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draft-ietf-mboned-interdomain-peering-bcp-12.txt
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draft-ietf-mboned-interdomain-peering-bcp-12.txt
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MBONED Working Group P. Tarapore, Ed.
Internet-Draft R. Sayko
Intended status: Best Current Practice AT&T
Expires: April 30, 2018 G. Shepherd
Cisco
T. Eckert, Ed.
Futurewei Technologies
R. Krishnan
SupportVectors
October 27, 2017
Use of Multicast Across Inter-Domain Peering Points
draft-ietf-mboned-interdomain-peering-bcp-12
Abstract
This document examines the use of Source Specific Multicast (SSM)
across inter-domain peering points for a specified set of deployment
scenarios. The objective is to describe the setup process for
multicast-based delivery across administrative domains for these
scenarios and document supporting functionality to enable this
process.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents 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 April 30, 2018.
Copyright Notice
Copyright (c) 2017 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
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(https://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.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of Inter-domain Multicast Application Transport . . 5
3. Inter-domain Peering Point Requirements for Multicast . . . . 6
3.1. Native Multicast . . . . . . . . . . . . . . . . . . . . 6
3.2. Peering Point Enabled with GRE Tunnel . . . . . . . . . . 7
3.3. Peering Point Enabled with an AMT - Both Domains
Multicast Enabled . . . . . . . . . . . . . . . . . . . . 9
3.4. Peering Point Enabled with an AMT - AD-2 Not Multicast
Enabled . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.5. AD-2 Not Multicast Enabled - Multiple AMT Tunnels Through
AD-2 . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4. Functional Guidelines . . . . . . . . . . . . . . . . . . . . 13
4.1. Network Interconnection Transport and Security Guidelines 13
4.2. Routing Aspects and Related Guidelines . . . . . . . . . 14
4.2.1. Native Multicast Routing Aspects . . . . . . . . . . 15
4.2.2. GRE Tunnel over Interconnecting Peering Point . . . . 15
4.2.3. Routing Aspects with AMT Tunnels . . . . . . . . . . 16
4.3. Back Office Functions - Provisioning and Logging
Guidelines . . . . . . . . . . . . . . . . . . . . . . . 18
4.3.1. Provisioning Guidelines . . . . . . . . . . . . . . . 18
4.3.2. Application Accounting Guidelines . . . . . . . . . . 20
4.3.3. Log Management Guidelines . . . . . . . . . . . . . . 20
4.4. Operations - Service Performance and Monitoring
Guidelines . . . . . . . . . . . . . . . . . . . . . . . 21
4.5. Client Reliability Models/Service Assurance Guidelines . 23
5. Troubleshooting and Diagnostics . . . . . . . . . . . . . . . 23
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6. Security Considerations . . . . . . . . . . . . . . . . . . . 24
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 25
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
10. Change log [RFC Editor: Please remove] . . . . . . . . . . . 26
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.1. Normative References . . . . . . . . . . . . . . . . . . 26
11.2. Informative References . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction
Content and data from several types of applications (e.g., live video
streaming, software downloads) are well suited for delivery via
multicast means. The use of multicast for delivering such content/
data offers significant savings of utilization of resources in any
given administrative domain. End user demand for such content/data
is growing. Often, this requires transporting the content/data
across administrative domains via inter-domain peering points.
The objective of this Best Current Practices document is twofold:
o Describe the technical process and establish guidelines for
setting up multicast-based delivery of application content/data
across inter-domain peering points via a set of use cases.
o Catalog all required information exchange between the
administrative domains to support multicast-based delivery. This
enables operators to initiate necessary processes to support
inter-domain peering with multicast.
The scope and assumptions for this document are stated as follows:
o For the purpose of this document, the term "peering point" refers
to an interface between two networks/administrative domains over
which traffic is exchanged between them. A Network-Network
Interface (NNI) is an example of a peering point.
o Administrative Domain 1 (AD-1) is enabled with native multicast.
A peering point exists between AD-1 and AD-2.
o It is understood that several protocols are available for this
purpose including PIM-SM and Protocol Independent Multicast -
Source Specific Multicast (PIM-SSM) [RFC7761], Internet Group
Management Protocol (IGMP) [RFC3376], and Multicast Listener
Discovery (MLD) [RFC3810].
