CDNI M. Stiemerling
Internet-Draft NEC Europe Ltd.
Intended status: Informational July 4, 2011
Expires: January 5, 2012
Considerations on Request Routing for CDNI
draft-stiemerling-cdni-routing-cons-00
Abstract
Request routing in CDNs and also in the case of interconnecting
multiple CDNs requires to match against a set functional requirements
but also operational requirements. This memo discusses a few
operational requirements and the impact to the current request
routing proposals.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Speed Matters . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Failure Detection and Recovery . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
Request routing in CDNs and also in the case of interconnecting
multiple CDNs requires to match against a set functional requirements
(see [I-D.lefaucheur-cdni-requirements]) but also operational
requirements. This memo discusses a few operational requirements and
the impact to the current request routing proposals
[I-D.peterson-cdni-strawman] and [I-D.xiaoyan-cdni-requestrouting].
This draft presents some initial considerations about request routing
in CDN interconnect scenarios.
Comments and discussions about this memo should be directed to the
CDNI WG: cdni@ietf.org.
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2. Speed Matters
The speed of content delivery matters a lot in CDNs for the actual
content consumer, but also for the content provider. The content
consumer does not like to wait for too long until the content is
being displayed on its device. The content provider wants to achieve
a fast and reliable content delivery. However, the current request
routing proposals suggest that the time from the first content
request to the actual start of delivery does not matter much.
For instance, method 1 of [I-D.peterson-cdni-strawman], shown in
Figure 1, requires 4 "transactions", as seen from the End-User to
start the delivery of content. The total time from the first request
to the actual data delivery is: t_start = t_I + t_II + t_III + t_IV.
End-User Operator B Operator A
|DNS cdn.cp.com | |
+--|-------------------------------------------------->|
(I)| | | |
| |IPaddr of A's Request Router |
+--|<--------------------------------------------------|
|HTTP cdn.cp.com | |
+--|-------------------------------------------------->|
(II)| | | |
| |302 peer.op-b.net/cdn.cp.com |
+--|<--------------------------------------------------|
|DNS peer.op-b.net | |
+--|------------------------>| |
(III)| | |(3) |
| |IPaddr of B's Delivery Node |
+--|<------------------------| |
|HTTP peer.op-b.net/cdn.cp.com |
+--|------------------------>| |
(IV)| | |(4) |
| | |DNS dca.cdn.cp.com |
| | |------------------------>|
| | | |
| | |IPaddr of A's Delivery Node
| | |<------------------------|
| | |HTTP dca.cdn.cp.com |
| | |------------------------>|
| | | |
| | |Data |
| | |<------------------------|
| |Data | |
+--|<------------------------| |
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Figure 1: Method 1 of CDNI Strawman proposal
To give an impression about the times to expect for t_total here are
some values for a DNS resolution process and also round trip times
(RTT). NB: These numbers are measured from Germany via an ADSL
access, German research network (DFN) access, and via a 3G network
operator in Germany (Eplus). NB: Those numbers are not
representative as they are out of single runs and not multiple runs
spread over a larger time windows. They are rather given to
illustrate the challenge.
+------------------+--------------------------------+---------------+
| Access-Type | DNS resolution (gmx.de,cached) | RTT (Germany) |
+------------------+--------------------------------+---------------+
| ADSL (11 MBit/s) | 26 ms | 30 ms |
| | | |
| DFN (32 MBit/s) | 12 ms | 10 to 20 ms |
| | | |
| 3G (EPlus) | 200 to 300 ms | 200 to 300 ms |
+------------------+--------------------------------+---------------+
Table 1: Some time measurements
As compared to a popular video site (e.g., youtube.com) where the
video is delivered after roughly 2 seconds (19 ms to resolve FQDN of
cache in charge, 2 ms for TCP 3-way handshake, and yet 2 seconds
until the content is actually requested). This has been test from
the DFN network connection. The 2 seconds time seem to come from the
usage of the Flash player, as the network connection is up,running,
and already being used for yet another request to the cache.
Here are the times, assuming that steps I, II, and III are consuming
the RTT, but neglect the processing times:
o ADSL: t_total = 3*30ms + t_IV = 90ms + t_IV
o DFN: t_total = 3*20ms + t_IV = 60ms + t_IV
o 3G: t_total = 3*300ms + t_IV = 900ms + t_IV
The numbers for step I to III may look reasonable low (except for the
3G case), but t_IV isn't know yet, leaving still potential to prolong
the long process anyhow.
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3. Failure Detection and Recovery
It is hard to foresee from the current request routing specifications
how a failure in the downstream CDN is detected by the upstream CDN
and such a failure case can be corrected.
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4. Security Considerations
TBD
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5. Conclusion
This draft lists some operational challenges for the request routing
for the interconnection of CDNs and is more than incomplete. The
current proposals ( [I-D.peterson-cdni-strawman] and
[I-D.xiaoyan-cdni-requestrouting]) for request routing seem not to
consider the overall time from the first service request to the start
of the content delivery.
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6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
6.2. Informative References
[I-D.lefaucheur-cdni-requirements]
Faucheur, F., Viveganandhan, M., Watson, G., and Y. Lee,
"Content Distribution Network Interconnection (CDNI)
Requirements", draft-lefaucheur-cdni-requirements-01 (work
in progress), March 2011.
[I-D.peterson-cdni-strawman]
Peterson, L. and J. Hartman, "A Simple Approach to CDN
Interconnection", draft-peterson-cdni-strawman-01 (work in
progress), May 2011.
[I-D.xiaoyan-cdni-requestrouting]
He, X., Li, J., Dawkins, S., and G. Chen, "Request Routing
for CDN Interconnection",
draft-xiaoyan-cdni-requestrouting-01 (work in progress),
June 2011.
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Author's Address
Martin Stiemerling
NEC Laboratories Europe
Kurfuerstenanlage 36
Heidelberg 69115
Germany
Phone: +49 6221 4342 113
Fax: +49 6221 4342 155
Email: martin.stiemerling@neclab.eu
URI: http://ietf.stiemerling.org
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