One document matched: draft-ma-cdni-publisher-use-cases-00.txt
Network Working Group K. Ma
Internet-Draft R. Nair
Intended status: Informational Azuki Systems, Inc.
Expires: September 8, 2011 March 7, 2011
Content Distribution Network Interconnection (CDNI) Publisher Use
Cases draft-ma-cdni-publisher-use-cases-00
Abstract
Content publishers are increasingly using multiple CDNs to publish
content to the consumers. It is important to take into account their
specific requirements with respect to workflow restrictions with
respect to content licensing rules. Also, certain content
applications have specific delivery requirements that need to
considered while negotiating or signaling inter-CDN arrangements.
This contribution highlights some of these use cases to help motivate
discussion.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 30, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. CDNI Model and CDNI APIs . . . . . . . . . . . . . . . . . . . 5
3. Workflow Management Use Cases . . . . . . . . . . . . . . . . . 7
3.1. Asymmetric Content Availability Use Case . . . . . . . . . 7
3.2. Content Purge Use Case . . . . . . . . . . . . . . . . . 7
3.3. Service Level Agreement Negotiation Use Case . . . . . . 8
4. Detailed Content Delivery Use Cases . . . . . . . . . . . . . . 8
4.1. Grouped File Delegation . . . . . . . . . . . . . . . . . 8
4.2. Adaptive Bitrate Streaming Use Case . . . . . . . . . . . 9
4.3 Session Shifting Use Case . . . . . . . . . . . . . . . . 9
4.4 Origin Server Failover Use Case . . . . . . . . . . . . 10
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
Many use cases for CDN Interconnection are discussed in [I-
D.bertrand-cdni-use-cases] from the viewpoint of the CDSP. However,
with the growing popularity of over-the-top (OTT) delivery, many
content providers (CP) are now choosing to run their own service,
without operating their own CDN. The CP may contract and manage
multiple CDNs, as opposed to selecting an "Authoritative CDN" to
manage CDN delegation, as described in [I-D.bertrand-cdni-use-cases].
This draft takes the viewpoint of these CPs using a federation of
CDNs.
This document provides additional use cases addressing the needs of
workflow management agents (WMA), as they manage multiple
Authoritative CDNs. More detailed use cases for unique content
delivery scenarios for CPs and end users (EU) are also provided.
1.1. Terminology
This document uses the terminology defined in section 1.1 of
[I-D.jenkins-cdni-problem-statement] and
[I-D.bertrand-cdni-use-cases].
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2. CDNI Model and CDNI APIs
For convenience Figure 1 from [I-D.jenkins-cdni-problem-statement]
illustrating the CDNI problem area and the CDNI APIs is replicated
below with the addition of the workflow management component.
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------- -------
/ \ / \
| CSP |***********| WMA |
\ / \ /
------- -------
* # # #
* # # #
* # # # /\
* # # # / \
--------------------- # # # |CDNI| ---------------------
/ Upstream CDN \ # # # | | / Downstream CDN \
| +-------------+ | # # # Control API | +-------------+ |
| |CDN Control |<======#===|====|=======>| CDN Control | |
| +------*-*-*--+ | # # | | | +-*-*-*-------+ |
| * * * | # # | | | * * * |
| +------*------+ | # # Logging API | +-----*-------+ |
| ****| Logging |<====#=====|====|=======>| Logging |**** |
| * --------------+ | # | | | +-------------+ * |
| * * * | # | | | * * * |
| * +--------*----+ | # Req-Routing API | +---*---------+ * |
| * **|Req-Routing |<==========|====|=======>| Req-Routing |** * |
| * * +-------------+ | # | | | +-------------+ * * |
| * * * | # | | | * * * |
| * * +----------*--+ | # CDNI Metadata API| +-*-----------+ * * |
| * * |Distribution |<==#=======|====|=======>| Distribution| * * |
| * * | | | \ / | | | * * |
| * * | +---------+ | | \/ | | +---------+ | * * |
| * ****| | | | | | | |**** * |
| ******|Surrogate|*****************************|Surrogate|****** |
| | +---------+ | | Acquisition | | +-----*---+ | |
| +-------------+ | | +-------*-----+ |
\ / \ * /
--------------------- ---------*-----------
*
* Delivery
*
+------+
| User |
| Agent|
+------+
<==> interfaces inside the scope of CDNI
**** interfaces outside the scope of CDNI
#### interfaces important to Workflow Management Agents
Figure 1: CDNI Model and CDNI APIs
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3. Workflow Management Use Cases
This section identifies generic requirements independent of the
individual CDNI APIs. Some of those are expected to affect multiple
or all APIs.