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o As described in Section 2, the source IP address of the multicast
stream in the originating AD (AD-1) is known. Under this
condition, PIM-SSM use is beneficial as it allows the receiver's
upstream router to directly send a JOIN message to the source
without the need of invoking an intermediate Rendezvous Point
(RP). Use of SSM also presents an improved threat mitigation
profile against attack, as described in [RFC4609]. Hence, in the
case of inter-domain peering, it is recommended to use only SSM
protocols; the setup of inter- domain peering for ASM (Any-Source
Multicast) is not in scope for this document.
o AD-1 and AD-2 are assumed to adopt compatible protocols. The use
of different protocols is beyond the scope of this document.
o An Automatic Multicast Tunnel (AMT) [RFC7450] is setup at the
peering point if either the peering point or AD-2 is not multicast
enabled. It is assumed that an AMT Relay will be available to a
client for multicast delivery. The selection of an optimal AMT
relay by a client is out of scope for this document. Note that
AMT use is necessary only when native multicast is unavailable in
the peering point (Use Case 3.3) or in the downstream
administrative domain (Use Cases 3.4, and 3.5).
o The collection of billing data is assumed to be done at the
application level and is not considered to be a networking issue.
The settlements process for end user billing and/or inter-provider
billing is out of scope for this document.
o Inter-domain network connectivity troubleshooting is only
considered within the context of a cooperative process between the
two domains.
Thus, the primary purpose of this document is to describe a scenario
where two AD's interconnect via a a peering point with each other.
Security and operational aspects for exchanging traffic on a public
Internet Exchange Point (IXP) with a large shared broadcast domain
between many operators, is not in scope for this document.
It may be possible to have a configuration whereby a transit domain
(AD-3) interconnects AD-1 and AD-2. Such a configuration adds
complexity and may require manual provisioning if, for example, AD-3
is not multicast enabled. This configuration is out of cope for this
document; it is for further study.
This document also attempts to identify ways by which the peering
process can be improved. Development of new methods for improvement
is beyond the scope of this document.
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2. Overview of Inter-domain Multicast Application Transport
A multicast-based application delivery scenario is as follows:
o Two independent administrative domains are interconnected via a
peering point.
o The peering point is either multicast enabled (end-to-end native
multicast across the two domains) or it is connected by one of two
possible tunnel types:
o A Generic Routing Encapsulation (GRE) Tunnel [RFC2784] allowing
multicast tunneling across the peering point, or
o An Automatic Multicast Tunnel (AMT) [RFC7450].
o A service provider controls one or more application sources in
AD-1 which will send multicast IP packets for one or more (S,G)s.
It is assumed that the service being provided is suitable for
delivery via multicast (e.g. live video streaming of popular
events, software downloads to many devices, etc.), and that the
packet streams will be part of a suitable multicast transport
protocol.
o An End User (EU) controls a device connected to AD-2, which runs
an application client compatible with the service provider's
application source.
o The application client joins appropriate (S,G)s in order to
receive the data necessary to provide the service to the EU. The
mechanisms by which the application client learns the appropriate
(S,G)s are an implementation detail of the application, and are
out of scope for this document.
The assumption here is that AD-1 has ultimate responsibility for
delivering the multicast based service on behalf of the content
source(s). All relevant interactions between the two domains
described in this document are based on this assumption.
Note that domain 2 may be an independent network domain (e.g., Tier 1
network operator domain). Alternately, domain 2 could also be an
Enterprise network domain operated by a single customer. The peering
point architecture and requirements may have some unique aspects
associated with the Enterprise case.
The Use Cases describing various architectural configurations for the
multicast distribution along with associated requirements is
described in section 3. Unique aspects related to the Enterprise
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network possibility will be described in this section. Section 4
contains a comprehensive list of pertinent information that needs to
be exchanged between the two domains in order to support functions to
enable the application transport.
3. Inter-domain Peering Point Requirements for Multicast
The transport of applications using multicast requires that the
inter-domain peering point is enabled to support such a process.
There are five Use Cases for consideration in this document.
3.1. Native Multicast
This Use Case involves end-to-end Native Multicast between the two
administrative domains and the peering point is also native multicast
enabled - Figure 1.
