Internet DRAFT - draft-zhang-decade-cdni-comparison
draft-zhang-decade-cdni-comparison
DECADE P. Zhang
Internet-Draft Mar 5, 2012
Intended status: Informational
Expires: September 6, 2012
Comparison of DECADE with CDNi
draft-zhang-decade-cdni-comparison-00
Abstract
This document gives a brief comparison of DECADE and CDNi, two
working groups on content delivery. CDNi aims at overcoming the
limited resource and footprints of a single CDN by interconnecting
multiple CDNs. While DECADE is mainly concerned with reducing the
last-mile bandwidth bottleneck and inter-domain traffics with in-
network storage. This in-network storage can also be utilized by
Content Service Providers (CSPs) as a CDN, whose footprints be across
multiple Internet Service Providers (CSPs). In this sense, DECADE
can also be a possible approach to overcome the limited footprints of
a single CDN. This document attempts to gain some understanding on
the relationship of these two solutions.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1. Content Service Provider (CSP) . . . . . . . . . . . . 3
1.1.2. DECADE server . . . . . . . . . . . . . . . . . . . . . 3
1.1.3. DECADE portal . . . . . . . . . . . . . . . . . . . . . 3
2. DECADE as a CDN across mutliple ISPs . . . . . . . . . . . . . 4
3. Comparison of DECADE with CDNi . . . . . . . . . . . . . . . . 5
3.1. Deployment complexity and cost . . . . . . . . . . . . . . 6
3.2. Support of individual users . . . . . . . . . . . . . . . . 6
3.3. Support of P2P mode . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
6. Normative References . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
Content Delivery Networks (CDNs) are widely utilized to deliver
videos, voices, and other content generated by Content Service
Providers (CSPs) to end users. However, a single CDN is mostly
constrained in geographical coverage and resource volume, and the
CDNi working group is aimed at interconnecting standalone CDNs so
that their geographic coverage and resources can be aggregated.
On the other hand, DECADE working group is aimed at introducing in-
network storage to alleviate last-mile bandwidth bottleneck, as well
as reduce inter-domain traffics. Seemingly the goals of DECADE and
CDNi are orthogonal, but actually the in-network storage of DECADE
can be leveraged by CSPs to deliver their content in a similar way as
using a CDN. For example, after an ISP have deployed DECADE servers
its network, a CSP can send their content to the DECADE Portal
provided by the ISP, which will distribute the content to DECADE
servers in multiple locations. When a content request the content
from CSP, it is directed to the DECADE portal, which then select a
DECADE server that is optimal for them. In this way, DECADE provides
a similar service like CDN in a single ISP. In the next section, we
will show how DECADE can be used as a CDN across multiple ISPs.
To this end, we are interested in comparing DECADE with CDNi as
another possible approach to overcome the geographical coverage
limitation of standalone CDNs.
1.1. Concepts
1.1.1. Content Service Provider (CSP)
A content service provider leverages CDNs to delivery their content
to content customers over Internet.
1.1.2. DECADE server
A DECADE server is implemented with DECADE protocols, management
mechanism and storage strategies. It is an important element to
provide DECADE services. In a DECADE server, we have a number of
Data Lockers each of which is a virtual account and private STORAGE
space for applications.
1.1.3. DECADE portal
A DECADE portal offers CSPs a portal site for file upload. It also
uses ALTO service to direct end users to an optimal DECADE Server to
download files.
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2. DECADE as a CDN across mutliple ISPs
The DECADE integration example document illustrates how to construct
a file distribution platform based on the DECADE+ALTO architecture.
In that document, DECADE is deployed in a single ISP, and CSPs can
use DECADE as a distribution platform or CDN in within this ISP. In
the following, we illustrate how this example can be extended to the
multiple-ISP scenarios, in which DECADE servers owned by multiple
ISPs can be leveraged to deliver content for CSPs.
For simplicity of illustration, let us take two ISPs for example. A
CSP register at ISP-1 and upload the file to the DECADE portal of
ISP-1, which then distributes the file to multiple DECADE servers. A
client in ISP-2 requests the file from the CSP, and is redirected to
the DECADE portal in ISP-1, which recognizes that the request is from
a client in ISP-2. Then, it redirects the request to the optimal
DECADE server (DECADE server B) at ISP-2 using information provided
by ALTO service. If server B has the file cached in its memory, then
it sends the file directly to the user. Otherwise, server B will
send a request to the DECADE portal of ISP-1. Recognizing this
request is from a DECADE server, it is redirected to the optimal
server DECADE server A in ISP-1. Then A sends the file to B, which
will cache the file and send it to the client that requested the
file.
