Content Delivery Networks (CDNs) improve user experience by reducing latency, packet loss, and jitter. They also increase scalability and fault tolerance. FirstPoint is a traffic management system that directs users to optimal mirrored websites. It uses topology discovery to cluster nameservers and importance sampling for congestion measurement to map users to the closest mirrors.

1. Content Delivery Networks -Content Delivery Networks -
Principles & PracticePrinciples & Practice
NortheasternNortheastern
&&
Akamai TechnologiesAkamai Technologies
Ravi Sundaram

2. OutlineOutline
• CDNs - Review of mechanicsCDNs - Review of mechanics
• FirstPoint - Traffic Management forFirstPoint - Traffic Management for
mirrored websitesmirrored websites

3. Internet
Content
Providers
End
Users
The Web:The Web:
Simple on the Outside…Simple on the Outside…

4. NAP
NAP
UUNetUUNet
QwestQwest
AOLAOL
Network
Providers
Content
Providers
End
Users
Peering
Points
……But Problematic on the InsideBut Problematic on the Inside

5. Why does my click not workWhy does my click not work
• Latency - Browser takes a long timeLatency - Browser takes a long time
to load the pageto load the page
• Packet Loss - Browser hangs, userPacket Loss - Browser hangs, user
needs to hit refreshneeds to hit refresh
• Jitter - Streams are jerkyJitter - Streams are jerky
• Server load - Browser connects butServer load - Browser connects but
does not fully load the pagedoes not fully load the page
• Broken/missing contentBroken/missing content

6. The Akamai SolutionThe Akamai Solution
Servers
at Network Edge
Content
Providers
End
Users
NAP
NAP

7. 3
Content Provider’s
Web Server
DNS
WWW.XYZ.COM1
Downloading www.xyz.comDownloading www.xyz.com
- before CDNs- before CDNs
• User enters www.xyz.comUser enters www.xyz.com
• Browser requests IPBrowser requests IP
address for www.xyz.comaddress for www.xyz.com
• Browser requestsBrowser requests
embedded objectsembedded objects
• Content provider’s webContent provider’s web
server returns HTMLserver returns HTML
10.10.123.82
• Browser requests HTMLBrowser requests HTML
• DNS returns IP addressDNS returns IP address
4
7
6
• Browser obtains IP addresses forBrowser obtains IP addresses for
hostnames listed in URLs of objectshostnames listed in URLs of objects
embedded on pageembedded on page
• Content provider’s web serverContent provider’s web server
returns embedded objectsreturns embedded objects
10.10.123.8
5

8. DNS ResolutionDNS Resolution
Browser’s
Cache
1
OS
2
Local NameLocal Name
ServerServer
3
.com .net
Root
(InterNIC)
4
xyz.com
DNS Servers
6
5
7
8
9
10
TTL:
1 Day
TTL:
30 Minutes

9. Origin - Content
Provider’s Web
Server
Delivery of Whole SiteDelivery of Whole Site
66
6. Browser obtains content6. Browser obtains content
from optimal Akamai serverfrom optimal Akamai server
WWW.XYZ.COMWWW.XYZ.COM
DNS
1. Browser requests DNS for IP1. Browser requests DNS for IP
of www.xyz.comof www.xyz.com
11
33
3. DNS returns IP of optimal3. DNS returns IP of optimal
Akamai serverAkamai server
5. Akamai server assembles5. Akamai server assembles
page, contacting origin aspage, contacting origin as
neededneeded
55
4. Browser requests Akamai4. Browser requests Akamai
server for contentserver for content
44
2. DNS follows CNAME redirect2. DNS follows CNAME redirect
to www.xyz.edgesuite.netto www.xyz.edgesuite.net
22

10. Delivery of Whole Site - DNSDelivery of Whole Site - DNS
RedirectRedirect
DNS CNAME RECORDDNS CNAME RECORD
www.xyz.com CNAME www.xyz.edgesuite.net 2Dwww.xyz.com CNAME www.xyz.edgesuite.net 2D

11. Delivery of Whole Site - PageDelivery of Whole Site - Page
AssemblyAssembly
Site owners create
container pages that
can be populated
with varying content
Container Page
[TTL=5d]
[XYZ news, content,
promotions, etc.
TTL=5d]
[Breaking headlines
TTL=2h]
[TTL=15m]
[TTL=8h]

