CDNI J. Seedorf
Internet-Draft NEC
Intended status: Informational Y. Yang
Expires: September 6, 2015 Yale
J. Peterson
Neustar
March 5, 2015
CDNI Footprint and Capabilities Advertisement using ALTO
draft-seedorf-cdni-request-routing-alto-08
Abstract
Network Service Providers (NSPs) are currently considering to deploy
Content Delivery Networks (CDNs) within their networks. As a
consequence of this development, there is a need for interconnecting
these local CDNs. The necessary interfaces for inter-connecting CDNs
are currently being defined in the Content Delivery Networks
Interconnection (CDNI) WG. This document focuses on the CDNI
Footprint & Capabilities Advertisement interface (FCI).
Specifically, this document specifies a new Application Layer Traffic
Optimization (ALTO) service to facilitate Footprint & Capabilities
Advertisement in a CDNI context.
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
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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 September 6, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. ALTO within CDNI Request Routing . . . . . . . . . . . . . . 3
3. Assumptions and High-Level Design Considerations . . . . . . 4
3.1. General Assumptions and Considerations . . . . . . . . . 4
3.2. Semantics for Footprint/Capabilities Advertisment . . . . 5
3.3. Advantages of using ALTO as the CDNI FCI protocol . . . . 7
3.4. Selection of a Downstream CDN with ALTO . . . . . . . . . 7
4. CDNI FCI ALTO Service . . . . . . . . . . . . . . . . . . . . 8
4.1. Server Response Encoding . . . . . . . . . . . . . . . . 8
4.1.1. CDNI FCI Map . . . . . . . . . . . . . . . . . . . . 8
4.1.2. Meta Information . . . . . . . . . . . . . . . . . . 8
4.1.3. Data Information . . . . . . . . . . . . . . . . . . 8
4.2. Protocol Errors . . . . . . . . . . . . . . . . . . . . . 9
4.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Useful ALTO extensions for CDNI Request Routing . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Many Network Service Providers (NSPs) are currently considering or
have already started to deploy Content Delivery Networks (CDNs)
within their networks. As a consequence of this development, there
is a need for interconnecting these local CDNs. Content Delivery
Networks Interconnection (CDNI) has the goal of standardizing
protocols to enable such interconnection of CDNs [RFC6707].
The CDNI problem statement [RFC6707] envisions four interfaces to be
standardized within the IETF for CDN interconnection:
o CDNI Request Routing Interface
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o CDNI Metadata Interface
o CDNI Logging Interface
o CDNI Control Interface
This document focuses solely on the CDNI Request Routing Interface,
which can be further divided into two interfaces (see [RFC6707] for a
detailed description): the CDNI Request Routing Redirection interface
(RI), and the CDNI Footprint & Capabilities Advertisement interface
(FCI). This document specifies a new Application Layer Traffic
Optimization (ALTO) [RFC7285] service called 'CDNI Footprint &
Capabilities Advertisement Service'. This service is used to
transport CDNI FCI JSON objects, which are defined in a separate
document [I-D.ma-cdni-capabilities]. An abstraction for managing
individual CDNI capabilities in an opaque manner is defined as
'FCIBase' object in [I-D.ietf-cdni-footprint-capabilities-semantics].
Throughout this document, we use the terminology for CDNI defined in
[RFC6707].
2. ALTO within CDNI Request Routing
The main purpose of the CDNI Request Routing Interface is described
in [RFC6707] as follows: "The CDNI Request Routing interface enables
a Request Routing function in an Upstream CDN to query a Request
Routing function in a Downstream CDN to determine if the Downstream
CDN is able (and willing) to accept the delegated Content Request.
It also allows the Downstream CDN to control what should be returned
to the User Agent in the redirection message by the upstream Request
Routing function." On a high level, the scope of the CDNI Request
Routing Interface therefore contains two main tasks:
o A) Determining if the downstream CDN is willing to accept a
delegated content request
o B) Redirecting the content request coming from an upstream CDN to
the proper entry point or entity in the downstream CDN
More precisely, in [RFC7336] the request routing interface is broadly
divided into two functionalities:
o 1) the asynchronous advertisement of footprint and capabilities by
a dCDN that allows a uCDN to decide whether to redirect particular
user requests to that dCDN (the CDNI FCI)
o 2) the synchronous operation of actually redirecting a user
request (the CDNI RI)
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Application Layer Traffic Optimization (ALTO) [RFC7285] is an
approach for guiding the resource provider selection process in
distributed applications that can choose among several candidate
resources providers to retrieve a given resource. By conveying
network layer (topology) information, an ALTO server can provide
important information to "guide" the resource provider selection
process in distributed applications. Usually, it is assumed that an
ALTO server conveys information these applications cannot measure
themselves [RFC5693].
