Multicast Considerations in Support of CDN-I
draft-tarapore-mboned-multicast-cdni-01
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| Authors | Percy Tarapore , Robert Sayko , Ramki Krishnan | ||
| Last updated | 2012-10-22 | ||
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draft-tarapore-mboned-multicast-cdni-01
MBONED Working Group Percy S. Tarapore
Internet Draft Robert Sayko
Intended status: BCP AT&T
Expires: January 21, 2013 Ram Krishnan
Brocade
October 22, 2012
Multicast Considerations in Support of CDN-I
draft-tarapore-mboned-multicast-cdni-01.txt
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Abstract
This document examines the current capabilities of multicast to
support content distribution in an environment involving multiple
Service Providers joining together to form a Content Distribution
Network Interconnection (CDN-I) Federation.
Table of Contents
1. Introduction...................................................2
2. CDN Nomenclature and High Level Overview.......................3
3. Multicast Use Cases for a CDN-I Federation.....................5
3.1. Native Multicast Use Case.................................5
3.2. Automatic Multicast Tunneling Use Cases...................6
3.2.1. AMT Interconnection Between P-CDN and S-CDN..........6
3.2.2. AMT Tunnel Connecting S-CDN and EU...................7
3.2.3. AMT Tunnel Connecting EU to P-CDN Through Non-Multicast
S-CDN.......................................................7
4. Content Types Suitable for Multicast-based CDN.................8
4.1. Live Content...................Error! Bookmark not defined.
4.2. "Delayed-Play" Download........Error! Bookmark not defined.
4.3. "Instant-Play" Download........Error! Bookmark not defined.
5. Evaluation of Native Multicast for CDN.........................8
6. Evaluation of AMT for CDN......................................9
7. Security Considerations.......................................14
8. IANA Considerations...........................................14
TBD..............................................................14
9. Conclusions...................................................14
10. References...................................................14
10.1. Normative References....................................14
10.2. Informative References..................................15
11. Acknowledgments..............................................15
1. Introduction
Content Providers (CP) are experiencing significant growth in demand
for all types of internet-based content. A single "over-the-top" CP
would require significant resources to deliver content that could be
requested from anywhere in the world. Service Providers (SP) are
taking advantage of this situation by forming Content Distribution
Network (CDN) Federations for the purpose of distributing content on
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behalf of Content Providers (CP). There are several advantages to
such CDN Federations:
o CPs can simply contract with one or more SPs in a CDN Federation
for delivery of their content. This enables CPs to concentrate on
their main objective - creation of content.
o SPs can expand their geographic reach via distribution agreements
with Federation members without developing costly resources
outside their local territories.
Multicast-based delivery mechanisms are a natural fit for content
distribution in the proposed CDN Federations. The scope of this
document is strictly focused on the interactions between CDN
Federation members to support multicast-based content distribution.
The purpose of this document is the detailed examination of
applicable multicast techniques and the identification of detailed
data/metadata/parameters that will have to be exchanged by CDN
Federation members to enable multicast-based content distribution.
2. CDN Nomenclature and High Level Overview
Terminology utilized to describe end-to-end user requests is
described as follows.
There are many entities involved in distribution of the content from
the CP all the way to the End User (EU). Figure 1 is a diagram
depicting the basic logical relationships among the various roles
involved in content delivery. Besides the CP and EU, the two
remaining major entities are the two members of a CDN Federation -
the Primary CDN Provider (P-CDN) and the Supporting CDN Provider (S-
CDN) [A-0200003]. The relationships between these entities are as
follows - see Figure 1.
1. The Content Provider owns the content and specifies conditions of
delivery and use. The End User interacts with the CP (link 1 in
the figure) for authentication and authorization, and to reach an
agreement to obtain specific content (content selection, content
purchase, acknowledgement of conditions of use). The CP has the
legal right to distribute content and specify conditions for
distribution.
2. The CP has an agreement and interacts with the P-CDN for deploying
content (link 2). The content is assumed to be retrieved by the P-
CDN from the CP Origin server.
