CSE 124 Networked Services Fall 2010 Lecture-6cseweb.ucsd.edu/classes/fa10/cse124/CSE-124-Fall2010... · 2010-10-12 · 10/12/2010 CSE 124 Network Services Fall 2010 Content distribution

10/12/2010 CSE 124 Network Services Fall 2010

CSE 124Networked Services Fall 2010

Lecture-6

Instructor: B. S. Manoj, Ph.D

http://cseweb.ucsd.edu/classes/fa10/cse124

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Updates

Project-2

10/12/2010 CSE 124 Network Services Fall 2010 2


Content distribution networks (CDNs)

Content replication

challenging to stream large files (e.g., video) from single origin server in real time

solution: replicate content at hundreds of servers throughout Internet

content downloaded to CDN servers ahead of time

placing content “close” to user avoids impairments (loss, delay) of sending content over long paths

CDN server typically in edge/access network

origin server

in North America

CDN distribution node

CDN server

in S. America CDN server

in Europe

CDN

server

in Asia

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Content distribution networks (CDNs)

Content replication

CDN (e.g., Akamai) customer is the content provider (e.g., CNN)

CDN replicates customers’ content in CDN servers.

when provider updates content, CDN updates servers

origin server

in North America

CDN distribution node

CDN server

in S. America CDN server

in Europe

CDN server

in Asia

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CDN example

origin server (www.foo.com)

distributes HTML

replaces:http://www.foo.com/sports.ruth.gif

withhttp://www.cdn.com/www.foo.com/sports/ruth.gif

HTTP request for

www.foo.com/sports/sports.html

DNS query for www.cdn.com

HTTP request for

www.cdn.com/www.foo.com/sports/ruth.gif

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origin server

CDN’s authoritative DNS server

CDN server near client

CDN company (cdn.com)

distributes gif files

uses its authoritative DNS server to route redirect requests

client

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More about CDNs

routing requests

CDN creates a “map”, indicating distances from leaf ISPs and CDN nodes

distance could include geographical, topological, latency, or energy considerations

when query arrives at authoritative DNS server:

server determines ISP from which query originates

uses “map” to determine best CDN server

CDN nodes create application-layer overlay network6


CDN as an overlay cache system

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Popular CDN techniques

Three popular CDN techniques DNS redirection (DR) URL rewriting (UR) Hybrid scheme (URDR)

DNS redirection (DR) The authoritative DNS name server is controlled by the CDN Two types

Full-site delivery (DR-F) Partial-site delivery (DR-P)

Full-site delivery (DR-F) The entire origin server is hidden from the client The zone (subtree) of the DNS is modified to reflect the authoritative

nature of CDN DNS All requests to content are forwarded to the CDN CDNs may either respond or forward the requests to origin server E.g., Adero, NetCaching, and Unitech Networks’ IntelliDNS


Popular CDN techniques

Partial-site delivery (DR-P) Origin server modified the URL of embedded objects host names in the URLs are resolved by the CDN’s DNS E.g. www.cnn.com/bar.gif to cnn.akamai.net/www.cnn.com/bar.gif CDN companies: Akamai, Digital Island, Mirrorimage, Solidspeed, and

Speedera

URL rewriting (UR) Origin server rewrites URL links as part of dynamic pages to redirect

clients to different CDNs Selected objects on origin sites are identified and pushed them to CDN

mirror servers The page is dynamically resolved with the IP address of the mirror

servers No further need for DNS (download the content from mirror) E.g., Clearway CDN

Hybrid scheme (URDR) DNS redirection +URL rewriting E.g., Fasttide


http://www.cnn.com/bar.gif to cnn.akamai.net/www.cnn.com/bar.gif

Other ways for Content Redirection

Manual hyperlink selection Users can be given a set of mirror choices Among the set, user can make a manual selection

HTTP redirection HTTP request option for redirect can be exploited

.htaccess file can contain redirection information line Redirect /path-to-origin-file /URL-to-CDN-mirror

HTTP refresh <meta http-equiv="refresh" content=“TImeout; URL=www.redirected-

address.com/index.html">

Layer 4 switching Transport layer information such as port number can be used to redirect the

queries to a different server Still the origin-server’s network resources may be consumed Not so suitable for effective CDN

Layer 7 switching Application layer switches can redirect the traffic to different mirror servers Mostly done through a collection of application layer switches at the entry point

to the origin server’s network Network resources for origin server may still be affected