Originally, ALTO was motivated by the huge amount of cross-ISP
traffic generated by P2P applications [RFC5693]. Recently, however,
ALTO is also being considered for improving the request routing in
CDNs [I-D.jenkins-alto-cdn-use-cases]. In this context, it has also
been proposed to use ALTO for selecting an entry-point in a
downstream NSP's network (see section 3.4 "CDN delivering Over-The-
Top of a NSP's network" in [I-D.jenkins-alto-cdn-use-cases]). Also,
the CDNI problem statement explicitly mentions ALTO as a candidate
protocol for "algorithms for selection of CDN or Surrogate by
Request-Routing systems" [RFC6707].
3. Assumptions and High-Level Design Considerations
In this section we list some assumptions and design issues to be
considered when using ALTO for the CDNI Footprint and Capabilities
Advertisement interface.
3.1. General Assumptions and Considerations
Below we list some general assumptions and considerations:
o As explicitly being out-of-scope for CDNI [RFC6707], it is assumed
that ingestion of content or acquiring content across CDNs is not
part of request routing as considered within CDNI standardization
work. The focus of using ALTO (as considered in this document) is
hence on request routing only, assuming that the content (desired
by the end user) is available in the downstream CDN (or can be
aquired by the downstream CDN by some means).
o Federation Model: "Footprint and Capabilities Advertisement" and
in general CDN request routing depends on the federation model
among the CDN providers. Designing a suitable solution thus
depends on whether a solution is needed for different settings,
where CDNs consist of both NSP CDNs (serving individual ASes) and
general, traditional CDNs (such as Akamai). We assume that CDNI
is not designed for a setting where only NSP CDNs each serve a
single AS only.
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o In this document, it is assumed that the upstream CDN (uCDN) makes
the decision on selecting a downstream CDN, based on information
that each downstream CDN has made available to the upstream CDN.
Further, we assume that in principle more than one dCDN may be
suitable for a given end-user request (i.e. different dCDNs may
claim "overlapping" footprints). The uCDN hence potentially has
to select among several candidate downstream CDNs for a given end
user request.
o It is not clear what kind(s) of business, contract, and
operational relationships two peering CDNs may form. For the
Internet, we see provider-customer and peering as two main
relations; providers may use different charging models (e.g.,
95-percentile, total volume) and may provide different SLAs.
Given such unknown characteristics of CDN peering business
agreements, we should design the protocol to support as much
diverse potential business and operational models as possible.
3.2. Semantics for Footprint/Capabilities Advertisment
The CDNI document on "Footprint and Capabilities Semantics"
[I-D.ietf-cdni-footprint-capabilities-semantics] defines the
semantics for the CDNI FCI. It thus provides guidance on what
Footprint and Capabilities mean in a CDNI context and how a protocol
solution should in principle look like. Here we briefly summarize
the key points of the semantics of Footprint and Capabilities (for a
detailed discussion, the reader is referred to
[I-D.ietf-cdni-footprint-capabilities-semantics]):
o Often, footprint and capabilities are tied together and cannot be
interpreted independently from each other. In such cases, i.e.
where capabilities must be expressed on a per footprint basis, it
may be beneficial to combine footprint and capabilities
advertisement.
o Given that a large part of Footprint and Capabilities
Advertisement will actually happen in contractual agreements, the
semantics of CDNI Footprint and Capabilities advertisement refer
to answering the following question: what exactly still needs to
be advertised by the CDNI FCI? For instance, updates about
temporal failures of part of a footprint can be useful information
to convey via the CDNI request routing interface. Such
information would provide updates on information previously agreed
in contracts between the participating CDNs. In other words, the
CDNI FCI is a means for a dCDN to provide changes/updates
regarding a footprint and/or capabilities it has prior agreed to
serve in a contract with a uCDN.
