone network internally running one IP address family (referred to as the internal IP or I-IP family) connects client networks running another IP address family (referred to as the external IP or E-IP family). In such cases, the I-IP backbone needs to offer both unicast and multicast transit services to the client E-IP networks.

This document describes a mechanism for supporting multicast across backbone networks where the I-IP and E-IP protocol families differ. The document focuses on the IPv4-over-IPv6 scenario, due to lack of real-world use cases for the IPv6-over-IPv4 scenario.

This document examines the use of Source-Specific Multicast (SSM) across inter-domain peering points for a specified set of deployment scenarios. The objectives are to (1) describe the setup process for multicast-based delivery across administrative domains for these scenarios and (2) document supporting functionality to enable this process.

This document defines a Dynamic Host Configuration Protocol version 6 (DHCPv6) Option for multicast IPv4 service continuity solutions, which is used to carry the IPv6 prefixes to be used to build unicast and multicast IPv4-embedded IPv6 addresses.

This document discusses point-to-point and multi-endpoint topologies used in environments based on the Real-time Transport Protocol (RTP). In particular, centralized topologies commonly employed in the video conferencing industry are mapped to the RTP terminology.

This document describes Automatic Multicast Tunneling (AMT), a protocol for delivering multicast traffic from sources in a multicast-enabled network to receivers that lack multicast connectivity to the source network. The protocol uses UDP encapsulation and unicast replication to provide this functionality.

The AMT protocol is specifically designed to support rapid deployment by requiring minimal changes to existing network infrastructure.

The Multicast Ping Protocol specified in this document allows for checking whether an endpoint can receive multicast -- both Source-Specific Multicast (SSM) and Any-Source Multicast (ASM). It can also be used to obtain additional multicast-related information, such as multicast tree setup time. This protocol is based on an implementation of tools called "ssmping" and "asmping". [STANDARDS-TRACK]

In most RTP-based multicast applications, the RTP source sends inter- related data. Due to this interdependency, randomly joining RTP receivers usually cannot start consuming the multicast data right after they join the session. Thus, they often experience a random acquisition delay. An RTP receiver can use one or more different approaches to achieve rapid acquisition. Yet, due to various factors, performance of the rapid acquisition methods usually varies. Furthermore, in some cases, the RTP receiver can do a simple multicast join (in other cases, it is compelled to do so). For quality reporting, monitoring, and diagnostic purposes, it is important to collect detailed information from the RTP receivers about their acquisition and presentation experiences. This document addresses this issue by defining a new report block type, called the Multicast Acquisition (MA) report block, within the framework of RTP Control Protocol (RTCP) Extended Reports (XRs) (RFC 3611). This document also defines the necessary signaling of the new MA report block type in the Session Description Protocol (SDP). [STANDARDS-TRACK]

When an RTP receiver joins a multicast session, it may need to acquire and parse certain Reference Information before it can process any data sent in the multicast session. Depending on the join time, length of the Reference Information repetition (or appearance) interval, size of the Reference Information, and the application and transport properties, the time lag before an RTP receiver can usefully consume the multicast data, which we refer to as the Acquisition Delay, varies and can be large. This is an undesirable phenomenon for receivers that frequently switch among different multicast sessions, such as video broadcasts.

In this document, we describe a method using the existing RTP and RTP Control Protocol (RTCP) machinery that reduces the acquisition delay. In this method, an auxiliary unicast RTP session carrying the Reference Information to the receiver precedes or accompanies the multicast stream. This unicast RTP flow can be transmitted at a faster than natural bitrate to further accelerate the acquisition. The motivating use case for this capability is multicast applications that carry real-time compressed audio and video. However, this method can also be used in other types of multicast applications where the acquisition delay is long enough to be a problem. [STANDARDS-TRACK]

The lack of up-to-date documentation on IP multicast address allocation and assignment procedures has caused a great deal of confusion. To clarify the situation, this memo describes the allocation and assignment techniques and mechanisms currently (as of this writing) in use. This document is not an Internet Standards Track specification; it is published for informational purposes.

The Session Description Protocol (SDP) has an attribute that allows RTP applications to specify an address and a port associated with the RTP Control Protocol (RTCP) traffic. In RTP-based source-specific multicast (SSM) sessions, the same attribute is used to designate the address and the RTCP port of the Feedback Target in the SDP description. However, the RTCP port associated with the SSM session itself cannot be specified by the same attribute to avoid ambiguity, and thus, is required to be derived from the "m=" line of the media description. Deriving the RTCP port from the "m=" line imposes an unnecessary restriction. This document removes this restriction by introducing a new SDP attribute. [STANDARDS-TRACK]

This memo outlines how RTP sessions are synchronised, and discusses how rapidly such synchronisation can occur. We show that most RTP sessions can be synchronised immediately, but that the use of video switching multipoint conference units (MCUs) or large source-specific multicast (SSM) groups can greatly increase the synchronisation delay. This increase in delay can be unacceptable to some applications that use layered and/or multi-description codecs.