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3. The P-CDN in turn has an agreement with an S-CDN for deploying and
distributing content (link 3).
4. The End User is attached to S-CDN for access and obtains the
content from the S-CDN (link 4). The End User also interacts with
the CP (link 1) as indicated above.
-----------------------------------------------
| (1) |
v |
+---------+ +---------+ +---------+ +---------+
| | | | | | | |
| Content | | Primary | | Suppor- | | End |
| Provider| --> | CDN | --> | -ting | --> | User |
| | (2) | | (3) | CDN | (4) | |
| | | | | | | |
+---------+ +---------+ +---------+ +---------+
Figure 1 - Relationships in a CDN Federation
Note that all SPs in the CDN Federation can play the role of P-CDN
(active relationship with a CP) as well as an S-CDN (attach EUs and
distribute content from P-CDN to EUs).
Using the above nomenclature, a CDN Federation is assumed to comprise
multiple SPs that agree to function as CDN Providers and distribute
content to End Users on behalf of CPs. The term 'SP' in this context
is synonymous with the term 'CDN Provider' for the purpose of this
document. A CP is assumed to have a contract with one or more SPs for
the purpose of content delivery. A high level content request flow is
described as follows:
o An End User discovers a specific content on a CP website and
requests delivery of the same. The CP selects one CDN Provider
with whom it has contracts for content delivery. The rules for
CDN Provider selection are part of the CP . CDN Provider
contract and are out of scope for this document. The selected
CDN Provider functions as the P-CDN.
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o The P-CDN then determines the mode of content delivery - either
cache/unicast or multicast depending on the type of content and
its own capabilities and resources. It then determines whether
to deliver the content directly to the End User or utilize
another CDN Provider based on rules such as proximity, available
resources, common delivery methods (e.g., multicast), etc. These
selection rules are out of scope of this document. In case
another CDN Provider is selected, then that entity assumes the
role of the S-CDN.
o The P-CDN then initiates the delivery process via the S-CDN's
domain - the S-CDN acts as the "point of delivery" to the End
User.
The simple scenario described here is common to both delivery
mechanisms - cache/unicast as well as multicast. The purpose of this
document is to address all multicast related aspects in support of
multicast-based content delivery.
3. Multicast Use Cases for a CDN-I Federation
Use cases involving multicast methods for distributing content in a
CDN Federation have been described in [A-0200004].
3.1. Native Multicast Architectural Use Case
------------------- -------------------
/ P-CDN \ / S-CDN \
/ (Multicast Enabled) \ / (Multicast Enabled) \
/ \ / \
| +----+ | | |
| | | +------+ | | +------+ | +----+
| | CS |------>| BR |-|---------|->| BR |-------------|--->| EU |
| | | +------+ | I1 | +------+ | I2 +----+
\ +----+ / \ /
\ / \ /
\ / \ /
------------------- -------------------
CS = Content Multicast Source (assumes that the Content Source
retrieves content from CP Origin)
BR = Border Router
I1 = P-CDN and S-CDN Multicast Interconnection (MBGP or BGMP)
I2 = S-CDN and EU Multicast Connection
Figure 1 - Content Distribution via End to End Native Multicast
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This case assumes that both CDN Providers as well as the
interconnection between them and the connection between the EU and S-
CDN are all multicast enabled.
3.2. A variation of this "pure" Native Multicast case is when the
interconnection I1 between the CDNs is multicast enabled via a
Generic Routing Encapsulation Tunnel (GRE) [RFC2784] and
encapsulating the multicast protocols across the interface.
Automatic Multicast Tunneling Architectural Use Cases
In reality, the initial introduction of multicast may not be fully
multicast enabled resulting in "Multicast Islands" requiring
Automatic Multicast Tunnels (AMT) for enabling multicast connections
between them [IETF-ID-AMT].