Content licensing is typically a complex mixture of temporal
restrictions (e.g., how soon after the original release date), geo-
location restrictions (e.g., in which countries), device and quality
restrictions (e.g., only on devices with resolutions less than WxH),
and NSP restrictions.
3.1. Asymmetric Content Availability Use Case
Often content is tailored to the NSP and devices supported by the
NSP, e.g., NSP1 only support smart phones but not tablet devices,
therefore only requires content with resolution less than
480x320. In this case, the content files available through the
CDN (CDN1), operated by the NSP (NSP1), will be a subset of all
available content files. A second NSP (NSP2) may support laptop
and tablet devices and may therefore require higher resolution
video. This CDN (CDN2), operated by NSP2, will require access to
and possibly pre-positioning of different content files than
CDN1. The ability to delegate requests from CDN2 to CDN1 is
diminished by the availability of only a limited subset of the
content files on CDN1. In this case, both CDN1 and CDN2 may be
considered Authoritative CDNs, however, any resiliency measures
introduced by CDN interconnection will be limited. The WMA must
track and manage the rights of each Authoritative CDN to
different content files and be able to set delegation policies
for those CDNs.
3.2. Content Purge Use Case
Temporal licensing restrictions typically consist of a
"sunrise" (activation time), a "sunset" (deactivation time), and
a "takedown" (expiration time). Sunrise and sunset refer to
logical availability, however, takedown refers to physical
availability. Service agreements must typically support
takedown guarantees. The ability to both issue and confirm the
expunging of content files from surrogates is required to
enforce these content licenses. These licenses may have
different sunrise, sunset, and takedown times for different
NSPs. The WMA must track, manage, and confirm the takedown of
content from each of the Authoritative CDNs that content was
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provided to. In the case that an Authoritative CDN delegated
delivery to a non-Authoritative CDN, confirmation of content
takedown from the non-Authoritative Downstream CDNs must be
confirmed as well.
3.3. Service Level Agreement Negotiation Use Case
For video streaming services, the content provided for
distribution is typically encoded at known bitrates. The
quality of the delivered content is dependent upon the network
capacity of the CDN. EU experience is critical to protecting CP
brand loyalty. The content provider may wish to restrict
delivery when insufficient bandwidth exists to deliver a high
quality content viewing experience. The "Overload Handling" use
case, discussed in [I-D.bertrand-cdni-use-cases], discusses
expansion of bandwidth, but not the specific enforcement of
minimum bandwidth or minimum latency requirements. Metadata
needs to support the specification of these requirements. The
WMA needs to be able to negotiate and set limitations for
content delivery.
4. Detailed Content Delivery Use Cases
This section identifies generic requirements independent of the
individual CDNI APIs. Some of those are expected to affect multiple
or all APIs.
4.1. Grouped File Delegation
Delegating or pre-positioning content which are commonly
requested in close temporal proximity is an important use case
for CDN optimization and affects metadata concepts in CDN
interconnection.
For the delivery of streaming video, the content may be
separated into multiple files, e.g., segment files for HTTP Live
Streaming (HLS) [I-D.pantos-http-live-streaming]. When
delegating requests for HLS content, it may not be efficient to
delegate each segment file request, but rather be able to
delegate sets of content files that are commonly requested as a
group. Web page images and icons may also fall into this
category. For streaming video, however, there is also a
sequential time component for which metadata may be used to
optimize paced on-demand pre-fetching of segment files.
Similarly, for the case of pre-positioning grouped files, the
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ability to set a priority for certain files (e.g., common video
starting points or hot-spots) allow the CDN to optimize storage
usage, while still pre-positioning content critical to
minimizing initial delivery latency. This information, combined
with geo-location information, may enable the CDN to further
optimize surrogate selection.
4.2. Adaptive Bitrate Streaming Use Case
Support for adaptive bitrate delivery an important use case for
HTTP-based streaming video (e.g., HTTP Live Streaming (HLS)
[I-D.pantos-http-live-streaming])
The CDN interconnection problem statement
[I-D.jenkins-cdni-problem-statement] clearly states as a
non-goal: "Content preparation, including encoding and
transcoding". While the actual transformation of content is
beyond the scope of CDN interconnection, the understanding about
the existence of pre-transcoded files which are related to each
other, is valuable for CDN pre-fetching, pre-positioning, and
delivery optimization. This may be considered a further
extension of the Grouped File Delegation use case. Metadata
relaying the relative access patterns for specific content
(e.g., switching from bitrate 6 to bitrate 7 is more likely than
switching from bitrate 7 to bitrate 1) may be used to further
optimize storage usage and surrogate selection.