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o It seems clear that "coverage/reachability" types of footprint
must be supported within CDNI. The following such types of
footprint are mandatory and must be supported by the CDNI FCI:
* List of ISO Country Codes
* List of AS numbers
* Set of IP-prefixes
A 'set of IP-prefixes' must be able to contain full IP addresses,
i.e., a /32 for IPv4 and a /128 for IPv6, and also IP prefixes
with an arbitrary prefix length. There must also be support for
multiple IP address versions, i.e., IPv4 and IPv6, in such a
footprint.
o For all of these mandatory-to-implement footprint types,
footprints can be viewed as constraints for delegating requests to
a dCDN: A dCDN footprint advertisement tells the uCDN the
limitations for delegating a request to the dCDN. For IP prefixes
or ASN(s), the footprint signals to the uCDN that it should
consider the dCDN a candidate only if the IP address of the
request routing source falls within the prefix set (or ASN,
respectively). The CDNI specifications do not define how a given
uCDN determines what address ranges are in a particular ASN.
Similarly, for country codes a uCDN should only consider the dCDN
a candidate if it covers the country of the request routing
source. The CDNI specifications do not define how a given uCDN
determines the country of the request routing source. Multiple
footprint constraints are additive, i.e. the advertisement of
different types of footprint narrows the dCDN candidacy
cumulatively.
o The following capabilities seem useful as 'base' capabilities,
i.e. ones that are needed in any case and therefore constitute
mandatory capabilities to be supported by the CDNI FCI:
* Delivery Protocol (e.g., HTTP vs. RTMP)
* Acquisition Protocol (for aquiring content from a uCDN)
* Redirection Mode (e.g., DNS Redirection vs. HTTP Redirection as
discussed in [RFC7336])
* Capabilities related to CDNI Logging (e.g., supported logging
mechanisms)
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* Capabilities related to CDNI Metadata (e.g., authorization
algorithms or support for proprietary vendor metadata)
3.3. Advantages of using ALTO as the CDNI FCI protocol
The following reasons make ALTO a suitable candidate protocol for
downstream CDN selection as part of CDNI request routing and in
particular for an FCI protocol:
o CDN request routing is done at the application layer. ALTO is a
protocol specifically designed to improve application layer
traffic (and application layer connections among hosts on the
Internet) by providing additonal information to applications that
these applications could not easily retrieve themselves. For
CDNI, this is exactly the case: a uCDN wants to improve
application layer CDN request routing by using dedicated
information (provided by a dCDN) that the uCDN could not easily
obtain otherwise.
o The semantics of an ALTO network map are an exact match for the
needed information to convey a footprint by a downstream CDN, in
particular if such a footprint is being expressed by IP-prefix
ranges.
o Security: ALTO maps can be signed and hence provide inherent
integrity protection (see Section 6)
o RESTful-Design: The ALTO protocol has undergone extensive
revisions in order to provide a RESTful design regarding the
client-server interaction specified by the protocol. A CDNI FCI
interface based on ALTO would inherit this RESTful design.
o Error-handling: The ALTO protocol has undergone extensive
revisions in order to provide sophisticated error-handling,
inparticular regarding unexpected cases. A CDNI FCI interface
based on ALTO would inherit this thought-through and mature error-
handling.
o Filtered network map: The ALTO Map Filtering Service (see
[RFC7285] for details) would allow a uCDN to query only for parts
of an ALTO map.
3.4. Selection of a Downstream CDN with ALTO
Under the considerations stated in Section 3, ALTO can help the
upstream CDN provider to select a proper downstream CDN provider for
a given end user request as follows: Each downstream CDN provider
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hosts an ALTO server which provides ALTO services which convey CDNI
FCI information to an ALTO client at the upstream CDN provider.
4. CDNI FCI ALTO Service
The ALTO protocol is based on an ALTO Information Service Framework
which consists of several services, where all ALTO services are
'provided through a common transport protocol, messaging structure
and encoding, and transaction model' [RFC7285]. The ALTO protocol
specification [RFC7285] defines several such services, e.g. the ALTO
map service.
This document defines a new ALTO Service called 'CDNI Footprint &
Capabilities Advertisement Service' which conveys JSON objects of
media type 'application/alto-fcimap+json'. This media type and JSON
object format is defined in [I-D.ma-cdni-capabilities]; this document
specifies how to transport such JSON objects via the ALTO protocol
with the ALTO 'CDNI Footprint & Capabilities Advertisement Service'.
An abstraction for managing individual CDNI capabilities in an opaque
manner is defined as 'FCIBase' object in
[I-D.ietf-cdni-footprint-capabilities-semantics].
4.1. Server Response Encoding
4.1.1. CDNI FCI Map
The media type of the CDNI FCI Map is 'application/alto-cdni-
fcimap+json'. The HTTP Method, Accept Input Parameters,
Capabilities, Uses, and Response of the CDNI FCI Map are specified in
[I-D.ma-cdni-capabilities].