3.2.1. AMT Interconnection Between P-CDN and S-CDN
------------------- -------------------
/ P-CDN \ / S-CDN \
/ (Multicast Enabled) \ / (Multicast Enabled) \
/ \ / \
| +----+ | | |
| | | +------+ | | +------+ | +----+
| | CS |------>| AR |-|---------|->| AG |-------------|--->| EU |
| | | +------+ | I1 | +------+ | I2 +----+
\ +----+ / \ /
\ / \ /
\ / \ /
------------------- -------------------
AR = AMT Relay
AG = AMT Gateway
I1 = AMT Interconnection between P-CDN and S-CDN
I2 = S-CDN and EU Multicast Connection
Figure 3 - AMT Interconnection between P-CDN and S-CDN
This configuration assumes both CDN Providers are multicast enabled.
Only the interconnection between them is not multicast enabled and
hence, an AMT tunnel is established between them as shown in Figure
3.
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3.2.2. AMT Tunnel Connecting S-CDN and EU
------------------- -------------------
/ P-CDN \ / S-CDN \
/ (Multicast Enabled) \ / (Multicast Enabled) \
/ \ / \
| +----+ | | |
| | | +------+ | | +------+ +------+ | +----+
| | CS |------>| BR |-|---------|->| BR |--->| AR |-|--->| EU |
| | | +------+ | I1 | +------+ +------+ | I2 +----+
\ +----+ / \ /
\ / \ /
\ / \ /
------------------- -------------------
CS = Content Server
BR = Border Router
AR = AMT Relay
I1 = P-CDN and S-CDN Multicast Interconnection (MBGP or BGMP)
I2 = AMT Connection between S-CDN and EU
Figure 4 - AMT Tunnel Connecting S-CDN and EU
This case involves EU devices that are not multicast enabled. Hence
an AMT Tunnel is established between the S-CDN AMT Relay and the EU
device. This implies one tunnel per EU - potentially several AMT
tunnels may need to be setup.
Note that there could be configurations involving both situations
described in 3.2.1 and 3.2.2.
3.2.3. AMT Tunnel Connecting EU to P-CDN Through Non-Multicast S-CDN
This Use Case assumes that EU attached to the non-multicast enabled
S-CDN has a device populated with a client that establishes an AMT
tunnel to the AMT Relay in the P-CDN.
This configuration is needed when the S-CDN is not multicast-enabled.
This is the most "extreme" AMT case as the length of the tunnels as
well as the number of tunnels can be large.
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------------------- -------------------
/ P-CDN \ / S-CDN \
/ (Multicast Enabled) \ / (Non-Multicast \
/ \ / Enabled) \
| +----+ | | |
| | | +------+ | | | +----+
| | CS |------>| AR |-|---------|-----------------------|--->| EU |
| | | +------+ | | | I2 +----+
\ +----+ / \ /
\ / \ /
\ / \ /
------------------- -------------------
CS = Content Source
AR = AMT Relay
I2 = AMT Tunnel Connecting EU to P-CDN Relay through Non-Multicast
Enabled S-CDN.
Figure 5 - AMT Tunnel Connecting P-CDN AMT Relay and EU
4. Content Types Suitable for Multicast-based CDN
This section highlights applications and content types that are
suitable for multicast-based delivery in a CDN Federation. Any unique
aspects of specific applications/content types that require special
attention are duly noted.
Note: Suggest we put in content types in tabular form followed by
this text:
For the purpose of this document, live streaming is chosen as a
typical multicast application for content distribution via a CDN
Federation. Note that a definition of live streaming needs to be
provided.
5. Evaluation of Existing Multicast Protocols to Support CDN-I
Use Case 3.1 describes Native Multicast configurations. This is the
"simplest" multicast case in that a single standard set of protocols
supports end-to-end content delivery from the CP to EU via two or
more fully multicast-enabled CDN Providers. It also provides for
efficient use of bandwidth and resources.
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Use Case 3.2.1 does deploy an AMT Tunnel for interconnecting two CDN
Providers; the rest of the configuration is Native Multicast - this
assumes that the EU devices are also multicast-enabled.