12. Benefits of CDNsBenefits of CDNs
• Improved end-user experienceImproved end-user experience
- reduce latencyreduce latency
- reduce lossreduce loss
- reduce jitterreduce jitter
• Reduced network congestionReduced network congestion
• Increased scalabilityIncreased scalability
• Improved fault-toleranceImproved fault-tolerance
• Reduced vulnerabilityReduced vulnerability
• Reduced costsReduced costs

13. OutlineOutline
• CDNs - Review of mechanicsCDNs - Review of mechanics
• FirstPoint - Traffic Management forFirstPoint - Traffic Management for
mirrored websitesmirrored websites

14. What is FirstPointWhat is FirstPoint
• Traffic management system forTraffic management system for
mirrored websitesmirrored websites
• Directs browser to the optimal mirrorDirects browser to the optimal mirror
• DNS basedDNS based
• Application level anycastApplication level anycast

15. Why FirstPointWhy FirstPoint
• Content providers have mirroredContent providers have mirrored
websiteswebsites
• Content providers only want toContent providers only want to
offload embedded contentoffload embedded content
- ControlControl
- SecuritySecurity
- PerformancePerformance

16. Mapping ProblemMapping Problem
How to improve user experience?

17. What is the Mapping ProblemWhat is the Mapping Problem
• Problem of directing requests toProblem of directing requests to
servers so as to optimize end-userservers so as to optimize end-user
experienceexperience
- reduce latencyreduce latency
- reduce lossreduce loss
- reduce jitterreduce jitter
• Assumption - servers are fineAssumption - servers are fine
• Applicable to 2 mirrors or 1500Applicable to 2 mirrors or 1500
Akamai locationsAkamai locations

18. AttemptAttempt
• Measure which is closerMeasure which is closer
- Closeness changes over timeCloseness changes over time
• Measure frequentlyMeasure frequently
- Bothers peopleBothers people
- Too many to doToo many to do
~500,000 unique nameservers on any given day
10 sec per measurement cycle

19. IdeaIdea
• TopologyTopology
- relatively staticrelatively static
- changes in BGP timechanges in BGP time
- order of hours if not daysorder of hours if not days
• CongestionCongestion
- dynamicdynamic
- changes in round-trip timechanges in round-trip time
- order of millisecondsorder of milliseconds

20. Topology Discovery - Proxy pointsTopology Discovery - Proxy points
Cluster
X
Y

21. AliasingAliasing
• Router fabrics using HSRP (hotRouter fabrics using HSRP (hot
stand-by routing protocol)stand-by routing protocol)
- correlate over timecorrelate over time
• Routers with multiple interfacesRouters with multiple interfaces
- source address of UDP/ICMP packetssource address of UDP/ICMP packets

22. Set coverSet cover
• Let sets represent proxy pointsLet sets represent proxy points
• Let elements represent nameserversLet elements represent nameservers
• Find minimum collection of proxyFind minimum collection of proxy
points covering nameserverspoints covering nameservers
X covers 1, 2, 3 and 4X covers 1, 2, 3 and 4
X
1 2 3 4

23. Topology DiscoveryTopology Discovery
• At each mirror maintain list of partial paths toAt each mirror maintain list of partial paths to
nameserversnameservers
• At each epoch extend paths by 1, inAt each epoch extend paths by 1, in
randomized fashion, and exchange with otherrandomized fashion, and exchange with other
mirrormirror
• If the two (partial) paths to a namerver haveIf the two (partial) paths to a namerver have
intersected then declare that nameserverintersected then declare that nameserver
done.done.
• If path has reached forbidden IP then waitIf path has reached forbidden IP then wait
• Use pair of proxies in case of failureUse pair of proxies in case of failure

24. Topology Discovery - Proxy pointsTopology Discovery - Proxy points
Data exchange

25. Topology DiscoveryTopology Discovery
500,000 nameservers500,000 nameservers
reduced toreduced to
90,000 proxy points (clusters)90,000 proxy points (clusters)

26. Histogram of cluster sizesHistogram of cluster sizes
HISTOGRAM
0
5000
10000
15000
20000
25000
30000
35000
1 2 3 4 5 6-99 100-999 1000-
5999
6000-
Cluster Size
Number