Some popular CDN services

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How measurements are conducted

National Internet Measurement Infrastructure (NIMI) A software system for building network measurement

infrastructures A command and control system for controlling measurement

tools Dedicated NIMI servers (probes) can be run at many locations

and controlled from a single point

PlanetLab Testbed More than 1000 machines world-wide Running virtual machines

Keynote’s streaming performance measurement services Multimedia performance


Distributed measurement of streaming services

• Agents attempt connection to a streaming server at 10 times/hour

• Attempt playing media files (e.g for 60s)

• Agents measure the following– Network parameters

• DNS time, end-to-end delay using traceroute, packet statistics, and player statistics

– Streaming statistics• connection success rate, bit rate, connection setup

/buffer/rebuffer time

– Server statistics• server type, serving platform, streaming protocol

– Presentation statistics• frame rate, metafiles, urls, player errors etc.


Source: Keynote, Inc.

Keynote’s agents’ location

Network studies

Two dozen NIMI client locations

East and west cost

Send queries to CDN and origin servers

Note the IP addresses, TTL values, transfer times

Attempt to overcome the institutional caches

There may be a chance of institutional cache influencing the performance measurement



CDN statistics (late 2000)

HOTMM127 (Hot sites from Media Metrix)

127 sites obtained Media Metrix top 50 list and the lOOhot.com list

31% used CDN for images

An increase from 2% in 1999

URL588-MM500

1030 sites obtained Media Metrix top 500 list and another web site list

17% used CDN for images

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Impact of DNS TTL and load balancing


TTL:10s

TTL:20s

TTL:20sTTL:120s

TTL:230s

TTL:N/A

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CDN Response Time performance

Response time (with and without DNS lookup time)



CDN performance (averaged over 18 objects)

Download time in seconds (mean,median, and 90%ile)

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CDN performance (serial Vs pipeline http)

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Number of unique IPs/client returned

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Key Traffic categories observed in CDNs

There exists four main traffic categories for CDNs

Web traffic (html objects over http)

Large software downloads

Media downloads (streaming video clips, full movie delivery, or movie download)

Large sized, long-tail content


Combined traffic pattern


Web traffic: html/images/scripts/formsPeak-to-Average: 1.8Peak traffic: 10-16pm EST

Large footprint, long tail traffic: OS downloadsPeak-to-Average: 2Peak traffic: 12-18pm EST

Software downloads Peak-to-Average: 1.4Peak traffic: Peaks early Morning; Otherwise Fairly flat

Multimedia: Streaming performance requirementPeak-to-Average: 7Peak traffic: 20-1am EST

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Some numbers from Akamai

In 2010 Akamai reports

Located in more than 1000 rented data center spaces

66K+ servers

400K+ disks

120K+ CPUs

Petabytes of content traffic

Very high rate per sec: 3.5Tbps

Power usage effectiveness (PUE) is a metric used to determine the energy efficiency of a data center. PUE is determined by dividing the amount of power entering a data center by the power used to run the computer infrastructure within it


http://whatis.techtarget.com/definition/0,289893,sid9_gci212560,00.html

http://whatis.techtarget.com/definition/0,289893,sid9_gci332661,00.html

Some numbers from Akamai

In 2010 Akamai reports

Located in more than 1000 rented data center spaces

66K+ servers

400K+ disks

120K+ CPUs

Petabytes of content traffic

Very high rate per sec: 3.5Tbps

How to save energy in such a large distributed set of servers


Saving energy in CDN systems

Power consumption Metric for data centers Power usage effectiveness (PUE) PUE is a ratio: the amount of power entering a data center/the

power used to run the computer infrastructure within it Current rates are low: 1.5-3.0

Most CDNs rent data centers With rented data centers, uncontrollables are

Data center PUE Source of Energy Efficiency of hardwares and other equipments

And the web traffic grows at a high rate

Solution: CDN traffic management server software efficiency are critical



Reading

CDN from Kurose and Ross

CDN research paper uploaded at the website

CDN paper for Writeup-2

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Documents

CSE 124 Networked Services Fall 2010 Lecture-6cseweb.ucsd.edu/classes/fa10/cse124/CSE-124-Fall2010... · 2010-10-12 · 10/12/2010 CSE 124 Network Services Fall 2010 Content distribution