Thus existing Multicast capabilities need to be examined to determine
their ability to fully support content distribution in a CDN
Federation. A list of issues requiring examination is as follows:
o Delivery - Identification and communication of {Source, Group}
information and DNS information for provisioning across CDNs.
Details to be provided.
o Routing/Peering - Identification and acknowledgement of external
IP addresses particularly when utilizing a GRE Tunnel for
interconnecting CDNs. Details to be provided.
o Back-Office Functions - Identification of appropriate
data/metadata collected by Native Multicast to support usage of
content for billing, settlements, logging, etc. Details to be
provided.
o Security - Determine ability of Native Multicast to deal with
security risks such as bot attacks, denial of service, etc.
Details to be provided. Also, EU authentication and
authorization
o Others - To Be Determined
5.1. Use Case 3.1
In this Use Case, with E-T-E multicast connectivity, the P-CDN
provides source, routing and reporting functionality. The S-CDN
provides routing and reporting functions.
Though the CP is the origin the interface between the origin and the
MC source is out of scope.
Issues:
-what about performance and reliability "tricks" that may be employed
do we address here?
-Moving from network to network? Addressed in separate RFC
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-IPv4 to IPv6 (assumption) not addressed or in scope - need to
reference a standard if there is one
-expand definition of S-CDN???
5.1.1. Delivery
1) If there exists end to end multicast between the EU and the MC
Source, then IGMP/MLD, PIM and MBGP protocols will ensure the
content stream is delivered to the requesting EU.
2) The (S,G) and in fact all parameters required by the application
related to the requested stream can be obtained by the client
application in a number of ways. None of which affects the MC
protocols and generally neither are the delivery mechanisms of the
parameters mutually exclusive. Examples are:
a. Upon selecting (clicking a link) on a web page for MC
content a file (Manifest file) is delivered via unicast to
the EU from the web page
b. An HTTP reply from the web page to the EU request may
contain the required parameters
c. An application may be "programmed" with the (S,G) and other
parameters. This method would require that the parameters
remain fairly static/stable.
d. An application may even require an EU to enter the (S,G) and
other parameters manually
3) There are a number of ways to control and communicate parameters
to the EU that direct the EU to the appropriate MC source. Eg.
a. The (S,G) can be FQDNs in which case DNS can be used to
select specific (S,G) address set.
b. When the EU selects the stream from the web page the
parameters forwarded back to to the EU can be selected based
on criteria related to the EU such as source IP, EU SP.
Decisions are driven by
i. Business relationship to the EU and/or EU CDN
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ii. Geographic location of SP
iii. On-net or off-net EU
iv. MC network conditions
v. TOD
vi. Etc
c. In ETE MC any intervening (transit) network or SP should not
make any attempt to change parameters forwarded to the EU
from the serving CDN.
i. Only a selected and participating S-CDN SP should, if
required, intercept and change any MC parameters
forwarded to the EU. There should be agreement between
the participating CDNs that this is permissible.
ii. If the S-CDN changes parameters this should be recorded
and reported to the upstream (P-CDN) CDN.
1. Generally reporting to the P-CDN will not be
required in real time
2. TBD = situations where it should be Real Time or
near RT
iii. An S-CDN should generally avoid unilaterally intercepting
and changing parameters values sent from an upstream
participating CDN (e.g. P-CDN)because this may cause
problems such as the following examples:
1. Performance issues in delivery to the EU
2. Conflicting/erroneous parameter values
3. Conflicting/erroneous authentication, authorization
or accounting
4) The MC Source application, which in the case of ETE is the P-CDN,
should employ techniques to ensure reliable deliver of the content
to the UE. The methodology or combination of methodologies will
often depend on the content type being delivered. There are
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several effective methods currently available, of which a few
examples are described below:
a. Carrouselling
b. FEC
c. Parallel streaming
d. Grid or burst severs
e. Unicast fallback
5.1.2. Routing and Peering
1) Routing between CDNi federation participants should be on a pair-
wise agreement and implementation
2) Route/peering preferences of the S-CDN should be communicated to
the P-CDN - how can this be done?????? How necessary is it?
a. Allow S-CDN to have some ability to balance peering traffic
b. Route around congestion.