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Multicast Enabled) \
/ \ / \
| +----+ | | |
| | | +------+ | | +------+ | +----+
| | AS |------>| BR |-|---------|->| BR |-------------|-->| EU |
| | | +------+ | I1 | +------+ |I2 +----+
\ +----+ / \ /
\ / \ /
\ / \ /
------------------- -------------------
AD = Administrative Domain (Independent Autonomous System)
AS = Application (e.g., Content) Multicast Source
BR = Border Router
I1 = AD-1 and AD-2 Multicast Interconnection (e.g., MBGP)
I2 = AD-2 and EU Multicast Connection
Figure 1: - Content Distribution via End to End Native Multicast
Advantages of this configuration are:
o Most efficient use of bandwidth in both domains.
o Fewer devices in the path traversed by the multicast stream when
compared to an AMT enabled peering point.
From the perspective of AD-1, the one disadvantage associated with
native multicast into AD-2 instead of individual unicast to every EU
in AD-2 is that it does not have the ability to count the number of
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End Users as well as the transmitted bytes delivered to them. This
information is relevant from the perspective of customer billing and
operational logs. It is assumed that such data will be collected by
the application layer. The application layer mechanisms for
generating this information need to be robust enough such that all
pertinent requirements for the source provider and the AD operator
are satisfactorily met. The specifics of these methods are beyond
the scope of this document.
Architectural guidelines for this configuration are as follows:
a. Dual homing for peering points between domains is recommended as
a way to ensure reliability with full BGP table visibility.
b. If the peering point between AD-1 and AD-2 is a controlled
network environment, then bandwidth can be allocated accordingly
by the two domains to permit the transit of non- rate adaptive
multicast traffic. If this is not the case, then it is
recommended that the multicast traffic should support rate-
adaption.
c. The sending and receiving of multicast traffic between two
domains is typically determined by local policies associated with
each domain. For example, if AD-1 is a service provider and AD-2
is an enterprise, then AD-1 may support local policies for
traffic delivery to, but not traffic reception from, AD-2.
Another example is the use of a policy by which AD-1 delivers
specified content to AD-2 only if such delivery has been accepted
by contract.
d. Relevant information on multicast streams delivered to End Users
in AD-2 is assumed to be collected by available capabilities in
the application layer. The precise nature and formats of the
collected information will be determined by directives from the
source owner and the domain operators.
e. The interconnection of AD-1 and AD-2 should, at a minimum, follow
guidelines for traffic filtering between autonomous systems
[BCP38]. Filtering guidelines specific to the multicast control-
plane and data-plane are described in section 6.
3.2. Peering Point Enabled with GRE Tunnel
The peering point is not native multicast enabled in this Use Case.
There is a Generic Routing Encapsulation Tunnel provisioned over the
peering point. In this case, the interconnection I1 between AD-1 and
AD-2 in Figure 1 is multicast enabled via a Generic Routing
Encapsulation Tunnel (GRE) [RFC2784] and encapsulating the multicast
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protocols across the interface. The routing configuration is
basically unchanged: Instead of BGP (SAFI2) across the native IP
multicast link between AD-1 and AD-2, BGP (SAFI2) is now run across
the GRE tunnel.
Advantages of this configuration:
o Highly efficient use of bandwidth in both domains, although not as
efficient as the fully native multicast Use Case.
o Fewer devices in the path traversed by the multicast stream when
compared to an AMT enabled peering point.
o Ability to support only partial IP multicast deployments in AD- 1
and/or AD-2 (the two Border Routers in Figure 1 do not need to be
the two "unicast" domain border routers; instead they can be
anywhere in AD-1 and AD-2).
o GRE is an existing technology and is relatively simple to
implement.
Disadvantages of this configuration:
o Per Use Case 3.1, current router technology cannot count the
number of end users or the number bytes transmitted.
o GRE tunnel requires manual configuration.
o The GRE must be established prior to stream starting.
o The GRE tunnel is often left pinned up.
Architectural guidelines for this configuration include the
following:
Guidelines (a) through (d) are the same as those described in Use
Case 3.1. Two additional guidelines are as follows:
e. GRE tunnels are typically configured manually between peering
points to support multicast delivery between domains.
f. It is recommended that the GRE tunnel (tunnel server)
configuration in the source network is such that it only
advertises the routes to the application sources and not to the
entire network. This practice will prevent unauthorized delivery
of applications through the tunnel (e.g., if application - e.g.,
content - is not part of an agreed inter-domain partnership).
