Internet DRAFT - draft-song-cdni-slr-based-footprint
draft-song-cdni-slr-based-footprint
CDNI H. Song
Internet-Draft Huawei
Intended status: Standards Track Y. Zhang
Expires: March 7, 2013 China Mobile
Y. Sun
ICT/CAS
Sep 3, 2012
A SLR (Service Level Requirements) based footprint for CDNI
draft-song-cdni-slr-based-footprint-02
Abstract
Footprint advertisement is a very important step for CDN
interconnection and generates a lot of discussion. Actually, each
CDN can serve the whole world if its surrogates are publicly
reachable by IP addresses. But if a CDN does that, it can not
satisfy the requirements from the applications. So CDNs deliver
contents for applications, and the basic requirements should be from
the applications. One CDN can serve different applications well with
different footprint. But there is rare discussion on service level
requirements based footprint. This document is used to generate the
discussion on this aspect.
Status of this Memo
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This Internet-Draft will expire on March 7, 2013.
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Copyright (c) 2012 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
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Why SLR Based Footprint . . . . . . . . . . . . . . . . . . . . 3
3. What are the Parameters for SLR . . . . . . . . . . . . . . . . 4
3.1. Average Response Time . . . . . . . . . . . . . . . . . . . 4
3.2. Throughput . . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Startup Delay . . . . . . . . . . . . . . . . . . . . . . . 4
3.4. Average downloading rate . . . . . . . . . . . . . . . . . 5
3.5. Hit Ratio . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.6. Capability . . . . . . . . . . . . . . . . . . . . . . . . 5
3.7. Up-time . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.8. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Dynamic Mapping for Footprint . . . . . . . . . . . . . . . . . 5
5. Message Flows . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Terminology
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 [RFC2119].
2. Why SLR Based Footprint
Each CDN's footprint can be worldwide, if its surrogates' IP
addresses are publicly reachable. However, not every CDN can serve
the applications for worldwide distribution because it can not
satisfy the serverice level required by those applications. So what
an application basically needs is a CDN to satisfy its service level,
and distribute the contents to certain areas. If a CDN or together
with its downstream CDNs, cannot meet the SLR (service level
requirements) in an area from an application, then we can say this
upstream CDN is not competent for this content distribution task.
This document specifies how the parameters of SLR impact a CDN's
footprint. There is other draft [I-D.he-cdni-cap-info-advertising]
mentioned capability advertisement, please note that capability
advertisement is also very important and footprint is impacted by
capability of a CDN. We consider capability as one service
requirement factor from applications. While each CDN serve many
tasks concurrently, the dynamic resources that it can allocate is
also variable at different time.
The physical deployment area of a CDN might be small, but it can have
larger footprint area where it can satisfy an application's SLR. The
footprint area might be even larger than a CDN that has larger
physical deployment area. Choosing SLR as the basis for footprint
can avoid some CDN magnifying its service level and service area on
purpose, and also make some other "small" but powerful CDN be treated
with justness.
We think that applications should participate in the CDN
interconnection process implicitly, i.e. its requirements for service
level should be transmitted between upstream and downstream CDNs
(message protection is required due to the privacy). A downstream
CDN should notify its capability information to its upstream CDN as
well when notifying its footprint that satisfies certain SLR, which
will allow a upstream CDN to choose multiple downstream CDN to
fullfill a task even in a same area.
From the application's perspective, a file downloading application
may not care about when the user receive the first bit, but more care
about the average downloading rate. While a streaming application
may have a different opinion. So for a same CDN, it can serve the
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file downloading application well with one wider footprint and serve
streaming application well with another smaller footprint.
In general, service level is the main driver for the definition of
footprint, and applications do not care about the locations where a
CDN's surrogates are deployed while it can satisfy its service
requirements. And topologically, ALTO [I-D.ietf-alto-protocol] is
used for the appropriate surrogate selection after the footprints are
defined. And ALTO network map information can also be used for the
footprint description to upstream CDN .