4.1.2. Meta Information
The 'meta' field of a FCIMapData response MUST include 'vtag', which
is an ALTO Version Tag of the retrieved FCIMapData according to
[RFC7285] (Section 10.3.). It thus contains a 'resource-id'
attribute, and a 'tag' is an identifier string.
4.1.3. Data Information
The data component of a CDNI FCI Map resource is named 'fcimap' which
is a JSON object of type FCIMapData. This JSON object of type
FCIMapData is derived from ResponseEntityBase as specified in the
ALTO protocol [RFC7285] (Section 8.4.) and specified in
[I-D.ma-cdni-capabilities].
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4.2. Protocol Errors
Protocol errors are handled as specified in the ALTO protocol
[RFC7285] (Section 8.5.).
4.3. Example
The following example shows an CDNI FCI Map as in
[I-D.ma-cdni-capabilities], however with meta-information as defined
in Section 4.1.2 of this document.
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GET /fcimap HTTP/1.1
Host: alto.example.com
Accept: application/alto-fcimap+json,application/alto-error+json
HTTP/1.1 200 OK
Content-Length: 439
Content-Type: application/alto-fcimap+json
{
"meta" : {
"vtag": {
"resource-id": "my-default-fcimap",
"tag": "da65eca2eb7a10ce8b059740b0b2e3f8eb1d4785"
}
},
"fcimap": [
{ "name": "delivery_protocol",
"values": [
"HTTP",
"RTSP",
"MMS"
]
},
{ "name": "delivery_protocol",
"values": [
"RTMP",
"HTTPS"
],
"footprint": [
{ "type": "IPv4CIDR",
"values": [
"10.1.0.0/16",
"10.10.10.0/24"
]
}
]
}
]
}
5. Useful ALTO extensions for CDNI Request Routing
It is envisioned that yet-to-be-defined ALTO extensions will be
standardized that make the ALTO protocol more suitable and useful for
applications other than the originally considered P2P use case
[I-D.marocco-alto-next]. Some of these extensions to the ALTO
protocol would be useful for ALTO to be used as a protocol within
CDNI request routing, and in particular within the "Footprint and
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Capabilities Advertisment" part of the CDNI request routing
interface.
The following proposed extensions to ALTO would be beneficial to
facilitate CDNI request routing with ALTO as outlined in Section 3.4:
o Server-initiated Notifications and Incremental Updates: In case
the footprint or the capabilities of a downstream CDN change
abruptly (i.e. unexpectedly from the perspective of an upstream
CDN), server initiated notifications would enable a dCDN to
directly inform an upstream CDN about such changes. Consider the
case where - due to failure - part of the footprint of the dCDN is
not functioning, i.e. the CDN cannot serve content to such clients
with reasonable QoS. Without server-initiated notifications, the
uCDN might still use a very recent network and cost map from dCDN,
and therefore redirect request to dCDN which it cannot serve.
Similarly, the possibility for incremental updates would enable
efficient conveyance of the aforementioned (or similar) status
changes by the dCDN to the uCDN. A proposal for server-initiated
ALTO updates can be found in [I-D.marocco-alto-ws]. A discussion
of incremental ALTO updates can be found in
[I-D.schwan-alto-incr-updates].
o Content Availability on Hosts: A dCDN might want to express CDN
capabilties in terms of certain content types (e.g. codecs/
formats, or content from certain content providers). A new
endpoint property for ALTO that would be able to express such
"content availability" would enable a dCDN to make available such
information to an upstream CDN. This would enable a uCDN to
determine if a given dCDN actually has the capabilities for a
given request with respect to the type of content requested.
o Resource Availability on Hosts or Links: The capabilities on links
(e.g. maximum bandwidth) or caches (e.g. average load) might be
useful information for an upstream CDN for optimized dowmstream
CDN selection. For instance, if a uCDN receives a streaming
request for content with a certain bitrate, it needs to know if it
is likely that a dCDN can fulfill such stringent application-level
requirements (i.e. can be expected to have enough consistent
bandwidth) before it redirects the request. In general, if ALTO
could convey such information via new endpoint properties, it
would enable more sophisticated means for downstream CDN selection
with ALTO.
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6. Security Considerations
One important security consideration is the proper authentication of
advertisement information provided by a downstream CDN. The ALTO
protocol provides a specification for a signature of ALTO information
(see 8.2.2. of [RFC7285]. ALTO thus provides a proper means for
protecting the integrity of FCI information.
More Security Considerations will be discussed in a future version of
this document.