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3.3. Peering Point Enabled with an AMT - Both Domains Multicast Enabled
Both administrative domains in this Use Case are assumed to be native
multicast enabled here; however, the peering point is not.
The peering point is enabled with an Automatic Multicast Tunnel. The
basic configuration is depicted in Figure 2.
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Multicast Enabled) \
/ \ / \
| +----+ | | |
| | | +------+ | | +------+ | +----+
| | AS |------>| AR |-|---------|->| AG |-------------|-->| EU |
| | | +------+ | I1 | +------+ |I2 +----+
\ +----+ / \ /
\ / \ /
\ / \ /
------------------- -------------------
AR = AMT Relay
AG = AMT Gateway
I1 = AMT Interconnection between AD-1 and AD-2
I2 = AD-2 and EU Multicast Connection
Figure 2: - AMT Interconnection between AD-1 and AD-2
Advantages of this configuration:
o Highly efficient use of bandwidth in AD-1.
o AMT is an existing technology and is relatively simple to
implement. Attractive properties of AMT include the following:
o Dynamic interconnection between Gateway-Relay pair across the
peering point.
o Ability to serve clients and servers with differing policies.
Disadvantages of this configuration:
o Per Use Case 3.1 (AD-2 is native multicast), current router
technology cannot count the number of end users or the number of
bytes transmitted to all end users.
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o Additional devices (AMT Gateway and Relay pairs) may be introduced
into the path if these services are not incorporated in the
existing routing nodes.
o Currently undefined mechanisms for the AG to automatically select
the optimal AR.
Architectural guidelines for this configuration are as follows:
Guidelines (a) through (d) are the same as those described in Use
Case 3.1. In addition,
e. It is recommended that AMT Relay and Gateway pairs be configured
at the peering points to support multicast delivery between
domains. AMT tunnels will then configure dynamically across the
peering points once the Gateway in AD-2 receives the (S, G)
information from the EU.
3.4. Peering Point Enabled with an AMT - AD-2 Not Multicast Enabled
In this AMT Use Case, the second administrative domain AD-2 is not
multicast enabled. Hence, the interconnection between AD-2 and the
End User is also not multicast enabled. This Use Case is depicted in
Figure 3.
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Non-Multicast \
/ \ / Enabled) \
| +----+ | | |
| | | +------+ | | | +----+
| | AS |------>| AR |-|---------|-----------------------|-->|EU/G|
| | | +------+ | | |I2 +----+
\ +----+ / \ /
\ / \ /
\ / \ /
------------------- -------------------
AS = Application Multicast Source
AR = AMT Relay
EU/G = Gateway client embedded in EU device
I2 = AMT Tunnel Connecting EU/G to AR in AD-1 through Non-Multicast
Enabled AD-2.
Figure 3: - AMT Tunnel Connecting AD-1 AMT Relay and EU Gateway
This Use Case is equivalent to having unicast distribution of the
application through AD-2. The total number of AMT tunnels would be
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equal to the total number of End Users requesting the application.
The peering point thus needs to accommodate the total number of AMT
tunnels between the two domains. Each AMT tunnel can provide the
data usage associated with each End User.
Advantages of this configuration:
o Highly efficient use of bandwidth in AD-1.
o AMT is an existing technology and is relatively simple to
implement. Attractive properties of AMT include the following:
o Dynamic interconnection between Gateway-Relay pair across the
peering point.
o Ability to serve clients and servers with differing policies.
o Each AMT tunnel serves as a count for each End User and is also
able to track data usage (bytes) delivered to the EU.
Disadvantages of this configuration:
o Additional devices (AMT Gateway and Relay pairs) are introduced
into the transport path.
o Assuming multiple peering points between the domains, the EU
Gateway needs to be able to find the "correct" AMT Relay in AD-1.
Architectural guidelines for this configuration are as follows:
Guidelines (a) through (c) are the same as those described in Use
Case 3.1.
d. It is recommended that proper procedures are implemented such that
the AMT Gateway at the End User device is able to find the correct
AMT Relay in AD-1 across the peering points. The application
client in the EU device is expected to supply the (S, G)
information to the Gateway for this purpose.
e. The AMT tunnel capabilities are expected to be sufficient for the
purpose of collecting relevant information on the multicast
streams delivered to End Users in AD-2.