This memo introduces three mechanisms to reduce the synchronisation delay for such sessions. First, it updates the RTP Control Protocol (RTCP) timing rules to reduce the initial synchronisation delay for SSM sessions. Second, a new feedback packet is defined for use with the extended RTP profile for RTCP-based feedback (RTP/AVPF), allowing video switching MCUs to rapidly request resynchronisation. Finally, new RTP header extensions are defined to allow rapid synchronisation of late joiners, and guarantee correct timestamp-based decoding order recovery for layered codecs in the presence of clock skew. [STANDARDS-TRACK]

This document specifies an extension to the Real-time Transport Control Protocol (RTCP) to use unicast feedback to a multicast sender. The proposed extension is useful for single-source multicast sessions such as Source-Specific Multicast (SSM) communication where the traditional model of many-to-many group communication is either not available or not desired. In addition, it can be applied to any group that might benefit from a sender-controlled summarized reporting mechanism. [STANDARDS-TRACK]

This document discusses current mobility extensions to IP-layer multicast. It describes problems arising from mobile group communication in general, the case of multicast listener mobility, and problems for mobile senders using Any Source Multicast and Source-Specific Multicast. Characteristic aspects of multicast routing and deployment issues for fixed IPv6 networks are summarized. Specific properties and interplays with the underlying network access are surveyed with respect to the relevant technologies in the wireless domain. It outlines the principal approaches to multicast mobility, together with a comprehensive exploration of the mobile multicast problem and solution space. This document concludes with a conceptual road map for initial steps in standardization for use by future mobile multicast protocol designers. This document is a product of the IP Mobility Optimizations (MobOpts) Research Group. This document is not an Internet Standards Track specification; it is published for informational purposes.

This memo describes security threats for the larger (intra-domain or inter-domain) multicast routing infrastructures. Only Protocol Independent Multicast - Sparse Mode (PIM-SM) is analyzed, in its three main operational modes: the traditional Any-Source Multicast (ASM) model, the source-specific multicast (SSM) model, and the ASM model enhanced by the Embedded Rendezvous Point (Embedded-RP) group-to-RP mapping mechanism. This memo also describes enhancements to the protocol operations that mitigate the identified threats. This memo provides information for the Internet community.

The Internet Group Management Protocol Version 3 (IGMPv3) and the Multicast Listener Discovery Protocol Version 2 (MLDv2) are protocols that allow a host to inform its neighboring routers of its desire to receive IPv4 and IPv6 multicast transmissions, respectively. Source-specific multicast (SSM) is a form of multicast in which a receiver is required to specify both the network-layer address of the source and the multicast destination address in order to receive the multicast transmission. This document defines the notion of an "SSM-aware" router and host, and clarifies and (in some cases) modifies the behavior of IGMPv3 and MLDv2 on SSM-aware routers and hosts to accommodate source-specific multicast. This document updates the IGMPv3 and MLDv2 specifications. [STANDARDS-TRACK]

IP version 4 (IPv4) addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are designated as source-specific multicast (SSM) destination addresses and are reserved for use by source-specific applications and protocols. For IP version 6 (IPv6), the address prefix FF3x::/32 is reserved for source-specific multicast use. This document defines an extension to the Internet network service that applies to datagrams sent to SSM addresses and defines the host and router requirements to support this extension. [STANDARDS-TRACK]

IP Multicast group addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are designated as source-specific multicast destination addresses and are reserved for use by source-specific multicast applications and protocols. This document defines operational recommendations to ensure source-specific behavior within the 232/8 range. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.

This document describes how to adapt the Session Description Protocol (SDP) to express one or more source addresses as a source filter for one or more destination "connection" addresses. It defines the syntax and semantics for an SDP "source-filter" attribute that may reference either IPv4 or IPv6 address(es) as either an inclusive or exclusive source list for either multicast or unicast destinations. In particular, an inclusive source-filter can be used to specify a Source-Specific Multicast (SSM) session. [STANDARDS-TRACK]

This document describes the Border Gateway Multicast Protocol (BGMP), a protocol for inter-domain multicast routing. BGMP builds shared trees for active multicast groups, and optionally allows receiver domains to build source-specific, inter-domain, distribution branches where needed. BGMP natively supports "source-specific multicast" (SSM). To also support "any-source multicast" (ASM), BGMP requires that each multicast group be associated with a single root (in BGMP it is referred to as the root domain). It requires that different ranges of the multicast address space are associated (e.g., with Unicast-Prefix-Based Multicast addressing) with different domains. Each of these domains then becomes the root of the shared domain-trees for all groups in its range. Multicast participants will generally receive better multicast service if the session initiator's address allocator selects addresses from its own domain's part of the space, thereby causing the root domain to be local to at least one of the session participants. This memo provides information for the Internet community.

The purpose of this document is to provide an overview of Source-Specific Multicast (SSM) and issues related to its deployment. It discusses how the SSM service model addresses the challenges faced in inter-domain multicast deployment, changes needed to routing protocols and applications to deploy SSM and interoperability issues with current multicast service models. This memo provides information for the Internet community.