4.3 Session Shifting Use Case
Session shifting between first (TV), second (PC), and third
(mobile) screen devices is a primary use case for CDN
interconnection.
The "Device and Network Technology Extension" use case,
discussed in [I-D.bertrand-cdni-use-cases], covers a single
device moving from one NSP/CDN to another (e.g., switching from
WiFi to 3G on a mobile device). An extension to this scenario
is switching between different devices either within the same
NSP (e.g., switching from a TV on a cable network, to a PC
connected to a cable modem or to a mobile device connected via
WiFi to the cable modem) or across multiple NSPs (e.g., from a
TV connected to a cable or a PC connected to a cable modem or a
mobile device connected via WiFi to the cable modem, to a mobile
device on a 3G/4G cellular connection). The requests may come
from different devices and/or access networks, but all belong to
the same virtual data stream.
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4.4 Origin Server Failover Use Case
Support for multiple origin servers from which Downstream
CDNs may retrieve content is an important use case for resilient
delivery.
The "Overload Handling" and "Resiliency" use cases,
discussed in [I-D.bertrand-cdni-use-cases], cover cases where an
EU is redirected to an alternate CDN (CDN2) when the CDN which
received the initial request (CDN1) is unable to service it due
to capacity issues or other failure. An extension to this
scenario is the condition where the origin server (OS1) becomes
either temporarily or permanently unreachable to CDN1. In this
case, there are two possible options:
o Redirect the request to CDN2, in the hope that CDN2 still
has connectivity to the origin server (OS1).
o Failover to a secondary origin server (OS2) and attempt to
retrieve the content from OS2 in order to service the
request.
There may be a arbitrary number of alternate origin servers
(which may in fact be other CDNs) and failover to an alternate
CDN should only occur after exhausting a possibly limited
alternate origin server search. In the case of live streaming
video, an origin server may go down unexpectedly, and retrieval
from an alternate CDN may not be feasible if it introduces too
much latency.
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5. Conclusions
This draft introduces some content publisher use cases that need to
be considered in the CDNI efforts. We covered the cases that apply to
workflow management as well as content delivery.
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5. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
Content licensing rights need to be managed across multiple CDN
domains as described in the workflow management use cases above.
7. Acknowledgements
The authors would like to thank the organizers of this effort to
discuss the requirements for delivering premium content over the
Internet.
8. References
8.1. Normative References
[I-D.bertrand-cdni-use-cases]
Bertrand, G. and E. Stephan, G. Watson, T. Burbridge,
P. Eardley, "Use Cases for Content Distribution Network
Interconnection", draft-bertrand-cdni-use-cases-01
(work in progress), January 2011.
[I-D.jenkins-cdni-problem-statement]
Niven-Jenkins, B., Faucheur, F., and N. Bitar, "Content
Distribution Network Interconnection (CDNI) Problem
Statement", draft-jenkins-cdni-problem-statement-01 (work
in progress), January 2011.
[I-D.watson-cdni-use-cases]
Watson, G., "CDN Interconnect Use Cases",
draft-watson-cdni-use-cases-00 (work in progress),
January 2011.
[I-D.pantos-http-live-streaming]
R. Pantos, "HTTP Live Streaming",
draft-pantos-http-live-streaming-05(work in progress),
November 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
8.2. Informative References
[Apache-Common]
"Apache Common Log File Format (http://www.w3.org/Daemon/
User/Config/Logging.html#common-logfile-format)".
[Apache-Format]
"Apache LogFormat Directive (http://httpd.apache.org/docs/
1.3/mod/mod_log_config.html#logformat)".
[I-D.amini-cdi-distribution-reqs]
Amini, L., "Distribution Requirements for Content
Internetworking", draft-amini-cdi-distribution-reqs-02
(work in progress), November 2001.
[I-D.cain-request-routing-req]
Cain, B., "Request Routing Requirements for Content
Internetworking", draft-cain-request-routing-req-03 (work
in progress), November 2001.
[I-D.gilletti-cdnp-aaa-reqs]
"CDI AAA Requirements,
draft-gilletti-cdnp-aaa-reqs-01.txt", June 2001.
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Authors' Addresses
Kevin Ma
Azuki Systems
43 Nagog Park
Acton, MA 01720
USA
Phone: +1 978-844-5100
Email: kevin.ma@azukisystems.com
Raj Nair
Azuki Systems
43 Nagog Park
Acton, MA 01720
USA
Phone: +1 978-844-5100
Email: raj.nair@azukisystems.com
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