3.5. AD-2 Not Multicast Enabled - Multiple AMT Tunnels Through AD-2
This is a variation of Use Case 3.4 as follows:
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------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Non-Multicast \
/ \ / Enabled) \
| +----+ | |+--+ +--+ |
| | | +------+ | ||AG| |AG| | +----+
| | AS |------>| AR |-|-------->||AR|------------->|AR|-|-->|EU/G|
| | | +------+ | I1 ||1 | I2 |2 | |I3 +----+
\ +----+ / \+--+ +--+ /
\ / \ /
\ / \ /
------------------- -------------------
AS = Application Source
AR = AMT Relay in AD-1
AGAR1 = AMT Gateway/Relay node in AD-2 across Peering Point
I1 = AMT Tunnel Connecting AR in AD-1 to GW in AGAR1 in AD-2
AGAR2 = AMT Gateway/Relay node at AD-2 Network Edge
I2 = AMT Tunnel Connecting Relay in AGAR1 to GW in AGAR2
EU/G = Gateway client embedded in EU device
I3 = AMT Tunnel Connecting EU/G to AR in AGAR2
Figure 4: - AMT Tunnel Connecting AMT Relay and Relays
Use Case 3.4 results in several long AMT tunnels crossing the entire
network of AD-2 linking the EU device and the AMT Relay in AD-1
through the peering point. Depending on the number of End Users,
there is a likelihood of an unacceptably large number of AMT tunnels
- and unicast streams - through the peering point. This situation
can be alleviated as follows:
o Provisioning of strategically located AMT nodes at the edges of
AD-2. An AMT node comprises co-location of an AMT Gateway and an
AMT Relay. One such node is at the AD-2 side of the peering point
(node AGAR1 in Figure 4).
o Single AMT tunnel established across peering point linking AMT
Relay in AD-1 to the AMT Gateway in the AMT node AGAR1 in AD-2.
o AMT tunnels linking AMT node AGAR1 at peering point in AD-2 to
other AMT nodes located at the edges of AD-2: e.g., AMT tunnel I2
linking AMT Relay in AGAR1 to AMT Gateway in AMT node AGAR2 in
Figure 4.
o AMT tunnels linking EU device (via Gateway client embedded in
device) and AMT Relay in appropriate AMT node at edge of AD-2:
e.g., I3 linking EU Gateway in device to AMT Relay in AMT node
AGAR2.
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The advantage for such a chained set of AMT tunnels is that the total
number of unicast streams across AD-2 is significantly reduced, thus
freeing up bandwidth. Additionally, there will be a single unicast
stream across the peering point instead of possibly, an unacceptably
large number of such streams per Use Case 3.4. However, this implies
that several AMT tunnels will need to be dynamically configured by
the various AMT Gateways based solely on the (S,G) information
received from the application client at the EU device. A suitable
mechanism for such dynamic configurations is therefore critical.
Architectural guidelines for this configuration are as follows:
Guidelines (a) through (c) are the same as those described in Use
Case 3.1.
d. It is recommended that proper procedures are implemented such that
the various AMT Gateways (at the End User devices and the AMT
nodes in AD-2) are able to find the correct AMT Relay in other AMT
nodes as appropriate. The application client in the EU device is
expected to supply the (S, G) information to the Gateway for this
purpose.
e. The AMT tunnel capabilities are expected to be sufficient for the
purpose of collecting relevant information on the multicast
streams delivered to End Users in AD-2.
4. Functional Guidelines
Supporting functions and related interfaces over the peering point
that enable the multicast transport of the application are listed in
this section. Critical information parameters that need to be
exchanged in support of these functions are enumerated, along with
guidelines as appropriate. Specific interface functions for
consideration are as follows.
4.1. Network Interconnection Transport and Security Guidelines
The term "Network Interconnection Transport" refers to the
interconnection points between the two Administrative Domains. The
following is a representative set of attributes that will need to be
agreed to between the two administrative domains to support multicast
delivery.
o Number of Peering Points.
o Peering Point Addresses and Locations.