7. Acknowledgements
The authors would like to thank Kevin Ma, Daryl Malas, and Matt
Caulfield for their timely reviews and invaluable comments.
Jan Seedorf is partially supported by the GreenICN project (GreenICN:
Architecture and Applications of Green Information Centric
Networking), a research project supported jointly by the European
Commission under its 7th Framework Program (contract no. 608518) and
the National Institute of Information and Communications Technology
(NICT) in Japan (contract no. 167). The views and conclusions
contained herein are those of the authors and should not be
interpreted as necessarily representing the official policies or
endorsements, either expressed or implied, of the GreenICN project,
the European Commission, or NICT.
8. References
8.1. Normative References
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693, October
2009.
[RFC6707] Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
Distribution Network Interconnection (CDNI) Problem
Statement", RFC 6707, September 2012.
[RFC6770] Bertrand, G., Stephan, E., Burbridge, T., Eardley, P., Ma,
K., and G. Watson, "Use Cases for Content Delivery Network
Interconnection", RFC 6770, November 2012.
[RFC7285] Alimi, R., Penno, R., Yang, Y., Kiesel, S., Previdi, S.,
Roome, W., Shalunov, S., and R. Woundy, "Application-Layer
Traffic Optimization (ALTO) Protocol", RFC 7285, September
2014.
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[RFC7336] Peterson, L., Davie, B., and R. van Brandenburg,
"Framework for Content Distribution Network
Interconnection (CDNI)", RFC 7336, August 2014.
[RFC7337] Leung, K. and Y. Lee, "Content Distribution Network
Interconnection (CDNI) Requirements", RFC 7337, August
2014.
8.2. Informative References
[I-D.peterson-CDNI-strawman]
Peterson, L. and J. Hartman, "Content Distribution Network
Interconnection (CDNI) Problem Statement", draft-peterson-
CDNI-strawman-01 (work in progress), May 2011.
[I-D.marocco-alto-next]
Marocco, E. and V. Gurbani, "Extending the Application-
Layer Traffic Optimization (ALTO) Protocol", draft-
marocco-alto-next-00 (work in progress), January 2012.
[I-D.marocco-alto-ws]
Marocco, E. and J. Seedorf, "WebSocket-based server-to-
client notifications for the Application-Layer Traffic
Optimization (ALTO) Protocol", draft-marocco-alto-ws-02
(work in progress), February 2014.
[I-D.schwan-alto-incr-updates]
Schwan, N. and B. Roome, "ALTO Incremental Updates",
draft-schwan-alto-incr-updates-02 (work in progress), July
2012.
[I-D.jenkins-alto-cdn-use-cases]
Niven-Jenkins, B., Watson, G., Bitar, N., Medved, J., and
S. Previdi, "Use Cases for ALTO within CDNs", draft-
jenkins-alto-cdn-use-cases-03 (work in progress), June
2012.
[I-D.ma-cdni-capabilities]
Ma, K. and J. Seedorf, "CDNI Footprint & Capabilities
Advertisement Interface", draft-ma-cdni-capabilities-06
(work in progress), June 2014.
[I-D.liu-cdni-cost]
Liu, H., "A Cost Perspective on Using Multiple CDNs",
draft-liu-cdni-cost-00 (work in progress), October 2011.
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[I-D.ietf-cdni-metadata]
Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma,
"CDN Interconnection Metadata", draft-ietf-cdni-
metadata-09 (work in progress), March 2015.
[I-D.ietf-cdni-logging]
Faucheur, F., Bertrand, G., Oprescu, I., and R.
Peterkofsky, "CDNI Logging Interface", draft-ietf-cdni-
logging-15 (work in progress), February 2015.
[]
Seedorf, J., Peterson, J., Previdi, S., Brandenburg, R.,
and K. Ma, "CDNI Request Routing: Footprint and
Capabilities Semantics", draft-ietf-cdni-footprint-
capabilities-semantics-05 (work in progress), March 2015.
Authors' Addresses
Jan Seedorf
NEC Laboratories Europe, NEC Europe Ltd.
Kurfuersten-Anlage 36
Heidelberg 69115
Germany
Phone: +49 (0) 6221 4342 221
Email: jan.seedorf@neclab.eu
URI: http://www.neclab.eu
Y.R. Yang
Yale University
51 Prospect Street
New Haven 06511
USA
Email: yry@cs.yale.edu
URI: http://www.cs.yale.edu/~yry/
Jon Peterson
NeuStar
1800 Sutter St Suite 570
Concord CA 94520
USA
Email: jon.peterson@neustar.biz
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