3) CDNi participants must ensure that advertisement of the Source IP
address is provided across the peering interface.
a. If an Anycast address is to be used for the Source, then
participants must coordinate use of the Anycast address
space.
b. Coordination of the address space should be spelled out in
the participating members business arrangement/agreement
c. Coordination can occur in a pair-wise manner, but each CDN
with multiple arrangements must ensure that there are no
conflicts introduced into any individual arrangement.
4) If the peering interface is not multicast enabled a GRE tunnel
should be provisioned between the CDNi participants
a. Source IP must be advertised across the GRE tunnel
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b. The GRE tunnel may be provisioned to be terminated on
participants border routers
c. Alternatively, the P-CDN may desire to terminate the GRE
directly to the Source. This will allow the P-CDN to have a
separate IP address for external and internal EUs.
5) Is there a way a P-CDN can instruct a S-CDN router to not
broadcast its IGMP group memberships across its subnet?????
a. How is that communicated to the router
b. Is it a provisioning only option
c. Or can it be interactively done via some protocol message?
5.1.3. Back Office Functions
5.1.4. Security
5.2. Use Case 3.2.1 (AMT only across the peering interface)
5.2.1. Delivery
All the recommended practices of 5.1.1 are applicable, plus the
following additional:
1) The P-CDN and S-CDN should each deploy and provision an AMT Relay
at their respective peering interface(s)
2) These AMT Relay must also include and AMT Gateway (GW) function
3) The P-CDN and S-CDN must have an agreement that allows the S-CDN
to advertise the Source IP address across the S-CDN multicast
enabled network.
4) If the AMT interface fails or is out of service the P-CDN and S-
CDN interface agreement should include provision for unicast
failover.
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5.2.2. Routing and Peering
1) The GW function in the S-CDN AMT Relay can be provisioned with the
proper address (this may be an Anycast address) of the P-CDN AMT
Relay with connectivity to the source. Alternatively, if the MC
source IP (or Anycast address) is not provisioned then a mechanism
for the GW function to find the P-CDN Relay with connectivity to
the source must be available
a. A recommended mechanism for the GW to find the correct Relay
is documented in "the RFC draft being constructed"
b. The P-CDN and S-CDN agreements should cover the methodology
used
c. The agreement should specify how notification of MC Source
IP is communicated (including timing)
5.2.3.
5.2.4.
6. Security Considerations
TBD
7. IANA Considerations
TBD
8. Conclusions
TBD
9. References
9.1. Normative References
[RFC2784] D. Farinacci, T. Li, S. Hanks, D. Meyer, P. Traina,
"Generic Routing Encapsulation (GRE)", RFC 2784, March 2000
[IETF-ID-AMT] G. Bumgardner, "Automatic Multicast Tunneling", draft-
ietf-mboned-auto-multicast-13, April 2012, Work in progress
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9.2. Informative References
[A-0200003] P. Tarapore, "CDN Interconnection Use Case Specifications
and High Level Requirements", ATIS Standard A-0200003, June 2011
(contact Nicole Butler at nbutler@atis.org using code IETF12 to
receive a free copy before September 30, 2012)
[A-0200004] P. Tarapore and R. Sayko, "CDN Interconnection Use Cases
and Requirements for Multicast-Based Content Distribution", ATIS
Standard A-0200004, January 2012 (contact Nicole Butler at
nbutler@atis.org using code IETF12 to receive a free copy before
September 30, 2012)
10. Acknowledgments
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Authors' Addresses
Percy S. Tarapore
AT&T
Phone: 1-732-420-4172
Email: tarapore@att.com
Robert Sayko
AT&T
Phone: 1-732-420-3292
Email: rs1983@att.com
Ram Krishnan
Brocade
Phone:
Email: ramk@brocade.com
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