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o Connection Type - Dedicated for Multicast delivery or shared with
other services.
o Connection Mode - Direct connectivity between the two AD's or via
another ISP.
o Peering Point Protocol Support - Multicast protocols that will be
used for multicast delivery will need to be supported at these
points. Examples of protocols include eBGP [RFC4760] and MBGP
[RFC4760].
o Bandwidth Allocation - If shared with other services, then there
needs to be a determination of the share of bandwidth reserved for
multicast delivery. When determining the appropriate bandwidth
allocation, parties should consider use of a multicast protocol
suitable for live video streaming that is consistent with
Congestion Control Principles [BCP41].
o QoS Requirements - Delay/latency specifications that need to be
specified in an SLA.
o AD Roles and Responsibilities - the role played by each AD for
provisioning and maintaining the set of peering points to support
multicast delivery.
4.2. Routing Aspects and Related Guidelines
The main objective for multicast delivery routing is to ensure that
the End User receives the multicast stream from the "most optimal"
source [INF_ATIS_10] which typically:
o Maximizes the multicast portion of the transport and minimizes any
unicast portion of the delivery, and
o Minimizes the overall combined network(s) route distance.
This routing objective applies to both Native and AMT; the actual
methodology of the solution will be different for each. Regardless,
the routing solution is expected:
o To be scalable,
o To avoid/minimize new protocol development or modifications, and
o To be robust enough to achieve high reliability and automatically
adjust to changes/problems in the multicast infrastructure.
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For both Native and AMT environments, having a source as close as
possible to the EU network is most desirable; therefore, in some
cases, an AD may prefer to have multiple sources near different
peering points. However, that is entirely an implementation issue.
4.2.1. Native Multicast Routing Aspects
Native multicast simply requires that the Administrative Domains
coordinate and advertise the correct source address(es) at their
network interconnection peering points(i.e., border routers). An
example of multicast delivery via a Native Multicast process across
two Administrative Domains is as follows assuming that the
interconnecting peering points are also multicast enabled:
o Appropriate information is obtained by the EU client who is a
subscriber to AD-2 (see Use Case 3.1). This information is in the
form of metadata and it contains instructions directing the EU
client to launch an appropriate application if necessary, as well
as additional information for the application about the source
location and the group (or stream) id in the form of the "S,G"
data. The "S" portion provides the name or IP address of the
source of the multicast stream. The metadata may also contain
alternate delivery information such as specifying the unicast
address of the stream.
o The client uses the join message with S,G to join the multicast
stream [RFC4604]. To facilitate this process, the two AD's need
to do the following:
o Advertise the source id(s) over the Peering Points.
o Exchange relevant Peering Point information such as Capacity
and Utilization.
o Implement compatible multicast protocols to ensure proper
multicast delivery across the peering points.
4.2.2. GRE Tunnel over Interconnecting Peering Point
If the interconnecting peering point is not multicast enabled and
both AD's are multicast enabled, then a simple solution is to
provision a GRE tunnel between the two AD's - see Use Case 3.2.2.
The termination points of the tunnel will usually be a network
engineering decision, but generally will be between the border
routers or even between the AD 2 border router and the AD 1 source
(or source access router). The GRE tunnel would allow end-to-end
native multicast or AMT multicast to traverse the interface.
Coordination and advertisement of the source IP is still required.
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The two AD's need to follow the same process as described in 4.2.1 to
facilitate multicast delivery across the Peering Points.
4.2.3. Routing Aspects with AMT Tunnels
Unlike Native Multicast (with or without GRE), an AMT Multicast
environment is more complex. It presents a dual layered problem
because there are two criteria that should be simultaneously met:
o Find the closest AMT relay to the end-user that also has multicast
connectivity to the content source, and
o Minimize the AMT unicast tunnel distance.
There are essentially two components to the AMT specification
AMT Relays: These serve the purpose of tunneling UDP multicast
traffic to the receivers (i.e., End-Points). The AMT Relay will
receive the traffic natively from the multicast media source and
will replicate the stream on behalf of the downstream AMT
Gateways, encapsulating the multicast packets into unicast packets
and sending them over the tunnel toward the AMT Gateway. In
addition, the AMT Relay may perform various usage and activity
statistics collection. This results in moving the replication
point closer to the end user, and cuts down on traffic across the
network. Thus, the linear costs of adding unicast subscribers can
be avoided. However, unicast replication is still required for
each requesting End-Point within the unicast-only network.