The detailed communication diagram is as follow, and we omit the
interaction of DECADE-1 portal with ALTO servers for limited space.
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_________ ____________ __________ __________ __________
| | |Publisher's | | DECADE-1 | | DECADE | | DECADE |
| Client | | Portal | | Portal | | Server A | | Server B |
|_________| |____________| |__________| |__________| |__________|
| | | | |
|Download Req | | | |
|------------->| | | |
| URLs&Tokens | | | |
|<-------------| | | |
| | | | |
| Download Require(Tokens) | | |
|------------------------------>| | |
| | | | |
| addree of the optimal server | | |
| in ISP-2 | | |
|<------------------------------| | |
| | | | |
| | Get Data (Tokens) | |
|------------------------------------------------------------>|
| | | | |
| | | Download Require(Tokens) |
| | |<----------------------------|
| | | | |
| | | addree of the optimal |
| | | server in ISP-1 |
| | |---------------------------->|
| | | | Get Data |
| | | | (Tokens) |
| | | |<--------------|
| | | | Send Data |
| | | |-------------->|
| | Send Data | | |
|<------------------------------------------------------------|
An example of distribution platform of DECADE across two ISPs
Figure 1
3. Comparison of DECADE with CDNi
In this section, we take DECADE as another possible solution to the
limited coverage problem of standalone CDNs, and try to compare it to
the CDNi solution.
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Before comparisons, we should note the similarity and relation
between DECADE and CDNi. First, note that these two solutions can
both benefit from using ALTO as a service to make decisions. In
DECADE, ALTO helps DECADE portal to decide which is the best server
for a specific end users; In CDNi, a CDN can use ALTO to decide to
which CDN it should redirect a client's requests. Secondly, as
outlined in the requirement document of CDNi, DECADE can be used by
CDNi for control message exchanges, acquisition of content objects
between different CDNs, and for content delivery within a given CDN.
But the benefits of using DECADE in CDNi are rather limited.
3.1. Deployment complexity and cost
Since DECADE provides a open standard for in-network storage
architecture, ISPs can easily deploy their own DECADE servers in
their networks. Moreover, it is more likely that ISP can deploy
their storage servers more widely and closer to end users in their
networks than third-party CDN providers can. When multiple ISPs have
deployed their DECADE storage systems, a CSP can just subscribe the
DECADE service provided by one ISP, and can distribute its content to
DECADE servers across these multiple ISPs, as shown in the example in
the last section. The possible requirement may be there should be a
charging model so that ISPs can charge each other on the DECADE
storage consumption incurred by delivering content generated by CSPs
in other ISPs. Since ISPs have already initiated contracts with each
other, this model can be built just like traffic charging model.
Moreover, no request routing interface is needed by DECADE. The
downside is that ISPs should deploy DECADE servers, and for ISPs that
have no DECADE service, their users can be outside of coverage.
While using CDNi, existing CDNs can be leveraged without the need to
deploy new servers. This implies a lower deployment cost.
3.2. Support of individual users
Apart from providing service to large CSPs, DECADE can also provide
services to personal users. For example, a user can register at a
nearby DECADE server deployed by the ISP she subscribes to. Using
this DECADE server, it is possible for her to stream videos or voices
to her friends, despite the uplink link bandwidth constraint. On the
other hand, most CDNs are CSP oriented and not practical for
individual end users. This will also be true for CDNi, which is a
interconnection of CDNs.
3.3. Support of P2P mode
Since DECADE service can be open to end users, CSPs can also
distribute their content using P2P. Under this mode, end users will
upload and download chunks of a file to and from the DECADE server
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they are connected to. By using P2P, CSPs can reduce the cost of
employing DECADE services provided by ISPs. But it is more likely
that CSPs still use DECADE services to distribute content, but can
use P2P simultaneously to reduce cost.
4. Security Considerations
This document does not contain any security considerations.
5. IANA Considerations
This document does not have any IANA considerations.
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Author's Address
Peng Zhang
Email: pzhang.thu@gmail.com
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