27. Congestion MeasurementCongestion Measurement
Problem - Still too many measurements to do.Problem - Still too many measurements to do.
90,000 measurements every 10s with 32B90,000 measurements every 10s with 32B
packets requires a few Mbps per mirror.packets requires a few Mbps per mirror.
Solution - Importance based samplingSolution - Importance based sampling

28. CDF of End-user LoadCDF of End-user Load
CDF
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Number of Clusters
Load

29. Load EstimationLoad Estimation
500,000 nameservers500,000 nameservers
reduced toreduced to
90,000 clusters90,000 clusters
7,000 account for 95% end-user load!7,000 account for 95% end-user load!

30. Mapping Problem - Solved!Mapping Problem - Solved!
Maps built every 10s

31. FirstPointFirstPoint
• Customers - how to tell?Customers - how to tell?
- look for CNAME to akadns.netlook for CNAME to akadns.net
• Customers - who?Customers - who?
- High traffic content providersHigh traffic content providers
- Yahoo!, Microsoft, TicketMaster etcYahoo!, Microsoft, TicketMaster etc
• Price - don’t ask :)Price - don’t ask :)
• Competitors - whoCompetitors - who
- one-of-a-kind serviceone-of-a-kind service
- boxes: Cisco, F5, Foundryboxes: Cisco, F5, Foundry

32. FirstPoint - other aspectsFirstPoint - other aspects
• Load-balancingLoad-balancing
- estimate-basedestimate-based
- feedback-based : https, snmpfeedback-based : https, snmp
- cost-based: 95/5cost-based: 95/5
• Fast cutout in case of failoverFast cutout in case of failover
• Highly fault-tolerantHighly fault-tolerant
- hardware duplication, leader electionhardware duplication, leader election
- overlay routing, BGP-based anycastoverlay routing, BGP-based anycast
• Integration with other servicesIntegration with other services
- DOS/Load failoverDOS/Load failover

33. MicrosoftMicrosoft

34. Related WorkRelated Work
• TopologyTopology
- Spring, Mahajan, Wetherall, Sigcomm ‘02Spring, Mahajan, Wetherall, Sigcomm ‘02
- Govindan, Tangmunarunkit, Infocom ‘00Govindan, Tangmunarunkit, Infocom ‘00
• ClusteringClustering
- Krishnamurthy, Wang, Sigcomm ‘00Krishnamurthy, Wang, Sigcomm ‘00
- Bezstavros, Mehrotra, WWC ‘01Bezstavros, Mehrotra, WWC ‘01
- Barford, Gast, Globecom 02Barford, Gast, Globecom 02
• ClusteringClustering
- Shaikh, Tewari, Agrawal, Infocom ‘00Shaikh, Tewari, Agrawal, Infocom ‘00
- Krishnamurthy, Wills, Zhang, Sigcomm IMW ‘01Krishnamurthy, Wills, Zhang, Sigcomm IMW ‘01

35. Patents (pending)Patents (pending)
• Global load balancing across mirrored data centers.Global load balancing across mirrored data centers.
Utility # 20020129134Utility # 20020129134
• Method for predicting file download time fromMethod for predicting file download time from
mirrored data centers in a global computer network.mirrored data centers in a global computer network.
Utility # 20020124080Utility # 20020124080
• Method for generating a network map. Utility #Method for generating a network map. Utility #
2002007823720020078237
• Method and system for protecting websites fromMethod and system for protecting websites from
public Internet threats. Filed 15 July 2002public Internet threats. Filed 15 July 2002

36. PrinciplesPrinciples
• Open design principleOpen design principle
- You need all the help you can getYou need all the help you can get
- Do not eliminate the obvious without trying firstDo not eliminate the obvious without trying first
- Give serendipity a chanceGive serendipity a chance
• Scaling principleScaling principle
- factor 10 difference means different domainfactor 10 difference means different domain
- different domains need different techniquesdifferent domains need different techniques
• The common case principleThe common case principle
- Zipf law is your friendZipf law is your friend
- things clusterthings cluster
- optimize the common caseoptimize the common case

37. ConclusionConclusion
• The Internet will never be fast enough in allThe Internet will never be fast enough in all
placesplaces
• People will want access to the Internet allPeople will want access to the Internet all
the time and everywherethe time and everywhere