3. What are the Parameters for SLR
The general principal for service level requirements is fast,
scalable, secure and reliable. But it needs detailed measurement
metrics for it. Here we put the capability requirements as one
parameter for SLR, as one upstream CDN can choose multiple downstream
CDNs to satisfy an customer application's requirements. It does not
matter that much if with one footprint, one downstream CDN can
satisfy the performance requirements but not capability requirements.
This section lists the possible parameters for SLR.
We consider the parameters that are not high dynamic. Those
parameters that are dynamic at a very brief time frame, but
statistically rather static at a reasonable time frame (like one
month) can be considered for footprint determination.
However, this document is not going to define the specifics for the
measurement methods.
3.1. Average Response Time
This value is to refelct the average response time in normal network
condition. This value impacts the footprint a lot.
3.2. Throughput
This parameter will also impact the footprint. If a CDN's available
throughput is very big then it can serve more than its deployment
area.
3.3. Startup Delay
This parameter is a very important metric for the streaming media
delivery. As a TCP connection throughput close to MTU/RTT. Long
distance transport maybe mean smaller MTU and longer RTT, as well as
more packet lost rate, which will result in a low rate data
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transport, and in consequence long startup delay.
3.4. Average downloading rate
Application usually needs the CDN to gurantee a certain downloading
rate for a certain service. More discussion is needed on this
parameter and how it impacts footprint.
3.5. Hit Ratio
This parameter is about the content availability. High hit ratio
means more local service and low burden on original servers. This
parameter is more related to the CDN's optimization policies than to
the footprint.
3.6. Capability
For the capability, we consider the processing power of the CDN and
its features that can support certain kinds of applications.
3.7. Up-time
Uptime is a measure of the time a machine has been up without any
downtime. For a CDN system, it usually needs to guarantee a 100% up-
time for system (not for each host).
3.8. Discussion
Not all parameters required for a certain service level are listed.
More discussion is needed. Some parameters might impact a CDN's
footprint, and some will not. Should all of them or just a portion
that affect the footprint be conveyed in the same way among CDNs?
4. Dynamic Mapping for Footprint
Each CDN participate in the CDN interconnection network should
maintain a map between the SLR parameters and its footprint. There
are choices to exchange the map information.
(1) An application's SLR is directly sent from upstream CDN to the
downstream CDN. So that downstream CDN can report its footprint to
upstream CDN accordingly. The downstream CDN should guarantee it
satisfies the SLR for users in its reported footprint. Although this
method requires message exchange for each application, but it is
simple to implement.
(2) Each CDN report its mapping between SLR parameters and footprint
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to upstream CDN. And the upstream CDN will make the final decision
on the downstream CDN's footprint according to a specific
application's SLR. This method reduces the messge exchanges but the
map itself might be very complicated, due to various combination of
these parameter values exist.
5. Message Flows
TBD.
6. Security Considerations
These security issues are open for discussion:
(1) Applications might take its service level requrements as a
confidential? Although it can be a confidential to users, but it can
be protected without leaking to any third party that is not involved
in the CDN interconnection?
(2) CDNs might take its footprint according to SLR as confidential?
(3) Footprint cheating. A CDN may cheat with its footprint. If the
behavior is disovered, the application cannot get the service level
in that announced footprint, punishment policies should be applied to
the CDN provider.
7. IANA Considerations
There is no IANA consideration for this document.
8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.he-cdni-cap-info-advertising]
He, X., Dawkins, S., Chen, G., Zhang, Y., and W. Ni,
"Capability Information Advertising for CDN
Interconnection", draft-he-cdni-cap-info-advertising-01
(work in progress), March 2012.
[I-D.seedorf-cdni-request-routing-alto]
Seedorf, J., "CDNI Request Routing with ALTO",
draft-seedorf-cdni-request-routing-alto-02 (work in
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progress), July 2012.
[I-D.ietf-alto-protocol]
Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
draft-ietf-alto-protocol-12 (work in progress), July 2012.
Authors' Addresses
Haibin Song
Huawei
Email: haibin.song@huawei.com
Yunfei Zhang
China Mobile
Email: zhangyunfei@chinamobile.com
Yi Sun
ICT/CAS
Email: sunyi@ict.ac.cn
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