AMT Gateway (GW): The Gateway will reside on an End-Point - this may
be a Personal Computer (PC) or a Set Top Box (STB). The AMT
Gateway receives join and leave requests from the Application via
an Application Programming Interface (API). In this manner, the
Gateway allows the End-Point to conduct itself as a true Multicast
End-Point. The AMT Gateway will encapsulate AMT messages into UDP
packets and send them through a tunnel (across the unicast-only
infrastructure) to the AMT Relay.
The simplest AMT Use Case (section 3.3) involves peering points that
are not multicast enabled between two multicast enabled AD's. An AMT
tunnel is deployed between an AMT Relay on the AD 1 side of the
peering point and an AMT Gateway on the AD 2 side of the peering
point. One advantage to this arrangement is that the tunnel is
established on an as needed basis and need not be a provisioned
element. The two AD's can coordinate and advertise special AMT Relay
Anycast addresses with each other. Alternately, they may decide to
simply provision Relay addresses, though this would not be an optimal
solution in terms of scalability.
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Use Cases 3.4 and 3.5 describe more complicated AMT situations as
AD-2 is not multicast enabled. For these cases, the End User device
needs to be able to setup an AMT tunnel in the most optimal manner.
There are many methods by which relay selection can be done including
the use of DNS based queries and static lookup tables [RFC7450]. The
choice of the method is implementation dependent and is up to the
network operators. Comparison of various methods is out of scope for
this document; it is for further study.
An illustrative example of a relay selection based on DNS queries and
Anycast IP addresses process for Use Cases 3.4 and 3.5 is described
here. Using an Anycast IP address for AMT Relays allows for all AMT
Gateways to find the "closest" AMT Relay - the nearest edge of the
multicast topology of the source. Note that this is strictly
illustrative; the choice of the method is up to the network
operators. The basic process is as follows:
o Appropriate metadata is obtained by the EU client application.
The metadata contains instructions directing the EU client to an
ordered list of particular destinations to seek the requested
stream and, for multicast, specifies the source location and the
group (or stream) ID in the form of the "S,G" data. The "S"
portion provides the URI (name or IP address) of the source of the
multicast stream and the "G" identifies the particular stream
originated by that source. The metadata may also contain
alternate delivery information such as the address of the unicast
form of the content to be used, for example, if the multicast
stream becomes unavailable.
o Using the information from the metadata, and possibly information
provisioned directly in the EU client, a DNS query is initiated in
order to connect the EU client/AMT Gateway to an AMT Relay.
o Query results are obtained, and may return an Anycast address or a
specific unicast address of a relay. Multiple relays will
typically exist. The Anycast address is a routable "pseudo-
address" shared among the relays that can gain multicast access to
the source.
o If a specific IP address unique to a relay was not obtained, the
AMT Gateway then sends a message (e.g., the discovery message) to
the Anycast address such that the network is making the routing
choice of particular relay - e.g., closest relay to the EU. (Note
that in IPv6 there is a specific Anycast format and Anycast is
inherent in IPv6 routing, whereas in IPv4 Anycast is handled via
provisioning in the network. Details are out of scope for this
document.)
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o The contacted AMT Relay then returns its specific unicast IP
address (after which the Anycast address is no longer required).
Variations may exist as well.
o The AMT Gateway uses that unicast IP address to initiate a three-
way handshake with the AMT Relay.
o AMT Gateway provides "S,G" to the AMT Relay (embedded in AMT
protocol messages).
o AMT Relay receives the "S,G" information and uses the S,G to join
the appropriate multicast stream, if it has not already subscribed
to that stream.
o AMT Relay encapsulates the multicast stream into the tunnel
between the Relay and the Gateway, providing the requested content
to the EU.
4.3. Back Office Functions - Provisioning and Logging Guidelines
Back Office refers to the following:
o Servers and Content Management systems that support the delivery
of applications via multicast and interactions between AD's.
o Functionality associated with logging, reporting, ordering,
provisioning, maintenance, service assurance, settlement, etc.
4.3.1. Provisioning Guidelines
Resources for basic connectivity between AD's Providers need to be
provisioned as follows:
o Sufficient capacity must be provisioned to support multicast-based
delivery across AD's.
o Sufficient capacity must be provisioned for connectivity between
all supporting back-offices of the AD's as appropriate. This
includes activating proper security treatment for these back-
office connections (gateways, firewalls, etc) as appropriate.
o Routing protocols as needed, e.g. configuring routers to support
these.